IMATRON INC
8-K, 1998-06-16
ELECTROMEDICAL & ELECTROTHERAPEUTIC APPARATUS
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                       SECURITIES AND EXCHANGE COMMISSION
                              WASHINGTON, DC 20549




                                    FORM 8-K


                             CURRENT REPORT PURSUANT
                              TO SECTION 13 OF THE
                         SECURITIES EXCHANGE ACT OF 1934



Date of report (Date of earliest event reported)              May 1, 1998
                                                         -----------------------

                                  IMATRON INC.
- --------------------------------------------------------------------------------
             (Exact Name of Registrant as Specified in Its Charter)

                                   New Jersey
- --------------------------------------------------------------------------------
                 (State or Other Jurisdiction of Incorporation)


        0-12405                                         94-2880078
- ------------------------------          ----------------------------------------
(Commission File Number)                (I.R.S. Employer Identification No.)

           389 Oyster Point Boulevard, South San Francisco, CA 94080
- --------------------------------------------------------------------------------
               (Address of Principal Executive Offices) (Zip Code)

                                 (415) 583-9964
- --------------------------------------------------------------------------------
              (Registrant's Telephone Number, Including Area Code)


- --------------------------------------------------------------------------------
              Name or Former Address, if Changed Since Last Report)



<PAGE>

ITEM 5.  Agreements with and regarding Positron Corporation

         Effective May 1, 1998, the Company entered into several agreements with
Positron  Corporation,  a Texas corporation,  pursuant to which the Company will
acquire a  majority  ownership  of  Positron.  In  addition,  the  Company  will
immediately  begin making working capital advances to Positron of up to $500,000
to enable that company to meet a portion of its current obligations. The Company
has agreed to support Positron in several other ways, by agreeing to take, after
the date of the closing,  all  reasonable  efforts to cause the placement of ten
Positron  (TM) PET  cameras  over the next three  years,  particularly  with the
Company's  affiliate Imatron Japan,  Inc., and by assisting  Positron to arrange
for  additional  third-party  financing  in an  aggregate  amount  of  at  least
$8,000,000.

ITEM 7.  Exhibits.

         7.1 Loan Agreement between the Company and Positron, with Schedules and
Exhibits.

     7.2 Stock Purchase  Agreement  between the Company and Positron,with
Schedules and Exhibits.


                                   SIGNATURES

         Pursuant to the  requirements  of the Securities  Exchange Act of 1934,
the  registrant  has duly  caused  this report to be signed on its behalf by the
undersigned hereunto duly authorized.


                              IMATRON INC.


Date: June     ,1998          By:
                                ----------------------------------------
                                   S. Lewis Meyer
                              Its: President & Chief Executive Officer


                                   EXHIBIT 7.1

                                 LOAN AGREEMENT
                                 with Schedules
                                  and Exhibits


                                 LOAN AGREEMENT

     THIS  AGREEMENT  is made as of the  first  day of May  1998 by and  between
POSITRON CORPORATION ("Borrower"),  a Texas corporation with its principal place
of business at 1304 Langham Creek Drive,  Houston,  Texas 77084 and IMATRON INC.
("Lender"), a New Jersey corporation with its principal place of business at 389
Oyster Point Blvd., So. San Francisco, CA 94080.

                                R E C I T A L S:

     WHEREAS,  Borrower has  requested  Lender to make certain loans to Borrower
for working  capital and  certain  other needs as provided  herein and Lender is
agreeable to make such loans upon the terms and conditions hereof;

     NOW  THEREFORE,  in  consideration  of these  premises  and the mutual
covenants and agreements herein contained and other valuable consideration,
the receipt  and  adequacy of which the  parties  hereto  acknowledge,  the
parties have agreed as follows: 1. DEFINITIONS.

     As used in  this  Loan  Agreement,  the  following  terms  shall  have  the
following meanings unless the context requires otherwise:

     Borrower's Obligations means all present and future obligations of Borrower
to  Lender  hereunder,  under  the  Note,  or any  other  document  executed  in
connection herewith.

     Default means any event set forth in Section 6.1 hereof.

     Lender's  Obligations means all present and future obligations of Lender to
Borrower hereunder, or any other document executed in connection herewith.

     Loan  Agreement  means this Loan Agreement and all  attachments,  exhibits,
schedules hereto, all as may be amended from time to time.

     Loan Rate means the Prime Rate  listed in the  Western  edition of the Wall
Street  Journal  or,  if not so  listed,  the  reference  rate in use by Bank of
America NS & TA on the final business day of each month,  plus one-half  percent
(1/2 %), as applied to the payment for the next month.

     Payment Dates means the first day of each calendar month.

     2.  LOANS.

     2.1. Lender agrees, on terms and conditions of this Loan Agreement, to make
loans (hereinafter called individually a "Loan" and,  collectively "The Loans"),
to Borrower in an aggregate  principal  amount at any one time outstanding up to
but not exceeding Five Hundred Thousand Dollars  ($500,000).  Within such limit,
and subject to the various  conditions  set forth  herein,  Borrower may borrow,
repay, re-borrow at any time or from time to time from the date hereof up to and
including the earlier of March 1, 2000 and the  termination of the commitment of
Lender, as provided at Section 6.2 below. The obligation of Lender to make Loans
up to but not exceeding such aggregate amount at any one time outstanding herein
is hereinafter called its "Commitment."

     2.2.  Except for the borrowing  contemplated  to be made upon  execution of
this Agreement,  as set forth in Schedule 3.1(g),  Borrower shall give Lender at
least three(3) calendar days' written notice (effective upon receipt) specifying
the  amount  and  date  of each  borrowing  under  Section  2.1.  The  foregoing
notwithstanding, and provided all conditions have otherwise been met, the timing
set forth in Schedule  3.1(g) shall be deemed  written notice of the amounts and
dates set forth in the Schedule.

     2.3.  Borrower's  obligations  to pay the  principal of and interest on the
Loans shall be  evidenced by its grid  promissory  note in the form of Exhibit A
hereto (the "Note")  payable to the order of Lender.  The Note shall reflect the
amount of the  Commitment,  with actual Loans,  repayments and balances noted by
Lender on the grid attached to the Note and made a part thereof.  The Note shall
bear interest on the unpaid principal amount thereof until such principal amount
shall be paid in full at a per annum  rate  equal to the Loan  Rate  (based on a
year of 365 or actual number of days elapsed).  The Loan Rate shall apply to the
average  outstanding  principal balance on the Note during any month which shall
be the summation of the daily  balances  during such month divided by the number
of days in the  particular  month.  Unless  accelerated  in accordance  with the
provisions  of this Loan  Agreement,  the  interest on the Note for any calendar
month shall be paid within  fifteen (15) days of each  consecutive  Payment Date
immediately  following  such calendar  month until full payment of the Loan (and
related interest),  with the first Payment Date being the first day of the month
immediately following execution of this Agreement. All principal and interest on
the Note shall be due and payable in full on March 1, 2000.  If any Payment Date
(or other  date for  payment  hereunder)  falls on a day which is not a business
day, such Payment Date (or other date of payment)  shall be the next  succeeding
business day.

     2.4. Mandatory Repayment. The foregoing  notwithstanding,  beginning on and
after  any date,  from the date of this Loan  Agreement  to the  termination  of
Lender's  Commitment,  that Borrower  receives  third party  financing,  whether
equity or debt ("Financing"), in an amount in excess of One Million U.S. Dollars
($1,000,000)  in the aggregate  ("Financing  Threshold"),  Borrower shall repay,
fifty percent (50%) of each dollar  received above the Financing  Threshold from
such Financing, toward any and all amounts of principal and interest outstanding
under this Loan Agreement until such amounts have been fully repaid and further,
Lender's  Commitment  shall  terminate  and  not be  renewed.  Solely  by way of
example, in the event Borrower shall receive Financing in an aggregate amount of
$750,000 at any time during the first nine (9) months of this Agreement, and six
(6)  months  thereafter  Borrower  receives  additional  Financing  in an amount
$500,000,  Borrower  shall repay to Lender,  promptly  following  receipt of the
$500,000,  the sum of $125,000 representing fifty percent (50%) of all Financing
received  above the  Financing  Threshold,  which amount shall be applied to all
interest  accrued on the Loans and unpaid to that date plus,  to the extent that
accrued unpaid interest constitutes less than $125,000, that amount of principal
outstanding  representing  the  difference  between the amount of accrued unpaid
interest  and  $125,000.  Thereafter,  fifty  percent  (50%) of every  dollar of
additional  Financing  provided to Borrower shall be paid over to Lender, and no
more  Loans  shall be  authorized,  until the full  amount of any and all unpaid
principal and interest on the Loans shall have been paid.

     2.5. All payments to Lender shall be paid by Borrower to Lender at Lender's
address as follows:  Imatron Inc., 389 Oyster Point Blvd., So. San Francisco, CA
94080, Attn. President.  All amounts paid shall be applied first, to the payment
of all interest accrued and payable with respect to the Note; and second, to the
payment of outstanding  principal of the Loan; and third,  following Default, to
the payment of all expenses and charges,  including reasonable  attorneys' fees,
included  by Lender for the  protection  of its rights or the  pursuance  of its
remedies.

     2.6.  The Loans or any part  thereof  may be  prepaid  at any time  without
penalty.

     2.7. The interest and other charges charged with respect to the Loans shall
not exceed the highest rate permissible under any law which a court of competent
jurisdiction  or an  arbitrator  or  panel  of  arbitrators  shall,  in a  final
determination, deem applicable to the Loans. As of the date of execution of this
Loan Agreement, the parties hereto, in good faith, agree that the total interest
and other  charges  payable by Borrower  to Lender  under the terms of this Loan
Agreement do not exceed the maximum legal interest rate applicable to the Loans.
If it is determined  that Lender has received  interest and other  consideration
with respect to the Loans in excess of the highest rate applicable to the Loans,
Lender shall  promptly  refund not more than such excess  amount to Borrower and
the provisions  hereof shall be deemed  amended to provide for such  permissible
rate.

     3.  CONDITIONS OF LENDING.

     The  obligations of Lender to make a Loan is subject to the  fulfillment of
the following conditions:

     3.1. The following documents shall have been duly authorized,  executed and
delivered  by the  Borrower  to the Lender,  and shall be in form and  substance
satisfactory to the Lender and its counsel and shall be in full force and effect
on the date of the Loan.

     Prior to the first Loan:

          (a)     an  executed  Loan  Agreement,  and  all  executed  documents,
                  certificates   and  instruments   contemplated  by  this  Loan
                  Agreement,   including   but  not  limited  to  the   Security
                  Agreement;

          (b)     a certified  copy of the  resolution of the Board of Directors
                  of  Borrower,  certified  by the  Secretary  or a  responsible
                  officer  thereof,  duly  authorizing  execution,  delivery and
                  performance of this Loan  Agreement and the Note  contemplated
                  hereby;

          (c)     a  certificate  of recent date from the  Secretary of State of
                  the  state  of  incorporation  of  Borrower  as  to  its  good
                  standing;

          (d)     an incumbency  certificate of Borrower dated as of the date of
                  funding, as to (i) the person or persons authorized to execute
                  and  deliver  this  Loan  Agreement,  the Note,  the  Security
                  Agreement, and any other documents to be executed on behalf of
                  them in connection with the transactions  contemplated  hereby
                  and (ii) the signature of each person or persons;

          (e)     the executed Note;

          (f)     documentary evidence satisfactory to Lender that any and all
                  liens or other  security  interests on any of  Borrower's
                  tangible or intangible property, including  but not limited to
                  accounts, computer  hardware and software, copyrights,
                  equipment, inventory,  licenses,  patents,  trade secrets,
                  trademarks, general intangibles,  chattel paper or other
                  property, and  all  proceeds  thereof, shall  have  been
                  released  or  otherwise subordinated to Lender's security
                  interests  contemplated herein, except as otherwise provided
                  by that certain agreement by and among ProFutures Bridge
                  Capital Fund, L.P., a Delaware limited partnership
                  ("ProFutures"),  Lender and Borrower, dated as of April 28,
                  1998 and attached hereto as Exhibit D, and except as provided
                  by that  certain  agreement  by and among  Uro-Tech, Ltd.,
                  Lender and Borrower,  dated as of April 28, 1998 and attached
                  hereto as Exhibit E; and

          (g)     an expense  plan and  budget,  including  an  acceptable  cash
                  control system for managing  expenditures  within the plan and
                  budget, ("Expense Plan"), attached hereto as Schedule 3.1(g) ;
                  and

          (h)     documentary evidence satisfactory to Lender that any Letter of
                  Intent or contract  arrangements  of whatever  nature  between
                  Borrower and CTI PET Systems,  Inc.  have expired or otherwise
                  been terminated, and that there are no obligations of whatever
                  nature in effect between Borrower and CTI PET Systems, Inc.

                   For each Loan (including the first):

          (i)     an officer's  certificate in the form of Exhibit B which shall
                  include the written  request from  Borrower  setting forth the
                  requested  amount  of  the  Loan  and  the  proposed  date  of
                  borrowing;

          (j)     for each  Loan  after  the first  Loan,  documentary  evidence
                  satisfactory  to Lender,  including but not limited to Exhibit
                  B, that Borrower is adhering strictly to the Expense Plan; and

          (k)     such other  documents and evidence with respect to Borrower as
                  Lender may reasonably request.

     3.2. On the date of each  borrowing  pursuant to Section 2.1 above,  (i) no
Default  or event  that with the giving of notice or lapse of time or both would
constitute a Default  hereunder  has occurred and is  continuing or would result
from the  performance of this Loan  Agreement,  (ii) no material  adverse change
shall  have  occurred  since the date of this Loan  Agreement  in the  financial
condition or operations  of the Borrower,  and (iii) there shall be no juridical
proceeding or regulatory  action  instituted by or against the Borrower,  or, to
the best of Borrower's knowledge,  any threatened proceeding or action which may
materially  adversely  affect the business,  property,  operation,  or financial
condition of the Borrower.  By acceptance of a Loan,  Borrower  represents as of
such  Loan  date,  that  each of the  foregoing  items  is true.  The  foregoing
notwithstanding,  Lender  acknowledges that it has been advised of the status of
Borrower's lease for space located at 1304 Langham Creek Drive,  #310,  Houston,
Texas 77084, as set forth on Schedule 4.5 herein,  and that such status will not
be deemed a breach of this Section 3.2.

     4.   REPRESENTATIONS AND WARRANTIES.

     4.1.     Borrower is a corporation duly organized and validly existing
 in good standing under the laws of the state
of Texas.

     4.2.  Borrower has full corporate power to own its properties,  to carry on
its business as now being  conducted  and has full  corporate  power to execute,
deliver and perform all of its  obligations  under this Loan  Agreement  and the
Note.

     4.3.  The  execution,  delivery  and  performance  by Borrower of this Loan
Agreement,   the  Note,  the  Security   Agreement  and  all  related  documents
contemplated  by this  transaction  have been duly  authorized  by all necessary
corporate  action of Borrower and do not violate any provision of law,  statute,
rule or regulation,  applicable to Borrower, or any judgment, franchise, permit,
order,  decree,  ruling, writ or injunction of any court or administrative body,
applicable to Borrower, or of Borrower's  certificate of incorporation,  by-laws
or the terms of any of its  securities or result in the breach of, or constitute
a Default under, or require any consent under, any indenture,  bank loan, credit
agreement or other  agreement or instrument  to which  Borrower is a party or by
which Borrower or any of its property may be bound or affected.

     4.4. No filings, recordations, notifications, registrations, notarizations,
authentications  or other  formalities  or property,  stamp or similar  taxes or
duties  and  no  approvals,  licenses,  orders,   authorizations,   consents  or
undertakings of any governmental bodies or regulatory,  supervisory  authorities
are necessary in connection  with the  execution,  delivery and  performance  by
Borrower of this Loan Agreement or the Note, or for the payment to Lender of all
sums hereunder or under the Note or for the legality,  validity,  binding effect
or enforceability hereof or thereof.

     4.5. Except as disclosed and described in Schedule 4.5 hereto, Borrower has
good and  marketable  title to, or a valid  leasehold  interest in, the tangible
personal  property or other  properties  and assets  used by it,  located on its
premises, or shown on the most recent balance sheet, free and clear of all liens
or other security interests.

     4.6.  This Loan  Agreement  and the  Note,  have  been  duly  executed  and
delivered by Borrower and are legal, valid and binding  obligations of Borrower,
enforceable in accordance with their respective terms, subject to (i) the effect
of any applicable bankruptcy,  insolvency,  reorganization,  moratorium or other
similar laws affecting the enforcement of creditors' rights generally,  (ii) the
availability  of the remedies of specific  performance  or injunctive  relief as
subject  to the  discretion  of the court  before  which a  proceeding  for such
remedies  may be brought,  and (iii) the  exercise by any court before which any
proceeding may be brought of equitable judicial discretion.

     4.7.  Borrower has delivered to Lender its  unaudited  balance sheet of the
Borrower and the related  statements of income,  retained earnings and cash flow
of Borrower  (collectively  "Financial  Statements")  for the nine month  period
ending  September 30, 1997. Such balance sheet and statement  fairly present the
financial  condition  of the  Borrower  as of such date and the  results  of the
operations of the Borrower for the period ended on such date, and such statement
has been prepared in accordance with generally  accepted  accounting  principles
consistently applied, and contain any disclosure that would normally be required
by  financial   statements   prepared  in  accordance  with  generally  accepted
accounting  principles.  Since the end of the period reflected in such financial
statements  there  has been no  material  adverse  change in such  condition  or
operations.

     4.8. Except as disclosed and described on Schedule 4.8,  Borrower has filed
all  applicable  tax  returns  required  to be filed by it, and has paid or made
provisions  for the payment of all taxes which have become due  pursuant to said
returns or pursuant to any assessment received by Borrower except such taxes, if
any, as are being contested in good faith and as to which adequate reserves have
been provided in accordance with generally accepted accounting  principles,  and
warrants that such returns properly  reflect the United States,  state and local
income and tax liability of the Borrower for the period covered thereby.

     4.9.  Except as disclosed and fully  described on Schedule 4.9, there is no
action,  suit  or  proceeding  pending  or,  to the  knowledge  of the  Borrower
threatened,  against  the  Borrower  or any of its  property  before  any court,
governmental department, administrative agency or instrumentality which, if such
action,  suit or proceeding were adversely  determined,  would materially affect
the  financial  condition  or the results of  operations  of the Borrower or its
business or the ability of the Borrower to perform its obligations hereunder.

     4.10.  Except as disclosed and described on Schedule 4.10 hereto,  Borrower
is not in  default  on or has  otherwise  delayed  or  postponed  payment of any
accounts payable or other  liabilities in excess of $25,000 outside the ordinary
course of business.

     4.11.  Each Loan shall be fully applied by Borrower  solely for its working
capital  needs or for the  purchase  of  equipment  or  leasehold  improvements,
consistent with Schedule  3.1(g) and the Cash Control  System,  and for no other
purpose.

     4.12.  No broker or finder  acting on behalf of Borrower  brought about the
obtaining,  making  or  closing  of this  Loan  Agreement  and  Borrower  has no
obligation  to pay any  finder's  or  brokerage  fees  in  connection  with  the
transactions contemplated herein.

     4.13.  As of the date of execution of this Loan  Agreement,  the  aggregate
interest and other charges payable by Borrower to Lender under the terms of this
Loan Agreement do not exceed the maximum legal  interest rate  applicable to the
Loans.

     5.   COVENANTS.

     Borrower  hereby  covenants and agrees that until  satisfaction  of all its
obligations, it shall:

     5.1.  Preserve and maintain its corporate  existence and all of its rights,
privileges and franchises,  and continue the conduct of its present  business in
an orderly,  efficient and regular manner;  comply in all material respects with
all  applicable  laws,  rules,   regulations  and  orders  of  any  governmental
authority,  non-compliance  with which  would  materially  affect the ability of
Borrower to perform its obligations.

     5.2. Make payments or  commitments  for payments only in strict  compliance
with the Expense Plan and Cash Control  System,  or otherwise as  authorized  by
Lender.

     5.3. Furnish Lender promptly with any financial  information or statements,
and other current information  regarding or relating to Borrower,  as reasonably
requested by Lender, other than information  relating to Borrower's  proprietary
know-how and technology information.

     5.4. Timely file any and all tax returns and tax filings required under any
governmental  statute or regulation and timely pay and discharge,  when due, all
tax  obligations,  and  material  obligations  to third  parties,  except  those
obligations  being  contested in good faith,  and for which  Borrower shall have
maintained,   in  accordance  with  generally  accepted  accounting  principles,
adequate reserves for the payment of the same.

     5.5.  Notify  Lender  immediately  upon  receipt  of  notice  of any  lien,
attachment,  administrative or judicial proceeding, pending or threatened claim,
dispute,  litigation  or  governmental  proceedings,  material to the  financial
condition or operations of Borrower,  which for this purpose shall be any amount
in excess of $ 10,000; provide immediate written notice to Lender of any Default
or event  which  with the  lapse  of time or  giving  of  notice  or both  would
constitute a Default.

     5.6.  Promptly  and  duly  execute  and  deliver  to  Lender  such  further
documents, instruments and assurances and take such further action as Lender may
from  time to time  reasonably  request  in order to carry  out the  intent  and
purpose of this Loan  Agreement  and to  establish  and  protect  the rights and
remedies created or intended to be created in favor of Lender hereunder.

     5.7.  Reimburse  Borrower  for its costs  and  reasonable  attorneys'  fees
incurred in enforcing its rights pursuant to the provisions of this Agreement.

     6.   DEFAULTS AND REMEDIES.

     6.1. Any of the following shall constitute a default by Borrower  hereunder
("Default"):  (a) failure by Borrower to pay any amounts  hereunder or under any
Note when due and such remains unremedied for a period of fifteen (15) days from
the due date;  or (b)  failure of  Borrower  to comply  with any  provisions  or
perform any of its  obligations  arising under this Loan  Agreement  (other than
those  referred  to in clause (a) above),  or if, but only if,  such  failure to
comply is remediable, it remains unremedied by Borrower for a period of ten (10)
days from notice to Borrower;  or (c) any  representations or warranties made or
given  by  Borrower  in  connection  with  this  Loan  Agreement  were  false or
misleading  when made,  in any  material  way; or (d)  subjection  of any of the
assets in an amount in excess of  $10,000.00  of Borrower to  attachment,  levy,
execution,  forfeiture  or  cancellation  or other  administrative  or  judicial
process which is not or cannot be removed with reasonable diligence within sixty
(60) days from the subjection  thereof,  or (e)  commencement of any insolvency,
bankruptcy  or  similar  proceedings,  by or  against  Borrower,  including  any
assignment  by  Borrower  for the benefit of  creditors,  and in the case of any
involuntary  proceedings,  such is not  dismissed  within  ninety  (90)  days of
institution;  or the  inability of Borrower to pay its debts as they become due;
or (f) the  liquidation or dissolution  of Borrower or the  commencement  of any
acts relative thereto,  or without the prior written consent of Lender, any sale
or other disposition of all or substantially  all of the assets of Borrower,  or
any merger or  consolidation  of  Borrower,  or the  cessation  of  business  by
Borrower; or (g) a default by Borrower under any agreement for borrowed money or
under any lease,  except with  regard to the lease of premises  located at 16350
Park Ten Place,  Houston,  Texas 77084, whereby the holder of the obligation has
accelerated it prior to its stated maturity and such accelerated  amount exceeds
$100,000.00,  except as otherwise disclosed on Schedule 4.10; or (h) there shall
be a money judgment,  in excess of $25,000.00  entered against Borrower which is
not fully  covered by  insurance  or remains  unvacated,  unbonded,  unstayed or
undischarged for more than sixty (60) days.

     6.2.  Upon any  default,  Lender,  upon  written  notice to  Borrower,  may
exercise any one or more of the  following  remedies  (which  remedies  shall be
cumulative to the extent permitted by law): (a) terminate any further obligation
of Lender  hereunder  (including  any  obligation  to make further  loans);  (b)
declare the remaining  unpaid  principal  balances of the Note, plus all accrued
but unpaid interest thereon, plus all other amounts due from Borrower hereunder,
immediately  due and payable in full without  notice or demand,  whereupon  such
shall become due and  payable;  (c) exercise any other right or remedy which may
be available to it under applicable law; or (d) require the Borrower to purchase
from Lender,  and Borrower  shall have the  obligation  to purchase  from Lender
("Put")  any, or all, or less than all, of any shares of common  stock issued by
Borrower  and owned by Lender at the price of $ 0.01 per  share.  Upon a default
any  proceeds  received  from  Borrower  shall  be  applied  by  Lender  to  the
obligations, in the order of application as Lender shall elect.

     7.   NOTICES; CHANGES.

     Notices,  requests or other communications required hereunder to be sent to
either party shall be in writing and shall be by: (a) United  States first class
mail, postage prepaid, and addressed to the other party at the address set forth
above (or to such other  address as such party shall have  designated  by proper
notice),  effective  five days  after  deposit;  (b) by  personal  or  overnight
delivery, effective upon receipt.

     8.   GOVERNING LAW.

     This Loan Agreement  shall be governed and construed in accordance with the
laws of the State of  California  without  giving  effect to the  principles  of
conflict of laws thereof.

     9.   DISPUTE RESOLUTION.

     9.1. Any  controversy or claim between or among the parties  arising out of
or relating to this Loan  Agreement  or any related  agreements  or  instruments
("Subject  Documents"),  including any claim based on or arising from an alleged
tort,  shall be  submitted  to and  determined  by  arbitration  before  one (1)
arbitrator  who shall be an attorney  admitted  to practice  law in the state of
California,  in  accordance  with  Title 9 of the U.S.  Code and the  Commercial
Arbitration  Rules  of the  American  Arbitration  Association  ("AAA")  then in
effect,  and shall be held in the county of San  Francisco,  CA. All statutes of
limitations  which would otherwise be applicable  shall apply to any arbitration
proceeding under this  subparagraph 9.1. Judgment upon the award rendered may be
entered in any court having jurisdiction. This subparagraph 9.1 shall apply only
if, at the time of the proposed  submission to AAA, none of the  obligations  to
Lender  described in or covered by any of the Subject  Documents  are secured by
real  property  collateral  or,  if so  secured,  all  parties  consent  to such
submission.

     9.2.  If the  controversy  or  claim is not  submitted  to  arbitration  as
provided  and  limited in Section  9.1,  but  becomes  the subject of a judicial
action,  any party may elect to have all decisions of fact and law determined by
a referee in accordance with applicable  state law. If such an election is made,
the parties shall  designate to the court a referee or referees  selected  under
the  auspices  of the AAA in the same  manner as  arbitrators  are  selected  in
AAA-sponsored proceedings. The referee, or presiding referee of the panel, shall
be an active  attorney or retired judge.  Judgment upon the award rendered shall
be entered in the court in which such proceeding was commenced.

     9.3.  Except as provided  herein,  no provision  of, or the exercise of any
rights under,  Section 9.1,  shall limit the right of any party to exercise self
help remedies such as setoff,  or to obtain  provisional  or ancillary  remedies
such as injunctive  relief or the  appointment of a receiver from a court having
jurisdiction  before,  during  or after the  pendency  of any  arbitration.  The
institution  and  maintenance  of an action  for  judicial  relief or pursuit of
provisional  or ancillary  remedies or exercise of self help remedies  shall not
constitute  a waiver of the right of any  party,  including  the  plaintiff,  to
submit the controversy or claim to arbitrators.

     9.4.  The  parties  understand  and  agree  the  arbitration  will be their
exclusive form of resolving  disputes  between them regarding the issues covered
by this Agreement.  BOTH PARTIES EXPRESSLY WAIVE THEIR  ENTITLEMENT,  IF ANY, TO
HAVE CONTROVERSIES BETWEEN THEM DECIDED BY A JURY OR COURT OF LAW.

     10.   MISCELLANEOUS.

     This Loan  Agreement  or any part  hereof,  may not be assigned by Borrower
without the written consent of Lender and shall be binding upon and inure to the
benefit of the parties hereto, their legal representatives, permitted successors
and  assigns.  This Loan  Agreement  and/or the note or any part  thereof may be
assigned by Lender without the consent of Borrower. No amendment hereunder shall
be  effective  unless in  writing  signed by the  parties  hereto  and no waiver
hereunder  shall be  effective  unless  in  writing,  signed  by the party to be
charged.  No  failure  to  exercise,  no delay in  exercising,  and no single or
partial exercise on the part of Lender of any right, remedy, or power hereunder,
shall operate as a waiver thereof or preclude  Lender from  exercising any other
right,  remedy or power  hereunder.  Any provision of this Loan Agreement or the
Note which is unenforceable in any jurisdiction  shall, as to such jurisdiction,
be ineffective to the extent of such  prohibition or  unenforceability,  without
invalidating   the   remaining   provisions   hereof   or  of  the   note.   The
representations,  warranties,  obligations  and  indemnities of Borrower  herein
shall survive the  termination of this Loan Agreement to the extent required for
their full observance and  performance.  The obligation of each comaker (if any)
of this Loan Agreement or the Note shall be primary,  joint and several and each
such comaker  hereby  irrevocably  consents to any extension of time of payments
and/or the execution of any refinancing or restructuring  agreements relative to
this  Loan  Agreement  or the  Note.  In the  event  Borrower  fails to meet any
obligation of it hereunder, Lender may at its option satisfy such obligation and
Borrower shall reimburse  Lender on demand  therefor.  The captions in this Loan
Agreement  are for  convenience  only and shall  not  define or limit any of the
terms hereof.  This Loan Agreement may be executed in counterparts  and all said
counterparts  taken  together  shall be  deemed to  constitute  one and the same
instrument.

     THIS LOAN IS SECURED BY THE TERMS OF THAT  CERTAIN  SECURITY  AGREEMENT  OF
EVEN DATE BY AND  BETWEEN  BORROWER  AND LENDER  HEREUNDER,  ATTACHED  HERETO AS
EXHIBIT C.

     IN  WITNESS  WHEREOF,  the  parties  hereto  have duly  executed  this Loan
Agreement as of the date first above written.  Borrower  acknowledges  that this
Loan  Agreement  shall not be effective  until accepted by Lender at its address
above.

LENDER:                                  BORROWER:


IMATRON INC.                             POSITRON CORPORATION


By:                                      By:
   -----------------------------            --------------------------------
Its:                                     Its:
   -----------------------------            ---------------------------------


Attest:                                   Attest:


By:                                       By:
   -----------------------------             --------------------------------

Its:                                      Its:
    ----------------------------              -------------------------------

<PAGE>


                                 SCHEDULE 3.1(g)

                                  Expense Plan

<TABLE>
<S>                              <C>                        <C>                        <C>

- --------------------------      --------------------------- ------------------------- ----------------------
Payroll                                       $65,000                $89,000(2)             $89,000(2)
- ------------------------------- --------------------------- ------------------------- ----------------------
AFCO (D&O/GL Ins.)                       15,972.72(1)                 16,000                 16,000
- ------------------------------- --------------------------- ------------------------- ----------------------
Medical/Dental/Life                      10,570.30(1)                 11,500                 11,500
- ------------------------------- --------------------------- ------------------------- ----------------------
Rent                                            4,800                  4,800                  4,800
- ------------------------------- --------------------------- ------------------------- ----------------------
Telephone                                       4,500                   3,500                  3,500
- ------------------------------- --------------------------- ------------------------- ----------------------
Shipping/Postage                                2,500                   3,000                  2,000
- ------------------------------- --------------------------- ------------------------- ----------------------
Churchill (AP)                                  5,000                   5,000
- ------------------------------- --------------------------- ------------------------- ----------------------
Consultants                                     7,000                   7,000                  7,000
- ------------------------------- --------------------------- ------------------------- ----------------------
Expenses/Travel                                 8,000                   8,000                 10,000
- ------------------------------- --------------------------- ------------------------- ----------------------
Pagenet                                         1,050                     400                    400
- ------------------------------- --------------------------- ------------------------- ----------------------
Supplies                                        1,000                   1,000                  1,000
- ------------------------------- --------------------------- ------------------------- ----------------------
Taxes/Licenses/ Professional                    1,000                   1,000                  1,000
Fees
- ------------------------------- --------------------------- ------------------------- ----------------------
Installation (Imatron Japan)                    7,500                     --                     --
- ------------------------------- --------------------------- ------------------------- ----------------------
Legal/Accounting/ Audit                        30,000(1)               20,000                 25,000
- ------------------------------- --------------------------- ------------------------- ----------------------
A/P                                            28,000                  27,500                 31,000
- ------------------------------- --------------------------- ------------------------- ----------------------
Personnel Costs                               164,407.34(1)
- ------------------------------- --------------------------- ------------------------- ----------------------
Profutures Payment                             50,000(1)
- ------------------------------- --------------------------- ------------------------- ----------------------
Miscellaneous                                   2,500                   2,500                  2,500
- ------------------------------- --------------------------- ------------------------- ----------------------
  SUBTOTAL                                   $408,800.36            $200,160                $204,660
- ------------------------------- --------------------------- ------------------------- ----------------------
Revenue from Service (average)               $107,000               $107,000                $107,000
- ------------------------------- --------------------------- ------------------------- ----------------------
  TOTAL                                      $301,800.36             $93,200                 $97,700
- ------------------------------- --------------------------- ------------------------- ----------------------

(1)    Simultaneous  with  execution of loan  agreement.  These  amounts will be
       loaned to Positron to be used by Positron as stated in chart.

(2)    Payroll Add On (2 Senior):  $22,000
- ------------------------------------------------------------------------------------------------------------
</TABLE>
<PAGE>

                                  SCHEDULE 4.5

                                 TITLE TO ASSETS

                                 LOAN AGREEMENT

To the best of our present  knowledge,  the following two liens are presently in
effect, as acknowledged and discussed:

      -  ProFutures Bridge Capital Fund, L.P.

      -  Uro-Tech, Ltd.


<PAGE>

                                  SCHEDULE 4.8

                              POSITRON CORPORATION

                      Schedule 4.8 - Tax Returns and Audits

Except as disclosed and described,  all federal,  state and local tax returns or
appropriate  extension  requests have been filed;  all federal,  state and local
taxes have been paid or due provision made;  there are no  delinquencies  in the
payment  of such  tax or  assessment  or  governmental  charge;  no  notices  of
deficiencies proposed or assessed has been received; Seller has not executed any
waiver of any statute of  limitations on assessment or collection of any tax; no
tax returns have been audited; there are no tax liabilities; except as follows:

1.  Property taxes in the approximate amount of $185,000, of which approximately
    $80,000 relates to prior years.

2. State sales taxes in the State of Texas in the approximate amount of $4,000.

3.  State  sales  taxes to the State of  Florida  in the  approximate  amount of
    $12,000.

4.  State  sales  taxes to the  State of New York in the  approximate  amount of
    $56,000.

<PAGE>

                                  SCHEDULE 4.9

                              POSITRON CORPORATION

              Schedule 4.9 - Litigation or Governmental Proceedings

Except  as  disclosed  and  described,   there  are  no  legal  actions,  suits,
arbitration  or other  legal,  administrative  or  governmental  proceedings  or
investigations  pending  or  threatened;  Seller is aware of no facts  likely to
result in or form a basis for such action; Seller is not in default with respect
to any  judgment,  order or  decree  or any  court  or  governmental  agency  or
instrumentality;  Seller is not threatened with any action or proceeding  except
as follows:

 1. We have been  informed  that Xin Xin  intends  to proceed  with  arbitration
relative to its  contract  with  Positron  Corporation  for the  purchase of two
POSICAM systems.

2. Numerous  letters have been received  from vendors  threatening  legal action
against the Company for its failure to pay outstanding trade payables.

3. The loan from  ProFutures  Bridge Capital is in default due to the failure of
the  Company to pay the full  $50,000 per month due on the loan.  The  Company's
payments  have  averaged   approximately  $45,000  per  month.   ProFutures  has
threatened legal action.

4. All former and existing  employees  who are owed unpaid  salaries,  wages and
benefits  have a claim  against the Company.  The amounts due could be collected
through legal action or by the Texas Workforce Commission.

5. Hadassah Medical Organization has threatened legal action if the Company does
not immediately  replace its existing POSICAM system with a new system.  To date
no formal legal action has been filed.

6. University Madrid PET Center has also threatened legal action if its existing
POSICAM is not upgraded to a newer machine that meets its expectations.

7. Nizar  Mullani,  a former  director  of the  Company,  claims that he is owed
consulting fees and royalties of  approximately  $150,000.  The Company disputes
the amount of royalty  actually owed to Mullani.  Mullani has  threatened  legal
action. To date no formal action has been taken by Mr. Mullani.

8. Harris County,  Texas has been awarded a default judgment against the Company
for its failure to pay property taxes in the approximate amount of $80,000.

9. Bowne of Dallas,  Inc. received a default judgment against the Company in the
amount of $31,277.05.

10. Boxer Property  (Landlord)  has issued a notice for Positron  Corporation to
vacate remaining  space.  Agreement has been reached for Positron to consolidate
its space and relocate to another facility as soon as possible.


<PAGE>


                                  SCHEDULE 4.10

               Defaults or Delays in Payments in excess of $25,000

               Schedule intentionally omitted.


<PAGE>

                                    EXHIBIT A

                                TO LOAN AGREEMENT


                                 PROMISSORY NOTE


U.S.$500,000.00                                                May 1, 1998

                                                     San Francisco, California


     The undersigned POSITRON  CORPORATION,  a corporation organized and validly
existing  under  the laws of the  State of Texas,  for  value  received,  hereby
unconditionally  promises to pay to the order of IMATRON INC.  (the  "Payee") at
389 Oyster  Point Blvd.,  So. San  Francisco,  CA 94080,  in lawful money of the
United  States of America and in  immediately  available  funds,  the  principal
amount of FIVE HUNDRED THOUSAND U.S. DOLLARS,  or, if less, the aggregate unpaid
principal  amount of all Loans (as more fully shown on the grid attached  hereto
and made a part hereof),  with interest on the principal amount hereof remaining
from time to time  unpaid at such  interest  rates and  payable at such times as
provided in the Loan Agreement.  Notwithstanding the foregoing,  Borrower hereby
authorizes  Lender  to record  and  adjust,  on the grid  attached  hereto,  the
principal amount of Loans, principal payments and balances by Borrower under the
Loan Agreement.

     This Note evidences Loans by the Payee to the  undersigned  pursuant to the
Loan  Agreement  between the  undersigned  and the Payee dated as of April ____,
1998  (the  "Loan  Agreement")  as from time to time may be  amended,  restated,
replaced, supplemented,  substituted for or renewed, and the holder of this Note
is entitled to the benefits thereof. Each term defined in the Loan Agreement and
not otherwise defined herein shall have the same definition when used herein.

     The principal  hereof (together with any accrued but unpaid interest) shall
become  forthwith  due and payable as provided in the Loan  Agreement.  Payments
hereunder  not  made  when due  shall  bear  interest  as  provided  in the Loan
Agreement.  Rights of Borrower,  if any, to prepay the Note are set forth in the
Loan Agreement.

     All payments made pursuant to the terms of this Note shall be made free and
clear of, and without deduction for, withholding,  setoff or counterclaim of any
kind.

     Neither  the  failure on the part of the holder of this Note in  exercising
any right or remedy nor any single or partial  exercise  or the  exercise of any
other right or remedy shall operate as any waiver. No amendment  hereunder shall
be effective unless in writing signed by the undersigned and holder of this Note
and no waiver  hereunder  shall be  effective  unless in writing,  signed by the
party  to  be  charged.  The  undersigned  hereby  waives  demand  for  payment,
presentment,  protest and notice of any kind in  connection  with the  delivery,
acceptance, performance, default or enforcement of this Note and hereby consents
to any extensions of time, renewals, releases of any party to this Note, waivers
or modifications  that may be granted or consented to by the holder of this Note
in respect of the time of payment or any other  matter.  Anything  contained  in
this Note to the  contrary  notwithstanding,  in the event  that any  payment of
interest  hereunder shall exceed the legal limit,  such amount in excess of such
limit shall be deemed a payment of principal hereunder.

     The terms and  provisions  hereof  shall  inure to the  benefit  of, and be
binding upon,  the  respective  successors  and assigns of the  undersigned  and
Payee. THIS NOTE SHALL BE GOVERNED BY, AND CONSTRUED IN ACCORDANCE WITH THE LAWS
OF THE STATE OF CALIFORNIA  WITHOUT  GIVING EFFECT TO THE PRINCIPLES OF CONFLICT
OF LAWS THEREOF.

     IN WITNESS  WHEREOF,  the undersigned has caused this Promissory Note to be
executed  by its  authorized  representative,  who  certifies  that  he has  all
necessary authority on behalf of the undersigned to execute this Promissory Note
and bind the undersigned to the terms hereof.


                              POSITRON CORPORATION


                              By:
                                 --------------------------------

                              Its:
                                  -------------------------------

ATTEST:                       By:
                                 --------------------------------

                              Its:
                                  -------------------------------


<PAGE>


                 GRID TO PROMISSORY NOTE DATED APRIL _____, 1998


                 ISSUED BY POSITRON CORPORATION TO IMATRON INC.


                       ADVANCES AND PAYMENTS OF PRINCIPAL
<TABLE>
<S>                    <C>                 <C>                   <C>                  <C>

- ---------------------- -------------------- --------------------- --------------------- ---------------------

                                            Amount of             Unpaid                Notation
Date                   Amount of            Principal             Principal             Made
                       Advance              Paid                  Balance               By
- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------


- ---------------------- -------------------- --------------------- --------------------- ---------------------

</TABLE>
<PAGE>

                                    EXHIBIT B

                                TO LOAN AGREEMENT


                         OFFICER & BORROWING CERTIFICATE


     Reference  is  made  to  that  certain  Loan  Agreement   between  Positron
Corporation  ("Borrower") and Imatron Inc. ("Lender"),  dated May 1, 1998 ("Loan
Agreement"). In connection therewith, Borrower pursuant to Section 3.1(i) of the
Loan  Agreement does hereby request a loan in the amount of U.S. $ , such amount
to be paid by wire  transfer  in  immediately  available  funds into  Borrower's
account number at .

     In connection with such request, and in my capacity as ____________________
of Borrower, I hereby represent and warrant to you the following:

    (a) I am the  _________________________  of Borrower  and am  authorized  to
borrow on behalf of Borrower the above mentioned funds.

    (b) The amount borrowed hereunder is in accordance with and will not exceed,
any limit in the Loan Agreement.

    (c) No default or event  which with the giving of notice or lapse of time or
both would  constitute a Default  under the Loan  Agreement  has occurred and is
continuing or would result from the requested borrowing.

    (d) No  material  adverse  change,  other  than as  relates  to the lease on
property  located at 1304 Langham  Creek  Drive,  #310,  Houston  Texas 77084 as
disclosed on Schedule 5.5 of the Loan  Agreement has occurred  since the date of
the Loan Agreement in the financial condition or operations of the Borrower.

    (e) There is no judicial  proceeding or regulatory  action  instituted by or
against the Borrower, or, to the best of my knowledge, any threatened proceeding
or  action  which  may  materially  adversely  affect  (as  defined  in the Loan
Agreement)  the business,  property,  operation,  or financial  condition of the
Borrower.


                                        ---------------------------------------
                                      NAME


                                        ---------------------------------------
                                      TITLE


<PAGE>

                                    EXHIBIT C
                                TO LOAN AGREEMENT

                               SECURITY AGREEMENT
                               ------------------


     THIS SECURITY  AGREEMENT is made and entered as of the 1st day of May, 1998
by and between POSITRON CORPORATION  ("Borrower"),  a Texas corporation with its
principal  place of business at 1304 Langham Creek Drive,  Houston,  Texas 77084
and IMATRON INC.  ("Secured Party") a New Jersey  corporation with its principal
place of business at 389 Oyster Point Blvd., So. San Francisco, CA 94080.

     1.   Definitions.

     As used in this  Security  Agreement,  the  following  terms shall have the
following meanings unless the context requires otherwise:

     Loan  Agreement  means that certain  Loan  Agreement  between  Borrower and
Lender of even date herewith and pursuant to which this Agreement is given.

     Collateral means all of Borrower's right,  title and interest in and to the
following,  whether now owned or existing or  hereafter  arising or acquired and
wheresoever located: accounts,  accounts receivable and other rights of Borrower
to  payment  for goods sold or leased or for  services  rendered  (except  those
evidenced by  instruments  or chattel  paper);  computer  hardware and software,
including  but not  limited  to  computer  systems  and units,  drives,  cables,
generators,  accessories and all peripheral  devices,  software programs whether
now owned or licensed or leased or hereafter acquired by Borrower,  all firmware
associated  therewith,  all  documentation  and all rights  with  respect to the
foregoing;  copyrights,  registered or  unregistered,  now or hereafter in force
throughout the world, and all applications,  extensions and renewals;  equipment
of every  type  whether  owned  or  hereafter  acquired  and  wherever  located;
inventory and goods now owned or hereafter acquired held for sale or lease or to
be furnished  under any contract or which are raw materials,  work in process or
materials used or consumed in Borrower's business; licenses including all rights
under or interest in any trademark or service mark license  agreements  with any
other  party,  whether  Borrower  is  licensee or  licensor,  together  with any
goodwill  connection with such agreements;  patents including all letters patent
and  applications,   all  patent  licenses  and  all  reissues,   continuations,
extensions,  renewals and the like,  and all  proceeds of and rights  associated
with the foregoing; trade secrets, whether common law or statutory and all other
confidential  or proprietary  information  and know-how;  trademarks and service
marks now owned or existing or hereafter  acquired or arising and all  renewals,
income, royalties and rights associated therewith; general intangibles including
all rights, interests, choses in action, claims and other intangible property of
Borrower of every kind and nature now owned or  hereafter  acquired  and however
and whenever arising;  chattel paper, instruments and documents and all payments
thereunder; and all other property now owned or hereafter acquired.

     Borrower means the owner of the Collateral.

     Lien means any security interest,  mortgage,  deed of trust,  pledge, lien,
attachment,  claim, charge, encumbrance,  agreement retaining title, or lessor's
interest covering the Collateral.

     Obligations means Borrower's existing and future obligations under the Loan
Agreement and this Security Agreement.

     Service  Contract  means  each  and  every  agreement,  whether  oral or in
writing,  pursuant to which  Borrower  provides  service  under  warranty to its
customers with respect to products  manufactured  and sold by Borrower to any of
its customers.

     2. Grant of  Security  Interest.  To secure  prompt and  complete  payment,
observance and  performance of all obligations and liabilities of Borrower under
the Loan Agreement, the Note and this Agreement:

         a. Borrower  hereby  assigns and pledges to Secured  Party,  and hereby
grants to Lender, a lien and security interest in all of Borrower's right, title
and interest in and to the Collateral,  subject only to the security interest of
ProFutures Bridge Capital Fund, L.P.  ("ProFutures") as described in the certain
agreement(s)  by and among  Profutures,  Secured Party and Borrower  dated April
___, 1998 ("Lien  Agreement"),  attached to the Loan Agreement as Exhibit D, and
further subject to the security  interest of Uro-Tech Ltd., and  subordinated to
Secured Party  pursuant to the  Subordination  Agreement by and between  Secured
Party and Uro-Tech Ltd. dated as of April ___, 1998 ("Uro-Tech Lien  Agreement")
attached to the Loan Agreement as Exhibit E.

          b. Anything herein to the contrary notwithstanding, (i) Borrower shall
remain  solely  liable  under  the  contracts  and  agreements  included  in the
collateral  to the  extent set forth  therein  to perform  all of its duties and
obligations  thereunder  to the same extent as if this  Agreement  and any other
security  documents  executed in  connection  with this  Agreement  had not been
executed;  (ii) the exercise by Lender of any of its rights  hereunder shall not
release  Borrower from any of its duties or obligations  under the contracts and
agreements  included in the  Collateral;  and, unless  specifically  accepted by
Lender in writing, (iii) Lender shall not have any responsibility, obligation or
liability  under the  contracts  and  agreements  included in the  Collateral by
reason of this  Agreement or any other  Security  Document,  nor shall Lender be
required or  obligated,  in any manner,  to perform or fulfill any of Borrower's
obligations or duties thereunder, make any payment or make any inquiry as to the
nature or sufficiency of any payment  received by Borrower or the sufficiency of
any performance by any party under any such contract or agreement, or present or
file any claim or take any action to collect  or enforce  any claim for  payment
assigned thereunder.

     3. Promises of Borrower. Borrower promises:

         a. To perform the Obligations to Secured Party when they are due.

         b.  To  preserve  all  rights,   privileges,  and  franchises  held  by
Borrower's business.

         c. To keep the Collateral in good repair.

         d. To keep the  Service  Contracts  listed on Schedule 5 hereto in full
force and effect and  otherwise not to breach or otherwise not to default on any
of its obligations pursuant to the Service Contracts.

         e. To give  Secured  Party  notice  of any  litigation  that may have a
material adverse affect on the Collateral or the Service Contracts.

         f. Not to change its name or place of business,  or to use a fictitious
business name, without first notifying Secured Party in writing.

         g. Not to permit  Liens on the  Collateral,  nor to assign  its  rights
under the Service  Contracts to any third party,  except as  contemplated by the
ProFutures Lien Agreement and the Uro-Tech Lien Agreement.

         h. To permit  Secured  Party,  its  representatives,  and its agents to
inspect the Collateral, the Service Contracts and records relating to either the
Collateral  or the Service  Contracts  at any  reasonable  time  during  regular
business  hours,  and to  make  copies  of  records  pertaining  to  either  the
Collateral and/or the Service Contracts,  at reasonable times at Secured Party's
request.

         i.  To  notify  Secured  Party  promptly  in  writing  of any  default,
potential default,  or any development that might have a material adverse affect
on the Collateral or the Service Contracts.

         j. To execute and deliver to Secured Party all financing statements and
other  documents  that  Secured  Party  requests,  in order to  maintain a first
perfected  security  interest  in the  Collateral,  and to pay the  costs of, or
incidental to, all  recordings or filings of all financing  statements and other
security documents.

         k. To furnish  Secured  Party the  reports,  statements  and  schedules
further  describing the Collateral and Service  Contracts and such other reports
in connection  with the  Collateral  and Service  Contracts as Secured Party may
reasonably request, all in reasonable detail.

         l. To maintain all such casualty and liability  insurance  covering the
Collateral as Secured Party may reasonably request and to cause Secured Party to
be named as a loss payee.

     4.  Appointment  of  Secured  Party as  Attorney-in-Fact.  Borrower  hereby
appoints Secured Party or any other person whom Secured Party may designate,  as
Borrower's  attorney-in-fact  (exercisable  only  during  the  continuance  of a
Default) with the following powers:

          a. To perform any of Borrower's  obligations  under this  Agreement in
Borrower's name or otherwise.

          b. To prepare and file financing statements,  continuation statements,
statements of assignment,  termination statements, and the like, as necessary to
perfect,  protect,   preserve,  or  release  Secured  Party's  interest  in  the
Collateral.

          c. To endorse  Borrower's  name on  instruments,  documents,  or other
forms of payment or security that come into Secured Party's possession.

          d. To give  notice of  Borrower's  right to payment,  to enforce  that
right, and to make extension agreements with respect to it.

          e. To  release  persons  liable on rights to  payment,  to  compromise
disputes with those  persons,  and to surrender  security,  all as Secured Party
determines  in its  sole  discretion  when  acting  in good  faith  based on the
information known to it when it acts.

          f. To take cash in payment of Obligations.

          g. To verify  information  concerning  rights to payment by inquiry in
its own name or in a fictitious name.

     5.  Borrower's   Covenants,   Warranties  and   Representations.   Borrower
covenants, warrants, and represents as follows:

          a. Borrower is a corporation duly organized,  validly existing, and in
good standing under the laws of the  jurisdiction of its  organization,  and has
all necessary authority to conduct its business wherever it is conducted.

          b. Borrower has been authorized to execute and deliver this Agreement.
This Agreement is a valid and binding obligation of Borrower. Borrower will file
all  appropriate   financing  statements  pursuant  to  the  applicable  Uniform
Commercial Code and filings with the U.S.  Patent and Trademark  Office in order
to create perfected  security interests against the Collateral in which Borrower
now has rights,  consistent with the Pro-Futures Lien Agreement and the Uro-Tech
Lien Agreement.

          c.  Neither the  execution  and  delivery of this  Agreement,  nor the
taking of any action in compliance  with it, will (1) violate or breach any law,
regulation,  rule, order, or judicial action binding on Borrower,  any agreement
to which Borrower is party,  Borrower's  articles or incorporation or bylaws; or
(2) result in the creation of a lien against the Collateral  except that created
by this Agreement.

          d.  Borrower  owns  and  has  possession  of the  Collateral,  and the
Collateral  is not subject to any Liens or adverse  claims,  except as disclosed
and set forth in Schedule 4.5 to the Loan Agreement.

          e. All of the  properties  and assets owned by Borrower are owned free
and clear of any lien of any  nature  whatsoever,  except as  permitted  by this
Agreement  and/or  by  the  arrangements  contemplated  by  the  Lien  Agreement
("Permitted  Liens")  which  for this  purpose  means:  liens for taxes or other
governmental charges or levies, or claims of landlords,  carriers, mechanics and
the like  arising by  operation of law for which sums are not yet payable or are
fully stayed and being  contested;  liens created by this Agreement,  other Loan
documents  and/or the Lien  Agreements;  deposits or pledges to secure public or
statutory  obligations;  inchoate  liens arising  under the Employee  Retirement
Income Security Act of 1974 as amended to secure benefit plans from time to time
in  effect;  and  rights  reserve  to or  vested  in an  governmental  or public
authority to control or regulate  any property of Borrower or use such  property
in a manner which does not  materially  impair the use of such  property for the
purposes for which it is held by Borrower.  The liens created and granted by the
Security  Agreement and related  security  documents  constitute valid perfected
liens on the  Collateral,  subject  to no prior or equal lien  except  Permitted
Liens.

          f. The Service  Contracts  listed on Schedule 5 constitute all Service
Contracts which currently exist by and between  Borrower and its customers;  all
such Service Contracts are legal, valid, binding,  enforceable and in full force
and  effect  and are  materially  in the  form of  Service  Contract  previously
supplied to Lender as a sample of such Service Contracts;  no party is in breach
or default,  and no event has occurred  which with notice or lapse of time would
constitute a material breach or default, or permit termination, modification, or
acceleration, and no such action is threatened.

     6.  Continuing  Security  Interest.  This Agreement will terminate when (a)
Borrower  completes  performance of all obligations to Secured Party,  including
without  limitation  the  repayment of all  indebtedness  by Borrower to Secured
Party; and (b) Borrower has notified Secured Party in writing of the termination
and  Secured  Party   acknowledges  that  Borrower  has  fulfilled  its  payment
obligations  pursuant to the Loan Agreement and this Agreement.  Borrower agrees
that until all liabilities hereunder have been fully satisfied,  Secured Party's
security  interest in and liens on and against the Collateral,  and all proceeds
and  products  thereof,  shall  continue in full force and effect,  and Borrower
shall  perform  any and all  steps  reasonably  requested  by  Secured  Party to
perfect, maintain and protect Secured Party's security interests in and liens on
and against the Collateral  granted or purported to be granted hereby and by the
other security documents,  or to enable Secured Party to exercise its rights and
remedies hereunder with respect to the Collateral.

     7. Default. Borrower will be in default under this Agreement if:

          a. A Default  occurs  under the Loan  Agreement  or Borrower  fails to
perform any Obligation.

          b.  Borrower  commits any material  breach of this  Agreement,  or any
present or future rider or supplement to this Agreement.

          c. Any warranty, representation, or statement, made by or on behalf of
Borrower in or with respect to the Loan  Agreement or this  Agreement,  is false
when made in a material way.

          d. There is a seizure or attachment  of, or a levy on, the  Collateral
or any material part of it.

          e.  There is a  termination  of any  Service  Contract,  other than by
expiration or by the normal operation of its own terms.

          f. Borrower ceases operations, is dissolved, terminates its existence,
does or fails to do  anything  that allows  obligations  in excess of $25,000 to
become due before their stated maturity.

     8. Secured Party's Remedies. When an event of default occurs:

          a.  Secured Party may:

              (i) Declare the Obligations  immediately due and payable  -without
demand,  presentment,  protest,  or notice to  Borrower,  all of which  Borrower
expressly waives.

              (ii) Exercise all rights and remedies  available to it pursuant to
this Agreement  and/or all rights and remedies  available to a secured  creditor
after  default,  including but not limited to the rights and remedies of secured
creditors under the California Uniform Commercial Code.

     9. No Waiver. No waiver by Secured Party of any breach or default will be a
waiver of any breach or default  occurring later. A waiver will be valid only if
it is in writing and signed by the Secured Party.

     10.  Survival.  Borrower's  representations  and  warranties  made  in this
Agreement will survive its execution, delivery and termination.

     11.  Governing  Law.  This Security  Agreement is hereby  delivered in, and
shall be governed,  interpreted and enforced in accordance with the laws, of the
State of California.

     12.  Dispute Resolution.

          a. Any  controversy or claim between or among the parties  arising out
of or  relating  to  this  Security  Agreement  or  any  related  agreements  or
instruments ("Subject Documents"),  including any claim based on or arising from
an alleged tort, shall be submitted to and determined by arbitration  before one
(1) arbitrator who shall be an attorney admitted to practice law in the state of
California  in  accordance  with  Title 9 of the U.S.  Code  and the  Commercial
Arbitration  Rules  of the  American  Arbitration  Association  ("AAA")  then in
effect,  and shall be held in the county of San  Francisco,  CA. All statutes of
limitations  which would otherwise be applicable  shall apply to any arbitration
proceeding under this subparagraph  12(a).  Judgment upon the award rendered may
be entered in any court having jurisdiction. This subparagraph 12(a) shall apply
only if, at the time of the proposed  submission to AAA, none of the obligations
to Lender described in or covered by any of the Subject Documents are secured by
real  property  collateral  or,  if so  secured,  all  parties  consent  to such
submission.

          b. If the  controversy  or claim is not  submitted to  arbitration  as
provided  and  limited in Section  12(a),  but becomes the subject of a judicial
action,  any party may elect to have all decisions of fact and law determined by
a referee in accordance with applicable  state law. If such an election is made,
the parties shall  designate to the court a referee or referees  selected  under
the  auspices  of the AAA in the same  manner as  arbitrators  are  selected  in
AAA-sponsored proceedings. The referee, or presiding referee of the panel, shall
be an active  attorney or retired judge.  Judgment upon the award rendered shall
be entered in the court in which such proceeding was commenced.

          c. Except as provided herein,  no provision of, or the exercise of any
rights  under,  Section 12, shall limit the right of any party to exercise  self
help remedies such as setoff,  or to obtain  provisional  or ancillary  remedies
such as injunctive  relief or the  appointment of a receiver from a court having
jurisdiction  before,  during  or after the  pendency  of any  arbitration.  The
institution  and  maintenance  of an action  for  judicial  relief or pursuit of
provisional  or ancillary  remedies or exercise of self help remedies  shall not
constitute  a waiver of the right of any  party,  including  the  plaintiff,  to
submit the controversy or claim to arbitrators.

          d. The  parties  understand  and agree the  arbitration  will be their
exclusive form of resolving  disputes  between them regarding the issues covered
by this Agreement.  BOTH PARTIES EXPRESSLY WAIVE THEIR  ENTITLEMENT,  IF ANY, TO
HAVE CONTROVERSIES BETWEEN THEM DECIDED BY A JURY OR COURT OF LAW.

     13.  Notices.  Notices  under this  Agreement  shall be given in the manner
provided in the Loan Agreement.  Either party may change its address for service
of notice by notice to the other.

     14.  Counterparts.  This Agreement may be executed in counterparts and
all said  counterparts  taken together shall be deemed to constitute one and the
same instrument.

     IN WITNESS  WHEREOF,  the  parties  to this  Security  Agreement  have duly
executed it as of the date first above written.


                                       BORROWER:

                                       POSITRON CORPORATION
Tax ID No:


- -------------------------              By:
                                         -------------------------------
                                       Its:
                                          ------------------------------



                                       SECURED PARTY:

                                       IMATRON INC.

Tax ID No:


- ------------------------               By:
                                         ----------------------------------
                                       Its:
                                         ----------------------------------

<PAGE>
                                    EXHIBIT D

                 MODIFICATION AND CONSENT AGREEMENT BY AND AMONG

                              POSITRON CORPORATION

                                       AND

                      PROFUTURES BRIDGE CAPITAL FUND, L.P.


                           dated as of April 28, 1998

                      SUBORDINATION AGREEMENT BY AND AMONG

                                  IMATRON INC.,

                      PROFUTURES BRIDGE CAPITAL FUND, L.P.

                                       AND

                              POSITRON CORPORATION


                           dated as of April 28, 1998


<PAGE>


                       MODIFICATION AND CONSENT AGREEMENT
                       ----------------------------------

     This  Modification and Consent  Agreement (the "Agreement") is entered into
this  28th day of  April,  1998 by  Positron  Corporation,  a Texas  corporation
("Borrower")  and  ProFutures  Bridge  Capital  Fund,  L.P., a Delaware  limited
partnership ("Lender").

                                     FACTS

     A. Lender and Borrower entered into a Loan and Security  Agreement dated as
of November 14, 1996 and Promissory  Note (the "Note") of even date therewith in
the original principal amount of $1,400,000.00  executed by Borrower and payable
to the  order of  Lender  (together  with  certain  riders,  addenda  and  other
instruments,  documents or agreements  entered into in connection  therewith and
any extensions, amendments replacements or modifications to any of the foregoing
being  referred to as the "Loan  Documents")  pursuant to which Lender agreed to
extend the Loans and financial accommodations to the Borrower.

     B. The Loans referenced in the Loan Documents  matured on June 30, 1997 and
Borrower failed and has continued to fail to pay the  outstanding  principal and
interest on the Loans.

     C. Lender has notified  Borrower of its default under the Note and the Loan
Documents.

     D. The Borrower has agreed to make a payment on the Note and requested that
the Lender modify the Loan Documents to, among other things, extend the Maturity
Date of the Note.

     E. The Lender has agreed to modify the Loan Documents as set forth herein.

     F. Any and all  initially  capitalized  terms  used  herein  shall have the
meaning  ascribed  to them in the Loan  Documents  unless  specifically  defined
herein.

     NOW THEREFORE,  in  consideration of the foregoing and the mutual covenants
and promises contained herein the parties hereto do hereby agree as follows:

     1.  Borrower  and  Lender  hereby  agree  that as of April  20,  1998,  the
outstanding  principal  balance due and owing under the Note is $840,706.76 plus
accrued interest to such date of $5,804.33.

     2.  Borrower  does  hereby  agree that in  addition  to the  principal  and
interest due Lender as described  in Section 1 above,  the Borrower  owes (i) an
additional  $7,346.35  for  collection  costs and  expenses  of  Lender  through
December 9, 1997 and (ii) an additional  but  undetermined  amount of additional
collection  cost,  attorney's fees and expenses of Lender incurred in connection
with  Borrower's  Default  and the  modification  of the  Loan  Documents  after
December 9, 1997 (all such costs and expenses being herein  referenced to as the
"Lender Costs").

     3. Lender and Borrower  hereby  modify  certain  terms of the Note and Loan
Agreement as follows:

     (a) New subsections  2(a)(iii) and 2(a)(iv) are hereby added to the Note to
read as follows:

               "(iii)  From June 30, 1997 to November 30, 1997: 15% per annum;
and

               (iv)    From December 1, 1997 to the Maturity Date: 18% per
annum."

          (b) The  Maturity  Date as defined in the Note and Loan  Agreement  is
hereby amended to be the earlier of (i) October 5, 1998 or (ii) the date Imatron
Inc. ("Imatron") notifies the Borrower that Imatron no longer commits to use its
best efforts to raise  $8,000,000.00  in third party  financing for the Borrower
over the  eighteen  (18)  month  period  beginning  April 1, 1998 or to take all
reasonable  efforts to cause the placement  and purchase of ten (10)  Cardiology
Machines from the Borrower.

          (C) Paragraph 4 of the Note is hereby  amended to read in its entirety
as follows:

               "4.  Principal  and interest are payable in monthly  installments
          until the Maturity  Date;  at that time the entire amount of principal
          and accrued  interest  remaining  unpaid will be due and payable.  The
          monthly  installment  due is the greater of (a) $50,000.00 for each of
          the months of April, May, June and July, 1998 and $100,000.00 for each
          of the  months  of August  and  September,  1998 or (b) the  aggregate
          amount  received  by Payee from BCPA  (including  the option  purchase
          price) under the BCPA Contract  during the calendar month in which the
          monthly  installment  is due. Maker shall pay to Payee an amount equal
          to the  payment  received  by Maker from BCPA under the BCPA  Contract
          each month prior to the Maturity  Date;  such payment shall be due not
          later  than one day after  Maker  receives  the BCPA  payment.  If the
          amount paid by Maker to Payee  pursuant to the  immediately  preceding
          sentence  prior to the last day of each month is less than $50,000 for
          each of the months of April,  May, June and July, 1998 and $100,000.00
          for each of the months of August and September,  1998, Maker shall pay
          not  later  than the 5th day of the  following  month  the  difference
          between  such  amount  set forth  above for such  month and the amount
          actually  paid by Maker during such month.  All amounts due  hereunder
          shall  be paid to  Payee  at its  address  in the  State  of  Colorado
          specified  in  Section  1.  Lender  and  Borrower  agree that the BCPA
          installment  dated March 31, 1998 and  deposited by Lender on April 6,
          1998 shall be treated as a March 1998 payment."

     4. The Loan Documents  require the Lender consents to certain action of the
Borrower. In this regard, the Lender hereby consents to the following actions:

          (a) Borrower is  authorized to issue and sell for $100.00 to Imatron a
number of shares of the Borrower's common stock,  $0.01 par value,  equal to 51%
of the  Borrower's  outstanding  voting  securities  on a fully  diluted  basis,
exclusive  of  out of the  money  warrants  and/or  options  and/or  convertible
securities,  calculated  as of the closing  date.  For  purposes of this Section
4(a),  the  terms  "closing  date"  and "out of the  money"  are as  defined  in
paragraph 1 of that certain  Stock  Purchase  Agreement  dated April 1998 by and
between Borrower and Imatron (the "Purchase Agreement").

          (b) Borrower is  authorized  to borrow  $500,000.00  from Imatron (the
"Imatron  Loan") upon terms and conditions  acceptable to the Board of Directors
of the Borrower.

          (c) In  connection  with the  Imatron  Loan,  the  Borrower  may grant
Imatron  a  subordinate  lien  on all the  personal  property  of the  Borrower;
provided that Imatron and Borrower execute a Subordination Agreement in the form
as that attached hereto as Exhibit A.

     5. Notwithstanding anything contained in the Subordination Agreement to the
contrary,  the Lender  agrees that the  proceeds  received  from the third party
subordinated   financing,   whether   equity  or  debt,   arranged   by  Imatron
("Financing")  may be used and  allocated as herein  described.  Financing in an
aggregate amount equal to the first $1,000,000 (the "Financing Threshold") shall
remain as working  capital for the Borrower and shall not be required to be used
by the Borrower to repay any  principal  owing on the Note that is not past due;
provided  such sums are not used to pay any  principal or interest  owing on the
Imatron  Loan.  The  Borrower  shall use one-half  (1/2) of each dollar  ($1.00)
received  above the  Financing  Threshold to repay any and all  principal  (and,
thereafter,  accrued  interest)  outstanding  under  the  terms  of the Note and
Borrower  shall use the other one-half (1/2) of such dollar ($1.00) to repay any
and all amounts of  principal  and interest  outstanding  under the terms of the
Imatron Loan.  The  provisions  of this  paragraph 5 shall not be construed as a
modification  of any of the  other  provisions  of  the  Loan  Agreement  or the
Subordination  Agreement,  shall not relieve the Borrower's  obligations to make
the monthly  payments  due under the Note from any source and shall not amend or
alter the  Maturity  Date or the  Borrower's  obligation  to pay the Note on the
Maturity Date.

     6. Borrower  acknowledges that certain Events of Default have occurred (the
"Prior Defaults") and are continuing as of the date of this Agreement.  In order
to allow the Borrower to consummate the Imatron Loan, the Lender agrees to waive
all Prior  Defaults  and not to pursue  any  remedies  available  under the Loan
Documents as a result of the Prior  Defaults.  The waiver of the Prior  Defaults
and Lender's agreement not to pursue its remedies with respect to Prior Defaults
shall in no way be construed as a waiver or impairment of the Lender's interests
and right under the Loan  Documents,  including,  but not  limited to,  Lender's
right to exercise any rights and remedies  provided in the Loan  Documents  with
respect  to Events of Default  occurring  at any time or from time to time after
the  date of this  Agreement,  and  such  rights  shall  be  cumulative  and not
exclusive.

     7. In order to induce the Lender to waive the Prior  Defaults  and  execute
this Agreement the Borrower agrees to issue and deliver to Borrower simultaneous
with the execution of this Agreement a Stock  Purchase  Warrant for Common Stock
to purchase  1,150,000 shares of Common Stock,  $0.01 par value, of the Borrower
at a purchase price of $0.25 per share (the  "Warrant") in the form of Exhibit B
attached  hereto and made a part hereof.  In addition,  simultaneously  with the
execution of this  Agreement,  the Borrower  shall  deliver to Lender the sum of
$50,000 cash (the "Special Payment"). The Special Payment shall be used first to
pay all Lender Costs and,  thereafter,  applied to the Note.  The portion of the
Special  Payment  applied to the Note is in addition to and shall not constitute
any portion of any scheduled monthly  installments  required by the terms of the
Note.  Lender  acknowledges that the Borrower does not currently have sufficient
shares of Common  Stock for  issuance  upon  exercise  of the  Warrants  and the
Additional Warrants described herein.

     8. Lender hereby  agrees that the Borrower  shall have the right and option
as  described  herein to redeem a portion of the shares of Common Stock that are
subject  to the  Warrant  by  payment  of all or a  portion  of the  outstanding
principal and interest on the Note as follows:

          (i) If the Note is paid in full prior to May 31,  1998,  the number of
shares of Common  Stock,  $0.01 par value,  represented  by the Warrant  will be
reduced by 650,000 shares to 500,000 shares;

          (ii) If the Note is paid in full prior to June 30, 1998, the number of
shares of Common  Stock,  $0.01 par value,  represented  by the Warrant  will be
reduced by 500,000 shares to 650,000 shares;

          (iii) If a portion  of the Note,  in excess of the  scheduled  monthly
payments,  is repaid to Lender  prior to May 31,  1998,  the number of shares of
Common Stock,  $0.01 par value,  represented  by the Warrant shall be reduced by
one (1) share of Common Stock,  $0.01 par value,  to a maximum of 650,000 shares
for each one dollar ($1.00) of principal (in excess of scheduled  payments) that
the Note is repaid prior to May 31, 1998; and

          (iv) If a portion  of the Note,  in  excess of the  scheduled  monthly
payments,  is repaid to Lender prior to June 30,  1998,  the number of shares of
Common Stock,  $0.01 par value,  represented  by the Warrant shall be reduced by
three-quarters  (3/4) of a share of  Common  Stock,  $0.01  par  value,  up to a
maximum of  500,000  shares  (rounded  down to the  nearest  share) for each one
dollar  ($1.00) of principal (in excess of scheduled  payments) that the Note is
repaid prior to June 30, 1998.

     9. The Borrower and Lender hereby modify Section 6 of the Loan Agreement to
add the following Affirmative Covenants at the end of such Section

                   "L. BCPA  Contract.  Borrower shall notify Lender within five
         (5) days of the  execution  of this  Agreement  of (i)  BCPA's  alleged
         option purchase price for the Cardiology Machine that is subject to the
         BCPA  Contract as  calculated by Borrower and (ii) the amount and terms
         of payment credits available in Borrower's  opinion to BCPA (in detail)
         under  the  terms  of the  BCPA  Contract.  Borrower  will use its best
         efforts to cause BCPA to exercise its option to purchase the Cardiology
         Machines in accordance with the BCPA Contract.

                   M. Increase in Authorized  Shares.  On or before the Maturity
         Date  of  the  Note,   the   Borrower   shall  cause  its  Articles  of
         Incorporation to be amended and its Certificate of Amendment duly filed
         to  increase  the  number of shares of common  stock  authorized  to be
         issued to am amount equal to (i) the outstanding  number of shares plus
         (ii) the number of shares  which could be issued  upon the  exercise of
         all outstanding warrants, options, contracts or commitments of any kind
         entitling  Person to purchase  or  otherwise  acquire  shares of common
         stock of Borrower.

                   N.  Notice of  Imatron  Termination.  Borrower  shall  advise
         Lender in  writing  within  twenty-four  (24)  hours  after  Borrower's
         receipt of notice (oral or written) from Imatron that Imatron no longer
         intends to use its best  efforts to assist the  Borrower  in  obtaining
         financing  or no longer  intends  to use its best  efforts to cause the
         placement  and  purchase  of ten  (10)  Cardiology  Machines  from  the
         Borrower."

     10. Except as otherwise set forth herein this  Agreement  shall not impair,
limit,  restrict or otherwise affect the obligations of Borrower to Lender under
the Loan Documents. Borrower hereby acknowledges, agrees and represents that (a)
Borrower  is  indebted  to Lender  pursuant to the terms of the Note as modified
hereby and Borrower agrees that the Loan Documents are valid and binding and are
in full force and effect according to their terms and conditions; (b) the Liens,
security  interests and assignments  created and evidenced by the Loan Documents
are,   respectively,   valid  and  subsisting  liens,   security  interests  and
assignments  of  the  respective  dignity  and  priority  recited  in  the  Loan
Documents;  (c)  Borrower  has no claims,  offsets,  defenses  or  counterclaims
against  Lender whether  arising under the Loan Documents or otherwise;  and (d)
Lender is not in default and no event has  occurred  which,  with the passage of
time,  giving of  notice,  or both,  would  constitute  a  default  by Lender of
Lender's  obligations under the Security  Documents.  To the extent Borrower now
has any  claims,  offsets,  defenses  or  counterclaims  against  Lender  or the
repayment of all or a portion of the Note,  whether  known or unknown,  fixed or
contingent, the same are hereby forever irrevocably waived and released in their
entirety.

     11.  Lender has been advised that Borrower has amended or modified the BCPA
Contract.  Lender  has not and  does  not  consent  to any  such  amendments  or
modifications  and  nothing in this  Agreement  shall  constitute  the  Lender's
agreement and consent to be bound by the terms or  conditions of any  amendments
or modifications. The provisions of this Agreement shall not constitute Lender's
consent or agreement  to the amount of the payment  credits  allegedly  given by
Borrower to BCPA under any amendments to the BCPA Contract.

     12. Lender and Borrower agree that,  except as modified herein,  all of the
terms and conditions of the Loan Documents are hereby ratified and reaffirmed.

     13. The terms and  conditions of this  Agreement  shall not be binding upon
Lender  unless  the  Borrower  satisfies  or  fulfills  each  of  the  following
conditions on or before May 1, 1998:

          (a)  Borrower's  delivery to Lender of a certificate  of an officer of
Borrower  certifying  that  attached  thereto  is a true  and  correct  copy  of
resolutions of the Board of Directors of Borrower  authorizing  the execution of
this Agreement, the Subordination Agreement and the issuance of the Warrant;

          (b) Borrower's delivery to Lender of a duly executed Warrant;

          (c)  Borrower's delivery to Lender of $50,000 cash;

          (d)  Borrower's  delivery to Lender of a duly  executed  Subordination
Agreement;

          (e)  Delivery to Lender of the written  consent  from  Uro-Tech,  Ltd.
(together  with  any  other  required   approvals  or   authorization)   to  the
transactions  contemplated  or described in this  Agreement and a  Subordination
Agreement in a form acceptable to Imatron;

          (f)  Delivery to Lender of evidence  of the  consummation  of the loan
transaction  between  Borrower  and  Imatron  and the  receipt by  Borrower of a
minimum of $200,000 in loan proceeds from Imatron; and

          (g)  Delivery  to Lender of the two (2)  agreements  representing  the
stock  purchase  warrants  (each for 50,000  shares)  previously  granted to the
Lender (the "Additional Warrants").


                                    POSITRON CORPORATION

                                    By:
                                       ---------------------------------------
                                        Gary Wood, Chairman



                      PROFUTURES BRIDGE CAPITAL FUND, L.P.


                                    By:  Bridge Capital Partners, Inc.,
                                          General Partner

                                         By:

<PAGE>
                                    EXHIBIT A


                             SUBORDINATION AGREEMENT


<PAGE>
                             SUBORDINATION AGREEMENT


         THIS SUBORDINATION  AGREEMENT ("Agreement") is made and entered into as
of  April 28,  1998,  by and  among  IMATRON,  INC.,  a  _____________  company
("Subordinated  Creditor"),  PROFUTURES  BRIDGE  CAPITAL FUND,  L.P., a Delaware
limited  partnership  ("Senior  Creditor"),  and POSITRON  CORPORATION,  a Texas
corporation ("Borrower").

                                    RECITALS:

         Senior Creditor and Borrower are parties to a certain Loan and Security
Agreement  dated  November  14,  1996  (as  at  any  time  amended,   the  "Loan
Agreement"),  pursuant to which Senior Creditor made Loans to or for the benefit
of Borrower from time to time, secured by all or substantially all of the assets
of Borrower.  Capitalized  terms used in these  Recitals  and  elsewhere in this
Agreement, unless otherwise defined, shall have the meanings ascribed to them in
the Loan Agreement as in effect on the date hereof.

         Borrower and Subordinated Creditor are parties to the Subordinated Loan
Agreement dated as of April __, 1998 pursuant to which Subordinated Creditor has
agreed to loan $500,000  pursuant to the terms of a certain  Promissory  Note of
even date therewith (the  "Subordinated  Note"), on the terms and conditions set
forth in the Subordinated  Loan Agreement and  Subordinated  Note and secured by
subordinate Liens on all or substantially all of the assets of the Borrower.

         Senior  Creditor and  Subordinated  Creditor  desire to agree as to the
relative  rights of payment and other  rights under their  respective  financing
arrangements  and to memorialize  certain other  agreements  with respect to the
enforcement of their respective rights and remedies against the Borrower.

         NOW,  THEREFORE,   for  TEN  DOLLARS  ($10.00)  in  hand  paid  and  in
consideration of the foregoing premises, and other valuable  consideration,  the
receipt  and  sufficiency  of which  are  hereby  acknowledged,  and the  mutual
covenants  herein,  and to induce Senior  Creditor to consent to the Subordinate
Debt by and between  Subordinated  Creditor and  Borrower,  the parties  hereto,
intending to be legally bound hereby, agree as follows:

 1.       Definitions; Rules of Construction.

          (a) In addition to such other terms as are elsewhere  defined  herein,
as used in this Agreement the following terms shall have the following meanings:

                   "Bankruptcy Code" shall mean title 11 of the United States
Code.

                   "Enforcement  Expenses"  shall mean all reasonable  costs and
expenses  incurred by Senior  Creditor in connection with its enforcement of any
rights or remedies under the Senior Creditor Loan  Documents,  the collection of
any of the Senior Debt or the protection of, or realization upon, any Collateral
after the  occurrence  and  during the  continuance  of a Senior  Debt  Default,
including, by way of example, reasonable attorneys' fees, court costs, appraisal
and consulting fees,  auctioneer's fees, rent,  storage,  insurance premiums and
like  items and  whether or not such  amounts  are  allowed  as a claim  against
Borrower under the Bankruptcy Code.

                   "Payment  Default"  shall  mean a Senior  Debt  Default  that
results  from  Borrower's  failure to pay any of the Senior Debt on the due date
thereof  (whether  due at  stated  maturity,  upon  acceleration,  on  demand or
otherwise).

                   "Plan" shall mean a plan  proposed in a proceeding  under the
Bankruptcy  Code  for  the  reorganization  or  rehabilitation  of  Borrower,  a
composition or extension of any of Borrower's Debts or a liquidation in whole or
in part of Borrower's assets.

                   "Reorganization  Securities" shall mean (i) the securities of
Borrower (including senior securities)  provided for by a plan of reorganization
of  Borrower  that has been  proposed  in a case under the  Bankruptcy  Code and
confirmed by final order of the bankruptcy court having  jurisdiction  over such
case,  and (ii)  shares of common  stock or other  equity  securities,  and debt
securities,  the  payment  of which  is  subordinated,  at  least to the  extent
provided in this Agreement with respect to the Subordinated Debt, to the payment
of all  Senior  Debt at the  time  outstanding  and to the  payment  of all debt
securities issued in exchange therefor to Senior Creditor, which shares or other
equity or debt  securities  have been  provided for by a plan of  reorganization
which has been adopted or agreed to other than pursuant to a proceeding referred
to in clause (i) of this  definition and which has been approved or agreed to by
Senior Creditor.

                   "Senior  Creditor Loan Documents"  shall mean and include (i)
the Loan  Agreement,  the other Loan  Documents,  and all other  instruments  or
agreements  now or hereafter  evidencing or securing the payment of the whole or
any part of the Senior Debt and (ii) all  renewals,  modifications,  extensions,
refinancings, restructurings or replacements thereof.

                   "Senior  Debt" shall mean (i) all  liabilities,  indebtedness
and  obligations of Borrower now or hereafter  existing under or with respect to
any of the Senior Creditor Loan Documents,  whether such  obligations are now or
hereafter existing and however and whenever made or incurred, and whether direct
or  indirect,  absolute  or  contingent,  due or to become  due,  or  secured or
unsecured,  including  all  principal,  interest  and  premium on, and all other
amounts  payable  in  respect  of, any of such  obligations,  and all  indemnity
amounts,  reimbursement obligations and other amounts owed by Borrower to Senior
Creditor  thereunder,  (ii) any and all loans made or other  credit  extended by
Senior Creditor to Borrower during the pendency of any insolvency  proceeding of
Borrower,  (iii) all interest at any time accrued with respect to the  foregoing
(including any interest that accrues during the pendency of any bankruptcy  case
of Borrower,  whether or not Senior Creditor is authorized by Section 506 of the
Bankruptcy  Code  to  collect  such  interest  from  Borrower),   and  (iv)  all
Enforcement  Expenses for which  Borrower is now or hereafter  becomes liable to
pay to  Senior  Creditor  in  connection  with any of the  foregoing  under  any
agreement or by applicable law.

                   "Senior Debt  Default"  shall mean an Event of Default  under
(and as defined in) the Senior Creditor Loan Documents.

                   "Subordinated   Debt"   shall   mean  (i)  all   liabilities,
indebtedness and obligations of Borrower to Subordinated  Creditor under or with
respect to any of the  Subordinated  Debt Documents,  whether such  liabilities,
indebtedness  or  obligations  are now or  hereafter  existing  and  however and
whenever  made  or  incurred,  and  whether  direct  or  indirect,  absolute  or
contingent,  due or to become  due,  or  secured  or  unsecured,  including  all
principal, interest and premium on, and all other amounts payable in respect of,
the  Subordinated  Note,  and all  fees,  charges,  commitment  or  other  fees,
indemnity amounts,  enforcement expenses (including  reasonable attorneys' fees)
and other amounts owing by Borrower to  Subordinated  Creditor  under any of the
Subordinated Debt Documents; and (ii) all renewals,  extensions,  substitutions,
refundings,   refinancings,   restructurings   or   replacements   of  any  such
liabilities,  indebtedness  or obligations  (including all successive  renewals,
extensions,   substitutions,   refundings,   refinancings,   restructurings   or
replacements of such liabilities, indebtedness or obligations).

                   "Subordinated  Debt  Default"  shall mean an Event of Default
under, and as defined in, the Subordinated Loan Agreement.

                   "Subordinated  Debt  Documents"  shall mean and  include  the
Subordinated  Loan Agreement,  the Subordinated  Note, and all other instruments
and agreements now or hereafter  evidencing or securing the payment of the whole
or any part of the Subordinated Debt.

          (b) The terms  "herein,"  "hereof' and  "hereunder" and other words of
similar  import  refer to this  Agreement  as a whole and not to any  particular
section,  paragraph  or  subdivision.  All  references  to statutes  and related
regulations shall include any amendments of same and any successor  statutes and
regulations.  All references to any instruments or agreements  shall include any
and all  modifications  thereto  and any and  all  restatements,  extensions  or
renewals  thereof.   All  references  to  "including"  and  "include"  shall  be
understood to mean "including, without limitation."

 2.       Subordination.

          (a) Except as  otherwise  provided  in the  Modification  and  Consent
Agreement  of  even  date by and  between  Borrower  and  Senior  Creditor  (the
"Consent"),  Subordinated  Creditor hereby postpones and subordinates all of the
Subordinated  Debt to the full and final  payment  and  discharge  of all of the
Senior Debt and Senior  Creditor shall be entitled to receive payment in full of
all Senior Debt before any payment (other than a distribution of  Reorganization
Securities) is made on account of or applied to any of Subordinated Debt.

          (b) Subordinated Creditor hereby subordinates any security interest or
liens it now has or may hereafter  acquire in the Collateral and other assets of
the Borrower to any security  interest in or liens upon the  Collateral or other
assets of Borrower  which  Senior  Creditor has under the Senior  Creditor  Loan
Documents or otherwise.

          (c) Each  holder of  Subordinated  Debt,  whether now  outstanding  or
hereafter  created,  incurred,  assumed or  guaranteed,  shall be deemed to have
acquired the Subordinated  Debt with full knowledge and subject to the terms and
provisions of this Agreement.

          (d) In the event of any distribution, division or application, partial
or complete,  voluntary or involuntary, by operation of law or otherwise, of all
or any part of the assets of the Borrower or the  proceeds  thereof to creditors
of the  Borrower  or upon any  indebtedness  of the  Borrower,  by reason of the
liquidation,  dissolution  or other winding up of the Borrower or the Borrower's
business,  or in the event of any sale of assets of the  Borrower or  insolvency
proceeding  involving the Borrower or its assets, then and in any such event any
payment or distribution of any kind or character, whether in cash, securities or
other property (excluding Reorganization Securities),  which shall be payable or
deliverable upon or with respect to any of the  Subordinated  Debt shall be paid
or  delivered  directly  to Senior  Creditor  for  application  as required by a
certain Inter-Creditor Agreement by and between Senior Creditor,  Uro-Tech, Ltd.
and Boston Financial & Equity  Corporation (the  "Inter-Creditor  Agreement") to
the Senior  Debt  (whether  or not the same is then due) until all of the Senior
Debt has been fully paid and discharged. Each instrument evidencing Subordinated
Debt shall at all times bear a  conspicuous  legend that the  Subordinated  Debt
evidenced thereby is subordinated to the Senior Debt pursuant to this Agreement.
The  books  and  records  of  Subordinated  Creditor  and any  other  holder  of
Subordinated  Debt shall be marked to evidence the  subordination  of all of the
Subordinated Debt to and in favor of the Senior Debt.

 3.       Warranties and Representations.

          (a) Except as otherwise provided in the Consent, Subordinated Creditor
hereby  represents  and warrants that: (i) it has not relied nor will it rely on
any  representation or information of any nature made by or received from Senior
Creditor  relative to Borrower in deciding to execute  this  Agreement;  (ii) no
part of the  Subordinated  Debt is evidenced by any instrument or writing except
the Subordinated Debt Documents; (iii) Subordinated Creditor is the lawful owner
of the Subordinated Debt; (iv) Subordinated Creditor has not heretofore assigned
or transferred any of the Subordinated  Debt, or any interest  therein;  and (v)
Subordinated  Creditor has not heretofore given any  subordination in respect of
the Subordinated Debt.

          (b) Subordinated  Creditor hereby represents and warrants that it will
vote the shares of Capital Stock of the Borrower owned by Subordinated  Creditor
in favor of any Amendment to the Articles of Incorporation of Borrower necessary
to  increase  the  number  of  shares  authorized  to an  amount  equal  to  the
outstanding shares and the number of shares deliverable upon the exercise of all
outstanding  options,   warrants  and  other  commitments  to  issue  shares  of
Borrower's Capital Stock.

          (c) Each of the parties hereto  represents and warrants to each of the
other parties hereto that this Agreement has been duly executed and delivered by
such party and is the valid and binding  obligation  of such party,  enforceable
against  such  party  in  accordance  with  the  terms  hereof,  except  as such
enforceability  may  be  limited  by  bankruptcy,  insolvency  or  similar  laws
affecting creditors' rights generally and by principles of equity.

          (d)  Subordinated   Creditor   acknowledges  that  the  Inter-Creditor
Agreement  subordinates the Senior Creditor's  priority in certain assets of the
Borrower.

          (e) Subordinated  Creditor agrees to copy the Senior Creditor with any
notices of default sent by Subordinated Creditor to the Borrower and with a copy
of any notices to Borrower advising Borrower that Subordinated Creditor will not
assist  the  Borrower  in raising  additional  capital  or  purchasing  ten (10)
Cardiology Machines from Borrower.

 4. Negative Covenants. For so long as this Agreement is in effect, Borrower and
Subordinated  Creditor  agree with Senior  Creditor  that,  except as  otherwise
expressly provided in this Agreement and in the Consent: (a) Borrower shall not,
directly  or  indirectly,  make  any  payment  on  account  of any  part  of the
Subordinated Debt; (b) Subordinated Creditor shall not demand, collect or accept
from  Borrower  any  payment  on account  of the  Subordinated  Debt or any part
thereof,  or accelerate the maturity of the Subordinated  Debt; (c) Subordinated
Creditor shall not exchange,  set off,  release,  convert to equity or otherwise
discharge any part of the Subordinated Debt; (d) Subordinated Creditor shall not
enforce or apply any security,  now or hereafter  existing for the  Subordinated
Debt; (e)  Subordinated  Creditor shall not hereafter give any  subordination in
respect  of any of the  Subordinated  Debt  or  transfer  or  assign  any of the
Subordinated  Debt;  (f) Borrower  shall not hereafter  issue any  instrument or
other  writing  evidencing  any part of the  Subordinated  Debt  other  than the
Subordinated Debt Documents, and Subordinated Creditor will not receive any such
writing;  (g)  Subordinated  Creditor  shall not commence or join with any other
creditors of Borrower in commencing any  bankruptcy,  assignment for the benefit
of  creditors or  creditor's  agreement;  (h)  Subordinated  Creditor  shall not
institute,  or  join  as a  party  in  the  institution  of,  or  assist  in the
prosecution of, any action,  suit or proceeding seeking a determination that the
security  interest  of Senior  Creditor  in any of the  Collateral  is  invalid,
unperfected or avoidable,  or is or should be  subordinated  to the interests of
any others; and (i) Subordinated Creditor otherwise shall not take or permit any
action  inconsistent with Senior Creditor's  priority position over Subordinated
Creditor that is created by this Agreement.  Notwithstanding  anything contained
herein to the  contrary,  the  parties  hereto  agree that the  Borrower  or the
Subordinated  Creditor,  as the  case  may  be,  may  take  any  of the  actions
restricted  in this  Section 4 with the  express  written  consent of the Senior
Creditor  (which  consent may be withheld at the sole  discretion  of the Senior
Creditor).

 5.  Payment and Remedy Bars.

          (a) Until  payment in full of the Senior Debt, no payment with respect
to the  Subordinated  Debt  (include  any  payment due at  maturity,  whether by
acceleration  or  otherwise)  shall  be  made  by  or  on  behalf  of  Borrower.
Notwithstanding the provisions of this Agreement, if the Borrower receives third
party subordinate financing from sources arranged by the Subordinated  Creditor,
whether  equity or debt  ("Financing"),  in an amount in excess of $1,000,000 in
the aggregate  ("Financing  Threshold")  after the date of this  Agreement,  the
Senior  Creditor hereby agrees that (provided that principal and interest on the
Senior Debt is not past due) one-half  (1/2) of each dollar  received  above the
Financing  Threshold  from such  Financing  may be used to repay  principal  and
interest owing to the Subordinated Creditor; provided that a like amount is used
to pay principal and interest owing to the Senior Debt.

          (b) The Subordinated Creditor agrees that until payment in full of the
Senior  Debt,  no holder  of  Subordinated  Debt  shall  take any  action to (x)
accelerate the maturity of, or demand as immediately due and payable, all or any
part of the  Subordinated  Debt,  (y) commence,  continue or  participate in any
judicial,  arbitral or other proceeding or any other  enforcement  action of any
kind  against  Borrower  or  any  of  such  Borrower's   assets  (including  any
involuntary   proceeding  under  the  Bankruptcy  Code)  seeking,   directly  or
indirectly, to enforce any of their rights or remedies, or to enforce any of the
obligations  incurred by Borrower under or in connection  with the  Subordinated
Debt or the Subordinated Debt Documents, or (z) commence or pursue any judicial,
arbitral or other proceeding or legal action of any kind,  seeking injunctive or
other equitable relief to prohibit,  limit or impair the commencement or pursuit
by Senior  Creditor of any of its rights or remedies under or in connection with
the Senior  Creditor Loan  Documents or otherwise  available to Senior  Creditor
under applicable law.

 6. Turnover of Prohibited Transfers.  If notwithstanding the provisions of this
Agreement  any  payment,  distribution,   Collateral  or  security  (other  than
Reorganization  Securities), or the proceeds thereof, are received by any holder
of  Subordinated  Debt on account of or with respect to any of the  Subordinated
Debt,   such  payment,   distribution,   Collateral  or  security   (other  than
Reorganization  Securities) shall be held in trust for the benefit of, and shall
immediately  be paid or delivered  by such holder to the Senior  Creditor in the
form  received  (except  for  the  addition  of any  endorsement  or  assignment
necessary  to effect a transfer of all rights  therein to Senior  Creditor)  for
application to the Senior Debt and other Borrower debt in the order  established
by the Inter-Creditor  Agreement.  Senior Creditor is irrevocably  authorized to
supply any required endorsement or assignment which may have been omitted. Until
so delivered,  Subordinated  Creditor  shall exercise its best efforts to ensure
that such payment,  distribution  or security shall not be commingled with other
funds or property of Subordinated Creditor.

 7.       Amendments to Documents.

          (a) Senior  Creditor and Borrower  shall be authorized to amend any of
the Senior  Creditor Loan Documents to which they are a party in accordance with
the terms  thereof,  and  without  prior  notice to or the consent of any of the
holders of the Subordinated Debt.

          (b)  Without  the prior  written  consent  of Senior  Creditor  (which
consent may be given or  withheld  in Senior  Creditor's  sole  discretion),  no
provision  of the  Subordinated  Debt  Documents  shall be amended,  modified or
supplemented  if the  effect  thereof  would be to (i)  advance  the  originally
scheduled dates for the payment of principal,  interest or other sums payable in
respect of any  Subordinated  Debt, or modify in any manner  adverse to Borrower
the dates for or premiums payable in connection with prepayments, (ii) impose on
Borrower  prepayment  charges,  closing  fees or other  fees or (iii)  impose on
Borrower any representations,  warranties, covenants, events of default or other
provisions  that are more  restrictive  or burdensome to Borrower than the terms
and  provisions of the  Subordinated  Debt Documents as in effect on the date of
this Agreement.

 8. Certain Waivers and Consents. Borrower and Subordinated Creditor each hereby
waives  any  defense  based on the  adequacy  of a remedy at law which  might be
asserted as a bar to the remedy of specific performance of this Agreement in any
action brought therefor by Senior  Creditor.  To the fullest extent permitted by
applicable law,  Borrower and Subordinated  Creditor each hereby further waives:
presentment,  demand, protest, notice of protest, notice of default or dishonor,
notice of payment or nonpayment and any and all other notices and demands of any
kind in connection with all negotiable instruments evidencing all or any portion
of the Senior  Debt;  the right to  require  Senior  Creditor  to  marshall  any
Collateral or security,  or to enforce any Lien that Senior  Creditor may now or
hereafter have in any Collateral securing the Senior Debt or to pursue any claim
it may have against any  guarantor of the Senior Debt,  as a condition to Senior
Creditor's  entitlement  to receive any  payment on account of the Senior  Debt;
notice of the acceptance of this Agreement by Senior Creditor; and notice of any
credit made available to Borrower, extensions of time granted, amendments to the
Loan  Agreement or the other Senior  Creditor  Loan  Documents,  or other action
taken in reliance hereon.  Subordinated Creditor hereby consents and agrees that
Senior  Creditor may,  without in any manner  impairing,  releasing or otherwise
affecting  the  subordination  provided  for in this  Agreement or any of Senior
Creditor's  rights  hereunder  and  without  prior  notice to or the  consent of
Subordinated Creditor:  release, renew, extend,  compromise or postpone the time
of payment of any of the Senior Debt; substitute, exchange or release any or all
of the Collateral or decline or neglect to perfect Senior  Creditor's  Lien upon
any of the Collateral; add or release any Person primarily or secondarily liable
from any of the Senior  Debt;  amend or modify any of the Senior  Creditor  Loan
Documents or waive any Senior Debt Default;  and increase or decrease the amount
of the Senior Debt or the rate of  interest  or the amount of any other  charges
payable in connection therewith.

 9.  Subrogation.  Provided that the Senior Debt has been  indefeasibly paid and
discharged  and any  commitment  that Senior  Creditor may have under the Senior
Creditor Loan Documents to make loans or extend other credit has been terminated
or expired,  the holders of Subordinated  Debt shall be subrogated  (without any
representation  by or  recourse  to  Senior  Creditor)  to the  rights of Senior
Creditor to receive payments or  distributions  of cash,  property or securities
payable or  distributable  on account of the Senior Debt, to the extent that the
Senior Creditor would be entitled to have such payments and  distributions  paid
over to or for its benefit; and for the purpose of such subrogation,  no payment
or distribution to Senior Creditor of any cash,  property or securities to which
the holders of  Subordinated  Debt would  otherwise  be entitled  except for the
provisions of this Agreement,  and no payment pursuant to the provisions of this
Agreement to Senior  Creditor by the holders of  Subordinated  Debt,  shall,  as
between Borrower and its creditors other than Senior Creditor and the holders of
Subordinated Debt, be deemed to be a payment by Borrower to or on account of any
Subordinated Debt, it being understood that the provisions of this Agreement are
solely for the purpose of defining the relative  rights of Senior  Creditor,  on
the one hand, and the holder of  Subordinated  Debt, on the other.  In no event,
however, shall any holder of Subordinated Debt have any rights or claims against
Senior Creditor for any impairment of Subordinated Creditor's subrogation rights
that  might  result  from  Senior  Creditor's  release  of  any  Lien  upon  any
Collateral, forgiveness,  compromise, extension or discharge of any Senior Debt,
release of Borrower, or vote to accept or reject any Plan.

 10.  Statement  of Account.  Subordinated  Creditor  agrees to render to Senior
Creditor from time to time upon Senior  Creditor's  request therefor a statement
of Borrower's  account with Subordinated  Creditor and Borrower agrees to afford
Senior Creditor access to the books and records of Borrower in order that Senior
Creditor may make a full  examination  of the state of accounts of Borrower with
Subordinated Creditor

 11.   Validity  of   Subordinated   Debt.  The  provisions  of  this  Agreement
subordinating  the  Subordinated  Debt to the  Senior  Debt are  solely  for the
purpose of defining the  relative  rights of Senior  Creditor  and  Subordinated
Creditor and shall not impair,  as between  Subordinated  Creditor and Borrower,
the  obligation of Borrower,  which is  unconditional  and absolute,  to pay the
Subordinated  Debt in accordance with its terms except as payment thereof may be
postponed in accordance with this Agreement.

 12.  Indulgences Not Waivers.  Neither the failure nor any delay on the part of
Senior  Creditor to exercise any right,  remedy,  power or  privilege  hereunder
shall operate as a waiver thereof or give rise to an estoppel,  nor be construed
as an agreement to modify the terms of this  Agreement,  nor shall any single or
partial  exercise of any right,  remedy,  power or privilege with respect to any
occurrence  be construed as a waiver of such right,  remedy,  power or privilege
with respect to any other  occurrence.  No waiver by a party  hereunder shall be
effective  unless it is in writing and signed by the party  making such  waiver,
and then only to the extent specifically stated in such writing.

 13.  Duration.  This Agreement shall become effective when executed by Borrower
and Subordinated  Creditor and accepted by Senior Creditor in Denver,  Colorado,
and, when so accepted, shall constitute a continuing agreement of subordination,
and shall remain in effect until all of the Senior Debt has been paid in full in
immediately available funds. Senior Creditor may, without notice to Subordinated
Creditor,  extend or continue credit and make other financial  accommodations to
or for the account of Borrower in reliance upon this  Agreement.  The provisions
of this Agreement  shall continue to be effective or be reinstated,  as the case
may be, if at any time payment of any Senior Debt is rescinded or otherwise must
be returned by Senior Creditor, all as if any such payment had not been made.

 14. Default and  Enforcement.  If at any time any holder of  Subordinated  Debt
fails to comply with any provision of this  Agreement that is applicable to such
holder,  Senior  Creditor may demand  specific  performance  of this  Agreement,
whether or not  Borrower  itself has  complied  with the terms  hereof,  and may
exercise  any other  remedy  available  at law or equity.  Without  limiting the
generality of the foregoing, if any holder of Subordinated Debt, in violation of
this Agreement, shall institute or participate in any action, suit or proceeding
against Borrower, then Borrower may interpose as a defense or dilatory plea this
Agreement  and Senior  Creditor is  irrevocably  authorized  to intervene and to
interpose  such  defense  or plea in its or  Borrower's  name.  If any holder of
Subordinated  Debt  attempts to assert or enforce  any Lien with  respect to any
Collateral  in  violation  of this  Agreement,  Borrower or Senior  Creditor (in
Borrower's or Senior  Creditors  name) may by virtue of this Agreement  restrain
such enforcement.

 15. Litigation; Jurisdiction and Venue. Borrower, Senior Creditor, Subordinated
Creditor  and each other  holder of  Subordinated  Debt each hereby  irrevocably
consents to the  jurisdiction  of the courts of the State of Colorado and of any
federal court located in the State of Colorado, in connection with any action or
proceeding arising out of or relating to this Agreement. In any such litigation,
Borrower,  Subordinated  Creditor,  each other holder of  Subordinated  Debt and
Senior Creditor each hereby waives personal service of any summons, complaint or
other process, and agrees that the service thereof may be made by certified mail
direct  to  Borrower,   Subordinated  Creditor  and  Senior  Creditor  at  their
respective  places of business set forth in Section 16 hereof,  and, in the case
of any other holder of  Subordinated  Debt,  at the last known  address for such
holder.  Within 30 days after such mailing, the party so served shall appear and
answer to such summons,  complaint or other process.  Should the party so served
fail to appear or answer within said 30-day  period,  then such party failing to
appear or answer shall be deemed in default and judgment may be entered  against
such party for the amount or other relief as demanded in any summons,  complaint
or other process so served.  In the  alternative,  in its sole  discretion,  any
party  may  effect  service  upon any other  party in any  other  form or manner
permitted by  applicable  law. The choice of forum set forth herein shall not be
deemed to preclude the enforcement of any judgment obtained in such forum or the
taking of any action under this Agreement to enforce the same in any appropriate
jurisdiction,  or the commencement by Senior Creditor or Subordinated  Creditor,
in its sole  discretion,  of any  action or suit in any  jurisdiction  where any
Collateral may be found to repossess or foreclose upon any such Collateral.

 16. Notices.  Except as otherwise provided herein, whenever any notice, demand,
request, consent,  approval,  declaration or other communication shall or may be
given to or served upon any of the parties by the other  party,  or whenever any
party  desires  to give or serve  upon any other  party any  communication  with
respect to this Agreement, each such notice, demand, request, consent, approval,
declaration  or other  communication  shall be in writing and shall be deemed to
have been  validly  served,  given or  delivered  (a) upon the earlier of actual
receipt and three (3) days after deposit in the United  States Mail,  registered
or certified mail, return receipt  requested,  with proper postage prepaid,  (b)
upon transmission, when sent by telecopy or other similar facsimile transmission
(with such  telecopy or  facsimile  promptly  confirmed by delivery of a copy by
personal  delivery or United  States Mail as otherwise  provided in this Section
16), (c) one (1) Business Day after deposit with a reputable  overnight  courier
with all  charges  prepaid  or (d) when  hand-delivered,  all of which  shall be
addressed  to the party to be  notified  and sent to the  address  or  facsimile
number set forth below or to such other address (or facsimile  number) as may be
substituted by notice given as herein provided:

  (a) If to Senior Creditor:        ProFutures Bridge Capital Fund, L.P.
                                    S. Roslyn Street, Suite 350
                                    Englewood, Colorado  80111
                                    Attention:  James H. Perry
                                    Facsimile: (303) 721-1190
                                  
                                    With copies to:

                                    Goins, Underkofler, Crawford & Langdon, LLP
                                    Elm Street, Suite 3300
                                    Dallas, Texas  75201
                                    Attention:  John O. Langdon
                                    Facsimile: (214) 969-5902

  (b) If to Subordinated Creditor:  Imatron, Inc.
                                    Oyster Point Blvd. South
                                    San Francisco, CA  94080
                                    Attention: Mr. S. Lewis Meyers, President
                                    Facsimile: (415) 871-0418

  (c)  If to Borrower:              Positron Corporation
                                    Park Ten Place
                                    Houston, Texas  77084
                                    Attention: President
                                    Facsimile: (281) 492-2961

          The giving of any notice  required  hereunder may be waived in writing
by the party  entitled to receive  such notice.  Failure or delay in  delivering
copies of any notice, demand, request, consent,  approval,  declaration or other
communication to any person (other than Senior Creditor,  Subordinated Lender or
Borrower)  designated  above to receive copies shall in no way adversely  affect
the  effectiveness  of  such  notice,  demand,   request,   consent,   approval,
declaration or other communication.

 17.  Entire  Agreement.  This  Agreement  constitutes  and expresses the entire
understanding  between the parties  hereto  with  respect to the subject  matter
hereof, and supersedes all prior agreements and  understandings,  inducements or
conditions,  whether express or implied, oral or written. Neither this Agreement
nor any portion or provision hereof may be changed,  waived or amended orally or
in any manner other than by an agreement in writing  signed by Senior  Creditor,
Borrower and Subordinated Creditor.

 18. Additional Documentation.  Borrower and Subordinated Creditor shall execute
and deliver to Senior  Creditor  such  further  instruments  and shall take such
further action as Senior  Creditor may  reasonably  request from time to time in
order to carry out the provisions and intent of this Agreement.

 19. Successors and Assigns. This Agreement shall inure to the benefit of Senior
Creditor,  its successors  and assigns,  and shall be binding upon both Borrower
and Subordinated Creditor and their respective successors and assigns; provided,
however,  that neither  Subordinated  Creditor nor any subsequent  holder of any
Subordinated  Debt  shall  assign  or  transfer  to any  Person  any part of the
Subordinated Debt.

 20. Defects Waived.  This Agreement is effective  notwithstanding any defect in
the  validity  or  enforceability  of any  instrument  or  document  at any time
evidencing or securing the whole or any part of the Senior Debt.

 21. Governing Law. The validity, construction and enforcement of this Agreement
shall be governed by the internal laws of the State of Colorado.

 22.  Severability.  The  provisions of this  Agreement are  independent  of and
separable from each other. If any provision  hereof shall for any reason be held
invalid or  unenforceable,  it is the intent of the parties that such invalidity
or unenforceability shall not affect the validity or enforceability of any other
provision hereof,  and that this Agreement shall be construed as if such invalid
or unenforceable provision had never been contained herein.

 23. Execution in Counterparts.  This Agreement may be executed in any number of
counterparts   and  by   different   parties  to  this   Agreement  on  separate
counterparts,  each of which, when so executed, shall be deemed an original, but
all such counterparts shall constitute one and the same agreement. Any signature
delivered by a party by facsimile transmission shall be deemed to be an original
signature hereto.

 24. MUTUAL WAIVER OF JURY TRIAL.  BECAUSE  DISPUTES  ARISING IN CONNECTION WITH
COMPLEX FINANCIAL  TRANSACTIONS ARE MOST QUICKLY AND ECONOMICALLY RESOLVED BY AN
EXPERIENCED AND EXPERT PERSON AND THE PARTIES WISH APPLICABLE  STATE AND FEDERAL
LAWS TO APPLY (RATHER THAN  ARBITRATION  RULES),  THE PARTIES  DESIRE THAT THEIR
DISPUTES BE RESOLVED BY A JUDGE APPLYING SUCH  APPLICABLE  LAWS.  THEREFORE,  TO
ACHIEVE  THE BEST  COMBINATION  OF THE  BENEFITS OF THE  JUDICIAL  SYSTEM AND OF
ARBITRATION,  THE PARTIES HERETO WAIVE ALL RIGHT TO TRIAL BY JURY IN ANY ACTION,
SUIT,  OR  PROCEEDING  BROUGHT TO  RESOLVE  ANY  DISPUTE,  WHETHER  SOUNDING  IN
CONTRACT,  TORT, OR  OTHERWISE,  BETWEEN THE PARTIES  ARISING OUT OF,  CONNECTED
WITH, RELATED TO, OR INCIDENTAL TO THE RELATIONSHIP  ESTABLISHED BETWEEN THEM IN
CONNECTION WITH, THIS AGREEMENT OR THE TRANSACTIONS HEREUNDER.

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
signed, sealed and delivered on the day and year first above written.

                             SUBORDINATED CREDITOR:

                            IMATRON, INC.,
                            a New Jersey corporation

                            By:
                            Name:
                            Title:

                            SENIOR CREDITOR:

                            PROFUTURES BRIDGE CAPITAL FUND, L.P.,
                            a Delaware limited partnership

                            By:      Bridge Capital Partners, Inc.
                                     its General Partner

                            By:
                                     James H. Perry, President

                            BORROWER:

                            POSITRON CORPORATION,
                            a Texas corporation

                            By:
                            Name:
                            Title:


<PAGE>





                                    EXHIBIT B

                                     WARRANT



          NOTICE THIS WARRANT AND THE UNDERLYING SHARES ARE SUBJECT TO
                  RESTRICTIONS ON TRANSFER AS SET FORTH HEREIN
                              POSITRON CORPORATION

                                             Right to Purchase 1,150,000 Shares
                                                        (Subject to adjustment)

                       Stock Purchase Warrant for Common Stock

         POSITRON  CORPORATION  (hereinafter  called  the  "Company"),  a  Texas
corporation, hereby certifies that, for value received,

                      PROFUTURES BRIDGE CAPITAL FUND, L.P.

or registered  assigns (the "Holder"),  is entitled to purchase from the Company
at any time or from time to time  during the  Exercise  Period  (as  hereinafter
defined) an  aggregate  of One Million One Hundred  Fifty  Thousand  (1,150,000)
fully paid and non-assessable  shares,  subject to adjustment as provided below,
of the Common Stock, $.01 par value (the "Common Stock") of the Company,  on the
payment  therefor of the purchase price (subject to adjustment as stated herein)
which  shall be equal to $0.25  (the  "Exercise  Price")  for each  share of the
Common Stock so purchased, upon the surrender of this Warrant duly signed by the
registered Holder hereof at the time of exercise,  accompanied by payment of the
purchase  price,  upon the terms and subject to the conditions  hereinafter  set
forth.

 I.  EXERCISE OF WARRANT.  This Warrant shall be  exercisable  during the period
beginning April 1, 1998 and ending at 5:00 p.m. (Houston time) on March 31, 2008
(the  "Exercise  Period").  During the  Exercise  Period,  this  Warrant  may be
exercised, in whole or in part at any time as follows:

                   The Holder shall surrender this Warrant to the Company at its
then principal  office or that of the duly  authorized and acting transfer agent
for its Common Stock,  together with an exercise form  substantially in the form
of the exercise  form on the last page of this Warrant  signifying  the Holder's
election to exercise this Warrant and  specifying the number of shares of Common
Stock to be  purchased,  duly signed,  together  with the purchase  price of the
Common Stock in the form of a certified or bank  cashier's  check payable to the
order of the  Company  in an  amount  equal  to the  aggregate  exercise  price,
adjusted  as  provided  herein,  for the number of shares of Common  Stock being
purchased.  Notwithstanding  the  foregoing  provisions,  in no  event  may this
Warrant be  exercised  by any Holder who is not an  accredited  investor as such
term is defined in Rule 501(a) of Regulation D under the Act.

 II. DELIVERY OF STOCK CERTIFICATE ON EXERCISE. As soon as practicable after the
exercise of this  Warrant and payment of the  purchase  price,  the Company will
cause to be issued in the name of and delivered to the registered  Holder hereof
or its  assigns,  or  such  Holder's  nominee  or  nominees,  a  certificate  or
certificates  for the number of full  shares of Common  Stock of the  Company to
which such Holder  shall be entitled  upon such  exercise  (and in the case of a
partial exercise,  a Warrant of like tenor for the unexercised portion remaining
subject to exercise  prior to the  expiration  of the Exercise  Period set forth
herein or, at the Holder's option,  this Warrant shall be returned to the Holder
with an  appropriate  notation made hereon).  For all corporate  purposes,  such
certificate or certificates  shall be deemed to have been issued and such Holder
or such  Holder's  designee to be named therein shall be deemed to have become a
holder of record of such shares of Common Stock as of the date the duly executed
exercise form pursuant to this Warrant,  together with full payment, is received
by the Company as  aforesaid.  No fraction of a share or scrip  certificate  for
such  fraction  shall be  issued  upon the  exercise  of this  Warrant;  in lieu
thereof, the Company will pay or cause to be paid to such Holder cash equal to a
like fraction at the prevailing market price for such share as determined by the
Company.

 III. NET ISSUE  EXERCISE.  In lieu of exercising  this Warrant,  the Holder may
elect to receive  shares of Common  Stock equal to the value of this Warrant (or
the  portion  thereof  being  canceled)  by  surrender  of this  Warrant  at the
principal office of the Company together with notice of such election,  in which
event  the  Company  shall  issue to the  Holder a number  of  shares  using the
following formula:
                                   X = Y (A- B)

                                         A

 Where X = The  number of shares to be issued to Holder Y = The number of shares
       then  purchasable  under this  Warrant A = The fair  market  value of one
       share  B  =  The  Exercise  Price  (as  adjusted  to  the  date  of  such
       calculations


<PAGE>


For  purposes of this  provision,  the fair market value of the shares of Common
Stock of the Company  shall mean the average of the closing bid and asked prices
of the shares quoted in the Over-The-Counter Market Summary or the closing price
quoted in any  exchange  or  quotation  system on which the shares  are  listed,
whichever is  applicable,  as  published in the Wall Street  Journal for the ten
(10) trading days prior to the date of  determination  of fair market value.  If
the  shares are not  traded  Over-The-Counter  or on an  exchange  or  quotation
system,  the fair  market  value  shall be the price per share which the Company
could obtain from a willing buyer for shares sold by the Company from authorized
but  unissued  shares,  as such  price  shall be agreed by the  Company  and the
Holder.

 IV.       ANTIDILUTION PROVISIONS.

          A.  Dividends.  Except as otherwise  provided in this Warrant,  in the
event that a dividend  shall be  declared  upon the Common  Stock of the Company
payable in shares of said stock, the number of shares of Common Stock covered by
this  Warrant  shall be  adjusted by adding  thereto the number of shares  which
would have been distributable thereon if such shares had been outstanding on the
date fixed for  determining  the  shareholders  entitled  to receive  such stock
dividend.  If at any  time  the  Company  shall  pay any  dividend  or make  any
distributions  upon its Common Stock other than a dividend  payable in shares of
said stock or shall offer to the holders of its Common Stock for subscription or
purchase by them any shares of any class or any other rights,  the Company shall
cause notice thereof to be mailed to the Holder at its address  appearing on the
registry  books of the Company at least  thirty days prior to the record date as
of which holders of shares shall  participate in such dividend,  distribution or
subscription rights, specifying such date.

          B. Reorganizations/Consolidation/Mergers. Except as otherwise provided
in this Warrant, in the event that the outstanding shares of Common Stock of the
Company  shall be changed  into or exchanged  for a different  number or kind of
shares of stock or other  securities of the Company or, of another  corporation,
whether through reorganization, recapitalization, stock split-up, combination of
shares, merger or consolidation,  then there shall be substituted for the shares
of Common Stock covered by this Warrant,  the number and kind of shares of stock
or other securities  which would have been  substituted  therefor if such shares
had been outstanding on the date fixed for determining the shareholders entitled
to receive such changed or substituted stock or other securities.

          C.       Other Changes.

                   1. Upon each  adjustment  of the Exercise  Price  pursuant to
Paragraph IV.D., the Holder shall thereafter  (until another such adjustment) be
entitled  to  purchase,  at the  adjusted  Exercise  Price in effect on the date
purchase rights under this Warrant are exercised, the number of shares of Common
Stock,  calculated to the nearest full share,  determined by (a) multiplying the
number of shares of Common Stock purchasable  hereunder immediately prior to the
adjustment  of the Exercise  Price by the Exercise  Price in effect  immediately
prior to such  adjustment,  and (b)  dividing  the  product so  obtained  by the
adjusted Exercise Price in effect on the date of such exercise.

                   2.  In the  event  there  shall  be any  change,  other  than
specified elsewhere in this Warrant, in the number or kind of outstanding shares
of Common  Stock of the Company or of any stock or other  securities  into which
such Common  Stock  shall be changed or for which it shall have been  exchanged,
and if such change  equitably  requires an  adjustment  in the number or kind of
shares covered by this Warrant,  such  adjustment  shall be made by the Board of
Directors of the Company and the Holder.

          D. Purchase Price Adjustments.  The Exercise Price shall be subject to
adjustment as follows:

                   1. In case the Company shall issue any shares of Common Stock
(i) by way of split-up of outstanding  shares of Common Stock, or (ii) by way of
dividends  payable in Common  Stock,  the  Exercise  Price  thereafter  shall be
immediately  adjusted  and the  adjusted  Exercise  Price  shall be equal to the
quotient determined by dividing (A) the product of the total number of shares of
Common Stock outstanding  immediately  prior to such issuance  multiplied by the
Exercise  Price in effect  immediately  prior to such  issuance by (B) the total
number of shares of Common Stock outstanding immediately after such issuance.

                   2. No  reorganization  of the Company and no consolidation or
merger  thereof  with or into  any  other  corporation  or  corporations  and no
conveyance of all or substantially all of the assets of the Company to any other
corporation   shall  be  made  unless,   as  a  part  of  such   reorganization,
consolidation  or merger or  conveyance  arrangements  shall be made whereby the
Holder of this Warrant  shall  thereafter be entitled to convert the same into a
warrant or warrants for any stock,  securities or other assets given in exchange
for the Common  Stock of the Company on such  reorganization,  or in  connection
with  such  consolidation,  merger or  conveyance,  in such  amount  and with an
Exercise  Price for such  value  (but not below the par value of the  securities
subject to the new warrant) as would,  at the time,  have been given in exchange
for the Common Stock.  The Company shall not increase the par value per share of
any stock or securities  issuable under the Warrant to an amount more than $0.01
per share.

                   3. In case the  Company,  by  reclassification  of its Common
Stock or by  amendment to its  Certificate  of  Incorporation,  shall reduce the
number of shares of such Common Stock outstanding, the Exercise Price thereafter
shall  be  immediately  adjusted,  and the  adjusted  Exercise  Price  shall  be
determined  by  multiplying  the  number of shares of Common  Stock  outstanding
immediately  before such  reduction by the then Exercise Price and the resulting
product  shall be  divided  by the  reduced  number of  shares  of Common  Stock
outstanding,  and the quotient resulting from such division (or the par value of
the Common Stock,  whichever is higher)  shall be the Exercise  Price after such
adjustment, until a further adjustment of the Exercise Price of the Common Stock
shall be required to be made by reason of a further  reduction  of the number of
shares of such Common Stock outstanding.

                   4. If the  Company at any time or from time to time after the
date of this  Warrant  issues  any  additional  shares  of  Common  Stock  for a
consideration per share less than the Exercise Price in effect immediately prior
to the issuance of such additional shares, or without  consideration (other than
pursuant to a transaction  covered by Paragraphs  IV.D.1. or 3. above) then, and
thereafter  successively  upon each  such  issuance,  but only if the  following
calculation  shall  result in a reduction of the  Exercise  Price,  the Exercise
Price in effect  immediately  prior to the  issuance of such  additional  shares
shall forthwith be reduced to a price determined by dividing (a) an amount equal
to (i) the  total  number of shares  of  Common  Stock  outstanding  immediately
following the last previous  adjustment of the Exercise  Price  pursuant to this
Paragraph  IV.D.  (or on the date of this  Warrant  if there  shall have been no
previous  adjustment)  multiplied  by the Exercise  Price in effect  immediately
prior to such issuance, plus (ii) the consideration,  if any, received or deemed
to have been received by the Company upon such issuance and upon the issuance of
any Common  Stock  issued  subsequent  to the last  previous  adjustment  of the
Exercise Price  pursuant to this  Paragraph  IV.D. (or subsequent to the date of
this Warrant if there shall have been no such previous  adjustment),  by (b) the
total  number  of  shares  of Common  Stock  outstanding  immediately  after the
issuance  of  such  additional  shares.  Without  limiting  the  foregoing  this
Paragraph  IV.D.  applies to the issuance of shares  pursuant to the exercise of
warrants  issuable by the Company pursuant to the Agreement to Issue Warrants of
even date herewith between the Company and ProFutures Bridge Capital Fund, L.P.

          E. No Fractional Shares. No adjustment or substitution provided for in
this Warrant  shall  require the Company to issue or to sell a fractional  share
and the total  adjustment or substitution  with respect to this Warrant shall be
limited accordingly.

          F.  Calculation.  Upon each  adjustment of the Exercise Price and upon
each  change  in the  number of shares  of  Common  Stock  deliverable  upon the
exercise  of this  Warrant,  and in the event of any change in the rights of the
holder by reason of other  events  hereinabove  set  forth,  the  Company  shall
forthwith  give  written  notice  thereof  to  the  holder  in  the  form  of  a
certificate,  executed by its President or one of its Vice  Presidents,  stating
the  adjusted  Exercise  Price and the new number of shares so  deliverable,  or
specifying  the other  shares  of stock,  securities  or assets  and the  amount
thereof so  deliverable  and setting  forth in  reasonable  detail the method of
calculation and the facts upon which such calculation is based.

          G. Exempt Transactions. Notwithstanding any provision contained herein
to the contrary, no adjustment shall be made to the Exercise Price or the number
of shares of Common Stock  purchasable  hereunder in respect of (a) any options,
warrants  or  other  securities  outstanding  as of the  date  hereof  that  are
exercisable or exchangeable  for or convertible into shares of common Stock, (b)
options that may  hereafter  be granted in  accordance  with any employee  stock
option plan in effect as of the date  hereof,  (c) the  issuance  after the date
hereof of any additional shares of Series A 8% Cumulative Convertible Redeemable
Preferred Stock or Series B 8% Cumulative Convertible Redeemable Preferred Stock
as dividend in respect of any such outstanding preferred stock, (d) the issuance
of any securities to General  Electric  Company (or its  affiliates) in order to
fund in all or in part the  acquisition  of assets  pursuant to the  Acquisition
Agreement (herein so called) dated July 15, 1996 between the Company and General
Electric  Company,  as such  agreement  is  amended  from  time to time,  or the
issuance of any  securities to finance in all or in part the  acquisition by the
Company of such  assets,  or (e) the issuance of any shares of Common Stock upon
the exercise,  conversion or exchange or any of the securities  described in any
one or more of clauses (a), (b), (c) or (d) above.

 V.      REGISTRATION RIGHTS.

     A. Certain Definitions.  As used in this Warrant, the following terms shall
have the following respective meanings:

                   1.  Act  means  the  Securities  Act of 1933  or any  similar
federal  statute,  and the rules and regulations of the Commission  issued under
the Act, as they each may, from time to time, be in effect.

                   2. Commission  means the Securities and Exchange  Commission,
or any other federal agency at the time administering the Act.

                   3. Exchange Act means the Securities  Exchange Act of 1934 or
any similar  federal  statute,  and the rules and  regulations of the Commission
issued under such Act, as they each may, from time to time, be in effect.

                   4.       Intentionally Deleted.

                   5.  Registration  Statement  means a  registration  statement
filed by the  Company  with the  Commission  for a public  offering  and sale of
securities of the Company  (other than a  registration  statement on Form S-8 or
Form S-4, or their successors,  or any other form for a limited purpose,  or any
registration  statement  covering  only  securities  proposed  to be  issued  in
exchange for  securities or assets of another  corporation  or any  registration
statement  filed to register the issuance of  securities,  the proceeds of which
are to fund or finance  in all or in part the  Company's  acquisition  of assets
pursuant to the GE Acquisition Agreement).

                   6.  Registrable  Shares  means the  shares  of  Common  Stock
issuable upon exercise of this Warrant,  and any other shares of Common Stock of
the Company  issued in respect of such shares  (because of stock  splits,  stock
dividends,  reclassifications,  recapitalizations,  anti-dilution provisions, or
similar  events);  provided,  however,  that  shares of Common  Stock  which are
Registrable  Shares  shall  cease  to be  Registrable  Shares  upon (a) any sale
pursuant to a  Registration  Statement or Rule 144 under the Act, or (b) at such
time that such shares of Common Stock may be sold  pursuant to Rule 144(k) under
the Act.

                   7. Selling Holders means the holders of  Registerable  Shares
that are registered by the Company pursuant to this Warrant.

                   8. Demand Registration Date means July 31, 1997.

     B. Registration on Request.

                   1. At any time after the Demand  Registration  Date, upon the
written  request of one or more persons  holding 75% or more of the  Registrable
Shares (the "Initiating Holders") that the Company effect the registration under
the Act of the  offer  and  sale of all or  part  of  such  Initiating  Holders'
Registrable  Shares,  the  Company  promptly  will give  written  notice of such
requested  registration to all of the other holders of Registrable  Shares,  and
thereupon  the  Company  will  effect,   at  the  earliest  possible  date,  the
registration  under the Act of (i) the Registrable  Shares which the Company has
been so requested  to register by such  Initiating  Holders,  and (ii) all other
Registrable Shares which the Company has been requested to register by the other
holders of the Registrable Shares by written request given to the Company within
30 days  after the  giving of such  written  notice by the  Company,  all to the
extent requisite to permit the public  disposition of the Registrable  Shares so
to be registered.  The Company shall be required to effect only one registration
pursuant to this Paragraph V.B.

                   2. Whenever the Company shall effect a registration  pursuant
to this Paragraph  V.B., no securities  other than  Registrable  Shares shall be
included  among the  securities  covered  by such  registration  unless  Selling
Holders of greater  than 50% of the  Registrable  Shares to be  included in such
registration  shall have  consented  in writing to the  inclusion  of such other
securities.

                   3.  Registrations  under this Paragraph V.B. shall be on such
appropriate  registration form of the Commission as shall be reasonably selected
by the Company, subject, however, to Paragraph V.A.5.

                   4. At the election of Selling  Holders of greater than 75% of
the  Registrable  Shares to be included in such  registration,  the  offering of
Registrable  Shares  pursuant to this  Paragraph V.B. shall be in the form of an
underwritten  offering.  The underwriter or  underwriters  of each  underwritten
offering of the Registrable  Shares so to be registered shall be selected by the
Selling Holders of at least 75% of the Registrable Shares to be included in such
registration and shall be reasonably acceptable to the Company.

                   5. The Company may  postpone for up to 120 days the filing or
effectiveness  of  a  Registration  Statement  for  a  registration  under  this
Paragraph V.B if the Company  reasonably  believes that such  registration  will
have a material adverse effect on the Company or any transaction contemplated by
it. The Company may postpone  such filing or  effectiveness  only once after any
request for registration pursuant to this Paragraph V.B.

     C. Piggy-Back Registration.

                   1.       Intentionally Deleted.

                   2.  Whenever  the  Company  proposes  to file a  Registration
Statement at any time and from time to time, it will, prior to such filing, give
written  notice to the Holder of its  intention  to do so and,  upon the written
request  of the Holder  given  within 20 days after the  Company  provides  such
notice,  the Company  shall cause all  Registrable  Shares which the Company has
been  requested by the Holder to register to be registered  under the Act to the
extent  necessary to permit their sale or other  disposition in accordance  with
the intended method of distribution proposed in such registration; provided that
the  Company  shall have the right to  postpone  or  withdraw  any  registration
effected  pursuant  to this  Paragraph  without  obligation  to the  Holder.  No
registration effected under this Paragraph V.C. shall relieve the Company of its
obligation to effect a registration upon request under Paragraph V.B.

                   3. No person may  participate in any  Registration  Statement
filed pursuant to this Paragraph V.C. unless such person (a) agrees to sell such
person's   Registrable   Shares  on  the  basis  provided  in  any  underwriting
arrangements  approved  by the  Company,  and (b)  completes  and  executes  all
questionnaires,  powers of attorney,  indemnities,  underwriting agreements, and
other  documents  reasonably  required  under  the  terms  of such  underwriting
arrangements;  provided,  however, that no such person shall be required to make
any representations or warranties in connection with any such registration other
than  representations and warranties as to (i) such person's ownership of his or
its  Registrable  Shares to be sold or transferred  free and clear of all liens,
claims and  encumbrances,  (ii) such person's power and authority to effect such
transfer,  and (iii) such matters  pertaining to compliance with securities laws
as may be reasonably requested;  provided further,  however, that the obligation
of such person to indemnify pursuant to any such underwriting arrangements shall
be  several,  not joint and  several,  among such  persons  selling  Registrable
Shares,  and the  liability  of each such person will be in  proportion  to, and
provided further that such liability will be limited to, the net amount received
by such person from the sale of his or its  Registrable  Shares pursuant to such
registration; and provided, further, that no Selling Holder shall be required to
agree to any lock-up period in excess of 120 days.

                   4. Unless the managing underwriter  otherwise agrees, each of
the Company and the Holders agrees,  and the Company agrees,  in connection with
any  underwritten  registration,  to use its  reasonable  efforts  to  cause  is
affiliates  to  agree,  not to  effect  any  public  sale or  private  offer  or
distribution  of any  Common  Stock or Common  Stock  equivalent  during the ten
business  days  prior  to the  effectiveness  under  the  Securities  Act of any
underwritten  registration  and during such time period after the  effectiveness
under the Securities  Act of any  underwritten  registration  (not to exceed 120
days) (except, if applicable, as part of such underwritten  registration) as the
Company and the managing underwriter may agree.

                   5. If the Registrable  Shares requested to be included in the
Registration  Statement  by  the  Holder  pursuant  to a  registration  effected
pursuant to Paragraph V.C.2.  differ from the type of securities  proposed to be
registered by the Company and the managing  underwriter advises the Company that
due  to  such  differences  the  inclusion  of  such  Registrable  Shares  would
materially  and  adversely  affect  the  price or  success  of the  offering  (a
"Material  Adverse  Effect"),  then (i) the number of such Holder's  Registrable
Shares to be  included  in the  Registration  Statement  shall be  reduced to an
amount which, in the judgment of the managing underwriter,  would eliminate such
Material  Adverse Effect or (ii) if no such reduction  would, in the judgment of
the managing  underwriter,  eliminate  such Material  Adverse  Effect,  then the
Company  shall have the right to exclude all such  Registrable  Shares from such
registration  statement  provided no other  securities of such type are included
and offered for the account of any other person in such Registration  Statement.
Any  partial  reduction  in number of  Registrable  Shares to be included in the
Registration  Statement  pursuant  to clause  (i) of the  immediately  preceding
sentence  shall be  effected  pro rata based on the ratio  which  such  Holder's
requested shares bears to the total number of shares requested to be included in
such Registration  Statement by all persons who have requested that their shares
be included in such Registration  Statement. If the Registrable Shares requested
to be included in the Registration Statement pursuant to a registration effected
pursuant  to  Paragraph  V.C.2.  are of the same  type as the  securities  being
registered by the Company and the managing  underwriter advises the Company that
the inclusion of such Registrable  Shares would cause a Material Adverse Effect,
the Company will be obligated to include in such Registration  Statement,  as to
each  Holder,  only a portion of the shares  such  Holder  has  requested  to be
registered equal to the ratio which such Holder's  requested shares bears to the
total number of shares requested to be included in such  registration  statement
by all  persons  (other  than (i) the  Company,  if such  registration  has been
initiated by the Company for securities to be offered by the Company and (ii) by
persons  exercising  their  right  to  cause a  Demand  Registration)  who  have
requested that their shares be included in such  Registration  Statement.  It is
acknowledged  by the Holder,  that  pursuant  to the  foregoing  provision,  the
securities to be included in such registration  shall be allocated (x) first, to
the  Company,  if such  registration  has  been  initiated  by the  Company  for
securities to be offered by the Company,  (y) second,  to securities  offered by
persons  exercising  their  right  to  cause  a  Demand  Registration,  if  such
registration is a Demand Registration and (z) third, to the Holder and all other
persons  requesting  securities to be included  therein in  accordance  with the
above described ratio. If as a result of the provisions of this Paragraph V.C.5.
any Holder  shall not be  entitled to include all  Registrable  Securities  in a
registration  that such Holder has requested to be so included,  such Holder may
withdraw  such  Holder's   request  to  include   Registrable   Shares  in  such
Registration  Statement.  As used herein, the term "Demand  Registration"  shall
mean a registration of Common Stock under the Act requested by a person pursuant
to a contractual right of such person to demand that the Company initiate such a
registration.  This Paragraph V.C.5.  does not apply to a registration  effected
pursuant to Paragraph V.C.1.

     D. Registration Procedures.  If and whenever the Company is required by the
provisions of this Warrant to effect the  registration of any of the Registrable
Shares under the Act, the Company shall:

                   1. File with the  Commission a  Registration  Statement  with
respect to such  Registrable  Shares and cause that  Registration  Statement  to
become and remain effective;

                   2. As soon as  reasonably  practicable  prepare and file with
the Commission any amendments and supplements to the Registration  Statement and
the  prospectus  included in the  Registration  Statement as may be necessary to
keep the  Registration  Statement  effective  until 180 days from the  effective
date;

                   3. As soon as reasonably  practicable  furnish to the Selling
Holders  such  reasonable  numbers  of copies  of the  prospectus,  including  a
preliminary prospectus, in conformity with the requirements of the Act, and such
other  documents  as the  Selling  Holders  may  reasonably  request in order to
facilitate the public sale or other disposition of the Registrable  Shares owned
by the Selling Holders;

                   4. As soon as reasonably  practicable register or qualify the
Registrable Shares covered by the Registration Statement under the securities or
Blue Sky laws of such states as any Selling Holder shall reasonably request, and
do any and all other acts and  things  that may be  necessary  or  desirable  to
enable the Selling Holder to consummate the public sale or other  disposition in
such states of the Registrable Shares; provided, however, that the Company shall
not be required in connection with this Paragraph V.D.4. to qualify as a foreign
corporation  or  execute  a  general  consent  to  service  of  process  in  any
jurisdiction; and

                   5.  Obtain a comfort  letter from the  Company's  independent
public  accountants  in  customary  form and  covering  such matters of the type
customarily covered by comfort letters and an opinion from the Company's counsel
in customary form and covering such matters of the type  customarily  covered in
public issuances of securities, in each case addressed to the Selling Holders.

          If the Company has delivered a preliminary or final  prospectus to the
Selling  Holders and after  having done so the  prospectus  is amended to comply
with the  requirements of the Act, the Company shall promptly notify the Selling
Holders and, if requested,  the Selling Holders shall  immediately  cease making
offers of Registrable  Shares and return all  prospectuses  to the Company.  The
Company shall promptly  provide the Selling  Holders revised  prospectuses  and,
following receipt of the revised prospectuses, the Selling Holders shall be free
to resume making offers of the Registrable Shares.

     E. Allocation of Expenses.  The Company will pay all Registration  Expenses
of all registrations under this Warrant.  For purposes of this Warrant, the term
"Registration  Expenses"  shall mean all  expenses  incurred  by the  Company in
complying with this Paragraph V., including without limitation, all registration
and  filing  fees,  exchange  listing  fees,  printing  expenses,  the  fees and
disbursements  of counsel for the Company and the fees and  disbursements of one
counsel  selected by all of the Selling Holders,  the fees and  disbursements of
the Company's accountants,  state Blue Sky fees and expenses, and the expense of
any  special  audits  incident  to or  required  by any such  registration,  but
excluding underwriting discounts,  selling commissions and the fees and expenses
of the  Selling  Holders'  own  counsel  (other  than the  counsel  selected  to
represent all of the Selling Holders).

     F.  Indemnification.

                    1.  In  the  event  of  any   registration  of  any  of  the
Registrable  Shares under the Act pursuant to this  Agreement,  the Company will
indemnify and hold harmless each of the Selling Holders,  each of its directors,
officers or partners and each other  person,  if any,  who controls  such seller
within the meaning of the Act or the Exchange Act,  against any losses,  claims,
damages or  liabilities,  joint or several,  to which such seller or controlling
person may become  subject  under the Act,  the Exchange  Act,  Blue Sky laws or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect  thereof) arise out of or are based upon any untrue statement or alleged
untrue  statement of any material fact contained in any  Registration  Statement
under  which  such  Registrable  Shares  were  registered  under  the  Act,  any
preliminary  prospectus  or  final  prospectus  contained  in  the  Registration
Statement,  or any amendment or supplement to such  Registration  Statement,  or
arise out of or are based  upon the  omission  or  alleged  omission  to state a
material fact required to be stated  therein or necessary to make the statements
therein,  in light of the circumstances in which they were made, not misleading;
and the Company will reimburse such seller and each such controlling  person for
any  legal  or  any  other  expenses  reasonably  incurred  by  such  seller  or
controlling  person in connection with investigating or defending any such loss,
claim, damage or liability or action;  provided,  however, that the Company will
not be liable in any such case to the extent that any such loss,  claim,  damage
or  liability  arises out of or is based upon any untrue  statement  or omission
made in such Registration  Statement,  preliminary prospectus or prospectus,  or
any such  amendment  or  supplement,  in reliance  upon and in  conformity  with
information  furnished to the Company,  in writing, by or on behalf of a Selling
Holder or controlling person specifically for use in the preparation thereof.

                   2. In the event of any  registration  of any of the  Holder's
Registrable Shares under the Act pursuant to this Agreement, each Selling Holder
will indemnify and hold harmless the Company, each of its directors and officers
and each person,  if any, who controls the Company within the meaning of the Act
or the Exchange Act, against any losses, claims,  damages or liabilities,  joint
or several,  to which the Company,  such  directors and officers or  controlling
persons  may  become  subject  under  the Act,  Exchange  Act,  Blue Sky laws or
otherwise, insofar as such losses, claims, damages or liabilities (or actions in
respect  thereof) arise out of or are based upon any untrue statement or alleged
untrue  statement of a material  fact  contained in any  Registration  Statement
under  which  such  Registrable  Shares  were  registered  under  the  Act,  any
preliminary  prospectus  or  final  prospectus  contained  in  the  Registration
Statement,  or any  amendment or supplement to the  Registration  Statement,  or
arise out of or are based  upon any  omission  or  alleged  omission  to state a
material fact required to be stated  therein or necessary to make the statements
therein in light of the  circumstances  in which they were made, not misleading,
if the statement or omission was made in reliance  upon and in  conformity  with
information  furnished  in writing  to the  Company by or on behalf of a Selling
Holder,  specifically  for  use in  connection  with  the  preparation  of  such
Registration Statement,  prospectus, amendment or supplement; provided, however,
that the  obligations  of the Selling  Holder  hereunder  shall be limited to an
amount  equal  to  the  proceeds  realized  by  such  Selling  Holder  from  the
Registrable Shares sold as contemplated herein.

                   3.  Each  party  entitled  to   indemnification   under  this
Paragraph (the  "Indemnified  Party") shall give notice to the party required to
provide   indemnification   (the  "Indemnifying   Party")  promptly  after  such
Indemnified Party has actual knowledge of any claim as to which indemnity may be
sought,  and shall  permit the  Indemnifying  Party to assume the defense of any
such claim or any litigation resulting therefrom;  provided that counsel for the
Indemnifying  Party,  who shall conduct the defense of such claim or litigation,
shall  be  approved  by the  Indemnified  Party  (whose  approval  shall  not be
unreasonably  withheld);  and,  provided,   further  than  the  failure  of  any
Indemnified  Party to give  notice as  provided  herein  shall not  relieve  the
Indemnifying  Party of its  obligations  under this  Paragraph.  The Indemnified
Party  may  participate  in such  defense  at such  party's  expense;  provided,
however, that the Indemnifying Party shall pay such expense if representation of
such Indemnified  Party by the counsel retained by the Indemnifying  Party would
be  inappropriate  due to actual or potential  differing  interests  between the
Indemnified  Party and any  other  party  represented  by such  counsel  in such
proceeding.  No  Indemnifying  Party,  in the  defense  of  any  such  claim  or
litigation shall, except with the consent of each Indemnified Party,  consent to
entry of any judgment or enter into any settlement  which does not include as an
unconditional  term  thereof  the giving by the  claimant or  plaintiff  to such
Indemnified  Party of a release  from all  liability in respect of such claim or
litigation,  and no Indemnified  Party shall consent to entry of any judgment or
settle  such  claim or  litigation  without  the prior  written  consent  of the
Indemnifying Party.

     G. Information by Holder.  The Selling Holders shall furnish to the Company
such information  regarding the Selling Holders and the distribution proposed by
the  Selling  Holders as the  Company  may  request  in writing  and as shall be
required  in  connection  with any  registration,  qualification  or  compliance
referred to in this Paragraph.

     H. Time. If a request for  registration is made pursuant to Paragraph V.B.,
and if for any  reason  (including  because  of a  postponement  by the  Company
pursuant to paragraph V.B.5.,  but excluding because of a default by the Selling
Holders with  respect to any  obligation  of theirs  hereunder  pertaining  such
registration)  a  Registration  Statement is not effective  with respect to such
Registrable  Shares within 120 days after the request for  registration is made,
the number of shares of Common Stock covered by this Warrant shall be increased,
and the Exercise Price shall be reduced,  as provided in Paragraph IV. as if the
Company on the 121st day after the request for registration  declared and paid a
dividend  upon the Common Stock of 4/10ths of one share of Common Stock for each
share of Common Stock then outstanding.

     I.  Suspension  of  Dispositions.  Each Selling  Holder  agrees that,  upon
receive of any notice (a "Suspension  Notice") from the Company of the happening
of any event which  makes any  statement  made in a  registration  statement  or
related  prospectus  untrue or which  requires the making of any changes in such
registration  statement,  prospectus  or documents so that they will not contain
any untrue  statement  of a  material  fact or omit to state any  material  fact
required to be stated  therein or necessary to make the  statements  therein not
misleading,   and,  such  Holder  will  forthwith  discontinue   disposition  of
Registrable Shares until such Holder's receipt of the copies of the supplemented
or amended  prospectus,  or until it is advised in writing (the "Advice") by the
Company that the use of the prospectus may be resumed,  and has received  copies
of any additional or supplemental filings which are incorporated by reference in
the prospectus,  and, if so directed by the Company, such Holder will deliver to
the Company all copies,  other than  permanent file copies then in such Holder's
possession,  of the prospectus  covering such Registrable  Shares current at the
time  of  receipt  of such  notice.  The  Company  shall  use  its  commercially
reasonable  efforts and take such actions as are reasonably  necessary to remedy
the Advice as promptly as practicable.

 VI. LOST STOLEN, DESTROYED OR MUTILATED WARRANT. Upon receipt by the Company of
evidence  satisfactory  (in the exercise of reasonable  discretion) to it of the
ownership of and the loss,  theft or  destruction  or mutilation of the Warrant,
and (in the case or loss,  theft or destruction) of indemnity  satisfactory  (in
the exercise of reasonable  discretion)  to it, and (in the case of  mutilation)
upon the surrender and cancellation thereof, the Company will issue and deliver,
in lieu thereof, a new Warrant of like tenor.

 VII.      RESTRICTIONS. TRANSFER AND TRANSFER

          A.  Owner of  Warrant.  The  Company  may deem and treat the person in
whose  name  this  Warrant  is   registered  as  the  Holder  and  owner  hereof
(notwithstanding  any  notations of  ownership or writing  hereon made by anyone
other than the Company) for all purposes and shall not be affected by any notice
to the contrary, until presentation of this Warrant for registration of transfer
as provided below.

          B.  Transfer  of Warrant.  The Company  agrees to maintain at its then
principal place of business books for the  registration of and the  registration
of transfers of the Warrant, and, subject to the provisions of subsections C and
D below, this Warrant and all rights hereunder are transferable,  in whole or in
part,  on said books at said  office,  upon  surrender  of this  Warrant at said
office,  together with a written assignment of this Warrant duly executed by the
Holder hereof or its duly authorized  agent or attorney and funds  sufficient to
pay any  transfer  taxes  payable  upon the making of such  transfer.  Upon such
surrender  and payment the  Company  shall  execute and deliver a new Warrant or
Warrants  in the name of the  assignee  or  assignees  and in the  denominations
specified in such  instrument of assignment,  and this Warrant shall promptly be
canceled.

          C.  Restrictions  on Transfer.  Neither this Warrant nor the shares of
Common Stock issuable on exercise of this Warrant have been registered under the
Securities Act of 1933 or any other securities laws (the "Acts").  Therefore, in
order,  among other things, to insure compliance with the Acts,  notwithstanding
anything  else in the  Warrant  to the  contrary,  the  Holder of this  Warrant,
including any  successive  Holder,  agrees by accepting this Warrant as follows:
This  Warrant  and the shares of Common  Stock which may be  purchased  upon the
exercise hereof,  may not be sold,  transferred,  pledged or hypothecated in the
absence of (i) an effective registration  statement or post-effective  amendment
thereto  for  such   Warrant,   or  shares  of  Common  Stock  of  the  Company,
respectively,  under  the  Acts,  or  (ii)  an  opinion  of  counsel  reasonably
satisfactory  to the Company that  registration is not required under such Acts.
In no  event  may  this  Warrant  be  transferred  to any  person  who is not an
accredited investor as such term is defined in Rule 501(a) of Regulation D under
the Act.

          D.  Legend on Shares.  Each  certificate  for  shares of Common  Stock
initially  issued upon exercise of this Warrant,  unless at the time of exercise
such Shares are registered  under the Acts, shall bear the following legend (and
any additional legend required under said acts or otherwise):

                   "The securities represented by this certificate have not been
                  registered  under  the  Securities  Act of 1933  or any  state
                  securities acts (the "Acts") and cannot be transferred  except
                  (i) pursuant to a registration  statement  effective under the
                  Acts, or (ii) pursuant to an exemption  from the  registration
                  requirements of the Acts."

          Any certificate issued at any time in exchange or substitution for any
certificate bearing such legend (except a new certificate issued upon completion
of a public distribution pursuant to a registration  statement under the Acts of
the securities  represented  thereby) shall also bear such legend unless, in the
opinion of such  counsel as shall be approved  by the  Company,  the  securities
represented  thereby  need no longer be  subject  to the  transfer  restrictions
contained in this Warrant. The transfer and transfer  restriction  provisions of
this Warrant shall be binding upon all subsequent Holders of the Warrant.

 VIII.  RESERVATION  OF SHARES.  The Company  covenants that during the Exercise
Period  it  will  reserve  from  its  authorized  and  unissued  common  stock a
sufficient number of shares to provide for the delivery of stock pursuant to the
exercise of this Warrant.

 IX. MISCELLANEOUS. This Warrant does not confer upon the Holder any rights of a
stockholder of the Company, including,  without limitation, any right to vote or
to consent to or  receive  notice as a  stockholder  of the  Company;  provided,
however, that this Paragraph is subject to Paragraph VI.

 X.     HEADINGS. The headings in this Warrant are for purposes of reference
only, and shall not limit or otherwise affect the meaning hereof.

Dated:  April 28, 1998

                                  POSITRON CORPORATION
ATTEST:
                                  By:
                                      Authorized Representative
By:

                                  Title:
Title:




<PAGE>


                   EXERCISE OF WARRANT AND DECLARATION

         To:

     Pursuant to the  provisions of the Stock  Purchase  Warrant dated April 28,
1996, the  undersigned  Holder hereby  exercises the right to purchase shares of
the                                 Common                                 Stock
of______________________________________________________________ (the "Company")
and delivers to the Company herewith the sum of  $______________  (in cash or by
certified or official bank check payable to the order of the Company) in payment
in full for those shares.

         The undersigned  hereby declares and represents to the Company that the
undersigned is an  "accredited  investor" as such term is defined in Rule 501(a)
of  Regulation  D under  the  Securities  Act of 1933 (the  "Act")  and has such
knowledge, sophistication and experience in financial and business matters so as
to be capable of  evaluating  the  merits  and risks of the  acquisition  of the
securities into which the Warrant is exercisable.

         The undersigned  hereby declares and represents to the Company that the
intention  of  this  exercise  is  to  acquire  the  aforementioned  shares  for
investment only and not for resale or with a view to distribution, except as the
same  may be made  in  compliance  with  all  applicable  securities  laws.  The
undersigned has been advised that the shares being issued to the undersigned are
not being registered under the Securities Act of 1933 (the "Act") on the grounds
that  this  transaction  is  exempt  under  Section  4 of  and/or  Regulation  D
promulgated under that Act as not involving any public offering.  As a result of
not being  registered under the Act, the undersigned has been advised that these
shares  may not be sold or  offered  for  sale in the  absence  of an  effective
registration  statement  as to the  securities  under  the  Act  and  any  other
applicable  securities acts or an opinion of counsel satisfactory to the Company
that such registration is not required.

         You will kindly  forward a certificate or  certificates  for the shares
purchased  hereby  and,  if such  shares  shall not include all of the shares as
provided in said  Warrant,  a new Warrant of like tenor and date for the balance
of the shares issuable  thereunder  shall be delivered to the undersigned at the
address shown below.

Dated:_______________                        __________________________________
                                                           Holder

                                            Address:
                                            -----------------------------------

                                            -----------------------------------

                                            -----------------------------------


<PAGE>



                                    EXHIBIT E

                  CONSENT TO SENIOR LOAN AND SECURITY AGREEMENT
                                  BY AND AMONG
                              POSITRON CORPORATION
                                AND URO-TECH LTD.
                           dated as of April 28, 1998


                      SUBORDINATION AGREEMENT BY AND AMONG
                                 URO-TECH, LTD.
                                  IMATRON INC.
                                       AND
                              POSITRON CORPORATION
                           dated as of April 28, 1998



                  CONSENT TO SENIOR LOAN AND SECURITY AGREEMENT

         This  Consent (the  "Consent")  is entered into this 28th day of April,
1998 by Positron  Corporation,  a Texas  corporation  ("Borrower")  and Uro-Tech
Ltd., a Texas limited partnership ("Lender").

                                    RECITALS

          A. Lender and  Borrower  entered  into a Loan and  Security  Agreement
dated as of  November  14,1995  and  Promissory  Note (the  "Note") of even date
therewith in the original principal amount of $1,000,000.00 executed by Borrower
and  payable to the order of Lender  (together  with  certain  addenda and other
instruments,  documents or agreements  entered into in connection  therewith and
any extensions, amendments replacements or modifications to any of the foregoing
being  referred to as the "Loan  Documents")  pursuant to which Lender agreed to
extend Loans and financial accommodations to the Borrower.

          B. The Parties  mutually agree that it is in their mutual  interest to
  modify  certain  terms of the Note and Loan  Documents  to enable  Borrower to
  obtain additional  financing and other support from Imatron Inc., a New Jersey
  corporation ("Imatron").

          C. Any and all initially  capitalized terms used herein shall have the
  meaning  ascribed to them in the Loan Documents  unless  specifically  defined
  herein.

         NOW  THEREFORE,  in  consideration  of the  foregoing  and  the  mutual
covenants and promises  contained  herein the parties  hereto do hereby agree as
follows:

          1.       Lender hereby consents to the following actions:

                  (a) Borrower is authorized to issue and sell to Imatron shares
of the Borrower's common stock,  $0.01 par value, for $100.00,  pursuant to that
certain Stock Purchase Agreement by and between Borrower and Imatron dated April
____, 1998.

                  (b) Borrower is authorized to borrow  $500,000.00 from Imatron
(the  "Imatron  Loan")  upon  terms and  conditions  acceptable  to the Board of
Directors of the Borrower.

                  (c) In  connection  with the Imatron  Loan,  the  Borrower may
grant to Imatron a lien on all the personal property of the Borrower, which lien
is senior to Lender's lien on such  property,  and Lender agrees to  subordinate
its interest in Borrower's property pursuant to a Subordination Agreement in the
form as that attached hereto as Exhibit A.

          2. Borrower  acknowledges that certain Events of Default have occurred
(the "Prior  Defaults") and are continuing as of the date of this Agreement.  In
order to allow

<PAGE>


the Borrower to consummate the Imatron Loan, the Lender agrees to waive
all Prior  Defaults  and not to pursue  any  remedies  available  under the Loan
Documents as a result of the Prior  Defaults.  The waiver of the Prior  Defaults
and Lender's agreement not to pursue its remedies with respect to Prior Defaults
shall in no way be construed as a waiver or impairment of the Lender's interests
and right under the Loan  Documents,  including,  but not  limited to,  Lender's
right to exercise any rights and remedies  provided in the Loan  Documents  with
respect  to Events of Default  occurring  at any time or from time to time after
the  date of this  Agreement,  and  such  rights  shall  be  cumulative  and not
exclusive.

          3. Except as otherwise  set forth  herein,  this  Agreement  shall not
impair,  limit,  restrict or  otherwise  affect the  obligations  of Borrower to
Lender  under the Loan  Documents.  Borrower  hereby  acknowledges,  agrees  and
represents  that (a) Borrower is indebted to Lender pursuant to the terms of the
Note as modified  hereby and Borrower  agrees that the Loan  Documents are valid
and  binding  and are in full  force and  effect  according  to their  terms and
conditions; (b) except as modified or deemed to be modified by the Subordination
Agreement attached hereto, the Liens, security interests and assignments created
and evidenced by the Loan  Documents  are,  respectively,  valid and  subsisting
liens, security interests and assignments of the respective dignity and priority
recited in the Loan Documents; (c) Borrower has no claims, offsets,  defenses or
counterclaims  against  Lender  whether  arising  under  the Loan  Documents  or
otherwise;  and (d) Lender is not in default  and no event has  occurred  which,
with the passage of time,  giving of notice, or both, would constitute a default
by Lender of Lender's obligations under the Security Documents.

          4. Lender and Borrower  agree that,  except as modified  herein and in
the  Subordination  Agreement,  all of the  terms  and  conditions  of the  Loan
Documents are hereby ratified and reaffirmed.

          5. The terms and  conditions  of this  Agreement  shall not be binding
upon Lender  until  Borrower's  satisfaction  or  fulfillment  of the  following
matters:

                  (a)  Borrower's  delivery  to  Lender  and  to  Imatron  of  a
certificate of an officer of Borrower certifying that attached thereto is a true
and  correct  copy  of  resolutions  of  the  Board  of  Directors  of  Borrower
authorizing the execution of this Agreement and of the Subordination Agreement;

                  (b)  Borrower's  delivery  to Lender  and to Imatron of a duly
executed Subordination Agreement;

                  (c) Delivery to Imatron of the written consent from ProFutures
Bridge  Capital  Fund, a Texas  limited  partnership,  (together  with any other
required  approvals  or  authorization  to  the  transactions   contemplated  or
described in this Agreement).


                              POSITRON CORPORATION,
                                            a Texas corporation


                                            By:_______________________________
                                                   Gary B. Wood, Chairman


                                            URO-TECH LTD.,
                           a Texas Limited Partnership



                                            By:_______________________________
                                            Title:____________________________


<PAGE>



                                EXHIBIT A

                        SUBORDINATION AGREEMENT


         THIS SUBORDINATION  AGREEMENT ("Agreement") is made and entered into as
of April 28, 1998,  by and among  URO-TECH,  LTD., a Texas  limited  partnership
("Subordinated  Creditor"),  IMATRON  INC.,  a California  corporation  ("Senior
Creditor"), and POSITRON CORPORATION, a Texas corporation ("Borrower").

                              RECITALS:

     Senior Creditor and Borrower intend to execute a certain Loan Agreement,  a
certain Security Agreement, and related agreements, all dated May 1, 1998 (as at
any time amended, the "Loan Agreement"),  pursuant to which Senior Creditor will
make Loans to or for the benefit of Borrower  from tune to time,  secured by all
or substantially all of the assets of Borrower.  Capitalized terms used in these
Recitals and elsewhere in this Agreement,  unless otherwise defined,  shall have
the  meanings  ascribed to them in the Loan  Agreement  as in effect on the date
hereof.

         Borrower and  Subordinated  Creditor are parties to a Loan and Security
Agreement dated as of November 14, 1995 ("Subordinated Loan Agreement") pursuant
to which  Subordinated  Creditor from time to time made loans up to an amount of
$1,500,000  to and for the  benefit  of  Borrower,  on  terms  set  forth in the
Subordinated  Loan  Agreement  and  related  Promissory  Note,  and  secured  by
subordinate Liens on all or substantially all of the assets of Borrower.

         As an inducement  to Senior  Creditor to conclude its Loan to Borrower,
and for the benefit of both Borrower and Subordinated Creditor, the parties wish
to agree  herein as to the  relative  rights of payment and other  rights  under
their  respective  financing  arrangements,  and  further  wish to agree  and to
memorialize  certain other  agreements  with respect to the enforcement of their
respective rights and remedies against the Borrower.

         NOW,  THEREFORE,   for  TEN  DOLLARS  ($10.00)  in  hand  paid  and  in
consideration of the foregoing premises, and other valuable  consideration,  the
receipt  and  sufficiency  of which  are  hereby  acknowledged,  and the  mutual
covenants herein, intending to be legally bound hereby, agree as follows:

          A.       Definitions; Rules of Construction.

          1. In addition to such other terms as are elsewhere defined herein, as
used in this Agreement the following terms shall have the following meanings:

          "Bankruptcy Code" shall mean title 11 of the United States Code.

          "Enforcement  Expenses"  shall mean all reasonable  costs and expenses
incurred by Senior  Creditor in connection with its enforcement of any rights or
remedies under the Senior Creditor Loan Documents,  the collection of any of the
Senior Debt or the protection of, or realization  upon, any Collateral after the
occurrence and during the  continuance of a Senior Debt Default,  including,  by
way  of  example,   reasonable  attorneys'  fees,  court  costs,  appraisal  and
consulting fees,  auctioneer's fees, rent, storage,  insurance premiums and like
items and whether or not such  amounts are allowed as a claim  against  Borrower
under the Bankruptcy Code.

          "Payment  Default"  shall mean a Senior Debt Default that results from
Borrower's  failure  to pay  any of the  Senior  Debt on the  due  date  thereof
(whether due at stated maturity, upon acceleration, on demand or otherwise).

          "Plan" shall mean a plan proposed in a proceeding under the Bankruptcy
Code for the  reorganization  or  rehabilitation  of Borrower,  a composition or
extension of any of  Borrower's  Debts or a  liquidation  in whole or in part of
Borrower's assets.

          "Reorganization  Securities" shall mean (i) the securities of Borrower
(including  senior  securities)  provided  for by a plan  of  reorganization  of
Borrower  that  has  been  proposed  in a case  under  the  Bankruptcy  Code and
confirmed by final order of the bankruptcy court having  jurisdiction  over such
case,  and (ii)  shares of common  stock or other  equity  securities,  and debt
securities,  the  payment  of which  is  subordinated,  at  least to the  extent
provided in this Agreement with respect to the Subordinated Debt, to the payment
of all  Senior  Debt at the  time  outstanding  and to the  payment  of all debt
securities issued in exchange therefor to Senior Creditor, which shares or other
equity or debt  securities  have been  provided for by a plan of  reorganization
which has been adopted or agreed to other than pursuant to a proceeding referred
to in clause (i) of this  definition and which has been approved or agreed to by
Senior Creditor.

          "Senior  Creditor Loan Documents"  shall mean and include (i) the Loan
Agreement,  the  Security  Agreement,  the other Loan  Documents,  and all other
instruments or agreements now or hereafter evidencing or securing the payment of
the whole or any part of the Senior Debt and (it) all  renewals,  modifications,
extensions, refinancings, restructurings or replacements thereof.

          "Senior  Debt"  shall  mean  (i)  all  liabilities,  indebtedness  and
obligations  of Borrower now or hereafter  existing under or with respect to any
of the Senior  Creditor  Loan  Documents,  whether such  obligations  are now or
hereafter existing and however and whenever made or incurred, and whether direct
or  indirect,  absolute  or  contingent,  due or to become  due,  or  secured or
unsecured,  including  all  principal,  interest  and  premium on, and all other
amounts  payable  in  respect  of, any of such  obligations,  and all  indemnity
amounts,  reimbursement obligations and other amounts owed by Borrower to Senior
Creditor  thereunder,  (ii) any and all loans made or other  credit  extended by
Senior Creditor to Borrower during the pendency of any insolvency  proceeding of
Borrower,  (iii) all interest at any time accrued with respect to the  foregoing
(including any interest that accrues during the pendency of any bankruptcy  case
of Borrower,  whether or not Senior Creditor is authorized by Section 506 of the
Bankruptcy  Code  to  collect  such  interest  from  Borrower),   and  (iv)  all
Enforcement  Expenses for which  Borrower is now or hereafter  becomes liable to
pay to  Senior  Creditor  in  connection  with any of the  foregoing  under  any
agreement or by applicable law.

          "Senior  Debt  Default"  shall mean an Event of Default  under (and as
defined in) the Senior Creditor Loan Documents.

          "Subordinated  Debt" shall mean (i) all liabilities,  indebtedness and
obligations of Borrower to Subordinated Creditor under or with respect to any of
the  Subordinated  Debt  Documents,  whether such  liabilities,  indebtedness or
obligations  are now or  hereafter  existing  and however and  whenever  made or
incurred,  and whether  direct or indirect,  absolute or  contingent,  due or to
become due, or secured or  unsecured,  including  all  principal,  interest  and
premium on, and all other amounts payable in respect of, flee Subordinated Note,
and all fees, charges, commitment or other fees, indemnity amounts,  enforcement
expenses  (including  reasonable  attorneys'  fees) and other  amounts  owing by
Borrower to Subordinated  Creditor under any of the Subordinated Debt Documents;
and (ii) all  renewals,  extensions,  substitutions,  refundings,  refinancings,
restructurings  or  replacements  of  any  such  liabilities,   indebtedness  or
obligations  (including  all  successive  renewals,  extensions,   substitutions
refundings,  refinancings,  restructurings  or replacements of such liabilities,
indebtedness or obligations).

          "Subordinated  Debt Default" shall mean an Event of Default under, and
as defined in, the Subordinated Loan Agreement.

          "Subordinated  Debt Documents" shall mean and include the Subordinated
Loan  and  Security  Agreement,  the  related  Promissory  Note,  and all  other
instruments  and agreements now or hereafter  evidencing or securing the payment
of the whole or any part of the Subordinated Debt.

          2. The terms  "herein,"  "hereof' and  "hereunder'  and other words of
similar  import  refer to this  Agreement  as a whole and not to any  particular
section,  paragraph  or  subdivision.  All  references  to statutes  and related
regulations shall include any amendments of same and any successor  statutes and
regulations.  All references to any instruments or agreements  shall include any
and all  modifications  thereto  and any and  all  restatements,  extensions  or
renewals  thereof.   All  references  to  "including"  and  "include"  shall  be
understood to mean "including, without limitation."

          B.       Subordination.

          1. Subordinated  Creditor hereby postpones and subordinates all of the
Subordinated  Debt to the full and final  payment  and  discharge  of all of the
Senior Debt and Senior  Creditor shall be entitled to receive payment in full of
all Senior Debt before any payment (other than a distribution of  Reorganization
Securities) is made on account of or applied to any of Subordinated Debt.

          2. Subordinated  Creditor hereby subordinates any security interest or
liens it now has or may hereafter  acquire in the Collateral and other assets of
the Borrower to any security  interest in or liens upon the  Collateral or other
assets of Borrower  which  Senior  Creditor has under the Senior  Creditor  Loan
Documents or otherwise.

          3. Each  holder of  Subordinated  Debt,  whether  now  outstanding  or
hereafter  created,  incurred,  assumed or  guaranteed,  shall be deemed to have
acquired the Subordinated  Debt with full knowledge and subject to the terms and
provisions of this Agreement.

          4. In the event of any distribution,  division or application, partial
or complete,  voluntary or involuntary, by operation of law or otherwise, of all
or any part of the assets of the Borrower or the  proceeds  thereof to creditors
of the  Borrower  or upon any  indebtedness  of the  Borrower,  by reason of the
liquidation,  dissolution  or other winding up of the Borrower or the Borrower's
business,  or in the event of any sale of assets of the  Borrower or  insolvency
proceeding  involving the Borrower or its assets, then and in any such event any
payment or distribution of any kind or character, whether in cash, securities or
other property (excluding Reorganization Securities),  which shall be payable or
deliverable upon or with respect to any of the  Subordinated  Debt shall be paid
or  delivered  directly to Senior  Creditor for  application  to the Senior Debt
(whether  or not the same is then  due)  until all of the  Senior  Debt has been
fully paid and discharged. Each instrument evidencing Subordinated Debt shall at
all times bear a conspicuous legend that the Subordinated Debt evidenced thereby
is  subordinated  to the Senior Debt pursuant to this  Agreement.  The books and
records of Subordinated Creditor and any other holder of Subordinated Debt shall
be marked to evidence the  subordination of all of the Subordinated  Debt to and
in favor of the Senior Debt.

          C.       Warranties and Representations.

          1.  Subordinated  Creditor hereby represents and warrants that: (i) it
has not  relied nor will it rely on any  representation  or  information  of any
nature made by or received from Senior Creditor relative to Borrower in deciding
to execute this Agreement; (ii) no part of the Subordinated Debt is evidenced by
any  instrument  or  writing  except  the  Subordinated  Debt  Documents;  (iii)
Subordinated  Creditor  is the  lawful  owner  of the  Subordinated  Debt;  (iv)
Subordinated  Creditor has not  heretofore  assigned or  transferred  any of the
Subordinated  Debt, or any interest therein;  and (v) Subordinated  Creditor has
not heretofore given any subordination in respect of the Subordinated Debt.

          2. Each of the parties  hereto  represents and warrants to each of the
other parties hereto that this Agreement has been duly executed and delivered by
such party and is the valid and binding  obligation  of such party,  enforceable
against  such  party in  accordance  tenth  the  terms  hereof,  except  as such
enforceability  may  be  limited  by  bankruptcy,  insolvency  or  similar  laws
affecting creditors' rights generally and by principles of equity.

          3.  Subordinated   Creditor   acknowledges  that  this   Subordination
Agreement is deemed to amend that certain Inter-Creditor  Agreement by and among
Borrower, Subordinated Creditor, ProFutures Bridge Capital Fund, L.P. and Boston
Financial  & Equity  Corporation  ("Inter-Creditor  Agreement")  in terms of the
order  of  perfection  of  security   interests  and  liens,   and  subordinates
Subordinated Creditor's priority in certain assets of the Borrower, as currently
set forth in the  Inter-Creditor  Agreement,  to Senior  Creditor's  priority in
certain assets of the Borrower, as set forth in this Agreement.

          4.  Subordinated  Creditor agrees to copy the Senior Creditor with any
notices of default sent by Subordinated Creditor to the Borrower.

          D.  Negative  Covenants.  For so long as this  Agreement is in effect,
Borrower and  Subordinated  Creditor agree with Senior Creditor that,  except as
otherwise expressly provided in this Agreement: (a) Borrower shall not, directly
or indirectly, make any payment on account of any part of the Subordinated Debt;
(b) Subordinated Creditor shall not demand,  collect or accept from Borrower any
payment on account of the  Subordinated  Debt or any part hereof,  or accelerate
the maturity of the  Subordinated  Debt;  (c)  Subordinated  Creditor  shall not
exchange, set off, release, convert to equity or otherwise discharge any part of
the Subordinated Debt; (d) Subordinated  Creditor shall not enforce or apply any
security,  now or hereafter existing for the Subordinated Debt; (e) Subordinated
Creditor  shall not hereafter  give any  subordination  in respect of any of the
Subordinated  Debt or  transfer  or assign  any of the  Subordinated  Debt;  (f)
Borrower shall not hereafter  issue any  instrument or other writing  evidencing
any part of the Subordinated  Debt other than the  Subordinated  Debt Documents,
and  Subordinated  Creditor will not receive any such writing;  (g) Subordinated
Creditor  shall not  commence  or join with any other  creditors  of Borrower in
commencing any bankruptcy, assignment for the benefit of creditors or creditor's
agreement;  (h) Subordinated Creditor shall not institute, or join as a party in
the  institution  of, or assist  in the  prosecution  of,  any  action,  suit or
proceeding seeking a determination that the security interest of Senior Creditor
In any of the Collateral is invalid,  unperfected or avoidable,  or is or should
be subordinated to the interests of any others;  and (i)  Subordinated  Creditor
otherwise  shall  not  take  or  permit  any  action  inconsistent  with  Senior
Creditor's priority position over Subordinated  Creditor that is created by this
Agreement.  Notwithstanding  anything  contained  herein  to the  contrary,  the
parties hereto agree that the Borrower or the Subordinated Creditor, as the case
may be,  may take any of tile  actions  restricted  in this  Section 4 with flee
express written consent of the Senior Creditor (which consent may be withheld at
the sole discretion of the Senior Creditor).

          E.       Payment and Remedy Bars.

         1. Until payment in full of the Senior Debt, no payment with respect to
the  Subordinated  Debt  (include  any  payment  due  at  maturity,  whether  by
acceleration or otherwise) shall be made by or on behalf of Borrower.

         2. The  Subordinated  Creditor agrees that until payment in full of the
Senior  Debt,  no holder  of  Subordinated  Debt  shall  take any  action to (x)
accelerate the maturity of, or demand as immediately due and payable, all or any
part of the  Subordinated  Debt,  (y) commence,  continue or  participate in any
judicial,  arbitral or other proceeding or any other  enforcement  action of any
kind  against  Borrower  or  arty  of  such  Borrower's  assets  (including  any
involuntary  proceeding;   under  the  Bankruptcy  Code)  seeking,  directly  or
indirectly, to enforce any of their rights or remedies, or to enforce any of the
obligations  incurred by Borrower under or in connection  with the  Subordinated
Debt or the  Subordinated  Debt  Documents,  or (z)  continence  or  pursue  any
judicial,  arbitral or other  proceeding  or legal  action of any kind,  seeking
injunctive  or  other  equitable  relief  to  prohibit,   limit  or  impair  the
commencement  or pursuit  by Senior  Creditor  of any of its rights or  remedies
under or in  connection  win the Senior  Creditor  Loan  Documents  or otherwise
available to Senior Creditor under applicable law.

          F. Turnover of Prohibited Transfers. If notwithstanding the provisions
of this Agreement any payment, distribution,  Collateral or security (other than
Reorganization  Securities), or the proceeds thereof, are received by any holder
of  Subordinated  Debt on account of or with respect to any of the  Subordinated
Debt,   such  payment,   distribution,   Collateral  or  security   (other  than
Reorganization  Securities) shall be held in trust for the benefit of, and shall
immediately  be paid or delivered  by such holder to the Senior  Creditor in the
form  received  (except  for  the  addition  of any  endorsement  or  assignment
necessary  to effect a transfer of all rights  therein to Senior  Creditor)  for
application to the Senior Debt and other Borrower debt in the order  established
by the Inter-Creditor  Agreement.  Senior Creditor is irrevocably  authorized to
supply any required endorsement or assignment which may have been omitted. Until
so delivered,  Subordinated  Creditor  shall exercise its best efforts to ensure
that such payment,  distribution  or security shall not be commingled with other
funds or property of Subordinated Creditor.

          G.       Amendments to Documents.

          1. Senior  Creditor and Borrower  shall be  authorized to amend any of
the Senior  Creditor Loan Documents to which they are a party in accordance with
the terms  thereof,  and  without  prior  notice to or the consent of any of the
holders of the Subordinated Debt.

          2. Without the prior written consent of Senior Creditor (which consent
may be given or withheld in Senior Creditor's sole discretion),  no provision of
the  Subordinated  Debt Documents shall be amended,  modified or supplemented if
the effect  thereof would be to (i) advance the originally  scheduled  dates for
the  payment of  principal,  interest  or other  sums  payable in respect of any
Subordinated  Debt, or modify in any manner adverse to Borrower the dates for or
premiums  payable  in  connection  with  prepayments,  (ii)  impose on  Borrower
prepayment  charges,  closing fees or other fees or (iii) impose on Borrower any
representations,  warranties,  covenants,  events of default or other provisions
that  are more  restrictive  or  burdensome  to  Borrower  than  the  terms  and
provisions of the  Subordinated  Debt Documents as in effect on the date of this
Agreement.

          H. Certain Waivers and Consents.  Borrower and  Subordinated  Creditor
each hereby  waives any defense  based on the  adequacy of a remedy at law which
might  be  asserted  as a bar to the  remedy  of  specific  performance  of this
Agreement  in any action  brought  therefor by Senior  Creditor.  To the fullest
extent  permitted by applicable  law,  Borrower and  Subordinated  Creditor each
hereby further waives:  presentment,  demand, protest, notice of protest, notice
of default or dishonor,  notice of payment or  nonpayment  and any and all other
notices and demands of any kind in connection  with all  negotiable  instruments
evidencing  all or any portion of the Senior Debt;  the right to require  Senior
Creditor  to marshal any  Collateral  or  security,  or to enforce any Lien that
Senior Creditor may now or hereafter have in any Collateral  securing the Senior
Debt or to pursue  any claim it may have  against  any  guarantor  of the Senior
Debt, as a condition to Senior Creditor's  entitlement to receive any payment on
account of the Senior Debt; notice of the acceptance of this Agreement by Senior
Creditor;  and notice of any credit made  available to Borrower,  extensions  of
time granted,  amendments to the Loan Agreement,  the Security  Agreement or the
other Senior Creditor Loan Documents,  or other action taken in reliance hereon.
Subordinated  Creditor  hereby  consents  and agrees that Senior  Creditor  may,
without  in  any  manner  impairing,   releasing  or  otherwise   affecting  the
subordination  provided for in this Agreement or any of Senior Creditor's rights
hereunder and without prior notice to or the consent of  Subordinated  Creditor:
release, renew, extend, compromise or postpone the time of payment of any of the
Senior Debt;  substitute,  exchange or release any or all of the  Collateral  or
decline or neglect to perfect Senior Creditor's Lien upon any of the Collateral;
add or release any Person primarily or secondarily liable from any of the Senior
Debt;  amend or modify any of the Senior  Creditor  Loan  Documents or waive any
Senior Debt  Default;  and increase or decrease the amount of the Senior Debt or
the rate of interest or the amount of any other  charges  payable in  connection
therewith

          I.  Subrogation.  Provided that the Senior Debt has been  indefeasibly
paid and discharged and any commitment  that Senior  Creditor may have under the
Senior  Creditor  Loan  Documents  to make loans or extend other credit has been
terminated  or expired,  the holders of  Subordinated  Debt shall be  subrogated
(without any  representation by or recourse to Senior Creditor) to the rights of
Senior  Creditor  to receive  payments  or  distributions  of cash,  property or
securities payable or distributable on account of the Senior Debt, to the extent
that  the  Senior   Creditor  would  be  entitled  to  have  such  payments  and
distributions  paid  over to or for its  benefit;  an for  the  purpose  of such
subrogation, no payment or distribution to Senior Creditor of any cash, property
or  securities  to which the holders of  Subordinated  Debt would  otherwise  be
entitled except for the provisions of this Agreement, and no payment pursuant to
the  provisions  of  this  Agreement  to  Senior   Creditor  by  the  holders  o
Subordinated  Debt,  shall,  as between  Borrower and its  creditors  other than
Senior Creditor and the holders of Subordinated  Debt, be deemed to be a payment
by Borrower to or on account of any Subordinated  Debt, it being understood that
the  provisions  of this  Agreement  are solely for the purpose of defining  the
relative  rights  of  Senior  Creditor,  on the  one  hand,  and the  holder  of
Subordinated  Debt,  on the  other.  In no event,  however,  shall any holder of
Subordinated  Debt have any rights or claims  against  Senior  Creditor  for any
impairment of Subordinated  Creditor's subrogation rights that might result from
Senior  Creditor's  release  of  any  Lien  upon  any  Collateral,  forgiveness,
compromise,  extension or discharge of any Senior Debt, release of Borrower,  or
vote to accept or reject any Plan.

          J.  Statement of Account.  Subordinated  Creditor  agrees to render to
Senior  Creditor  from time to time upon Senior  Creditor's  request  therefor a
statement of Borrower's  account with Subordinated  Creditor and Borrower agrees
to afford Senior  Creditor  access to the books and records of Borrower in order
that Senior  Creditor  may make a full  examination  of the state of accounts of
Borrower with Subordinated Creditor.

          K. Validity of  Subordinated  Debt.  The  provisions of this Agreement
subordinating  the  Subordinated  Debt to the  Senior  Debt are  solely  for the
purpose of defining the  relative  rights of Senior  Creditor  and  Subordinated
Creditor and shall not impair,  as between  Subordinated  Creditor and Borrower,
the  obligation of Borrower,  which is  unconditional  and absolute,  to pay the
Subordinated  Debt in accordance with its terms except as payment thereof may be
postponed in accordance with this Agreement.

          L.  Indulgences Not Waivers.  Neither the failure nor any delay on the
part of Senior  Creditor  to  exercise  any right,  remedy,  power or  privilege
hereunder shall operate as a waiver thereof or give rise to an estoppel,  nor be
construed as an agreement to modify the terms of this  Agreement,  nor shall any
single or partial exercise of any right, remedy, power or privilege with respect
to any  occurrence  be  construed  as a waiver of such right,  remedy,  power or
privilege with respect to any other  occurrence.  No waiver by a party hereunder
shall be effective  unless it is in writing and signed by the party snaking such
waiver, and then only to the extent specifically stated in such writing.

          M. Duration.  This Agreement  shall become  effective when executed by
Borrower and  Subordinated  Creditor and accepted by Senior  Creditor in So. San
Francisco, CA and, when so accepted,  shall constitute a continuing agreement of
subordination,  and shall remain in effect until all of the Senior Debt has been
paid in full in immediately available funds. Senior Creditor may, without notice
to  Subordinated  Creditor,  extend or continue  credit and make other financial
accommodations  to or  for  the  account  of  Borrower  in  reliance  upon  this
Agreement. The provisions of this Agreement shall continue to be effective or be
reinstated,  as the case may be, if at any time  payment of any  Senior  Debt is
rescinded or otherwise must be returned by Senior  Creditor,  all as if any such
payment had not been made.

          N. Default and Enforcement.  If at any time any holder of Subordinated
Debt fails to comply with any provision of this  Agreement that is applicable to
such holder,  Senior Creditor may demand specific performance of this Agreement,
whether or not  Borrower  itself has  complied  with the terms  hereof,  and may
exercise  any other  remedy  available  at law or equity.  Without  limiting the
generality of the foregoing, if any holder of Subordinated Debt, in violation of
this Agreement, shall institute or participate in any action, suit or proceeding
against Borrower, then Borrower may interpose as a defense or dilatory plea this
Agreement  and Senior  Creditor is  irrevocably  authorized  to intervene and to
interpose  such  defense  or plea in its or  Borrower's  name.  If any holder of
Subordinated  Debt  attempts to assert or enforce  any Lien with  respect to any
Collateral  in  violation  of this  Agreement,  Borrower or Senior  Creditor (in
Borrower's or Senior  Creditors  name) may by virtue of this Agreement  restrain
such enforcement.

          O.  Litigation;  Jurisdiction  and Venue.  Borrower,  Senior Creditor,
Subordinated  Creditor  and each other holder of  Subordinated  Debt each hereby
irrevocably  consents  to  the  jurisdiction  of the  courts  of  the  State  of
California  and of any  federal  court  located in the State of  California,  in
connection  with any action or  proceeding  arising  out of or  relating to this
Agreement. In any such litigation,  Borrower,  Subordinated Creditor, each other
holder of  Subordinated  Debt and Senior  Creditor each hereby  waives  personal
service of any summons,  complaint or other process, and agrees that the service
thereof may be made by certified mail direct to Borrower,  Subordinated Creditor
and Senior Creditor at then  respective  places of business set forth in Section
16 hereof,  and, in the case of any other holder of  Subordinated  Debt,  at the
last known address for such holder. Within 30 days after such mailing, the party
so served shall appear and answer to such summons,  complaint or other  process.
Should the party so served fail to appear or answer  within said 30-day  period,
then such  party  failing  to appear or answer  shall be deemed in  default  and
judgment  may be entered  against  such party for the amount or other  relief as
demanded  in  any  summons,  complaint  or  other  process  so  served.  In  the
alternative, in its sole discretion, any party may effect service upon any other
party in any other form or mariner  permitted by  applicable  law. The choice of
forum set forth herein shall not be deemed to preclude  the  enforcement  of any
judgment obtained in such forum or the taking of any action under this Agreement
to enforce the same in any  appropriate  jurisdiction,  or the  commencement  by
Senior Creditor or Subordinated Creditor, in its sole discretion,  of any action
or suit in any  jurisdiction  where any  Collateral may be found to repossess or
foreclose upon any such Collateral.

          P. Notices.  Except as otherwise provided herein, whenever any notice,
demand, request, consent, approval,  declaration or other communication shall or
may be given to or  served  upon  any of the  parties  by the  other  party,  or
whenever  any  party  desires  to  give  or  serve  upon  any  other  party  any
communication with respect to this Agreement, each such notice, demand, request,
consent,  approval,  declaration or other  communication shall be in writing and
shall be deemed to have been validly  served,  given or  delivered  (a) upon the
earlier of actual  receipt and three (3) days after deposit in the United States
Mail,  registered  or certified  mail,  return  receipt  requested,  with proper
postage prepaid,  (b) upon transmission,  when sent by telecopy or other similar
facsimile  transmission  (with such telecopy or facsimile  promptly confirmed by
delivery of a copy by  personal  delivery  or United  States  Mail as  otherwise
provided in this Section  16),  (c) one (1)  Business  Day after  deposit with a
reputable overnight courier with all charges prepaid or (d) when hand-delivered,
all of which  shall be  addressed  to the party to be  notified  and sent to the
address  or  facsimile  number  set forth  below or to such  other  address  (or
facsimile number) as may be substituted by notice given as herein provided:

       (a)  If to Senior Creditor:     Imatron Inc.
                                       389 Oyster Point Blvd.
                                       So. San Francisco, CA 94080
                                       Attention: S. Lewis Meyer
                                       Facsimile: (650) 871-0418

                                       With copies to:

                                       Severson & Werson, P.C.
                       One Embarcadero Center, Suite 2600
                             San Francisco, CA 94111
                         Attention: Roger S. Mertz, Esq.
                            Facsimile: (415) 956-0439

                                       If to Subordinated Creditor:

        (b) If to Subordinated Lender: Uro-Tech Ltd.
                                       1500 Three Lincoln Center
                                       5430 LBJ Freeway
                                       Dallas, Texas 75240
                                       Attention:  Gary B. Wood, Ph.D.
                                       Facsimile: (214)_________

        (c) If to Borrower:            Positron Corporation
                       1304 Langham Creek Drive, Suite 310
                              Houston, Texas 77084
                           Attention: Howard R. Baker
                            Facsimile: (281) 492-2961

          The giving of any notice  required  hereunder may be waived in writing
by the party  entitled to receive  such notice.  Failure or delay in  delivering
copies of any notice, demand, request, consent,  approval,  declaration or other
communication to any person (over than Senior Creditor,  Subordinated  Lender or
Borrower)  designated  above to receive copies shall in no way adversely  affect
the  effectiveness  of  such  notice,  demand,   request,   consent,   approval,
declaration or other communication.

          17. Entire  Agreement.  This Agreement  constitutes  and expresses the
entire  understanding  between  the parties  hereto with  respect to the subject
matter  hereof,   and  supersedes  all  prior  agreements  and   understandings,
inducements or conditions,  whether express or implied,  oral or written Neither
this  Agreement  nor any portion ox provision  hereof may be changed,  waived or
amended  orally or in any manner other than by an agreement in writing signed by
Senior Creditor, Borrower and Subordinated Creditor.

          18. Additional Documentation. Borrower and Subordinated Creditor shall
execute and deliver to Senior  Creditor such further  instruments and shall take
such further action as Senior Creditor may reasonably  request from tune to time
in order to carry out the provisions and intent of this Agreement.

          19. Successors and Assigns.  This Agreement shall inure to the benefit
of Senior Creditor,  its successors and assigns,  and shall be binding upon both
Borrower and Subordinated  Creditor and their respective successors and assigns;
provided,  however, that neither Subordinated Creditor nor any subsequent holder
of any Subordinated  Debt shall assign or transfer to any Person any part of the
Subordinated Debt.

          20. Defects Waived.  This Agreement is effective  notwithstanding  any
defect in the validity or  enforceability  of any  instrument or document at any
time evidencing or securing the whole or any part of the Senior Debt.

          21. Governing Law. The validity,  construction and enforcement of this
Agreement shall be governed by the internal laws of the State of California.

          22. Severability.  The provisions of this Agreement are independent of
and separable from each other.  If any provision  hereof shall for any reason be
held  invalid  or  unenforceable,  it is the  intent  of the  parties  that such
invalidity or  unenforceability  shall not affect the validity or enforceability
of any other provision hereof,  and that this Agreement shall be construed as if
such invalid or unenforceable provision had never been contained herein.

          23. Execution in  Counterparts.  This Agreement may be executed in any
number of  counterparts  and by different  parties to this Agreement on separate
counterparts,  each of which, when so executed, shall be deemed an original, but
all such counterparts shall constitute one and the same agreement. Any signature
delivered by a party by facsimile transmission shall be deemed to be an original
signature hereto.

         24. MUTUAL WAIVER OF JURY TRIAL. BECAUSE DISPUTES ARISING IN CONNECTION
WITH COMPLEX FINANCIAL  TRANSACTIONS ARE MOST QUICKLY AND ECONOMICALLY  RESOLVED
BY AN EXPERIENCED  AND EXPERT PERSON AND THE PARTIES WISH  APPLICABLE  STATE AND
FEDERAL LAWS TO APPLY (RATHER THAN ARBITRATION  RULES),  THE PARTIES DESIRE THAT
THEIR DISPUTES BE RESOLVED BY A JUDGE APPLYING SUCH APPLICABLE LAWS.  THEREFORE,
TO ACHIEVE THE BEST  COMBINATION  OF THE BENEFITS OF THE JUDICIAL  SYSTEM AND OF
ARBITRATION,  THE PARTIES HERETO WAIVE ALL RIGHT TO TRIAL BY JURY IN ANY ACTION,
SUIT,  OR  PROCEEDING   BROUGHT  TO  RESOLVE  ANY  DISPUTE,   WHETHER   SOUNDING
IN-CONTRACT,  TORT, OR OTHERWISE,  BETWEEN THE PARTIES ARISING OUT OF, CONNECTED
WITH, RELATED TO, OR INCIDENTAL TO THE RELATIONSHIP  ESTABLISHED BETWEEN THEM IN
CONNECTION WITH, THIS AGREEMENT OR THE TRANSACTIONS HEREUNDER.

         IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
signed, sealed and delivered on the day and year first above written.

                           SUBORDINATED CREDITOR:

                           URO-TECH LTD.,
                           a Texas limited partnership


                           By:______________________________________
                           Name:____________________________________
                           Title:___________________________________


                           SENIOR CREDITOR:

                           IMATRON INC.
                           a California corporation



                           By:______________________________________
                           Name:____________________________________
                           Title:___________________________________

                           BORROWER:

                           POSITRON CORPORATION,
                           a Texas corporation



                           By:______________________________________
                           Name:____________________________________
                           Title:___________________________________



                            EXHIBIT 7.2
                       STOCK PURCHASE AGREEMENT
                      with Schedules and Exhibits


                        STOCK PURCHASE AGREEMENT

         This Stock  Purchase  Agreement  ("Agreement")  is made this 1st day of
May,  1998  by and  between  POSITRON  CORPORATION,  a  Texas  corporation  with
principal  offices  located at 1304 Langham  Creek Drive,  Houston,  Texas 77084
("SELLER") and IMATRON INC., a New Jersey  corporation  with  principal  offices
located at 389 Oyster Point Blvd., So. San Francisco, CA 94080 ("BUYER").

         WHEREAS, Seller wishes to issue and sell to Buyer certain shares of its
common stock ("Shares") in exchange for certain consideration; and

         WHEREAS,  Buyer wishes to purchase such certain  shares of common stock
issued by and from Seller pursuant to certain terms and conditions.

         NOW,   THEREFORE,   in   consideration  of  the  mutual  covenants  and
agreements, the Seller and Buyer hereby agree as follows:

                               AGREEMENT

         1. Sale and  Purchase of Shares.  On the  closing  date as set forth in
Section 3 ("Closing Date"), Seller shall deliver to Buyer, for the consideration
set forth in Section 2 hereof, the greater of Nine Million (9,000,000) shares of
Seller's common stock or whatever number of common shares in excess of 9,000,000
common shares constitutes fifty-one percent (51%) of Seller's outstanding voting
securities on a fully  diluted  basis,  exclusive of out of the money  warrants,
and/or  options,  and/or  convertible  securities,  calculated as of the Closing
Date.  For this purpose,  "out of the money" shall mean warrants  and/or options
and /or  convertible  securities in which the purchase  price of the  underlying
common  stock  for which the  warrant  or the  option  may be  exercised  or the
security  converted exceeds the fair market value of the underlying common stock
by more than 10%, as  determined  by  averaging  the bid and asked prices of the
common  stock during the last ten (10)  trading  days  immediately  prior to the
Closing Date.

         2. Consideration. In consideration of the purchase of the Shares on the
Closing Date, Buyer hereby agrees to pay the following consideration:

                   (a)      The affirmative covenants of Buyer as described in
Section 10 herein.

                   (b) Payment of One Hundred U.S. Dollars ($100.00), payable at
Closing.

         3.  Closing.  The closing of the sale to, and purchase by, Buyer of the
Shares  shall take place at the  offices  of Imatron  Inc.  at the hour of 10:00
a.m., on the first business day after all conditions  precedent  shall have been
met or waived, or on such other day or at such other time or place as the Seller
and Buyer shall agree.

         At the Closing, Seller will deliver to Buyer certificates  representing
the Shares being purchased by Buyer, registered in its name.

         4. Restriction on Transfer of Securities.

                   4.1. Restrictions.  The Shares are transferable only pursuant
to (a) a public offering registered under the Securities Act of 1933, as amended
(the  "Securities  Act"),  (b) Rule 144 (or any  similar  rule  then in  effect)
adopted under the Securities Act, if such rule is available,  and (c) subject to
the  conditions  elsewhere  specified  in this  Section  4,  any  other  legally
available means of transfer.

                   4.2. Each  certificate  representing  Shares will be endorsed
with the following legend:

                   (a)      Legend

                            "The   securities   evidenced   hereby  may  not  be
                  transferred without (i) the opinion of counsel satisfactory to
                  the Company that such  transfer  may be lawfully  made without
                  registration   under  the  Securities  Act  of  1933  and  all
                  applicable state securities laws or (ii) such registration."

                   (b) Stop  Transfer  Order.  A stop  transfer  order  shall be
  placed with the  Seller's  transfer  agent  preventing  transfer of any of the
  securities  referred to in paragraph  (a) above  pending  compliance  with the
  conditions set forth in any such legend.

                   4.3. Removal of Legend.  Any legend endorsed on a certificate
or  instrument  evidencing  a security  pursuant to Section 4.2 hereof  shall be
removed,  and Seller shall issue a certificate or instrument without such legend
to the holder of such  security,  (a) in accordance  with Section 4.2(a) hereof,
(b) if such  security is being  disposed of pursuant to  registration  under the
Securities  Act and any  applicable  state acts or  pursuant  to Rule 144 or any
similar  rule then in effect,  or (c) if such  holder  provides  Seller  with an
opinion  of counsel  satisfactory  to it to the  effect  that a sale,  transfer,
assignment, offer, pledge or distribution for value of such security may be made
without  registration  and that  such  legend is not  required  to  satisfy  the
applicable exemption from registration.

         5.  Representations  and Warranties by Seller.  Except as disclosed and
  described in Schedule 5 hereto, Seller represents and warrants to Buyer that:

                   5.1. Organization,  Standing,  Power. Seller is a corporation
  duly  organized,  validly  existing and in good standing under the laws of the
  State of Texas, and has the requisite corporate power and authority to own its
  properties and to carry on its business in all material  respects as it is now
  being  conducted.  Seller has, or at the Closing Date will have, the requisite
  corporate  power and  authority to issue the Common  Shares,  and to otherwise
  perform its obligations  under this  Agreement.  The copies of the Articles of
  Incorporation and Bylaws of the Company delivered to Buyer or its agents prior
  to the execution of this  Agreement  are true and complete  copies of the duly
  and legally adopted Articles of  Incorporation  and Bylaws of Seller in effect
  as of the date of this Agreement.

                   5.2. Qualification. Seller is duly qualified or licensed as a
  foreign  corporation in good standing in each jurisdiction  wherein the nature
  of  its  activities  or  of  its   properties   owned  or  leased  makes  such
  qualification  or  licensing  necessary  and  failure  to be so  qualified  or
  licensed would have a material adverse impact on its business.

                   5.3. Financial Statements.  Attached hereto as Exhibit A are:
  (a) a  balance  sheet  at  September  30,  1997,  together  with  the  related
  statements of operations  and cash flow, and changes to  shareholders'  equity
  for the 9 month  period  then  ended,  and (b) a draft of a  balance  sheet at
  December 31, 1997 (the "Balance  Sheet Date"),  and the related  statements of
  operations and cash flow for the quarter then ended,  prepared by Seller. Such
  financial statements (i) are true and correct and in accordance with the books
  and records of Seller,  (ii) present fairly the financial  condition of Seller
  at the balance sheet dates and the results of its  operations  for the periods
  therein specified,  and (iii) have, in all material respects, been prepared in
  accordance with generally  accepted  accounting  principles applied on a basis
  consistent  with prior  accounting  periods,  except that the balance sheet at
  December 31, 1997 and related  statements  of  operations  and cash flow is in
  draft form and does not  contain  footnotes.  Specifically,  but not by way of
  limitation,  the balance  sheets or notes  thereto  disclose all of the debts,
  liabilities  and  obligations  of any  nature  (whether  absolute,  accrued or
  contingent  and whether  due or to become due) of Seller at December  31, 1997
  and at the Balance Sheet Date which,  individually  or in the  aggregate,  are
  material and which in accordance with generally accepted accounting principles
  would be required to be disclosed in such balance sheets,  and the omission of
  which would, in the aggregate,  have a material adverse impact on Seller.  The
  balance  sheets  include   appropriate   reserves  for  all  taxes  and  other
  liabilities accrued at such date but not yet payable.

                   5.4.  Tax  Returns  and  Audits.   Except  as  disclosed  and
  described on Schedule 5.4 hereto,  all required  federal,  state and local tax
  returns or appropriate  extension  requests of Seller have been filed, and all
  federal,  state and local  taxes  required  to be paid  with  respect  to such
  returns have been paid or due provision for the payment thereof has been made.
  Except as disclosed and described on Schedule 5.4, Seller is not delinquent in
  the  payment  of  any  such  tax  or in  the  payment  of  any  assessment  or
  governmental  charge,  Seller has not  received  notice of any tax  deficiency
  proposed or assessed against it, and Seller has not executed any waiver of any
  statute of  limitations  on the  assessment  or collection of any tax. None of
  Seller's tax returns has been audited by governmental  authorities in a manner
  to bring such audits to the Seller's  attention.  Seller does not have any tax
  liabilities  except those  reflected in Schedule 5.4 hereto and those incurred
  in the ordinary course of business since the Balance Sheet Date.

                   5.5.   Litigation;   Governmental   Proceedings.   Except  as
  disclosed  and described on Schedule 5.5 hereto:  there are no legal  actions,
  suits, arbitrations or other legal, administrative or governmental proceedings
  or investigations  pending or, to the knowledge of Seller,  threatened against
  Seller, its properties,  assets or business;  Seller is not aware of any facts
  which are likely to result in or form the basis for any such  action,  suit or
  other proceeding; Seller is not in default with respect to any judgment, order
  or decree of any court or any governmental agency or  instrumentality;  Seller
  has not been  threatened  with any action or proceeding  under any business or
  zoning ordinance, law or regulation.

                   5.6.  Compliance with Applicable Laws and Other  Instruments.
  The business  and  operations  of Seller have been and are being  conducted in
  accordance with all applicable laws, rules and regulations of all governmental
  authorities.  Subject to shareholder approval of appropriate amendments to the
  Articles of Incorporation  as contemplated by this Agreement,  and except with
  respect to  existing  registration  rights of  holders  of certain  securities
  issued by Seller,  as disclosed  and  described on Schedule  5.6,  neither the
  execution nor delivery of, nor the  performance  of or compliance  with,  this
  Agreement nor the  consummation of the transactions  contemplated  hereby will
  conflict  with,  or,  with or without the giving of notice or passage of time,
  result in any  breach  of, or  constitute  a default  under,  or result in the
  imposition  of any lien or  encumbrance  upon any asset or  property of Seller
  pursuant to, any applicable law, administrative  regulation or judgment, order
  or decree of any court or governmental body, any agreement or other instrument
  to which Seller is a party or by which it or any of its properties,  assets or
  rights  is  bound  or   affected,   and  will  not  violate  the  Articles  of
  Incorporation or Bylaws of Seller.  Seller is not in violation of its Articles
  of Incorporation or its Bylaws.

                   5.7. Common Shares.  The Common Shares,  when issued and paid
for pursuant to the terms of this Agreement,  will be duly  authorized,  validly
issued and  outstanding,  fully  paid,  nonassessable  and free and clear of all
pledges, liens,  encumbrances and restrictions.  The Common Shares, when issued,
will contain no  undisclosed  interest,  present or future,  and Seller does not
know,  and at Closing will not know, of any  assertion of such an interest.  The
Common  Shares will be genuine,  and Seller has no  knowledge  of any fact which
would impair the validity thereof.

                   5.8.     Capital Stock.  The currently authorized capital
stock of Seller is as follows:

        SECURITY      AUTHORIZED    ISSUED    COMMON SHARE EQUIVALENT  RESERVED
Common                15,000,000   5,128,990     5,128,990
Series A Preferred     5,450,000   1,595,005     1,614,705
Series B Preferred        35,000      25,000       632,721



         All of the outstanding shares of capital stock of Seller have been duly
authorized  and validly issued and are fully paid and  nonassessable.  Except as
disclosed and  described in Schedule 5.8,  neither the offer nor the issuance or
sale of the Common  Shares as  contemplated  by this  Agreement  constitutes  an
event,  under any anti-dilution  provisions of any securities issued or issuable
by Seller or any  agreements  with  respect to the  issuance  of  securities  by
Seller,  which will either  increase the number of shares  issuable  pursuant to
such provisions or decrease the consideration per share to be received by Seller
pursuant to such  provisions.  All  outstanding  securities  of Seller have been
issued in full compliance with an exemption or exemptions from the  registration
and  prospectus  delivery  requirements  of the  Securities  Act  and  from  the
registration and  qualification  requirements of all applicable state securities
laws. Seller is not a party or subject to any agreement or understanding, and to
Seller's knowledge,  there is no agreement or understanding  between any persons
or entities or by a director of Seller,  which  affects or relates to the voting
or giving of written consents with respect to any security of Seller.

                   5.9.  Warrants,   Options,  Exchange  Rights  and  Conversion
Rights. Except as otherwise disclosed and described in Schedule 5.9 hereto or as
contemplated by this Agreement,  there are no outstanding or authorized options,
warrants,  purchase rights,  subscription  rights,  calls,  contracts,  demands,
commitments, Convertible Securities (as hereinafter defined) or other agreements
or  arrangements of any character or nature  whatever,  under which Seller is or
may be  obligated  to  issue  capital  stock  or  other  securities  of any kind
representing an ownership  interest or contingent  ownership interest in Seller.
Except as  otherwise  disclosed  and  described  in  Schedule  5.9  hereto or as
contemplated by this Agreement,  there are no voting trusts,  proxies,  or other
agreements or understandings  with respect to the voting of the capital stock of
Seller.

                   5.10. No Brokers or Finders.  No person,  firm or corporation
has or will  have,  as a result of any act or  omission  of  Seller,  any right,
interest or valid claim against or upon the Seller or Buyer for any  commission,
fee or other compensation as a finder or broker, or in any similar capacity,  in
connection with the  transactions  contemplated  by this Agreement.  Seller will
indemnify and hold Buyer harmless  against any and all liability with respect to
any  such  commission,  fee  or  other  compensation  which  may be  payable  or
determined to be payable in connection  with the  transactions  contemplated  by
this Agreement.

                   5.11.  Composition  of  the  Board  of  Directors.  As of the
Execution  Date,  the complete  Board of  Directors of Seller  consists of those
persons, including vacant positions, as set forth on Schedule 5.11.

         6.  Representations  and  Warranties  of Buyer.  Buyer  represents  and
warrants that:

                   6.1.  Investment  Intent.  The Common  Shares being  acquired
hereunder are being  purchased for Buyer's own account and not with the view to,
or for resale in connection  with, any  distribution or public offering  thereof
within the meaning of the  Securities  Act.  Buyer  understands  that the Common
Shares have not been registered under the Securities Act or any applicable state
laws by reason of their  issuance  or  contemplated  issuance  in a  transaction
exempt  from  the  registration  and  prospectus  delivery  requirements  of the
Securities  Act and such laws,  and that the  reliance of Seller and others upon
this  exemption is  predicated  in part upon this  representation  and warranty.
Buyer  further  understands  that the Common  Shares may not be  transferred  or
resold  without (a)  registration  under the  Securities  Act and any applicable
state  securities  laws,  or (b)  an  exemption  from  the  requirements  of the
Securities Act and applicable state securities laws.

                   6.2.  Accredited   Investor.   The  state  in  which  Buyer's
principal office is located is set forth in Buyer's address as set forth in this
Agreement.  Buyer qualifies as an accredited investor within the meaning of Rule
501  under the  Securities  Act.  Buyer has such  knowledge  and  experience  in
financial and business  matters that Buyer is capable of  evaluating  the merits
and risks of the investment to be made hereunder by Buyer.

                   6.3.  Acts and  Proceedings.  This  Agreement  has been  duly
authorized by all necessary  action on the part of Buyer, has been duly executed
and delivered by Buyer,  and is a valid and binding  agreement  upon the part of
Buyer.

                   6.4. No Brokers or Finders.  No person,  firm or  corporation
has or will  have,  as a result  of any act or  omission  by Buyer,  any  right,
interest  or  valid  claim  against  Seller  for any  commission,  fee or  other
compensation as a finder or broker,  or in any similar  capacity,  in connection
with the transactions  contemplated by this Agreement.  Buyer will indemnify and
hold Seller  harmless  against any and all  liability  with  respect to any such
commission,  fee or other  compensation which may be payable or determined to be
payable as a result of the actions of Buyer in connection with the  transactions
contemplated by this Agreement.

         7. Conditions of Buyer's Obligation. Buyer's obligation to purchase and
pay for the Common  Shares on the  Closing  Date is  subject to the  fulfillment
prior to or on the Closing Date of the conditions set forth below.  In the event
that any such  condition is not  satisfied to Buyer's  satisfaction,  then Buyer
shall not be obligated  to proceed  with the purchase of such Common  Shares nor
otherwise with any further of its obligations pursuant to this Agreement.

                   7.1.     No  Errors.  etc.  The  representations  and
warranties  of Seller  under  this Agreement  shall be true in all  material
respects  as of the  Closing  Date with the same effect as though made on and as
of the Closing Date.

                   7.2.  Compliance with Agreement.  Seller shall have performed
and complied in all material respects with all agreements or conditions required
by this  Agreement to be performed and complied with by it prior to or as of the
Closing Date.

                   7.3.   Qualification   Under  State   Securities   Laws.  All
registrations,  qualifications,  permits and approvals required under applicable
state  securities  laws for the lawful  execution and delivery of this Agreement
and the offer, sale,  issuance and delivery of the Common Shares shall have been
obtained.

                   7.4.  Proceedings  and  Documents.  All  corporate  and other
proceedings and actions taken in connection with the  transactions  contemplated
hereby and all  certificates,  opinions,  agreements,  instruments and documents
mentioned  herein or incident to any such  transaction  shall be satisfactory in
form and substance to Buyer and its counsel.

                   7.5.   Resignation  of  Officers  and  Appointment  of  Chief
Executive  Officer.  Seller will obtain and deliver to Buyer the resignations of
each of the officers of Seller, including but not limited to its chief executive
officer,  effective as of the Closing Date, and  simultaneously  therewith shall
cause the  appointment of a chief  executive  officer and such other officers as
are designated by Buyer.  Seller  acknowledges  that the officers'  resignations
pursuant  to this  Section  7.5  will  not  constitute  resignation  by any such
employee  from  employment by Seller,  unless  specifically  so  indicated,  and
further that such resignation  pursuant to this Section 7.5 will not be deemed a
breach of any employment  agreement  which might be in effect between Seller and
such employee.  Seller further acknowledges that delivery and acceptance of such
resignation  does not  otherwise  modify the terms of any  employment  agreement
which may be in  effect,  nor is it  intended  to  effect  Seller's  ability  to
negotiate  mutually  acceptable  changes in future to any  employment  agreement
which may be currently in effect.

                   7.6.  Special  Shareholders'   Meeting.   Promptly  following
execution of this Agreement,  Seller shall take, with the assistance of Buyer as
set forth in this  Agreement,  all such  actions as may be  necessary  and shall
cause the convening of a Special Meeting of Shareholders as promptly as possible
to  amend  the  Articles  of  Incorporation  to  authorize  an  increase  in its
authorized  common stock in such an amount as to fully effectuate the provisions
of this Agreement,  taking into account such obligations as Seller may currently
have or may be  expected  to have in the  foreseeable  future  in  light  of its
business  plan.  It is the  reasonable  expectation  of  the  parties  that  the
appropriate  number of authorized  shares  resulting from such amendment will be
not less than 100,000,000 common shares.

                   7.7.  Board  Resignations.  (a) Upon  request of Buyer at any
time between  execution of this  Agreement and the Closing Date, to be effective
upon the Closing Date,  Seller will obtain and deliver to Buyer the resignations
of at least three of the four members of its Board of Directors, as reflected on
Schedule 5.11 to this Agreement. (b) Immediately upon Closing, Seller will cause
a sufficient  number of  directors'  resignations  to be effective and thereupon
will cause the  nominees of Buyer to be elected as  directors of Seller in place
of the resigned  directors or otherwise to fill vacancies on the Board, so that,
following such action,  the nominees of Buyer will  constitute a majority of the
members of the Board then in office.

         8. Conditions of Seller's  Obligation.  Seller's obligation to sell the
Common Shares to Buyer on the Closing Date is subject to the  fulfillment  prior
to or on the Closing Date of the conditions  set forth below.  In the event that
any such  condition is not  satisfied,  Seller shall not be obligated to proceed
with the sale of such Common Shares.

                   8.1. Shareholder  Authorization.  The shareholders shall have
authorized  an  increase  in the  number of  authorized  shares of common  stock
sufficient to fully effectuate the purposes of this Agreement.

                   8.2. No Errors,  etc. The  representations  and warranties of
Buyer  under this  Agreement  shall be true in all  material  respects as of the
Closing Date with the same effect as though made on and as of the Closing Date.


                   8.3.  Compliance with Conditions.  Buyer shall have performed
and complied with all agreements or conditions  required by this Agreement to be
performed and complied with by it prior to or as of the Closing Date.

         9. Seller Affirmative Covenants. Seller covenants and agrees that:

                   9.1. Corporate Existence. Seller will maintain and cause each
Subsidiary (as hereinafter  defined) to maintain its corporate existence in good
standing  and comply  with all  applicable  laws and  regulations  of the United
States or of any state or states thereof or of any political subdivision thereof
and of any  governmental  authority  where  failure  to so comply  would  have a
material adverse impact on Seller or its business or operations.

                   9.2.  Books of Account and  Reserves.  Seller will,  and will
cause each of its  Subsidiaries  to,  keep books of record and  account in which
full,  true and  correct  entries  are made of all of its and  their  respective
dealings, business and affairs, in accordance with generally accepted accounting
principles.  Seller will employ  certified  public  accountants  selected by the
Board who are "independent" within the meaning of the accounting  regulations of
the  Commission,  and  have  annual  audits  made  by  such  independent  public
accountants   in  the  course  of  which  such   accountants   shall  make  such
examinations,  in accordance with generally accepted auditing standards, as will
enable  them to give such  reports or  opinions  with  respect to the  financial
statements of Seller and its  Subsidiaries  as will satisfy the  requirements of
the Commission in effect at such time with respect to certificates  and opinions
of accountants.

                   9.3.  Furnishing  of  Financial  Statements and Information.
Seller will deliver to Buyer:

     (a) as soon as practicable, but in any event within 45 days after the close
of each quarterly period,  unaudited  consolidated  balance sheets of Seller and
its  Subsidiaries  as of the end of  such  period,  together  with  the  related
consolidated  statements  of operations  and cash flow for such period,  setting
forth the budgeted  figures for such period prepared and submitted in connection
with  Seller's  annual  business  plan and in  comparative  form figures for the
corresponding  quarterly  period of the previous  fiscal year, all in reasonable
detail and certified by an authorized  accounting officer of Seller,  subject to
year-end adjustments;

     (b) as soon as  practicable,  but in any event within 90 days after the end
of  each  fiscal  year,  a   consolidated   balance  sheet  of  Seller  and  its
Subsidiaries,  as of the end of such  fiscal  year,  together  with the  related
consolidated  statements of operations,  shareholders'  equity and cash flow for
such fiscal year,  setting  forth in  comparative  form figures for the previous
fiscal year, all in reasonable detail and duly certified by Seller's independent
public  accountants  (except for the fiscal year ended 1997, for which certified
materials  will be supplied as soon as  practicable  following  Closing),  which
accountants  shall have given Seller an opinion,  unqualified as to the scope of
the audit, regarding such statements;

     (c) with reasonable  promptness,  such other financial data relating to the
business,  affairs and financial  condition of Seller and any Subsidiaries as is
available to Seller and as from time to time Buyer may reasonably request; and

     (d) at  least 20 days  prior to the  earlier  of (i) the  execution  of any
agreement  relating  to any  merger  or  consolidation  of  Seller or any of its
Subsidiaries  with  another  corporation,  or a plan of exchange  involving  the
outstanding  capital  stock of Seller or any of its  Subsidiaries,  or the sale,
transfer  or other  disposition  of all or  substantially  all of the  property,
assets or business of Seller or any of its Subsidiaries to another  corporation,
or (ii) the holding of any meeting of the shareholders of Seller for the purpose
of approving  such action,  written  notice of the terms and  conditions of such
proposed  merger,  consolidation,  plan of  exchange,  sale,  transfer  or other
disposition.

                   9.4.  Indemnification  Rights.  For a period of not less than
six (6) years from the Closing Date,  unless  otherwise  required by law, Seller
will  maintain  provisions  in its  articles of  incorporation  and by-laws with
respect to  indemnification  of directors and officers,  whether then current or
former,  that are no less  favorable than as currently set forth in its articles
of  incorporation  and by-laws.  Further,  for a period of not less than six (6)
years from the Closing  Date,  unless  otherwise  required  by law,  Seller will
continue to provide indemnification of its directors and officers,  whether then
current or former, to the fullest extent permissible under Texas law.

         10. Buyer's  Affirmative  Covenants.  Upon execution of this Agreement,
Buyer agrees as follows:

                   10.1.  Special  Shareholders'  Meeting.  In  connection  with
Special Shareholders' Meeting to be called pursuant to Section 7.6 herein, Buyer
agrees to  assist  Seller  as  reasonably  requested  and  agreed  in  preparing
materials and soliciting  proxies in connection  with obtaining  approval of its
shareholders to increase its  authorization  to issue common stock in connection
with  the  transaction  contemplated  by this  Agreement.  As  part  of  Buyer's
obligations  hereunder,  Buyer agrees reimburse Seller for expenses  incurred in
preparing  materials and  soliciting  proxies,  not in excess of the amounts set
forth in  Schedule  10.1,  and  further to  furnish  Seller,  within  reasonably
sufficient  time to be reviewed  and  included in the  materials to be mailed to
shareholders in connection with the Special Shareholders'  Meeting, the names of
Buyer's  nominees  for election to the Board,  together  with  information  with
respect to each nominee  equivalent to the information  required to be disclosed
to stockholders  with respect to director nominees pursuant to Regulation 14A of
the Securities and Exchange Act and such other similar  information  that Seller
may thereafter  reasonably  request.  It is understood that Seller may refuse to
cause the  nomination  and  election  as a  director  of  Seller of any  nominee
proposed by Buyer if (i) the information described above is not timely furnished
by Buyer or (ii) if, having been  furnished,  it is the  reasonable  judgment of
Seller and its counsel  that the  election of such  nominee  would not be in the
best interests of Seller or might tend to subject Seller to liability  therefor.
The foregoing notwithstanding, Buyer and Seller agree to cooperate and use their
mutual best efforts for the purpose of preparing for and  conducting the Special
Shareholders' Meeting as promptly as possible following the Execution Date.

                   10.2.  Orders for Product.  As soon as practicable  following
the Closing Date,  but not later than eight (8) months from the Execution  Date,
Buyer  will  take all  reasonable  efforts  to cause the  placement  of ten (10)
product  orders,   in  the  aggregate   including  any  orders  currently  under
discussion,  from Buyer's  affiliate in Japan over a period of  thirty-six  (36)
months from the placement of the first order.

                   10.3. Additional Equity. As soon as practicable following the
Closing Date,  Buyer will use its best efforts to arrange for  additional  third
party equity financing for Seller,  to be contributed to Seller over a period of
no greater than eighteen (18) months from the Closing Date,  and in an aggregate
amount  not  less  than  Eight  Million  U.S.  Dollars   ($8,000,000)   ("Equity
Financing").  The parties  specifically  acknowledge  and  anticipate  that this
Equity  Financing will involve  and/or cause a substantial  dilution of existing
shareholders, including but not limited to Buyer.

         11. Negative Covenants.  Seller will not, without the prior approval of
a majority  of all of the  members  of the Board of  Directors:  (a)  guarantee,
endorse or otherwise be or become contingently  liable, or permit any Subsidiary
to guarantee,  endorse or otherwise become  contingently  liable,  in connection
with the obligations,  securities or dividends of any person, firm,  association
or corporation, other than Seller or any of its Subsidiaries, except that Seller
and any  Subsidiary  may endorse  negotiable  instruments  for collection in the
ordinary course of business;  or (b) make or permit any Subsidiary to make loans
or advances to any person (including without limitation to any officer, director
or shareholder of Seller or any Subsidiary),  firm,  association or corporation,
except  loans and  advances  to Seller  and its  wholly-owned  Subsidiaries  and
advances to suppliers and employees made in the ordinary course of business;  or
(c) purchase or invest,  or permit any Subsidiary to purchase or invest,  in the
stock or  obligations  of any other person,  firm or  corporation,  other than a
wholly-owned  Subsidiary;   or  (d)  pay,  or  permit  any  Subsidiary  to  pay,
compensation,  whether by way of salaries, bonuses, participations in pension or
profit  sharing  plans,  fees under  management  contracts  or for  professional
services or fringe  benefits  to any  officer in excess of amounts  fixed by the
Board of Directors prior to any payment to such officer.

         12.  Registration  of Stock.  Subject to the  provisions of the several
registration rights agreements and /or other agreements containing  registration
rights provisions, to which Seller is a party, all as disclosed and described on
Schedule 12 hereto, Seller agrees as follows:

                   12.1. Rights to Registration.  (a) If, at any time during the
period  commencing on the effective  date of this  Agreement and ending ten (10)
years thereafter, Seller shall determine to register under the Securities Act of
1933,  as  amended,  any shares of Stock to be offered for cash by it or others,
pursuant to a  registration  statement on Form S-1 (or its  equivalent),  Seller
will (i)  promptly  give written  notice to Buyer of its  intention to file such
registration  statement  and (ii) at  Seller's  expense  (which  shall  include,
without limitation,  all registration and filing fees,  printing expenses,  fees
and  disbursements of counsel and independent  accountants for Seller,  and fees
and expenses  incident to compliance  with state  securities  law, but shall not
include  fees  and  disbursements  of  counsel  for  Buyer)  include  among  the
securities  covered by the  registration  statement  such portions of the Shares
then held by Buyer as shall be specified in a written  request to Seller  within
thirty  (30) days after the date on which  Seller gave the notice  described  in
(a)(i)  above.  (b) Upon  receipt of such  written  request and of the shares of
Stock specified in the request (any shareholder  requesting  registration  being
individually  called  a  "Selling  Shareholder"),  Seller  shall:  (i)  use  its
reasonable best efforts to effect the registration,  qualification or compliance
of the Shares under the  Securities Act and under any other  applicable  federal
law and any applicable  securities or blue sky laws of jurisdictions  within the
United States;  (ii) furnish each Selling  Shareholder  such number of copies of
the  prospectus  contained  in  the  registration   statement  filed  under  the
Securities  Act  (including  preliminary  prospectus)  in  conformity  with  the
requirements  of the  Securities  Act,  and such other  documents as the Selling
Shareholder may reasonably request in order to facilitate the disposition of the
Stock  covered by the  registration  statement;  and (iii)  notify each  Selling
Shareholders,  at any time when a  prospectus  relating to the Stock  covered by
such  registration  statement is required to be delivered  under the  Securities
Act, of the happening of any event as a result of which the prospectus forming a
part of such  registration  statement,  as then in  effect,  includes  an untrue
statement of a material  fact or omits to state any material fact required to be
stated therein or necessary to make the statements  therein not misleading,  and
at the  request of the Selling  Shareholders  prepare and furnish to the Selling
Shareholders  any reasonable  number of copies of any supplement to or amendment
of such  prospectus  as may be necessary  so that,  as  thereafter  delivered to
purchasers of the Stock,  such prospectus  shall not include an untrue statement
of a  material  fact or omit to state a  material  fact  required  to be  stated
therein or necessary to make the statements therein not misleading.

                   12.2.  Registration of Underwritten Offering. If the offering
of  securities  to  be  registered  by  Seller  is  underwritten,  each  Selling
shareholder  shall  sell  the  Stock to or  through  the  underwriter(s)  of the
securities  being  registered  for the account of Seller or others upon the same
terms  applicable  to  Seller  or  others,  and if the  managing  underwriter(s)
reasonably  determine that all or any portion of the shares of Stock held by the
Selling Shareholders should not be included in the registration statement,  then
notwithstanding  anything to the contrary in this Section,  the determination of
such  underwriter(s)  shall  be  conclusive;   provided  however  that  if  such
underwriter(s)  determine  that  some but not all of the  Stock  of the  Selling
Shareholders  shall be included  in the  registration  statement,  the number of
shares  of  Stock  owned  by each  Selling  Shareholder  to be  included  in the
registration  statement will be  proportionately  reduced in accordance with the
respective written requests given as provided above.

                   12.3.  Indemnification.  In the event that  Shares  purchased
pursuant to this Agreement are included in a registration  statement  under this
Section 11, Seller will indemnify and hold harmless each Selling Shareholder and
each other  person,  if any, who controls  such Selling  shareholder  within the
meaning  of  the  Securities  Act,  against  any  losses,   claims,  damages  or
liabilities,  joint or several, to which such Selling Shareholder or controlling
person may become subject under the Securities Act or otherwise, insofar as such
losses, claims, damages or liabilities (or actions in respect thereof) arise out
of are based  upon any  untrue  statement  or alleged  untrue  statement  of any
material fact  contained,  on the effective  date thereof,  in any  registration
statement pursuant to which the Shares were registered under the Securities Act,
any  preliminary  prospectus  or  final  prospectus  contained  therein,  or any
amendment or supplement  thereto, or arise out of or are based upon the omission
or alleged  omission  to state  therein a material  fact  required  to be stated
therein or necessary to make the statements therein not misleading, or arise out
of or are based upon the failure by Seller to file any  amendment or  supplement
thereto  that was  required  to be filed  under  the  Securities  Act,  and will
reimburse  such Selling  Shareholder  and each such  controlling  person for any
legal or any other  expenses  reasonably  incurred  by them in  connection  with
investigating or defending any such loss,  claim,  damage,  liability or action.
Notwithstanding the foregoing, Seller will not be liable in any such case to the
extent that any such loss, claim, damage, or liability arises out of or is based
upon an  untrue  statement  or  omission  made in such  registration  statement,
preliminary prospectus,  final prospectus or amendment or supplement in reliance
upon and in conformity with written  information  furnished to Seller through an
instrument duly executed by or on behalf of any Selling Shareholder specifically
for  use  in  the  preparation  of  such  registration  statement,   preliminary
prospectus, final prospectus, or amendment or supplement.

         It shall be a condition  precedent to the  obligation of Seller to take
any  action  pursuant  to this  Section  that  seller  shall  have  received  an
undertaking  satisfactory  to it from each Selling  Shareholder to indemnify and
hold harmless  Seller (in the same manner and to the same extent as set forth in
this  Section),  each  director  of  Seller,  each  officer  who shall sign such
registration statement, and any persons who control Seller within the meaning of
the  Securities  Act,  with  respect  to any  statement  or  omission  from such
registration  statement,   preliminary  prospectus,   or  any  final  prospectus
contained therein,  or any amendment or supplement thereto, if such statement or
omission was made in reliance  upon and in conformity  with written  information
furnished to Seller  through an  instrument  duly  executed by the  indemnifying
party  specifically for use in the preparation of such  registration  statement,
preliminary prospectus, final prospectus, or amendment or supplement.

         Promptly  following  receipt by an  indemnified  party of notice of the
commencement  of any action  involving a claim referred to above in this Section
11.3, such  indemnified  party will, if a claim in respect thereof is to be made
against  an  indemnifying  party,  give  written  notice  to the  latter  of the
commencement  of such  action.  In case any such  action is  brought  against an
indemnified party, the indemnifying party will be entitled to participate in and
to  assume  the  defense  thereof,  jointly  with any other  indemnifying  party
similarly  notified,  to the extent that it may wish,  with  counsel  reasonably
satisfactory to such  indemnified  party, and after notice from the indemnifying
party to such  indemnified  party of its election to assume the defense thereof,
the  indemnifying  party  will not be liable to such  indemnified  party for any
legal or other expenses  subsequently  incurred by the latter in connection with
the defense thereof.

                   12.4. Binding  provisions.  The provisions of this Section 11
shall be binding on the  successors  of Seller.  No  Shareholder  may assign the
provisions  of this  Section  11 or all or any  part of its or their  rights  or
obligations  hereunder,  except that in the event of a merger or  consolidate in
which the Seller is not the survivor,  the Seller shall assign and transfer, and
successor shall assume, the provisions of this Section 11.

                   12.5. Conflicts.  To the extent that Seller's compliance with
the  obligations  set forth in Sections  12.1 through 12.4 above would  conflict
with or  otherwise  cause a  breach  of or  default  under  any of its  existing
obligations pursuant to the agreements set forth on Schedule 12 attached hereto,
Seller's failure to comply with those  obligations  shall not be deemed a breach
of this Agreement.

         13. Remedies Cumulative,  and not Waived. (a) No right, power or remedy
conferred  upon any party  shall be  exclusive,  and each such  right,  power or
remedy  shall be  cumulative  and in  addition to every  other  right,  power or
remedy,  whether  conferred  hereby or by any such  security or now or hereafter
available  at law or in  equity or by  statute  or  otherwise.  (b) No course of
dealing  between the parties or the holder of any Shares  purchased  pursuant to
this Agreement,  and no delay in exercising any right, power or remedy conferred
hereby or by any such security or now or hereafter  existing at law or in equity
or by statute or otherwise,  shall operate as a waiver of or otherwise prejudice
any such right, power or remedy;  provided,  however, that this Section 13 shall
not be  construed  or applied so as to negate the  provisions  and intent of any
statute which is otherwise applicable.

         14.  Changes.  Waivers.  etc.  Neither this Agreement nor any provision
hereof may be changed,  waived,  discharged or terminated  orally, but only by a
statement  in  writing  signed by the party  against  which  enforcement  of the
change, waiver, discharge or termination is sought.

         15. Notices. All notices,  requests,  consents and other communications
required or permitted  hereunder shall be in writing and shall be delivered,  or
mailed  first-class  postage  prepaid,  registered  or  certified  mail,  or via
overnight  delivery  with by a service  providing  evidence  of  receipt  to the
addresses below:

                  If to Buyer:      Imatron Inc.
                                    389 Oyster Point Blvd.
                                    South San Francisco, CA 94080
                       Attn: Mr. S. Lewis Meyer, President

                                    Telephone: (415) 583-9964
                                    Facsimile: (415) 871-0418

                  Copy to:          Roger S. Mertz, Esq.
                                    Severson & Werson, P.C.
                                    One Embarcadero Center
                                    Suite 2600
                                    San Francisco, CA 94111

                                    Telephone: (415) 398-3344
                                    Facsimile: (415) 956-0439

                  If to Seller:     Positron Corporation
                                    1304 Langham Creek Drive, Suite 310
                                    Houston, Texas 77084
                                    Attn:  President

                                    Telephone: (281) 492-7100
                                    Facsimile: (281) 492-2961


                  Copy to:          Michael D. Wortley, Esq.
                                    Vinson & Elkins
                                    3700 Trammell Crow Center
                                    2001 Ross Avenue
                                    Dallas, Texas 75201

                                    Telephone: (214) 220-7700
                                    Facsimile: (214) 999-7732

and such  notices  and  other  communications  shall  for all  purposes  of this
Agreement  be  treated as being  effective  or having  been  given if  delivered
personally,  or, if sent by first class mail,  three days after  posting,  or if
sent via  overnight  delivery,  when  received as  evidenced  by an  appropriate
receipt.

         16.   Survival   of   Representations   and   Warranties,    etc.   All
representations and warranties  contained herein shall survive the execution and
delivery of this Agreement,  any  investigation  at any time made by Buyer or on
its behalf,  and the sale and  purchase  of the Common  Shares.  All  statements
contained in any  certificate,  instrument or other  writing  delivered by or on
behalf of Seller pursuant hereto or in connection with or  contemplation  of the
transactions  herein  contemplated  (other than legal opinions) shall constitute
representations  and warranties by Seller  hereunder,  and not by the individual
officer  who signed the  certificate,  instrument  or writing by or on behalf of
Seller.

         17. Parties in Interest. All the terms and provisions of this Agreement
shall be  binding  upon and inure to the  benefit of and be  enforceable  by the
respective successors and assigns of the parties hereto, whether so expressed or
not, and, in particular, shall inure to the benefit of and be enforceable by the
holder or holders at the time of any of the Common Shares.  The former,  current
and hereafter  appointed officers and directors  referenced in Section 9.4 above
are intended and deemed to be third party  beneficiaries of Section 9.4, and are
entitled to enforce its provisions.

         18.  Headings.  The  headings of the Sections  and  paragraphs  of this
Agreement  have been  inserted  for  convenience  of  reference  only and do not
constitute a part of this Agreement.

         19.  Choice of Law. It is the intention of the parties that the laws of
California shall govern the validity of this Agreement,  the construction of its
terms and the interpretation of the rights and duties of the parties.

         20. Counterparts. This Agreement may be executed concurrently in two or
more counterparts,  each of which shall be deemed an original,  but all of which
together shall constitute one and the same instrument.

         21.  Severability.  In the  event  that any part of this  Agreement  is
determined by a court of competent jurisdiction to be unenforceable, the balance
of the Agreement shall remain in full force and effect.

         IN WITNESS  WHEROF,  the parties  execute this Agreement as of the date
first written above.

SELLER:                                 BUYER:
POSITRON CORPORATION                    IMATRON INC.



By: /s/ Gary B. Wood                    By: /s/ S. Lewis Meyer
Its: Chief Executive Officer            Its:  President/CEO


ATTEST:                                 ATTEST:



By: /s/ Howard R. Baker                 By: /s/ Gary H. Brooks
Its: Executive Vice President           Its:  CFO


<PAGE>


                               EXHIBIT A

                         FINANCIAL STATEMENTS

      [9/30/97 10Q previously filed with SEC by Positron not reprinted here]



<PAGE>


                                    SCHEDULES

                              DISCLOSURE SCHEDULES
                                       TO
                        STOCK PURCHASE AGREEMENT BETWEEN
                              POSITRON CORPORATION
                                       AND
                                  IMATRON INC.



<PAGE>



                              POSITRON CORPORATION

                      Schedule 5.4--Tax Returns and Audits

Except as disclosed and described,  all federal,  state and local tax returns or
appropriate  extension  requests have been filed;  all federal,  state and local
taxes have been paid or due provision made;  there are no  delinquencies  in the
payment  of such  tax or  assessment  or  governmental  charge;  no  notices  of
deficiencies proposed or assessed has been received; Seller has not executed any
waiver of any statute of  limitations on assessment or collection of any tax; no
tax returns have been audited; there are no tax liabilities, except as follows:

          1.  Property  taxes in the  approximate  amount of $185,000,  of which
approximately $80,000 relates to prior years.

          2. State sales taxes in the State of Texas in the  approximate  amount
of $4,000.

          3. State sales taxes to the State of Florida in the approximate amount
of $12,000.

          4.  State  sales  taxes to the  State  of New York in the  approximate
amount of $56,000.





<PAGE>



                              POSITRON CORPORATION

              Schedule 5.5--Litigation or Governmental Proceedings

Except  as  disclosed  and  described,   there  are  no  legal  actions,  suits,
arbitration,  or other legal,  administrative  or  governmental  proceedings  or
investigations  pending  or  threatened;  Seller is aware of no facts  likely to
result in or form a basis for such action; Seller is not in default with respect
to any  judgment,  order or  decree  or any  court  or  governmental  agency  or
instrumentality;  Seller is not threatened with any action or proceeding  except
as follows:

 1. We have been  informed  that Xin Xin  intends  to proceed  with  arbitration
relative to its  contract  with  Positron  Corporation  for the  purchase of two
POSICAM systems.

 2. Numerous  letters have been received from vendors  threatening  legal action
against the Company for its failure to pay outstanding trade payables.

 3. The loan from ProFutures  Bridge Capital is in default due to the failure of
the  Company to pay the full  $50,000 per month due on the loan.  The  Company's
payments  have  averaged   approximately  $45,000  per  month.   ProFutures  has
threatened legal action.

 4. All former and existing  employees who are owed unpaid  salaries,  wages and
benefits  have a claim  against the Company.  The amounts due could be collected
through legal action or by the Texas Workforce Commission.

 5. Hadassah  Medical  Organization  has threatened  legal action if the Company
does not immediately  replace its existing POSICAM system with a new system.  To
date no formal legal action has been filed.

 6.  University  Madrid  PET  Center  has also  threatened  legal  action if its
existing POSICAM is not upgraded to a newer machine that meets its expectations.

 7. Nizar  Mullani,  a former  director of the  Company,  claims that he is owed
consulting fees and royalties of  approximately  $150,000.  The Company disputes
the amount of royalty  actually owed to Mullani.  Mullani has  threatened  legal
action. To date no formal action has been taken by Mr. Mullani.

 8. Harris County, Texas has been awarded a default judgment against the Company
for its failure to pay property taxes in the approximate amount of $80,000.

 9. Bowne of Dallas, Inc. received a default judgment against the Company in the
amount of $31,277.05.

 10. Boxer Property  (Landlord) has issued a notice for Positron  Corporation to
vacate remaining  space.  Agreement has been reached for Positron to consolidate
its space and relocate to another facility as soon as possible.



<PAGE>



                              POSITRON CORPORATION

            Schedule 5.6--Compliance With Laws and Other Instruments

Disclosure of any existing  registration rights of holders of certain securities
issued by Seller.  Further,  except as disclosed and  described,  the execution,
delivery and performance of the transactions  contemplated by the Agreement will
not conflict with, result in a breach of, constitute, agreement or instrument to
which  Seller  is a party or by which it or any of its  properties  or assets is
bound, nor violate its Articles or Bylaws, except as follows:

 A.       93 Registration Rights

          A.       Covers "Registrable Securities" consisting of:

                   (i)     353,531 shares of Common Stock issued upon
                           conversion of the Series E  Preferred Stock;

                   (ii)    Warrants  issued in the 93  Placement  and  shares of
                           Common Stock  issuable  upon exercise of the Warrants
                           (the Warrants are currently  exercisable  for 527,743
                           shares of Common Stock at $5.51 per share);

                           Upon the registration of the Warrants  pursuant to an
                           exercise of a demand  right or piggyback  right,  the
                           terms  and  provisions  of  such  Warrants  are to be
                           amended to be identical or substantially identical to
                           the terms and  provisions  as then  existing  for the
                           Redeemable Warrants.

          B.       Demand Rights:

                   (i)     exercisable by 30% of holders of Registrable
                           Securities (calculated assuming exercise of
                           Warrants);

                   (ii) have 2 demand rights exercisable as follows:

                            a.      one demand right is exercisable commencing
                                    day 180 (measured from the
                                    effective date) and ending day 270;

                            b.      The  second  demand  right  is   exercisable
                                    commencing  day 271 and  ending 5 years from
                                    the effective  date,  if exercised  prior to
                                    the second anniversary of the effective date
                                    and  not  as a  part  of a  firm  commitment
                                    underwriting,  unless waived by  Josephthal,
                                    Lyon & Ross, such demand right is limited to
                                    the offering during any 90-day period of:

                                     1.      200,000 shares of Common Stock

                                     2.      Warrants exercisable for 200,000
                             shares of Common Stock

                                     3.      200,000 shares of Common Stock
                                             issuable upon the exercise of
                            the registered Warrants.

                            c.      Unless  waived by JL&R,  the  demand  rights
                                    individually  or in the aggregate may not be
                                    exercised  prior to day 390 in a  manner  to
                                    exceed:

                                     1.      325,000 shares of Common Stock

                                     2.      Warrants exercisable for 325,000
                             shares of Common Stock

                                     3.      325,000 shares of Common Stock
                                             issuable upon the exercise of
                             the registered warrants

          C.       Piggyback Rights:

                   (i) Have 3 piggyback rights that become exercisable after
day 390.

 B.       General Registration Rights

          A.      Covers  Common Stock held by certain  shareholders  other than
                  Common Stock received as a part of the 93 Placement.

          B.       Demand Rights

                   (i)   exercisable by 30% of the holders of "Registrable
                         Securities"

                   (ii) Have 2 demand rights exercisable as follows:

                            a.  The demand rights are exercisable commencing
                                day 570 and ending the 5th anniversary of the
                                effective date;

          C.       Piggyback Rights

                   (i)      Have 3 piggyback rights

                   (ii)    Cut back provisions give priority to the Underwriter,
                           the Company and then to the 93 registration rights if
                           the 93 holders are exercising a demand right.

          D.       Overall Restriction

                   (i)     Unless  waived by JL&R any exercise of a demand right
                           or piggyback  right prior to the 2nd  anniversary  of
                           the  effective  date  and  not  as a  part  of a firm
                           commitment  underwriting  is limited to the  offering
                           during any 90-day period of 200,000  shares of Common
                           Stock.

 C.       Other Registration Rights

          A.       One holders has piggyback rights for 977 shares of Common
                   Stock.

Note:  The Underwriter warrants from the IPO were exchanged for
 Series A Preferred Stock.



<PAGE>



                              POSITRON CORPORATION

                           Schedule 5.8--Capital Stock

Except as  disclosed  and  described,  neither the offer nor issuance or sale of
additional   stock  as   contemplated   will   constitute  an  event  under  any
anti-dilution  provisions of any securities issued or issuable or any agreements
with  respect to issuance  of Seller  which will  increase  the number of shares
issuable  pursuant to such provisions or decrease the consideration per share to
be received  by the  Seller,  except as  described  in  Footnotes 6 and 7 to the
Company's Annual Report on Form 10 KSB for the Year Ended December 31, 1996.

See attached capital structure.



<PAGE>



Section 5.8 requirements:
- --------------------- ------------ ------------ -------------- ---------------
                                     COMMON
 SECURITY              AUTHORIZED     ISSUED      EQUIVALENT      RESERVED
- --------------------- ------------ ------------ -------------- ---------------
- --------------------- ------------ ------------ -------------- ---------------

Common Stock           15,000,000    5,128,990    5,128,990       9,871,010
- --------------------- ------------ ------------ -------------- ---------------
- --------------------- ------------ ------------ -------------- ---------------
Series A Preferred
Stock                  5,450,000     1,595,005    1,595,005
- --------------------- ------------ ------------ ------------- ----------------
- --------------------- ------------ ------------ ------------- ----------------
Series B Preferred
Stock                     25,000        25,000      625,000
- --------------------- ------------ ------------ ------------- ----------------



<PAGE>



                              POSITRON CORPORATION

     Schedule 5.9--Warrants, Options, Exchange Rights and Conversion Rights

Except as  disclosed  and  described,  there are no  outstanding  or  authorized
options,  warrants,  purchase rights,  subscription  rights,  calls,  contracts,
demands,  or  commitments,   convertible  securities,  or  other  agreements  or
arrangements under which Seller may be obligated to issue capital stock or other
securities.  Further,  except as disclosed  and  described,  there are no voting
trusts, proxies or other agreements or understandings with respect to the voting
of Seller's  capital  stock,  except as  described  in  Footnotes 6 and 7 to the
Company's Annual Report on Form 10 KSB for the Year Ended December 31, 1996.

See attached "Capital Structure, as of January 31, 1998."



<PAGE>

                               Capital Structure
                             as of January 31, 1998

                                                 Pre-Imatron       Post-Imatron

Common stock                                      5,128,990          5,128,990

Series A Preferred stock              (A)         1,703,258          2,917,197

Series B Preferred stock              (G)           667,415          1,113,825

Preferred stock dividends             (C)           203,000                  0

Shares issued to Imatron              (L)                           12,000,000

ProFutures warrants                               1,500,000          2,503,242

Shares issued in private placement                        0                  0
                                                 ----------        -----------

Total "in-the-money" shares                       9,202,663         23,663,254
                                                  ---------         ----------

                                      (F)           635,276            635,276

Stock options

Series A Preferred stock warrants     (B)         1,621,940          2,696,042

Series B Preferred stock warrants     (H)           105,955            176,105

                                      (J)            67,500             67,500

UroTech warrant

BF&E warrant                          (K)            45,000             45,000

Redeemable warrants                   (D)         5,737,573         10,038,228

1993 warrants                         (E)           527,743            923,318
                                                -----------         ----------

Total "out-of-the-money" shares
                                                  8,740,987         14,581,469
                                                -----------         ----------

Total shares                                     17,943,650         38,244,723
                                                -----------         ----------

If all "out-of-the-money" shares exercise approximately $38,900,000 will come to
the Company.




<PAGE>



                              POSITRON CORPORATION

                                    Footnotes

 A.      Series A Convertible Preferred Stock converts into common stock one for
         one. Dividends are payable  semi-annually at 8%. Initially  convertible
         at $1.33 per share; $1.31 after giving effect to the Series A Preferred
         Stock dividends;  $.86 after giving effect to the issuance of shares to
         Imatron;  $.75 after  giving  effect to the issuance of shares at $.50;
         and, $.68 after giving effect to the issuance of shares at $.375.

 B.      Series A Preferred  Stock warrants,  convertible  into common stock one
         for one at $1.33 per share initially; $1.29 after ratcheting effect for
         shares issued to Imatron;  $1.04 after  ratcheting to give effect to $8
         million  raised at $.50 per share;  and, $.94 after  ratcheting to give
         effect to $8 million raised at $.375 per share.

 C.     Series A Preferred Stock dividends  accumulated dividends since issuance
        of preferred stock.

 D.      Prior to  issuance  of shares to  Imatron  at $.01 per share the strike
         price  of  the  warrant  is  $5.51;   subsequent  to  issuance  of  the
         aforementioned  shares the strike price is $3.61 per share. $2.48 after
         ratcheting to give effect to $8 million raised at $.50 per share;  and,
         $2.21 after ratcheting to give effect to $8 million raised at $.375 per
         share. Expire 12/3/98.

 E.      1993 warrants have same provisions as the Redeemable Warrants.

 F. Employees' stock options generally exercisable at $2.65 per option.

 G.      Series B Convertible Preferred Stock converts into common stock one for
         one.  Initially  convertible  at $1.33 per share;  $1.31  after  giving
         effect to the Series A Preferred  Stock  dividends;  $.86 after  giving
         effect to the issuance of shares to Imatron;  $.75 after giving  effect
         to the issuance of shares at $.50, and, $.68 after giving effect to the
         issuance of shares at $.375.

 H.      Series B Preferred  Stock warrants,  convertible  into common stock one
         for one at $1.33 per share initially; $1.29 after ratcheting effect for
         shares issued to Imatron;  $1.04 after  ratcheting to give effect to $8
         million  raised at $.50 per share;  and, $.94 after  ratcheting to give
         effect to $8 million raised at $.375 per share.

 I.      Ten-year warrants expiring in 2006, exercisable 200,000 at $2.40 and
         100,000 at $1.91.

 J.      Uro-Tech warrants exercisable at $2.00 until 2/7/00.

 K. BF&E warrants exercisable at $2.00 until 2/7/00.

 L. Shares issued to give Imatron at least 51% control.



<PAGE>



                                  SCHEDULE 5.9

              Warrants, Options, Exchange and/or Conversion Rights

Except as  disclosed  and  described,  there are no  outstanding  or  authorized
options,  warrants,  purchase  rights,  subscription  rights,  calls,  contract,
demands,  or  commitments,   convertible  securities,  or  other  agreements  or
arrangements under which Seller may be obligated to issue capital stock or other
securities.  Further,  except as disclosed  and  described,  there are no voting
trusts, proxies or other agreements or understandings with respect to the voting
of Seller's capital stock.

                                                  Rate of       Adjusted Price
                   Number                      Conversion (if     Following
Security         Outstanding   Exercise Price    applicable)     Transaction
- --------         -----------   --------------  --------------   --------------

Series A         -----------   --------------  --------------   --------------

Series B         -----------   --------------  --------------   --------------

Series A
Warrants         -----------   --------------  --------------   --------------

Series B
Warrants         -----------   --------------  --------------   --------------

1987 Employee
SOP              -----------   --------------  --------------   --------------

1994 Employee
SOP              -----------   --------------  --------------   --------------

1993 Warrants    -----------   --------------  --------------   --------------

Redeemable
Warrants         -----------   --------------  --------------   --------------

UroTech
Warrants         -----------   --------------  --------------   --------------

Boston
Financial
Warrants         -----------   --------------  --------------   --------------

ProFutures
Warrants         -----------   --------------  --------------   --------------

K. Lance Gould   -----------   --------------  --------------   --------------

Gary Wood        -----------   --------------  --------------   --------------


<PAGE>



                              POSITRON CORPORATION

                        Schedule 5.11--Board of Directors


      Name                    Age             Position
      ----                    ---             --------

Gary B. Wood, Ph.D.           47         Director and Chairman of the Board

K. Lance Gould, M.D.          57         Director

John H. Laragh, M.D.          69         Director

Ronald B. Schilling, Ph.D.    56         Director



<PAGE>



                                  Schedule 10.1

                                       to

                            Stock Purchase Agreement

In connection  with the Special  Shareholders'  Meeting to be called pursuant to
Section 7.6,  Buyer will  reimburse  Seller for  expenses  incurred in preparing
materials and soliciting proxies up to $50,000.



<PAGE>



                                   Schedule 12

Provisions of  registration  rights  agreements or other  agreements  containing
registration rights provisions to which Seller is a party.





                                See Schedule 5.6





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