Exhibit 4.3

THIS SECURED CONVERTIBLE NOTE
(NOTE) HAS NOT BEEN REGISTERED WITH THE SECURITIES AND EXCHANGE COMMISSION
UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE ACT). IN ADDITION, THE NOTE
HAS NOT BEEN REGISTERED UNDER APPLICABLE STATE SECURITIES LAWS IN RELIANCE UPON EXEMPTIONS
PROVIDED UNDER SUCH LAWS. THE NOTE MAY NOT BE PLEDGED, SOLD OR TRANSFERRED IN THE ABSENCE
OF (1) AN EFFECTIVE REGISTRATION STATEMENT COVERING THE SHARES FILED UNDER THE ACT, (2) AN
OPINION OF QUALIFIED COUNSEL, WHICH OPINION AND COUNSEL ARE SATISFACTORY TO THE
MANAGEMENT, THAT REGISTRATION IS NOT REQUIRED OR (3) OTHER EVIDENCE SATISFACTORY TO THE
MANAGEMENT THAT SUCH REGISTRATION IS NOT REQUIRED.

# SECURED CONVERTIBLE
NOTE

|$500,000 | November 20, 2003    
|-------- | ---------------------
|         | San Diego, California

For value received PFC Therapeutics,
LLC, a Delaware limited liability company (Payor) promises to pay to
Technology Gateway Partnership, L.P. or its assigns (Holder) the
principal sum of $500,000.

1.              This
note (the Note) is referred to in and is executed and
          delivered in connection with that certain Security Agreement executed by Payor
          in favor of the Holder (as the same may be amended, modified, supplemented or
          restated from time to time, the Security Agreement).
          Additional rights and obligations of Holder are set forth in the Security
          Agreement. The full amount of this Note is secured by the collateral identified
          and described as security therefor in the Security Agreement.

2.              To
the extent applicable, upon consummation of a Financing (as defined below),           the
outstanding principal amount of this Note shall, at the option of the           Holder,
convert into an equity interest in the Payor on the terms of equity           portion (if
any) of the Financing. For purposes of this Note, Financing means a
financing pursuant to which the Payor           receives gross proceeds of $10,000,000
(or such other amount approved by the           Holder) from one or more investors,
strategic partners, or other sources (or any           combination of the foregoing). By
way of example, the equity financing           contemplated by the Term Sheet dated
November 7, 2003 by and among Alliance           Pharmaceutical Corp. (Alliance)
and SRS Capital-West, Inc.           (as the same may be amended, modified, supplemented
or restated from time to           time) would be a Financing under this Note.

3.              In
the event this Note is not converted in connection with a Financing, Alliance
          shall, pursuant to an amendment to the Guaranty and Security Agreement executed
          by Alliance in favor of Holder (as the same may be amended, modified,
          supplemented or restated from time to time), irrevocably, absolutely and
          unconditionally collaterally assign to the Holder, as full repayment of this
          Note, 100% of the Earnout (as defined below), up to an aggregate maximum amount
          of $1,500,000, to be paid to Oxygent Creditors (as defined in the Asset
Purchase           Agreement (as defined below)) after January 1, 2006 pursuant to
Section 1.3 of           that certain Asset Purchase Agreement dated June 18, 2003 by and
between           Alliance and Photogen Technologies, Inc (the Asset Purchase
          Agreement). For purposes of this Note, the term Earnout means
the right of Alliance to receive royalty           payments from the sale of Imagent products
pursuant to the Asset Purchase           Agreement.

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4.              In
the event of any default hereunder, Payor shall pay all reasonable           attorneys fees
and court costs incurred by Holder in enforcing and           collecting this Note.

5.              If
there shall be any Event of Default hereunder, at the option and upon the
          declaration of the Holder of this Note and upon written notice to the Payor
          (which election and notice shall not be required in the case of an Event of
          Default under Section 7(c) or 7(d)), this Note shall accelerate and all
          principal and unpaid accrued interest shall become due and payable. The
          occurrence of any one or more of the following shall constitute an Event of
          Default:

(a)              Payor
shall default in its performance of any covenant under the Security           Agreement
and such default is not cured within thirty (30) days following notice           to Payor
of such default;

(b)              Payor
files any petition or action for relief under any bankruptcy,           reorganization,
insolvency or moratorium law or any other law for the relief of,           or relating
to, debtors, now or hereafter in effect, or makes any assignment for           the
benefit of creditors or takes any corporate action in furtherance of any of           the
foregoing; or

(c)              An
involuntary petition is filed against Payor (unless such petition is           dismissed
or discharged within thirty (30) days) under any bankruptcy statute           now or
hereafter in effect, or a custodian, receiver, trustee, assignee for the
          benefit of creditors (or other similar official) is appointed to take
          possession, custody or control of any property of Payor.

6.              Payor
hereby waives demand, notice, presentment, protest and notice of dishonor.

7.              This
Note is exempt from California usury laws by reason of California           Corporations
Code Section 25118. Notwithstanding any provision of this Note,           Payor shall not
and will not be required to pay interest at a rate or any fee or           charge in an
amount prohibited by applicable law. If interest or any fee or           charge payable
on any date would be prohibited, then such interest, fee or           charge will be
automatically reduced to the maximum amount that is not           prohibited. In the
event that Holder receives payment of any interest, fee, or           charge that would
cause the amount so received to exceed the maximum amount           permitted under
applicable law, then, to the extent that the amount so received           exceeds the
maximum amount permitted under applicable law: (a) in the first           instance, the
amount received shall be applied to principal and (b) in the           second instance,
in the event that the principal amount of this Note has been           paid in full, the
remaining amount so received shall be deemed to be a loan from           Payor to Holder,
repayable upon the demand of the Payor with interest at the           legal rate from the
date of Holders receipt of each payment in excess           interest, fees, or
charges.

8.              This
Note shall be governed by and construed under the laws of the State of
          California, as applied to agreements among California residents, made and to be
          performed entirely within the State of California, without giving effect to
          conflicts of law principles.

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9.              Any
term of this Note (or any Event of Default hereunder) may be amended or           waived
with the written consent of Payor and Holder.

| | PFC THERAPEUTICS, LLC          
| | -------------------------------
| | /s/ Duane J. Roth              
| | Duane J. Roth, Manager         
| | ACKNOWLEDGED AND AGREED:       
| | ALLIANCE PHARMACEUTICAL CORP.  
| | /s/ Duane J. Roth              
| | Duane J. Roth, Chairman and CEO