POSITRON CORPORATION CONVERTIBLE PROMISSORY NOTE

THE SECURITIES EVIDENCED HEREBY HAVE NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE " ACT "), AND MAY NOT BE SOLD, TRANSFERRED, ASSIGNED OR HYPOTHECATED UNLESS (A) THERE IS AN EFFECTIVE REGISTRATION STATEMENT UNDER THE ACT, AND APPLICABLE STATE SECURITIES LAWS, COVERING ANY SUCH TRANSACTION INVOLVING SAID SECURITIES, (B) THE COMPANY RECEIVES AN OPINION OF LEGAL COUNSEL FOR THE HOLDER OF THESE SECURITIES SATISFACTORY TO THE COMPANY STATING THAT SUCH TRANSACTION IS EXEMPT FROM REGISTRATION, OR (C) THE COMPANY OTHERWISE SATISFIES ITSELF THAT SUCH TRANSACTION IS EXEMPT FROM REGISTRATION.

POSITRON CORPORATION, a Texas corporation (the " Company "), the principal office of which is located at 1304 Langham Creek Drive, #300, Houston, Texas 77084, for value received hereby promises to pay to Imagin Diagnostic Centres, Inc., 1835 Yonge St., Suite 500, Toronto, Ontario, Canada M4S, or its registered assigns (the " Holder "), the sum of ___________________ Dollars ($_________), or such lesser amount as shall then equal the outstanding principal amount hereof on the terms and conditions set forth hereinafter. The principal hereof and any unpaid accrued interest hereon, as set forth below, shall be due and payable on the earlier to occur of (i) August 7, 2008 (the " Maturity Date ") or (ii) when declared due and payable by the Holder upon the occurrence of an Event of Default (as defined below). Commencing on the Maturity Date, all principal and accrued interest hereunder shall be payable upon demand. Payment for all amounts due hereunder shall be made by mail to the registered address of the Holder. All numbers expressed herein as "$" or "dollars" are in United States dollars.

The following is a statement of the rights of the Holder of this Note and the conditions to which this Note is subject, and to which the Holder hereof, by the acceptance of this Note, agrees:

1.    Definitions . Except as otherwise defined herein, each capitalized term used herein shall have the meaning assigned to it in the Note Purchase Agreement dated as of August 8, 2005 (the " Purchase Agreement "). As used in this Note, the following terms, unless the context otherwise requires, have the following meanings:

(a)    " Business Day " shall mean a day other than Saturday, Sunday or a public holiday under the laws of the State of Texas.

(b)    " Company " includes any corporation that shall succeed to or assume the obligations of the Company under this Note.

(c)    " Holder ," when the context refers to a holder of this Note, shall mean any person who shall at the time be the registered holder of this Note.

(d)    " Operating Cash Flow " shall mean the sum of net income, depreciation, change in accruals and change in accounts payable, minus change in accounts receivable, minus change in inventories.

2.    Interest . Simple interest shall accrue at the rate of ten percent (10%) per annum on the principal of this Note outstanding during the period beginning the date of funding of this Note and ending on the date that the principal amount of this Note is repaid. Interest shall be calculated on the basis of a 365-day year for the actual number of days elapsed. Accrued interest shall be payable in cash annually on the anniversary date of this note; provided however, that at the Company's option, the accrued interest shall be payable by issuance to Holder of a new note identical in form to this Note and in an amount equal to the accrued interest not otherwise paid in cash. In the event that a payment date falls on a non-Business Day, payment shall be made on the next Business Day, while taking into account such extra days in calculating the accrued interest. In the event of an earlier conversion, acceleration or payment of the Note, interest shall be payable in cash on such date.

3.    Events of Default . If any of the events specified in this Section 3 shall occur (herein individually referred to as an " Event of Default "), the Holder of the Note may, so long as such condition exists, declare the entire principal and unpaid accrued interest hereon immediately due and payable, by notice in writing to the Company:

(a)    The Company shall default in the payment of any part of the principal or accrued and unpaid interest on this Note after it shall become due and payable, whether at maturity or at a date fixed for prepayment or by acceleration or otherwise; or

(b)    The institution by the Company of proceedings to be adjudicated as bankrupt or insolvent, or the consent by it to institution of bankruptcy or insolvency proceedings against it or the filing by it of a petition or answer or consent seeking reorganization or release under the federal Bankruptcy Act, or any other applicable federal or state law, or the consent by it to the filing of any such petition or the appointment of a receiver, liquidator, assignee, trustee or other similar official of the Company, or of any substantial part of its property, or the making by it of an assignment for the benefit of creditors, or the taking of corporate action by the Company in furtherance of any such action; or

(c)    If, within sixty (60) days after the commencement of an action against the Company, without the consent or acquiescence of the Company (and service of process in connection therewith on the Company) seeking any bankruptcy, insolvency, reorganization, liquidation, dissolution or similar relief under any present or future statute, law or regulation, such action shall not have been resolved in favor of the Company or all orders or proceedings thereunder affecting the operations or the business of the Company stayed, or if the stay of any such order or proceeding shall thereafter be set aside, or if, within sixty (60) days after the appointment without the consent or acquiescence of the Company of any trustee, receiver or liquidator of the Company or of all or any substantial part of the properties of the Company, such appointment shall not have been vacated; or

(d)    Any material breach by the Company of any representation, warranty or covenant contained in the Purchase Agreement or this Note.

(e)    As of January 1, 2006, the Company shall not have obtained stockholder approval to amend its Articles of Incorporation to increase the number of shares of its authorized Common Stock to account for the conversion of this Note.

In the case of an Event of Default pursuant to (b) or (c) above, all amounts shall automatically, without notice, become immediately due and payable and collectible by Holder pursuant to applicable law.

4.    Conversion .

4.1    Conversion . The principal amount of this Note, or any portion thereof may be converted by the Holder at any time prior to Maturity into the number of fully paid shares of the Company's Common Stock as is determined by dividing the unpaid principal under the Note by the Conversion Price (as hereinafter defined) in effect at the time of conversion. Accrued but unpaid interest shall be payable in cash at the time of conversion.

4.2    Conversion Price. The Conversion Price (the "Conversion Price") applicable per share of Common Stock shall initially be equal to $0.02, subject to adjustment from time to time in accordance with Section 4.3 below.

4.3    Adjustments to the Conversion Price. The Conversion Price shall be subject to adjustment from time to time as follows:

4.3.1    Adjustment Upon Stock Dividends, Subdivisions or Splits . If, at any time, the number of shares of Common Stock outstanding is increased by a stock dividend payable in shares of Common Stock or by a subdivision or split-up of shares of Common Stock, then, following the record date for the determination of holders of Common Stock entitled to receive such stock dividend, or to be affected by such subdivision or split-up, the Conversion Price shall be appropriately decreased so that the number of shares of Common Stock issuable on conversion of Note shall be increased in proportion to such increase in outstanding shares.

4.3.2    Adjustment Upon Combinations . If, at any time, the number of shares of Common Stock outstanding is decreased by a combination of the outstanding shares of Common Stock into a smaller number of shares of Common Stock, then, following the record date to determine shares affected by such combination, the Conversion Price shall be appropriately increased so that the number of shares of Common Stock issuable on conversion of the Note shall be decreased in proportion to such decrease in outstanding shares.

4.3.3    Adjustment Upon Reclassifications, Reorganizations, Consolidations or Mergers . If, at any time when the Note is issued and outstanding, there shall be any merger, consolidation, share exchange, recapitalization, reorganization, business combination, or other similar event, as a result of which shares of Common Stock shall be changed into the same or a different number of shares of another class or classes of stock or securities of the Company or another entity, or in case of any sale or conveyance of all or substantially all of the assets of the Company then the Holder shall thereafter have the right to receive upon conversion of the Note, upon the basis and upon the terms and conditions specified herein and in lieu of the shares of Common Stock immediately theretofore issuable upon conversion, such stock, securities, cash or other assets which the Holder of would have been entitled to receive in such transaction had the Note been converted in full immediately prior to such transaction (without regard to any limitations on conversion contained herein), and in any such case appropriate provisions shall be made with respect to the rights and interests of the Holder to the end that the provisions hereof (including, without limitation, provisions for adjustment of the applicable Conversion Price and of the number of shares of