EXHIBIT 10.1

                               FIRST AMENDMENT TO
                        OPTISON PRODUCT RIGHTS AGREEMENT


         This First Amendment to OPTISON Product Rights Agreement ("Amendment")
is made as of the 7th day of August, 2000 by and between Mallinckrodt Inc., a
Delaware corporation with its principal place of business at 675 McDonnell
Boulevard, St. Louis, Missouri 63042 ("Mallinckrodt") and Molecular Biosystems,
Inc., a Delaware corporation with its principal place of business at 10030
Barnes Canyon Road, San Diego, California 92121 ("MBI").

                                    RECITALS

         A. MBI and Mallinckrodt are parties to the OPTISON Product Rights
Agreement dated as of May 9, 2000 ("OPRA").

         B. The parties desire to amend and clarify OPRA as more specifically
set forth herein. It is therefore agreed that OPRA is hereby amended as follows:

         1. SCHERING CREDIT. Mallinckrodt acknowledges that MBI has advanced
$450,000 to Schering AG which, under a license agreement between MBI and
Schering may be applied as a credit against payments required either as a
license fee or royalties under any future license that may be entered into
between Schering and MBI. Mallinckrodt agrees to use good faith to arrange to
utilize this credit in the future on terms acceptable to Mallinckrodt in its
sole discretion; provided, however, that Mallinckrodt shall not be obligated to
effect an arrangement to utilize the credit. If, for example, Mallinckrodt
desires to enter into a license with Schering, it may seek to effect the license
through MBI or effect an assignment of MBI's credit to Mallinckrodt. If
Mallinckrodt so arranges to utilize the credit, Mallinckrodt will repay the full
amount of the utilized credit to MBI as and when the same would otherwise be due
from Mallinckrodt to Schering.

         2. FEINSTEIN ROYALTY. The present rate at which Mallinckrodt has been
paying royalties to MBI on United States sales of OPTISON in respect of MBI's
obligations under the





Restated License Agreement dated June 1, 1989, between Dr. Feinstein and MBI
(the "Feinstein License Agreement") is 3%. Until United States OPTISON sales
reach an aggregate of $66,667,000, Mallinckrodt will continue to pay the 3%
royalty directly to MBI. MBI will apply the 3% Feinstein royalty against
prepayments made by MBI of earned royalties under the Feinstein License
Agreement. At such time as aggregate United States OPTISON sales equal
$66,667,000, Mallinckrodt shall commence paying the entire 3% royalty in respect
of United States OPTISON sales directly to Dr. Feinstein.

         MBI and Mallinckrodt agree that the provisions of this Amendment shall
supersede and govern any inconsistent provisions of OPRA.

         IN WITNESS WHEREOF the Parties hereto have signed this Amendment as of
the date first above written.


                                  MOLECULAR BIOSYSTEMS, INC.


                                  By:      /s/ BOBBA VENKATADRI
                                           ------------------------------------
                                           Bobba Venkatadri
                                           President and Chief Executive Officer


                                  MALLINCKRODT INC.


                                  By:      /s/ RICHARD T. HIGGONS
                                           ------------------------------------
                                           Richard T. Higgons
                                           Vice President, Corporate Development


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