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                                                                 Exhibit 10.43
                                          
                                          
                                          
                                    May 30, 1997
                                          
                                          


Mr. Allan H. Mizoguchi, Ph.D.
Vice President, Clinical & Quality
Molecular Biosystems, Inc.
10030 Barnes Canyon Road
San Diego, California  92121

          Re:  Terms of Separation from MBI
               ----------------------------

Dear Al:

     In accordance with our recent discussions, this letter ("Letter 
Agreement") will set forth the terms of our agreement regarding your 
voluntary departure from MBI.

     1.   DESCRIPTION.  Both parties shall regard your departure as a 
voluntary resignation to pursue personal goals and other opportunities.

     2.   TIMING.  You shall resign as an employee and officer of MBI 
effective as of May 30, 1997 ("Resignation Date").  Your resignation shall be 
in the form attached hereto.

     3.   EFFECTIVE DATE.  This Letter Agreement shall become effective on 
the eighth day following your execution of the agreement, unless you have 
revoked acceptance during the seven days prior thereto.  (SEE Paragraph 
15(b).) Regardless of when this takes place, the Agreement shall be deemed to 
have been in effect retroactive to May 30, 1997.  The Agreement shall not 
become effective unless executed by you and MBI.

     4.   SEPARATION PAYMENTS.  In consideration of your undertakings in this 
Agreement, MBI shall provide you with severance benefits equivalent to one 
year current salary.  This amount shall be paid to you in bi-weekly 
installments for the one year period following your Resignation Date (last 
payment May 29, 1998). Taxes and other appropriate deductions will be 
withheld, however, contributions to your 401(k) or any other benefit 
deductions will not be allowed.

     5.   WELFARE BENEFITS.  Regular medical, dental, vision, as well as 
basic and optional life and accidental death and dismemberment insurance will 
continue through May 31, 1997.  Long-Term disability coverage will continue 
through the Resignation Date and end thereafter.  In addition:

          (a)  Medical, dental, and vision insurance under MBI's policies for 
you and currently insured dependents will be extended through COBRA from June 
1, 1997 through May 31, 1998 (unless you obtain other coverage during that 
time, in which you must notify MBI) at MBI's expense. Thereafter, you may 
elect to continue COBRA coverage at your expense for an additional six 
months.  (Maximum COBRA coverage is 18 months.) 

          (b)  You will be provided the information needed to request the 
option of converting the group life insurance and/or accidental death and 
dismemberment insurance coverage to an individual 


                                       

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Mr. Allan H. Mizoguchi, Ph.D.
May 30, 1997
Page 2

policy.  You will work directly with CIGNA should you elect this option.  You 
would need to exercise this option within 31 days of the benefits termination 
date, May 31, 1997.

                                       

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Mr. Allan H. Mizoguchi, Ph.D.
May 30, 1997
Page 3

          (c)  You will be provided the information needed to request the 
option of converting the Long Term disability (LTD) insurance coverage to an 
individual policy.  You should work directly with UNUM should you elect this 
option.  You would need to exercise this option within 31 days of your 
resignation date, May 30, 1997.

          (d)  Depending on the amount of your 401(k) plan balance, you may 
either elect to remain in the plan with no further deposits (balance greater 
than $3500), or elect a distribution of your funds (balance less than $3500). 
You will notify CIGNA within 30 days of the Resignation Date as to how and to 
whom your funds should be distributed. Information on how to initiate your 
desired option will be provided by Human Resources.

          (e)  If you are a participant in the health care reimbursement 
plan, you will have until the end of 1997 to request reimbursement for 
charges incurred through the Resignation Date.  Any such request should be 
made directly to UNUM.

          (f)  You will be paid for all earned and unused vacation hours.  
You will not accrue any additional vacation following the Resignation Date.

Representatives of Human Resources will be available to explain details of 
the above items. 

     6.   STOCK OPTIONS.

          (a)  CURRENT OPTIONS.  You have been granted stock options as 
described in the attached schedule.  As of May 30, 1997 MBI will accelerate 
the vesting of all unvested options.  MBI will also extend the period of 
exercisability of those options to the maximum period available under our 
plans. (That is, the lapse dates in the charts, which are ALREADY at the 
maximum, will not be reduced on account of your ceasing to be an employee.)

          (b)  RESTRICTIONS AND TRANSACTIONS.  Until November 30, 1997 
("Reporting Period"), you will be under the same constraints imposed by MBI 
and securities laws on MBI vice presidents regarding the exercise of options 
and the purchase and sale of MBI shares.  During the Reporting Period, you 
shall notify us of your intentions in this regard (including option 
exercises) and shall execute such forms, if any, as MBI and the U.S. 
securities laws require.  If you wish, you may use the services of MBI's 
Finance department to assist you in exercising your options and selling your 
shares (if that is how you choose to proceed) during the Reporting Period.  
You acknowledge that taxes and commissions will be withheld from any profit 
you make on the sale of the stock following exercise and sale during the 
Reporting Period.  During the Reporting Period, you will be notified monthly, 
along with other MBI Section 16(b) reporting persons, as to the current 
trading status of MBI stock (i.e., "green light," "yellow light," or "red 
light").  At no time -- presently, or at any future time, during or after the 
Reporting Period -- may you trade on inside MBI information.

     7.   PLACEMENT.  MBI will provide you with six months outplacement 
counseling and services through Right Management Consultants.  In addition, 
MBI will also allow you to continue to use the company's phone voicemail 
system and your current voice mailbox for a period of three months following 
your Resignation Date.
                                       

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Mr. Allan H. Mizoguchi, Ph.D.
May 30, 1997
Page 4

     8.   COOPERATION;  NO RAIDING; NON-DISPARAGEMENT.  You shall cooperate 
with MBI in any and all governmental and/or third-party proceedings, 
including but not limited to lawsuits and other disputes.  Following your 
resignation such cooperation shall be at MBI's expense (except that MBI 
cannot pay for the content of sworn testimony).  You shall keep MBI advised 
of contacts by governmental agencies and third parties, and shall reasonably 
cooperate with MBI in handling any response.  At your request, MBI shall 
provide counsel to you, if the parties deem counsel necessary or desirable, 
in any such proceeding.  You shall not voluntarily cooperate with, testify 
for, or otherwise assist parties adverse to MBI in a dispute, although you 
may respond to compulsory process (i.e., a valid subpoena).  

     For a period of one year following the Resignation Date, you shall not 
contact persons employed by MBI at the time to recruit them for your business 
or any business by which you are employed or with which you are affiliated, 
or otherwise encourage them to leave MBI.

     You shall not materially disparage MBI, and MBI shall not materially 
disparage you, to any third parties.

     9.   CONTACTS BY POTENTIAL EMPLOYERS.  Potential employers contacting 
MBI will be told only that your resignation was voluntary; your title; your 
dates of employment; and your final salary.  MBI will provide you with a 
positive letter of reference.  The letter will be agreed upon between you and 
me.

     10.   CONFIDENTIALITY.  You will not remove any MBI information, 
documents, or other property from its premises, and you will return any MBI 
information currently in your possession or control off MBI's premises.  In 
addition:

          (a)  You acknowledge that in the course of your employment with MBI 
you have had and will have access to and familiarity with information of 
substantial value to MBI which is not old or generally known to the public 
and which gives MBI an advantage over its competitors who do not know or use 
it, including but not limited to strategies, business plans, research, 
formulas and formulations, techniques, designs, drawings, processes, 
inventions, developments, equipment, prototypes, sales and customer 
information, and financial information, relating to the business, products, 
and practices of MBI (hereinafter referred to as "Confidential Information"). 
 You agree at all times following your resignation to regard and preserve as 
confidential such Confidential Information, and to refrain from publishing or 
disclosing any part of such Confidential Information and from using it except 
on behalf of MBI.  You further agree at all times to refrain from any other 
acts or omissions that would reduce the value of such Confidential 
Information to MBI and to take all reasonably necessary and desirable 
precautions to prevent such Confidential Information from being disseminated 
to any third parties.

          (b)  You acknowledge that a breach of the terms of this paragraph 
would threaten MBI with immediate and irreparable harm not readily 
compensable in money damages, and that MBI would be entitled to injunctive 
and declaratory relief to stop or prevent any such breach.

Nothing in this paragraph shall be construed to prevent you from using or 
disclosing your general knowledge of the imaging industry (as opposed to 
MBI-specific information) acquired at any time prior to or during the course 
of your employment.

                                       

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Mr. Allan H. Mizoguchi, Ph.D.
May 30, 1997
Page 5


     11.  EMPLOYMENT BY COMPETITORS.  This Letter Agreement does not limit 
your ability to work for competitors of MBI, PROVIDED THAT for a period of 
one year from the Resignation Date, reasonably in advance of accepting any 
employment with any of the companies listed below ("Competitor"), you shall 
notify the President and Chief Executive Officer of MBI.  

    Abbott Laboratories                ImaRx Pharmaceutical
    Accusphere                         Interactive Medical
    Alliance Pharmaceuticals           Technologies
    Berlex Imaging                     Medisperse
    Bracco                             Nycomed
    Delta Biotechnology                Schering
    DuPont/Merck                       Sonus Pharmaceuticals


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Mr. Allan H. Mizoguchi, Ph.D.
May 30, 1997
Page 6

Prior to accepting any such employment, or promptly following your engagement 
in any consulting relationship with a Competitor, you shall give MBI the 
opportunity to discuss your plans with you in order to explore any possible 
problems or conflicts.  While MBI shall not disparage you or attempt to 
dissuade any Competitor from employing or engaging you, you acknowledge that 
MBI may contact such Competitor informing it truthfully of your 
confidentiality obligations to MBI.  MBI shall have no liability to you in 
the event of a decision by a Competitor not to employ or engage you following 
such contact by MBI.  Failure to provide this notice to MBI during this 
period shall be deemed a material breach of this Agreement.

     You remain bound by your confidentiality obligations even if you work 
for a Competitor.

     12.  RELEASE.  In consideration for the payments, options, and other 
consideration described in this Letter Agreement, you hereby unconditionally, 
irrevocably, and absolutely release and discharge MBI, its employees, 
officers, directors, agents, stockholders, independent contractors, 
attorneys, consultants, predecessors, successors and assigns from any and all 
claims related in any way to any acts, transactions, or occurrences between 
you and MBI to date, including but not limited to all losses, liabilities, 
claims, charges, demands and causes of action, known or unknown, suspected or 
unsuspected, arising directly or indirectly out of, or in any way connected 
with, your employment with or resignation from MBI.  This includes, but is 
not limited to, any claim of employment discrimination arising under federal, 
state or local law, including the Age Discrimination in Employment Act of 
1967, as amended, the Americans with Disabilities Act, the California Fair 
Employment and Housing Act, any other statutory cause of action, and any tort 
or contract claims.

     WAIVER OF ADDITIONAL CLAIMS.  Section 1542 of the Civil Code of the 
State of California provides as follows:

     A GENERAL RELEASE DOES NOT EXTEND TO CLAIMS WHICH THE CREDITOR DOES NOT 
KNOW OR SUSPECT TO EXIST IN HIS FAVOR AT THE TIME OF EXECUTING THE RELEASE, 
WHICH IF KNOWN BY HIM MUST HAVE MATERIALLY AFFECTED HIS SETTLEMENT WITH THE 
DEBTOR.

You waive and relinquish any right or benefit which you may have under this 
section or any other provision of the statutory or nonstatutory law or any 
other jurisdiction to the full extent that you may lawfully waive all such 
rights and benefits.  In connection with such waiver and relinquishment, you 
acknowledge that you are aware that you, your attorneys or agents may 
hereafter discover claims or facts in addition to or different from those 
which they now know or believe to exist, but that it is your intention 
thereby fully, finally, and forever to release all claims, disputes, and 
differences, known or unknown, suspected or unsuspected, which now exist, may 
exist, or have existed between the parties, their employees, agents, assigns, 
and other privies.  Unless this provision shall have been procured by fraud, 
the releases given herein shall be effective regardless of the discovery or 
existence of any such claim or fact.

     13.  CONSEQUENCES OF BREACH.  If you breach this Letter Agreement, MBI 
may terminate it, cease providing payments and benefits hereunder, cancel 
your stock options, and recover all payments and benefits already paid, in 
addition to any other remedies it may have.

     14.  OTHER MATTERS.  You will receive materials prepared by Human 
Resources describing various rights and duties, including optional benefits, 
which will come into effect following your resignation.  You will also 
receive instruments as are customarily submitted to resigning employees.  You 
will cooperate fully in these separation meetings and execute or complete 
such instruments at the time of your resignation.

     15.  ACKNOWLEDGMENTS.  

                                       

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Mr. Allan H. Mizoguchi, Ph.D.
May 30, 1997
Page 7

          (a)  NO PRE-EXISTING OBLIGATION.  You acknowledge that but for the 
entry by you and MBI into this Letter Agreement, you are not entitled to the 
payments, stock options, and other consideration provided for in these 
agreements (with the exception of federal rights such as COBRA).

          (b)  TIME FOR REVIEW; EFFECTIVE DATE.  You acknowledge that you 
have been given 21 days to consider the terms of this Letter Agreement.  In 
addition, both parties acknowledge that you may revoke your acceptance of 
this Letter Agreement within seven days following your signature (which may 
occur during the 21-day period).  

          (c)  ADVICE OF COUNSEL AND OTHER PROFESSIONAL ADVISORS.  You 
acknowledge that you have been advised in writing to consult with an attorney 
and an accountant or tax advisor before entering into these agreements.  You 
acknowledge either that you have done so and received counseling to your 
satisfaction, or that you have declined to do so and voluntarily executed 
this Letter Agreement without fraud or undue influence.

     16.  PROHIBITION AGAINST ASSIGNMENT.  You shall not assign this Letter 
Agreement or any of the rights, interests and benefits hereunder.  However, 
you may provide for the assignment, gift, bequest, or transfer of such 
benefits under this Letter Agreement to your survivor(s), or to a trust for 
their benefit, on your death, or in the event that you suffer a major 
disability. 

     17.  ENTIRE AGREEMENT.  This Letter Agreement between the parties dated 
May 30, 1997, constitutes the entire Agreement between the parties hereto and 
contains all of the agreements between the parties with respect to its 
subject matter.  This Letter Agreement supersedes any and all other 
agreements, either oral or in writing, between the parties hereto with 
respect to their subject matter, PROVIDED THAT Paragraphs 3 (Confidentiality) 
and 4-9 (relating to inventions made within a year of termination) of your 
Employment Agreement dated August 1, 1994, shall remain in effect.

     18.  BINDING EFFECT.  This Letter Agreement shall be binding upon and 
inure to the benefit of both parties and their respective heirs, legal 
representatives, executors, administrators, and successors.

     19.  GOVERNING LAW.  This Letter Agreement shall be subject to and 
governed by the laws of the State of California irrespective of the fact that 
you may become a resident of a different state.

     20.  AMENDMENT OF LETTER AGREEMENT.  No change or modification of this 
Letter Agreement shall be valid unless the same be in writing and signed by 
both parties.  No waiver of any provision of this Letter Agreement shall be 
valid unless in writing and signed by the person or party to be charged.

     21.  SEVERABILITY.  If any portion or portions of this Letter Agreement 
shall be, for any reason, deemed to be invalid or unenforceable, the 
remaining portion or portions shall nevertheless be valid, enforceable and 
carried into effect, unless to do so would clearly violate the present legal 
and valid intention of the parties hereto.

     22.  HEADINGS.  The headings of this Letter Agreement are inserted for 
convenience only and are not to be considered in construction of the 
provisions hereof.

                                       

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Mr. Allan H. Mizoguchi, Ph.D.
May 30, 1997
Page 8

     23.  WAIVER OF BREACH.  The waiver by  either of the parties hereto of 
any breach of any provision hereof shall not be construed to be a waiver of 
any succeeding breach of that provision or a waiver of any other provision of 
this Letter Agreement.

     24.  INDEMNIFICATION.  With respect to any claim against you arising out 
of your work for MBI as an officer or employee, you shall have rights of 
indemnification against MBI under MBI's certificate of incorporation and 
bylaws equivalent to those of an MBI officer.

                                      * * * *

     If you are in agreement with these items, please execute the duplicate 
originals of this Letter Agreement and return them to Pam Alexandra.

     Let me take this opportunity to thank you for your services to MBI over 
the past several years.  We all wish you every success in your future 
endeavors.

                              Sincerely,


                              /s/ Bobba Venkatadri
                              -------------------------
                              Bobba Venkatadri
                              President and Chief Executive Officer


AGREED TO BY:


/s/ Allan H. Mizoguchi
--------------------------
Allan H. Mizoguchi

Date:  June 3, 1997