<PAGE>

                                                                    Exhibit 10.6

                                      CONFIDENTIAL TREATMENT HAS BEEN SOUGHT FOR
                                 PORTIONS OF THIS EXHIBIT PURSUANT TO RULE 24B-2
                           UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED

                                    AGREEMENT

                 This Agreement ("Agreement") is entered into effective as of
August 9, 1999 by and among Alliance Pharmaceutical Corp. (as successor to
Fluoromed Pharmaceuticals, Inc.) ("Alliance "), Photogen Technologies, Inc.
("Photogen"), and Gerald Wolf, Ph.D., M.D. ("Dr. Wolf").

                                    RECITALS

                  Dr. Wolf entered into an exclusive License Agreement dated
January 21, 1989 with Fluoromed Pharmaceuticals, Inc., a copy of which is
attached as Exhibit A hereto (the "1989 License Agreement"), granting the
licensee an exclusive license to utilize, manufacture, sell, license and
sublicense and otherwise treat as its exclusive property, inventions relating to
the use of various compounds as contrast agents for imaging the lymph nodes
and/or lymphatic system, together with all related technical information,
know-how, patents, and related patent rights.

                 The inventions are now covered by two United States patents,
U.S. Patents No. [****] and No. [****] (respectively, the "[****] Patent" and
the "[****] Patent") and all corresponding or related foreign patents and patent
applications as more fully described in Exhibit B hereto (the "Patents");

                  Photogen desires to acquire the Patents and to grant Alliance
an exclusive license to use the Patents in the field of Ultrasound. The term
"Ultrasound" means: percutaneous lymphography utilizing the ultrasonic modality;
the practice of the Patents using materials intended to change the acoustic
properties of the lymph node so as to identify its location or image the
intranodal architecture via the ultrasonic modality following percutaneous
administration; such materials will usually be composed of a relatively
insoluble gas such as hexafluorine contained within a biologically compatible
matrix. Photogen also desires to acquire all of Dr. Wolf's Know-How and
Improvements in all fields other than the field of Ultrasound. The term
"Know-How" means any and all rights to any discovery, invention (whether or not
patentable), know-how, substances, data including clinical trial data,
techniques, processes,
------------

[****]            REPRESENTS MATERIALS WHICH HAS BEEN REDACTED PURSUANT TO A
                  REQUEST FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2
                  UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED

                                       -1-

<PAGE>



systems, formulations and designs relating to the Patents. The term
"Improvements" means any improvements to the Patents developed by either
Alliance or Dr. Wolf subsequent to the execution of the 1989 License Agreement.

                  Alliance desires to sell to Photogen all of its right, title
and interest in the Patents, subject to an exclusive license from Photogen to
use the same in the field of Ultrasound and Alliance's retention of the Know-How
and Improvements described in Exhibit C hereafter (the "Retained Technology"),
all as set forth below. Dr. Wolf desires that all of his right, title and
interest in the Patents and all his Know-How and Improvements related to the
Patents other than his Know-How and Improvements related to the Patents in the
field of Ultrasound shall be transferred to and vested in Photogen at the
Closing and that all of his right, title and interest, if any, in his Know-How
and Improvements related to the Patents in the field of Ultrasound shall be
transferred to and vested in Alliance at the Closing.

                                    AGREEMENT

                  Now, therefore, in consideration of the mutual promises herein
and for other legally sufficient consideration, the parties hereby agree as
follows:

                  1. As of the Closing (defined below) the effectiveness of the
1989 License Agreement shall be suspended and have no force and effect except as
provided in Section 10 below.

                  2. As of the Closing, Alliance and Dr. Wolf hereby release and
discharge one another (and their employees, directors, agents and other
affiliates) from all known and unknown claims, demands, allegations,
liabilities, expenses (including attorneys' fees and expenses) and losses any of
them may have incurred through the date of this Agreement arising out of or
relating to the 1989 License Agreement and the transactions contemplated in the
1989 License Agreement. This release shall not be construed or admissible in any
proceeding as an admission by any party of the validity of any such claims.

                  3. As of the Closing, Alliance hereby assigns, transfers and
conveys to Photogen all of it its right, title and interest in and to the
Patents; Alliance, however, retains the Retained Technology.

                  4. As of the Closing, Dr. Wolf hereby assigns all of his
right, title and interest in and to the 1989 License Agreement, the Patents and
all Know-How and Improvements related thereto to Photogen, other than Know-How
and Improvements in the field of Ultrasound. As of the Closing, Dr. Wolf hereby
assigns to Alliance all of his right, title and interest in and to all Know-How
and Improvements in the field of Ultrasound.

                  5. As of the Closing, Photogen grants Alliance an exclusive,
paid-up, royalty-free, world-wide perpetual license, with all rights to
sublicense or assign it rights under

                                       -2-

<PAGE>



this license, under the Patents to develop, make, have made, import, use, offer
for sale and sell products solely in the field of Ultrasound. It is expressly
understood and agreed that Alliance shall have no rights under the Patents in
any field other than Ultrasound.

                  6. Alliance represents and warrants to, and covenants with Dr.
Wolf only with respect to Section 6(j) and with Photogen and Dr. Wolf with
respect to Sections 6(a) through 6(i), that the same are true, correct and
complete as of the date hereof and will be true, correct and complete at and as
of the Closing. For purposes of this Agreement, the knowledge of Alliance means
actual knowledge without obligation of investigation.

                     (a)      No consent or waiver of any third party is
necessary for Alliance to execute and deliver this Agreement and to perform all
of its obligations hereunder.

                     (b)      Exhibit B hereto sets forth an accurate and
complete list and description of the Patents (all U.S. patents and patent
applications and all corresponding or related foreign patents and patent
applications). Alliance is the co-owner with Dr. Wolf of the [****] Patent
and the EPO Patent, free and clear of any lien, encumbrance or claim of any
third party (except for the 1989 License Agreement and a lien held by the
Imperial Bank which will be released at Closing). There are no liens,
encumbrances or claims of any third party on Alliance's rights in the 1989
License Agreement.

                     (c)      Alliance has no interest in the [****] Patent,
other than through the 1989 License Agreement.

                     (d)      To Alliance's knowledge, neither the Patents nor
any products, methods or other inventions related thereto, interferes,
infringes, misappropriates or conflicts with the intellectual property rights,
contract or other rights of any third party. To Alliance's knowledge, there are
no pending or threatened, claims or proceedings either against Alliance or
relating to the Patents. To Alliance's knowledge, no third party has interfered
with, infringed upon, misappropriated or otherwise come into conflict with the
Patents. Alliance warrants and represents that all granted patents listed in
Exhibit B are in full force and effect and that all maintenance fees or other
fees associated with maintaining the Patents are current as of the Closing.

                     (e)      As of the date of this Agreement, Alliance has not
licensed or permitted any other person or entity to use the Patents outside the
field of ultrasound.

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

[****]            REPRESENTS MATERIALS WHICH HAS BEEN REDACTED PURSUANT TO A
                  REQUEST FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2
                  UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED

                                       -3-

<PAGE>



                     (f)      Alliance is an "Accredited Investor" as defined
under the Securities Act of 1933 (the "Securities Act"). Alliance is acquiring
the Photogen shares referred to in Sections 9(b)(i) and 9(b)(ii), below, for its
own account for the purpose of investment and not with a view to the sale or
distribution thereof; and, in any event, Alliance will not sell or otherwise
transfer any of the Photogen shares except pursuant to a registration statement
effective under the Securities Act or a valid exemption from registration under
the Securities Act. Alliance agrees that the certificates representing those
Photogen shares will bear a legend consistent with the foregoing.

                     (g)      Alliance has been furnished with a copy of
Photogen's most recent Form 10-KSB and Form 10-QSB report, and has had access to
the business records of Photogen and all such additional information and
documents as Alliance has requested. Alliance has been afforded an opportunity
to ask questions of and receive answers from representatives of Photogen
concerning the terms and conditions of this Agreement and the purchase of
Photogen shares.

                     (h)      There are no claims for brokerage commissions or
finder's fees or similar compensation in connection with the transactions
contemplated by this Agreement based on any arrangement or agreement made by or
on behalf of Alliance, and Alliance agrees to indemnify and hold Photogen and
Dr. Wolf harmless against any damages incurred as a result of any such claims.

                     (i)      Alliance is the successor in interest to all
right, title and interest of Fluoromed Pharmaceuticals Inc. with respect to
the 1989 License Agreement and the Patents. Alliance is also the owner by
assignment of all of David Long's right, title and interest in the [****]
Patent and all corresponding and related foreign patents and applications,
including the EPO Patent.

                     (j)      Alliance is not now and never has been obligated
to pay a royalty or other payment to Dr. Wolf pursuant to the terms of the 1989
License Agreement.

                  7. Photogen hereby represents and warrants to Alliance that:

                     (a)      Photogen is a corporation duly organized, validly
existing and in good standing under the laws of the State of Nevada and is
qualified to do business as a foreign corporation in each jurisdiction where
failure to qualify would have a materially adverse effect on the business and
properties of Photogen.

                     (b)      Photogen has full power to execute, deliver and
perform this Agreement. This Agreement when executed and delivered will be a
legal, valid and, assuming due execution by the other parties hereto and
thereto, binding obligation of Photogen, enforceable in accordance with its
terms, subject to applicable bankruptcy, insolvency, moratorium, reorganization
or similar laws affecting creditors' rights generally, and to general equitable
principles.

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

[****]    REPRESENTS MATERIALS WHICH HAS BEEN REDACTED PURSUANT TO
          RULE 24B-2 UNDER THE SECURITIES EXCHANGE ACT, AS AMENDED

                                       -4-

<PAGE>




                     (c)      When issued in accordance with the terms of this
Agreement, the Photogen shares will be duly authorized, validly issued and
outstanding, fully paid and non-assessable, and the certificates representing
the same will be duly and validly authorized, executed and delivered by
Photogen. Photogen has authorized and reserved for issuance sufficient shares of
its common stock to fulfill its obligations to issue any Contingent Shares
referred to in Section 9(b)(ii). The Contingent Shares will, upon issuance in
accordance with the terms of this Agreement, be duly authorized, validly issued
and outstanding, fully paid and nonassessable, and the certificates representing
the same will be duly and validly authorized, executed and delivered by
Photogen.

                     (d)      Assuming that Alliance's representations and
warranties contained in Section 6 of this Agreement are and continue to be true
and correct, the offer, issuance and sale to Alliance of the Photogen shares and
the Contingent Shares are and will be exempt from the registration requirements
of the Securities Act, and from all applicable state securities laws.

                     (e)      There are no claims for brokerage commissions of
finder's fees or similar compensation in connection with the transactions
contemplated by this Agreement based on any arrangement made by or on behalf of
Photogen. Photogen agrees to indemnify and hold Alliance harmless against any
damages incurred as a result of any such claim.

                  8. Except in the field of Ultrasound, Alliance will promptly
refer to Photogen any request or inquiry received from a third party regarding
the Patents or products utilizing the same.

                  9. As of the Closing, Photogen will deliver or caused to be
delivered a total of [****] of value to Alliance as follows:

                     (a)      Photogen will deliver or caused to be delivered to
Alliance a total of [****] in cash as follows: (i) [****] at the Closing, (ii)
[****] on December 31, 1999, and (iii) [****] on March 31, 2000.

                     (b)      (i)     At the Closing, Photogen will deliver to
Alliance [****] shares of the common stock of Photogen based on a "current
market price" (the average closing bid price of the stock for the 20 trading
days prior to the date of determination (I.E., August 9, 1999) as quoted on the
over-the-counter bulletin board market or on any exchange on which the common
stock is listed) of $9.45 per share discounted by 25% to $7.0875.

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

[****]            REPRESENTS MATERIALS WHICH HAS BEEN REDACTED PURSUANT TO A
                  REQUEST FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2
                  UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED

                                       -5-

<PAGE>



                      (ii)    If on the first anniversary of the date of this
Agreement the aggregate current market price of the Photogen shares delivered
pursuant to the previous sentence is not at least [****], Photogen will, within
30 days of such first anniversary date, deliver additional shares of Photogen
common stock so that the current market price of the additional common stock
(discounted by 25%) together with the other Photogen common stock delivered to
Alliance at Closing equals [****] (the "Contingent Shares"). For example, if the
current market price of Photogen common stock on the first anniversary of this
Agreement is $6.00 per share, Photogen will deliver to Alliance an additional
[****] shares of Photogen common stock, determined as follows: (i) $6.00 x
[****] = [****] (the current market value of the original shares on the first
anniversary date of this Agreement); (ii) [****] - [****] = [****] (the value
Photogen must provide Alliance to equal [****] in value); (iii) $6.00 x .75 =
$4.50 (the current market price discounted by 25%); (iv) [****] / $4.50 = [****]
(the number of additional shares Photogen must provide). Fractional share
amounts shall be rounded up or down to the nearest whole share.

                  10. Photogen may cure any default in either of the [****]
payments due on December 31, 1999 and March 31, 2000 pursuant to Section
9(a)(ii) or 9(a)(iii) by paying to Alliance within 30 days of the due date the
amount due for that installment plus interest from the date due until paid at
the prime rate as published in The Wall Street Journal. Cure will restore all of
Photogen 's rights under this Agreement. If Photogen fails to cure a default in
either the December 31, 1999, March 31, 2000 payments, or fails to issue the
Contingent Shares if required to do so, within 30 days of the first anniversary
date of this Agreement, the 1989 License Agreement will be effective and will
continue in full force and effect in accordance with its terms with Photogen ,
as assignee of Dr. Wolf, the licensor. The 1989 License Agreement will not be
effective for any other reason; and if Photogen makes both payments due on
December 31, 1999 and March 31, 2000, and issues the Contingent Shares as
required hereunder or the Contingent Shares are not required to be issued, the
1989 License Agreement shall become null and void without any further action on
the part of Photogen or Alliance.

                  11. The closing and consummation of the transactions herein
that are to be completed at the Closing shall take place as soon as practicable
after the date of this Agreement, but in no event later than 60 days after the
date hereof. The Closing shall be deemed complete upon the delivery of the cash
called for by Section 9(a)(i) and the delivery of the stock called for by
Section 9(b)(i) (the "Closing").

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

[****]            REPRESENTS MATERIALS WHICH HAS BEEN REDACTED PURSUANT TO A
                  REQUEST FOR CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2
                  UNDER THE SECURITIES EXCHANGE ACT OF 1934, AS AMENDED


                                       -6-

<PAGE>



                  12. Photogen grants Alliance "piggy back" registration rights
for those Photogen shares delivered to Alliance pursuant to Sections 9(b)(i) and
9(b)(ii) above, as more fully set forth in Exhibit D attached hereto.

                  13. The parties hereto agree to take all actions and do all
things necessary and appropriate to fully consummate the transactions
contemplated by this Agreement, including to vest in any party the intellectual
property rights conveyed hereby, promptly upon the request of any party entitled
to such action. Such further actions shall include executing and delivering any
further instruments, documents or agreements, in recordable form as appropriate,
containing commercially reasonable and customary terms for such matters that are
reasonably satisfactory to the parties and their counsel.

                  14. This Agreement and the recitals and exhibits hereto (all
of which are incorporated herein by reference): (i) contain the entire agreement
and understanding between the parties concerning the subject matter hereof and
supersede and replace all prior or other contemporaneous negotiations,
representations, arrangements, proposed agreements and agreements, written or
oral, with respect to such subject matter (none of which prior or
contemporaneous communications shall be binding upon the parties); (ii) may be
amended or modified only by a written instrument dated after the date hereof and
signed by the parties or their successors in interest; (iii) shall be
interpreted, enforced and governed by the laws of the State of Massachusetts,
without regard to its conflict of laws provisions; (iv) shall be construed as if
the parties jointly prepared them and any uncertainty or ambiguity shall not be
interpreted against any one party; and (v) may be executed in counterparts which
when taken together constitute the entire agreement between the parties hereto,
and each counterpart shall bind the party executing it (and any party may become
bound hereunder by executing this Agreement and delivering it by facsimile).

                  15. A communication relating to this Agreement shall have
legal effect only if it is in writing, and shall be deemed duly given three
business days after it is sent by registered or certified mail, return receipt
requested, postage prepaid, and addressed to the intended recipient as set forth
beneath its signature below. Any party may deliver any written communication
using any other means (including personal delivery, expedited courier, messenger
service, telecopy, telex, or ordinary mail), but no such communication shall be
deemed to have been duly given unless and until it actually is received by the
individual for whom it is intended. Any party may change the name and address to
which communications hereunder are to be delivered by giving the other parties
notice in the manner herein set forth.

                  16. Photogen may file and refer to this Agreement with its
Securities and Exchange Commission or stock exchange filings; however, Photogen
will provide a copy thereof to Alliance prior to such filing and, if
appropriate, seek confidential treatment of some portion thereof if requested by
Alliance. Any press release or publicity concerning this transaction shall be
subject to the prior approval of Alliance, which approval shall not be
unreasonably withheld.


                                       -7-

<PAGE>



                  17. Alliance will indemnify and hold Photogen and Dr. Wolf
harmless from any actual or alleged claim or liability arising out of any
product made, distributed or used resulting from the exclusive license granted
under the Patents by Photogen to Alliance in the Ultrasound Field.

                          [The signature page follows]




                                       -8-

<PAGE>



                  IN WITNESS WHEREOF, the undersigned have executed this
Agreement as of the date first set forth above.


                                            Alliance Pharmaceutical Corp., for
                                            itself and as successor to
                                            Fluoromed Pharmaceuticals, Inc.


                                            By:    Theodore D. Roth
                                                 -------------------------------
                                            Its:    President and COO
                                                 -------------------------------
                                            3040 Science Park Rd.
                                            San Diego, CA 92121
                                            Phone:   858/410-5275
                                            Fax:     858/410-5343


                                            Photogen Technologies, Inc.


     /s/ Gerald L. Wolf                     By:        /s/  John Smolik
-----------------------------                    -------------------------------
Gerald L. Wolf, Ph.D., M.D.                 Its:          President
                                                 -------------------------------

3 Gable Ridge Road                          7327 Oak Ridge Highway, Suite B
Westboro, MA 01581-2216                     Knoxville, TN  37931
Phone:   508/898-3053                       Phone:    423/769-4011
Fax:     508/898-3578                       Fax:      423/769-4013








                                       -9-

<PAGE>



                                    EXHIBITS

A        1989 License Agreement
B        The Patents
C        Retained Technology
D        Registration Rights



                                      -10-

<PAGE>



                                                                       EXHIBIT A




<PAGE>



                                                                       EXHIBIT B



                                   THE PATENTS


                  The Patents means the patent family containing the patents
and/or applications listed below including all extensions, continuations,
continuations-in-part, divisionals, patents-of-addition, reexaminations,
reissues, supplementary protection certificates and any additional foreign
counterparts of such patents and patent applications and any patents issuing
thereon and extensions of any patents listed below:

         (a)      [****]

         (b)      [****]

         (c)      [****]

         (d) The following additional patents or patent applications:

                           [****]
















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

                  [****]            REPRESENTS MATERIAL WHICH HAS BEEN REDACTED
                                    PURSUANT TO A REQUEST FOR CONFIDENTIAL
                                    TREATMENT PURSUANT TO RULE 24B-2 UNDER THE
                                    SECURITIES EXCHANGE ACT OF 1934, AS AMENDED.




<PAGE>



                                                                       EXHIBIT C



                             THE RETAINED TECHNOLOGY


         Alliance hereby retains the following technology:

         (a)      All Know-How and Improvements in the field of Ultrasound
                  currently owned, licensed or controlled by Alliance relating
                  to the Patent;

         (b)      All Know-How and Improvements currently owned, licensed or
                  controlled by Alliance relating to Alliance's products known
                  as "IMAGENT LN" and "OXYGENT;"

         (c)      For avoidance of doubt, the Retained Technology, however, does
                  not include any and all Know-How and Improvements known to
                  Gerald L. Wolf, Ph.D., M.D. relating to the Patents in all
                  fields other than Ultrasound.




<PAGE>



                                                                       EXHIBIT D

                  REGISTRATION UNDER THE SECURITIES ACT OF 1933

                             PIGGYBACK REGISTRATION


                           (a)      If at any time after August 9, 1999,
Photogen Technologies, Inc. ("Photogen") proposes to register any common stock
under the Securities Act of 1933 (the "Securities Act") on any form for the
general registration of securities under the Securities Act, whether or not for
its own account (other than a registration on a form relating to (i) a
registration of a stock option, stock purchase or compensation or incentive plan
or stock issued or issuable pursuant to any such plan, or a dividend investment
plan; (ii) a registration of stock proposed to be issued in exchange for
securities or assets of, or in connection with a merger or consolidation with,
another corporation; or (iii) a registration of stock proposed to be issued in
exchange for other securities of Photogen) in a manner which would permit
registration of common stock for sale to the public under the Securities Act (a
"Piggyback Registration"), it will at such time give prompt written notice to
Alliance of its intention to do so and of its rights under this Exhibit D. Upon
the written request of Alliance made within 15 days after the receipt of any
such notice (which request shall specify the common stock intended to be
disposed of by Alliance, Photogen will include in the Registration Statement the
common stock which Photogen has been so requested to register by Alliance
pursuant to Section 12 of the Agreement to which this is Exhibit D.

                           (b)      If, at any time after giving written notice
of its intention to register any securities but prior to the effective date of
the Registration Statement filed in connection with such registration, Photogen
shall determine for any reason not to register such securities, Photogen may, at
its election, give written notice of such determination to Alliance and,
thereupon shall be relieved of its obligation to register any common stock in
connection with such registration. All reasonable efforts obligations of
Photogen pursuant hereto shall cease if Photogen determines to terminate any
registration where common stock is being registered pursuant to this Exhibit D.

                           (c)      If a Piggyback Registration requested
pursuant hereto involves an underwritten offering, then, (i) Alliance must sell
its common stock to the underwriters selected by Photogen on the same terms and
conditions as apply to other selling shareholders or Photogen, if there are no
selling shareholders; and (ii) Alliance may elect in writing, not later than
five (5) Business Days prior to the effectiveness of the Registration Statement
filed in connection with such registration, not to register such securities in
connection with such registration.

                           (d)      Photogen will pay all Registration Expenses
in connection with each registration of common stock requested pursuant hereto,
except for the fees and

                                       -1-

<PAGE>



disbursements of any counsel retained by Alliance and Alliance's pro rata share
of any filing fees or other expenses directly and solely resulting from the
inclusion of the common stock in the Registration Statement, including
underwriting discounts and commissions.

                           (e)      If a registration pursuant hereto involves
an underwritten offering and the managing underwriter advises Photogen in
writing that, in its opinion, the number of shares of common stock requested to
be included in such registration would have a material adverse effect on such
offering, including an adverse decrease in the price at which such securities
can be sold, then the amount of common stock to be offered for the account of
Alliance shall be eliminated entirely or reduced pro rata as to all Selling
Stockholders on the basis of the relative number of shares of common stock each
such Selling Stockholder has requested to be included in such registration, to
the extent necessary to reduce the total amount of common stock to be included
in such offering to the amount recommended by such managing underwriter;
provided, however, that no securities may be offered in such registration for
the account of persons other than Photogen by virtue of their also having
"piggyback" registration rights, or otherwise, unless the common stock requested
to be included by Alliance in such registration are so included on a pro rata
basis.

                           (f)      The Piggyback Registration rights granted to
Alliance hereunder shall terminate in all events one year after the issuance of
the Contingent Shares if any; otherwise, after one year after the date hereof.

                           (g)      If and whenever Photogen is required
pursuant hereto to use its reasonable efforts to effect the registration of the
common stock under the Securities Act, Photogen will, as expeditiously as
possible:

                           (1)      prepare and file with the SEC a Registration
                                    Statement which includes the common stock
                                    and use its reasonable efforts to cause such
                                    Registration Statement to become and remain
                                    effective until the distribution described
                                    in the registration statement has been
                                    completed or until Alliance can sell all
                                    such common stock pursuant to Rule 144;

                           (2)      prepare and file with the SEC such
                                    amendments and supplements to such
                                    Registration Statement and the Prospectus
                                    used in connection therewith as may be
                                    necessary to keep such Registration
                                    Statement effective and to comply with the
                                    provisions of the Securities Act with
                                    respect to the sale or other disposition of
                                    common stock covered by such Registration
                                    Statement whenever Alliance shall desire to
                                    sell or otherwise dispose of the same, but
                                    only to the extent provided herein;


                                       -2-

<PAGE>



                           (3)      furnish (and to each underwriter, if any, of
                                    common stock) such number of copies of a
                                    Prospectus, including a preliminary
                                    Prospectus, in conformity with the
                                    requirements of the Securities Act, and such
                                    other documents, as Alliance may reasonably
                                    request in order to facilitate the public
                                    sale or other disposition of the common
                                    stock;

                           (4)      use its reasonable efforts to register or
                                    qualify the common stock covered by such
                                    registration statement under such state
                                    securities or blue sky laws of such
                                    jurisdiction as Alliance shall reasonably
                                    request and do any and all other acts and
                                    things which may be necessary under such
                                    securities or blue sky laws to enable
                                    Alliance to consummate the public sale or
                                    other disposition in such jurisdictions of
                                    the common stock, except that Photogen shall
                                    not for any purpose be required to consent
                                    generally to service of process or qualify
                                    to do business as a foreign corporation in
                                    any jurisdiction wherein it is not so
                                    qualified;

                           (5)      before filing the Registration Statement or
                                    Prospectus or amendments or supplements
                                    thereto, furnish to counsel selected by
                                    Alliance copies of such documents proposed
                                    to be filed which shall be subject to the
                                    reasonable approval of such counsel;

                           (6)      enter into and perform its obligations under
                                    an underwriting agreement, in usual and
                                    customary form, with the managing
                                    underwriter of such offer;

                           (7)      notify Alliance at any time when a
                                    Prospectus relating to any common 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
                                    included in such Registration Statement, as
                                    then in effect, includes an untrue statement
                                    of a material fact or omits to state a
                                    material fact required to be stated therein
                                    or necessary to make the statements therein
                                    not misleading in light of the circumstances
                                    then existing and promptly file such
                                    amendments and supplements as may be
                                    necessary so that, as thereafter delivered
                                    to Alliance, 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 in light of the circumstances
                                    then existing and use its best efforts to
                                    cause each such amendment and supplement to
                                    become effective;


                                       -3-

<PAGE>



                           (8)      furnish at the request of Alliance on the
                                    date that such common stock is delivered to
                                    the underwriters for sale in connection with
                                    a registration pursuant hereto an opinion,
                                    dated such date, of the counsel representing
                                    Photogen, for purposes of such registration,
                                    in form and substance as is customarily
                                    given by Photogen counsel to the
                                    underwriters in an underwritten public offer
                                    addressed to the underwriters, if any, and
                                    to Alliance, and (ii) a letter dated such
                                    date, from the independent certified public
                                    accountants of Photogen, in form and
                                    substance as is customarily given by
                                    independent certified public accountants to
                                    underwriters in an underwritten public
                                    offer, addressed to the underwriters and to
                                    Alliance; and

                           (9)      use its reasonable efforts to cause all such
                                    common stock to be listed on any securities
                                    exchange or Nasdaq market, if any, on which
                                    Photogen's common stock is then listed.

                           (h)      Photogen may require each seller of common
stock as to which any registration is being effected to furnish to Photogen such
information regarding the distribution of such securities and such other
information as may otherwise be required to be included in such Registration
Statement, as Photogen may from time to time reasonably request in writing.

                           (i)      Alliance agrees by acquisition of such
common stock that, upon receipt of any notice from Photogen of the happening of
any event of the kind described in paragraph (g)(7) hereof, Alliance will
forthwith discontinue disposition of such common stock covered by such
Registration Statement or Prospectus until Alliance's receipt of the copies of
the supplemented or amended Prospectus, or until it is advised in writing by
Photogen that the use of the applicable Prospectus may be resumed, and has
received copies of any additional or supplemental filings which are incorporated
by reference in such Prospectus, and, if so directed by Photogen, Alliance will
deliver to Photogen (at Photogen's expense) all copies, other than permanent
file copies then in Alliance's possession, of the Prospectus covering such
common stock current at the time of receipt of such notice.

                           (j)      In the event Common stock are registered
pursuant hereto:

                           (1)      To the extent permitted by law, Photogen
                                    will indemnify and hold harmless Alliance of
                                    common stock which is included in a
                                    Registration Statement filed pursuant to the
                                    provisions of this Agreement and any
                                    underwriter (within the meaning of the
                                    Securities Act) with respect to the common
                                    stock, and each officer, director, employee
                                    and agent thereof and each person, if any,
                                    who otherwise controls Alliance or
                                    underwriter (within the meaning of the
                                    Securities Act), against any losses or
                                    claims, damages,

                                       -4-

<PAGE>



                                    expenses or liabilities, joint or several,
                                    to which they may become subject under the
                                    Securities Act, the Exchange Act or other
                                    federal or state law, or otherwise, insofar
                                    as such losses, claims, damages, expenses or
                                    liabilities (or actions in respect thereof)
                                    arise out of or are based upon any untrue or
                                    allegedly untrue statement of any material
                                    fact contained in the Registration Statement
                                    for the Common stock, including any
                                    preliminary Prospectus or final Prospectus
                                    contained therein or any amendments or
                                    supplements thereto, or any document
                                    incident to the registration or
                                    qualification of any common stock, 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
                                    allegedly necessary to make the statements
                                    therein not misleading or arise out of any
                                    violation or alleged violation by Photogen
                                    of the Securities Act, the Exchange Act, any
                                    state securities law or any rule or
                                    regulation promulgated under the Securities
                                    Act, the Exchange Act or any state
                                    securities law; and will reimburse Alliance,
                                    any underwriter, officer, director,
                                    employee, agent or controlling person for
                                    any legal or other expenses reasonably
                                    incurred by them in connection with
                                    investigating or defending any such loss,
                                    claim, damage, liability or action;
                                    provided, however, that the indemnity
                                    agreement contained herein shall not apply
                                    to amounts paid in settlement of any such
                                    loss, claim, damage, expense, liability or
                                    action if such settlement is effected
                                    without the written consent of Photogen,
                                    which shall not be unreasonably withheld,
                                    nor shall Photogen be liable under hereunder
                                    to Alliance, such underwriter, officer,
                                    director, employee, agent or controlling
                                    person for any such loss, claim, damage,
                                    expense, liability or action to the extent
                                    that it arises out of, or is based upon, an
                                    untrue statement or allegedly untrue
                                    statement or omission or alleged omission
                                    made in connection with such Registration
                                    Statement, preliminary Prospectus, final
                                    Prospectus, or amendments or supplements
                                    thereto, in reliance upon and in conformity
                                    with information furnished in writing
                                    expressly for use in connection with such
                                    registration by Alliance, such underwriter,
                                    officer, director, employee, agent or such
                                    controlling person.

                           (2)      To the extent permitted by law, Alliance's
                                    common stock which is included in a
                                    Registration Statement filed pursuant to the
                                    provisions of this Agreement will indemnify
                                    and hold harmless Photogen, each of its
                                    employees, agents, directors and officers,
                                    each person, if any, who controls Photogen
                                    within the meaning of the Securities Act,
                                    and any underwriter (within the meaning of
                                    the

                                       -5-

<PAGE>



                                    Securities Act) against any losses, claims,
                                    damages, expenses or liabilities to which
                                    Photogen or any such person or underwriter
                                    may become subject, under the Securities
                                    Act, the Exchange Act or other federal or
                                    state law or otherwise, insofar as such
                                    losses, claims, damages, expenses or
                                    liabilities (or actions in respect thereof)
                                    arise out of, or are based upon any untrue
                                    or allegedly untrue statement of any
                                    material fact contained in a Registration
                                    Statement for the common stock, including
                                    any preliminary Prospectus or final
                                    Prospectus contained herein or any
                                    amendments or supplements thereto, or any
                                    document incident to the registration or
                                    qualification of any Common stock, 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
                                    allegedly necessary to make the statements
                                    therein not misleading; in each case to the
                                    extent that such untrue statement or
                                    allegedly untrue statement or omission or
                                    alleged omission was made in such
                                    Registration Statement, preliminary
                                    Prospectus, final Prospectus or amendments
                                    or supplements thereto, in reliance upon and
                                    in conformity with information furnished in
                                    writing by Alliance expressly for use in
                                    connection with such registration; provided,
                                    however, that the indemnity agreement
                                    contained hereunder shall not apply to
                                    amounts paid in settlement of any such loss,
                                    claim, damage, expense, liability or action
                                    if such settlement is effected without the
                                    written consent of Alliance, which shall not
                                    be unreasonably withheld; and Alliance will
                                    reimburse Photogen or any such person or
                                    underwriter for any legal or other expenses
                                    reasonably incurred by Photogen or any such
                                    person or underwriter in connection with
                                    investigating or defending such loss, claim,
                                    damage, liability, expense or action.

                           (3)      Promptly after receipt by an indemnified
                                    party hereunder of notice of the
                                    commencement of any action, such indemnified
                                    party will, if a claim in respect thereof is
                                    to be made against any indemnifying party
                                    hereunder, notify the indemnifying party in
                                    writing of the commencement thereof and
                                    generally summarize such action. The
                                    indemnifying party shall have the right to
                                    participate in and to assume the defense
                                    thereof with counsel mutually satisfactory
                                    to the parties. An indemnifying party shall
                                    not have the right to direct the defense of
                                    such an action on behalf of an indemnified
                                    party if such indemnified party has
                                    reasonably concluded that there may be
                                    defenses available to it that are different
                                    from or additional to those available to the
                                    indemnifying party; provided, however, that
                                    in such event, the indemnifying party shall
                                    bear the fees and expenses

                                       -6-

<PAGE>



                                    of only one (1) separate counsel for all
                                    indemnified parties, such separate counsel
                                    to be reasonably satisfactory to the
                                    indemnifying party. The failure to notify an
                                    indemnifying party promptly of the
                                    commencement of any such action if
                                    prejudicial to the ability to defend such
                                    action, shall relieve such indemnifying
                                    party of any liability to the indemnified
                                    party hereunder, but the omission so to
                                    notify the indemnifying party will not
                                    relieve such party of any liability that
                                    such party may have to any indemnified party
                                    otherwise than under this Section.

                           (4)      To the extent permitted by law, the
                                    indemnification provided for hereunder will
                                    remain in full force and effect regardless
                                    of any investigation made by or on behalf of
                                    the indemnified party or any officer,
                                    director or controlling person (within the
                                    meaning of the Securities Act) of such
                                    indemnified party and will survive the
                                    transfer of securities.

                           (5)      If for any reason the foregoing indemnity is
                                    unavailable to, or is insufficient to hold
                                    harmless an indemnified party, then the
                                    indemnifying party shall contribute to the
                                    amount paid or payable by the indemnified
                                    party as a result of such losses, claims,
                                    damages, liabilities or expenses (i) in such
                                    proportion as is appropriate to reflect the
                                    relative benefits received by the
                                    indemnifying party on the one hand and the
                                    indemnified party on the other or (ii) if
                                    the allocation provided by clause (i) above
                                    is not permitted by applicable law, or
                                    provides a lesser sum to the indemnified
                                    party than the amount hereinafter
                                    calculated, in such proportion as is
                                    appropriate to reflect not only the relative
                                    benefits received by the indemnifying party
                                    on the one hand and the indemnified party on
                                    the other but also the relative fault of the
                                    indemnifying party and the indemnified party
                                    as well as any other relevant equitable
                                    considerations. Notwithstanding the
                                    foregoing, no underwriter, if any, shall be
                                    required to contribute any amount in excess
                                    of the amount by which the total price at
                                    which the securities underwritten by it and
                                    distributed to the public were offered to
                                    the public exceeds the amount of any damages
                                    which underwriter has otherwise been
                                    required to pay by reason of such untrue or
                                    alleged untrue statement or omission or
                                    alleged omission. No person guilty of
                                    fraudulent misrepresentation (within the
                                    meaning of Section 11(f) of the Securities
                                    Act) shall be entitled to contribution from
                                    any person who was not guilty of such
                                    fraudulent misrepresentation. The obligation
                                    of any underwriters to contribute pursuant
                                    to this provision shall be several in

                                       -7-

<PAGE>


                                    proportion to their respective underwriting
                                    commitments and not joint.

                           (k)      Alliance agrees, if requested by the
managing underwriters in an underwritten offering, not to effect any public sale
or distribution of any securities of Photogen of the same class as the
securities included in such Registration Statement, including a sale pursuant to
Rule 144 under the Securities Act (except as part of such underwritten
registration), during the 10-day period prior to, and during the 90-day period
beginning on, the closing date of the underwritten offering made pursuant to
such Registration Statement, to the extent timely notified in writing by the
managing underwriters.

                           (l)      With a view to making available to Alliance
the benefits of Rule 144 promulgated under the Securities Act and any other rule
or regulation of the SEC that may at any time permit Alliance to sell its common
stock of Photogen to the public without registration, Photogen shall:

                           (1)      make available adequate current public
                                    information as contemplated by Rule
                                    144 (c)(1) or (2);

                           (2)      file with the SEC in a timely manner all
                                    reports and other documents required of
                                    Photogen under the Securities Act and the
                                    Exchange Act; and

                           (3)      furnish to Alliance owning any common stock
                                    upon request (i) a written statement by
                                    Photogen that it has complied with the
                                    reporting requirements of Rule 144, the
                                    Securities Act and the Exchange Act, (ii) a
                                    copy of the most recent annual or quarterly
                                    report of Photogen and such other reports
                                    and documents so filed by Photogen, and
                                    (iii) such other information as may be
                                    reasonably required in availing Alliance of
                                    any rule or regulation of the SEC which
                                    permits the selling of any such common stock
                                    without registration.



                                       -8-