<PAGE>

                                                                 EXHIBIT 10.8


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


                                                               EXECUTION COPY

                           SECURITIES PURCHASE AGREEMENT

              SECURITIES PURCHASE AGREEMENT (this "AGREEMENT"), dated as of
October 20, 1999, among PHOTOGEN TECHNOLOGIES, INC., a Nevada corporation (the
"COMPANY"), and ELAN INTERNATIONAL SERVICES, LTD., a Bermuda exempted limited
liability company ("EIS"), and a wholly owned subsidiary of ELAN CORPORATION,
PLC, an Irish public limited company ("ELAN").

                                  R E C I T A L S:

              A.     The Company desires to issue and sell to EIS, and EIS
desires to purchase from the Company, (i) 12,015 shares of a newly-created
series of the Company's Preferred Stock, par value U.S.$.01 per share, captioned
"Series A Convertible Exchangeable Preferred Stock" (the "SERIES A PREFERRED
STOCK"), (ii) 461,538 shares of the Company's Common Stock, par value U.S.$.001
per share ((the "COMMON STOCK"); together with the Series A Preferred Stock, the
"SHARES") (subject to adjustment, as described in Section 1(f) below) and (iii)
a warrant (the "WARRANT") in the form attached hereto as EXHIBIT A to purchase
up to 100,000 shares of   Common Stock subject to the conditions contained
herein and therein.  In addition, EIS has agreed to lend certain funds to the
Company pursuant to a convertible promissory note in the form attached hereto as
EXHIBIT B (as amended at any time, the "NOTE"; together with the Shares and the
Warrant, the "SECURITIES"), with a maximum aggregate principal amount of
U.S.$$4,806,000, amounts in respect of which shall be disbursed in accordance
with its terms and subject to the conditions contained herein and therein.  The
rights, preferences and privileges of the Series A Preferred Stock are as set
forth in the Certificate of Designations, Preferences and Rights (the
"CERTIFICATE OF DESIGNATIONS"), the form of which is attached hereto as EXHIBIT
C.

B.     The Company and EIS have previously formed PHOTOGEN NEWCO LTD., a Bermuda
exempted limited liability company incorporated under the laws of Bermuda
("NEWCO"), and pursuant to the terms of a Subscription, Joint Development and
Operating Agreement, dated as of the date hereof (as amended at any time, the
"JDOA"), simultaneously with the transactions contemplated by this Agreement,
(i) the Company shall acquire 12,000 common shares of Newco, par value U.S.$1.00
per share ("NEWCO COMMON STOCK"), representing 100% of the outstanding shares of
such class of stock and (ii) EIS shall acquire 2,980 non-voting convertible
preferred shares of Newco, par value of U.S.$1.00 ("NEWCO PREFERRED STOCK")
representing, on a fully diluted basis 19.9% of the outstanding shares of such
class of stock..  Additionally, as of the date hereof, Newco has entered into
license agreements with (i) ELAN PHARMA INTERNATIONAL LIMITED, an Irish private
limited company ("EPIL"), (such agreement, as amended at any time, the "ELAN
LICENSE AGREEMENT"), and (ii) the Company (such agreement, as amended at any
time, the "COMPANY LICENSE AGREEMENT" and, together with the Elan License
Agreement, the "LICENSE AGREEMENTS").

<PAGE>

              C.     The Company and EIS are executing and delivering on the
date hereof a Registration Rights Agreement, in the form attached hereto as
EXHIBIT D (as amended at any time, the "COMPANY REGISTRATION RIGHTS AGREEMENT"),
in respect of the Common Stock issued or issuable upon (i) conversion of the
Series A Preferred Stock and the Note and (ii) exercise of the Warrant, the
Common Stock being purchased hereunder, and any other Common Stock issued to EIS
or any of its affiliates or permitted transferees upon any stock split, stock
dividend, recapitalization or similar event affecting the Securities.  The
Company, EIS and Newco are also executing and delivering on the date hereof a
Registration Rights Agreement in the form attached hereto as EXHIBIT E (as
amended at any time, the "NEWCO REGISTRATION RIGHTS AGREEMENT").  Additionally,
the Company and EIS are executing and delivering on the date hereof a Funding
Agreement in the form attached hereto as EXHIBIT F (the "FUNDING AGREEMENT;"
and, together with this Agreement, the Certificate of Designations, the JDOA,
the Company Registration Rights Agreement, the Newco Registration Rights
Agreement, the License Agreements and each other document or instrument executed
and delivered in connection with the transactions contemplated hereby and by the
JDOA, the "TRANSACTION DOCUMENTS").

                                 A G R E E M E N T:

              The parties hereto agree as follows:

              SECTION 1.  CLOSING.

              (a)    TIME AND PLACE.  The closing of the transactions
contemplated hereby (the "CLOSING") shall occur on the date hereof (the "CLOSING
DATE"), at the offices of Brock Silverstein LLC, 800 Third Avenue, 21st Floor,
New York, NY 10022.

              (b)    ISSUANCE OF SECURITIES.  At the Closing, the Company shall
issue and sell to EIS, and EIS shall purchase from the Company:  (i) 12,015
shares of Series A Preferred Stock, (ii) 461,538 shares of Common Stock and
(iii) the Warrant.

              (c)    PURCHASE PRICE.  The purchase price (the "PURCHASE PRICE")
for the Securities shall be U.S.$18,015,000.

              (d)    CONVERTIBLE NOTE FACILITY.  EIS shall lend up to
U.S.$4,806,000 to the Company pursuant to the terms and conditions of the Note.

              (e)  DELIVERY.  At the Closing:

              (i)    EIS shall pay the Purchase Price by wire transfer to an
       account designated by the Company and the parties hereto shall execute
       and deliver to each other, as applicable: (A) a certificate or
       certificates for the Series A Preferred Stock and the Common Stock; (B)
       the Warrant, (C) the Note; (D) the Company Registration Rights Agreement;
       (E) the Newco Registration Rights Agreement; (F) the JDOA; (G) the
       Certificate of Designations, as filed with the Secretary of State of the
       State of Nevada; (H) the License Agreements; (I) the Funding Agreement;
       (J) certificates as to the

<PAGE>

       incumbency of the officers of the Company executing any of the
       Transaction Documents; and (K) any other documents or instruments
       reasonably requested by a party hereto; and

              (ii)   The Company shall cause to be delivered to EIS an opinion
       of counsel in the form attached hereto as EXHIBIT G.

              (f)  COMMON STOCK PURCHASE PRICE ADJUSTMENT.  In the event that
       the effective price per share of the Common Stock in the Company's next
       BONA FIDE third party financing (other than the Company's presently
       contemplated Series B Preferred Stock private placement and of the
       Company's existing options and/or warrants or the exercise thereof) is
       less than U.S.$13.00, the Company shall, upon consummation of such
       financing, cause to be issued to EIS that number of additional shares of
       Common Stock such that, after giving effect to such issuance, the average
       price per share paid by EIS for its aggregate ownership of Common Stock
       in the Company, including such additional Shares, shall be equal to the
       effective price per share in such BONA FIDE financing.

              (g)  EXEMPTION FROM REGISTRATION.  The Securities and any
       underlying shares of Common Stock will be issued under an exemption or
       exemptions from registration under the Securities Act of 1933, as amended
       (the "SECURITIES ACT").  Accordingly, the certificates evidencing the
       Series A Preferred Stock and the Common Stock, the Warrant, the Note and
       any shares of Common Stock or other securities issuable upon the
       exercise, conversion or exchange of any of the Securities shall, upon
       issuance, contain a legend, substantially in the form as follows:

              THE SECURITIES REPRESENTED HEREBY HAVE NOT BEEN REGISTERED UNDER
              THE SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE
              SECURITIES LAWS AND NO INTEREST MAY BE SOLD, TRANSFERRED OR
              OTHERWISE DISPOSED OF UNLESS THERE IS AN EFFECTIVE REGISTRATION
              STATEMENT FOR SUCH SECURITIES UNDER THE SECURITIES ACT OF 1933, AS
              AMENDED, AND ANY APPLICABLE STATE SECURITIES LAWS OR THIS
              CORPORATION RECEIVES AN OPINION OF COUNSEL FOR THE HOLDER OF THESE
              SECURITIES SATISFACTORY TO THIS CORPORATION THAT REGISTRATION IS
              NOT REQUIRED UNDER SUCH ACT OR APPLICABLE STATE SECURITIES LAWS.

              THE TRANSFER OF THE SECURITIES REPRESENTED BY THIS CERTIFICATE IS
              ALSO SUBJECT TO THE RESTRICTIONS CONTAINED IN THAT CERTAIN
              SECURITIES PURCHASE AGREEMENT, DATED AS OF OCTOBER __, 1999, BY
              AND BETWEEN PHOTOGEN TECHNOLOGIES, INC. AND ELAN INTERNATIONAL
              SERVICES, LTD.

              SECTION 2.  REPRESENTATIONS AND WARRANTIES OF THE COMPANY.  The
Company hereby represents and warrants to EIS, as of the date hereof, as
follows:

              (a)    ORGANIZATION.  The Company is duly organized, and validly
existing under the laws of the state of Nevada and has all requisite corporate
power and authority to own and lease

<PAGE>

its properties, to carry on its business as presently conducted and as
proposed to be conducted and to consummate the transactions contemplated
hereby.  The Company is duly qualified as a foreign corporation and in good
standing to do business in each jurisdiction in which the nature of the
business conducted or the property owned by it requires such qualification,
except where the failure to be so qualified would not, individually or in the
aggregate, have a material adverse effect on the business, assets,
liabilities (contingent or otherwise), operations, condition (financial or
otherwise), or prospects of the Company (a "COMPANY MATERIAL ADVERSE EFFECT").

              (b)  CAPITALIZATION. As of the Closing Date, the Company has
reserved a sufficient number of shares of Common Stock (i) for issuance upon
conversion of the Series A Preferred Stock being purchased hereunder by EIS
(including dividends in-kind thereon), (ii) for issuance upon exercise of the
Warrant and (iii) for issuance upon conversion of the Note (including interest
payable thereon).  The Shares, when issued against payment therefor in
accordance with this Agreement, will be duly and validly issued, fully paid and
nonassessable, and will not be issued in violation of any preemptive or similar
rights.  The shares of Common Stock underlying the Series A Preferred Stock, the
Warrant and the Note (the "UNDERLYING SHARES"), when issued upon conversion or
exercise in accordance with the terms thereof, will be duly and validly issued,
fully paid and nonassessable, and will not be issued in violation of any
preemptive or similar rights.

              (c)  AUTHORIZATION OF TRANSACTION DOCUMENTS.  The Company has full
corporate power and authority to execute and deliver this Agreement and each of
the other Transaction Documents to which it is a party, and to perform its
obligations hereunder and thereunder.  The execution, delivery and performance
by the Company of this Agreement and each of the other Transaction Documents to
which it is a party, including the issuance and sale of the Securities, have
been duly authorized by all requisite corporate action by the Company and, when
executed and delivered by the Company, this Agreement and each of the other
Transaction Documents to which it is a party will be the valid and binding
obligations of the Company, enforceable against the Company in accordance with
their respective terms.

              (d)  NO VIOLATION.  The execution, delivery and performance by the
Company of this Agreement and each other Transaction Document to which it is a
party, including the issuance and sale of the Securities, and compliance with
the provisions hereof and thereof by the Company, does not conflict with or
constitute or result in a breach of or default under (or an event which with
notice or passage of time or both would constitute a default) or give rise to
any right of termination, cancellation or acceleration under (i) the Restated
Articles of Incorporation, as amended, or by-laws, of the Company, (ii)
applicable law, statute, rule or regulation, or any ruling, writ, injunction,
order, judgment or decree of any court, arbitrator, administrative agency or
other governmental body applicable to the Company or any of its properties or
assets, or (iii) any contract filed or required by applicable law to be filed as
an exhibit to the Company's Annual Report on Form 10-KSB for the year ended
December 31, 1998 (the "1998 FORM 10-KSB"), except where such breach, default,
termination, cancellation or acceleration would not, individually or in the
aggregate, have a Company Material Adverse Effect

              (e)  APPROVALS.  No material permit, authorization, consent,
approval, or order of or by, or any notification of or filing with, any person
or entity (governmental or otherwise) is required in connection with the
execution, delivery or performance of this Agreement or the

<PAGE>

Transaction Documents, including the issuance and sale of the Securities, by
the Company, other than the filing of a Form D by the Company pursuant to
Regulation D under the Securities Act ("REGULATION D") and the filing of the
Certificate of Designations by the Company with the State of Nevada.

              (f)  SEC FILINGS.  The Company has filed with the Securities and
Exchange Commission (the "SEC") all forms, reports, schedules, statements,
exhibits and other documents (collectively, the "SEC FILINGS") required to be
filed by the Company on or before the date hereof.  At the time filed, the SEC
Filings, including without limitation, any financial statements, exhibits and
schedules included therein or documents incorporated therein by reference (i)
did not contain any untrue statement of a material fact or omit to state a
material fact required to be stated therein or necessary in order to make the
statements therein, in light of the circumstances under which they were made,
not misleading and (ii) complied in all material respects with the applicable
requirements of the Securities Act or the Securities Exchange Act of 1934, as
amended (the "EXCHANGE ACT"), as the case may be.

              (g)  FINANCIAL STATEMENTS.  The audited balance sheets of the
Company at December 31, 1998 and 1997, together with the related statements of
operations, stockholders' equity (deficit) and cash flows for each of the two
years ended December 31, 1998, 1997, together with the reports and opinions
thereon of BDO Seidman, LLP, contained in the 1998 Form 10-KSB, comply as to
form in all material respects with applicable accounting requirements and the
published rules and regulation of the SEC with respect thereto, and fairly
present, in all material respects, the financial position of the Company and the
results of its operations and its cash flows at such dates and for the years
then ended and were prepared in conformity in all material respects with
generally accepted accounting principles applied on a consistent basis.

              (h)  LITIGATION. There is no legal, administrative, arbitration or
other action or proceeding or governmental or investigation pending, or to the
Company's knowledge, threatened against the Company, or any director, officer or
employee of the Company that challenges the validity or performance of this
Agreement or the other Transaction Documents to which the Company is a party.

              (i)  ABSENCE OF CERTAIN EVENTS.  Since December 31, 1998, except
as  contemplated by the Transaction Documents or as set forth on SCHEDULE 2(i)
hereto, (A) the Company has not (i) made, paid or declared any dividend or
distribution to any equity holder (in such capacity) or redeemed any of its
capital stock, (ii) varied its business plan or practices, in any material
respect, from past practices, (iii) entered into any financing, joint venture,
license or similar arrangement that would limit or restrict its ability to
perform its obligations hereunder and under each of the other Transaction
Documents to which it is a party, or (iv) suffered or permitted to be incurred
any liability or obligation or any lien or encumbrance against any of its
properties or assets that would limit or restrict its ability to perform its
obligations hereunder and under each of the other Transaction Documents to which
it is a party, and (B) there has not been any change or development which has
had, or in the Company's reasonable judgement is likely to have, a Company
Material Adverse Effect except as disclosed on Schedule 2 (i) hereto.

              (j)  DISCLOSURE.  The representations and warranties set forth
herein and in the

<PAGE>

other Transaction Documents, when viewed collectively, do not contain any
untrue statement of a material fact or omit to state any material fact
necessary to make the statements contained herein not misleading in light of
the circumstances in which they were made.

              (k)  BROKERS OR FINDERS.  There have been no investment bankers,
brokers or finders used by the Company in connection with the transactions
contemplated by the Transaction Documents and no persons or entities are
entitled to a fee or compensation in respect thereof.

              SECTION 3.  REPRESENTATION AND WARRANTIES OF EIS.  EIS hereby
represents and warrants to the Company, as of the date hereof, as follows:

              (a)  ORGANIZATION.  EIS is duly organized, validly existing and in
good standing under the laws of Bermuda and has all requisite corporate power
and authority to own and lease its properties, to carry on its business as
presently conducted and as proposed to be conducted and to consummate the
transactions contemplated hereby.  EIS is duly qualified as a foreign
corporation and in good standing to do business in each jurisdiction in which
the nature of the business conducted or the property owned by it requires such
qualification, except where the failure to be so qualified would not,
individually or in the aggregate, have a material adverse effect on the
business, assets, liabilities (contingent or otherwise), operations, condition
(financial or otherwise), or prospects of EIS (an "EIS MATERIAL ADVERSE
EFFECT").

              (b)  AUTHORIZATION OF TRANSACTION DOCUMENTS.  EIS has full
corporate power and authority to execute and deliver this Agreement and each of
the other Transaction Documents to which it is a party, and to perform its
obligations hereunder and thereunder.  The execution, delivery, and performance
by EIS of this Agreement and each other Transaction Document to which it is a
party, including the purchase and acceptance of the Securities, have been duly
authorized by all requisite corporate action by EIS and, when executed and
delivered by EIS, this Agreement and each of the other Transaction Documents to
which it is a party, will be the valid and binding obligations of EIS,
enforceable against it in accordance with their respective terms.

              (c)  NO VIOLATION.  The execution, delivery and performance by EIS
of this Agreement and each other Transaction Document to which it is a party,
including the purchase and acceptance of the Securities, and compliance with
provisions hereof and thereof by EIS, will not conflict with or constitute or
result in a breach of or default under (or an event which with notice or passage
of time or both would constitute a default) or give rise to any right of
termination, cancellation or acceleration under (i) the by-laws of EIS, (ii)
applicable law, statute, rule or regulation, or any ruling, writ, injunction,
order, judgment or decree of any court, arbitrator, administrative agency or
other governmental body applicable to EIS or any of its properties or assets, or
(iii) any material contract to which EIS is a party, except where such breach,
default, termination, cancellation or acceleration would not, individually or in
the aggregate, have an EIS Material Adverse Effect.

              (d)  APPROVALS.  Except for consent required under the Mergers and
Takeovers (Control) Acts 1978-1996 (Ireland), no material permit, authorization,
consent, approval or order of or by, or any notification of or filing with, any
person or entity (governmental or otherwise) is required in connection with the
execution, delivery or performance of this Agreement or the Transaction

<PAGE>

Documents by EIS.

              (e)  INVESTMENT REPRESENTATIONS.

                     (i)    EIS is sophisticated in transactions of this type
       and capable   of evaluating the merits and risks of the transactions
       described herein and in the other Transaction Documents to which it is a
       party, and has the capacity to protect its own interests.  EIS has not
       been formed solely for the purpose of entering into the transactions
       described herein and therein and is acquiring the Securities (and the
       Underlying Shares) for investment for its own account, not as a nominee
       or agent, and not with the view to, or for resale, distribution or
       fractionalization thereof, in whole or in part, and no other person
       (other than Elan) has a direct or indirect interest, beneficial or
       otherwise in the Securities (or the Underlying Shares); provided,
       however, that EIS shall be permitted to convert or exchange such
       Securities in accordance with their terms.

                     (ii)   EIS has not and does not intend to enter into any
       contract, undertaking, agreement or arrangement with any person or entity
       to sell, transfer or pledge the Securities (or the Underlying Shares).

                     (iii)  EIS acknowledges its understanding that the private
       placement and sale of the Securities (and the Underlying Shares) is
       exempt from registration under the Securities Act by virtue of the
       provisions of Regulation D and Section 4(2) of the Securities Act.  In
       furtherance thereof, EIS represents and warrants that it is an
       "accredited investor" as that term is defined in Regulation D, has the
       financial ability to bear the economic risk of its investment, has
       adequate means for providing for its current needs and personal
       contingencies and has no need for liquidity with respect to its
       investment in the Company.

                     (iv)   EIS agrees that it shall not sell or otherwise
       transfer any of the Securities (or the Underlying Shares) without
       registration under the Securities Act or pursuant to an opinion of
       counsel reasonably satisfactory to the Company that an exemption from
       registration is available, and fully understands and agrees that it must
       bear the total economic risk of its purchase for an indefinite period of
       time because, among other reasons, none of the Securities (or the
       Underlying Shares) have been registered under the Securities Act or under
       the securities laws of any applicable state or other jurisdiction and,
       therefore, cannot be resold, pledged, assigned or otherwise disposed of
       unless subsequently registered under the Securities Act and under the
       applicable securities laws of such states or jurisdictions or an
       exemption from such registration is available.  EIS understands that the
       Company is under no obligation to register the Securities (or the
       Underlying Shares) on its behalf with the exception of certain
       registration rights with respect to certain of the Securities (and the
       Underlying Shares), as provided in the Company Registration Rights
       Agreement.  EIS understands the lack of liquidity and restrictions on
       transfer of the Securities (and the Underlying Shares) and that this
       investment is suitable only for a person or entity of adequate financial
       means that has no need for liquidity of this investment and that can
       afford a total loss of its investment.

              (f)  LITIGATION.  There is no legal, administrative, arbitration
or other action or

<PAGE>

proceeding or governmental investigation pending, or to EIS's knowledge
threatened, against EIS that challenges the validity or performance of this
Agreement or the other Transaction Documents to which EIS is a party.

              (g)  BROKERS OR FINDERS.  There have been no investment bankers,
brokers or finders used by EIS in connection with the transactions contemplated
by the Transaction Documents and no persons or entities are entitled to a fee or
compensation in respect thereof.

              SECTION 4.  COVENANTS OF THE PARTIES.

              (a)  CERTAIN COVENANTS.  From and after the Closing Date for so
long as the Note and until the earlier to occur of the exercise or expiration of
the EIS Exchange Right (as such term is defined in Section 6 hereof), the
Company shall not without the prior written consent of EIS:  (i)  sell,
transfer, encumber, pledge or otherwise affect, in any respect, (A) any shares
of Newco Common Stock owned by the Company, including, without limitation, those
shares of Newco Common Stock transferable to EIS upon exercise by EIS of the EIS
Exchange Right, or (B) affect, in any respect, the Company's ability to permit
EIS to exercise the EIS Exchange Right in full, as provided herein or (ii) enter
into any material transaction with a director, officer or more than 20%
beneficial owner of Common Stock on other than an arm's length basis.

              (b)  FULLY-DILUTED STOCK OWNERSHIP.  Notwithstanding any other
provision of this Agreement, in the event that EIS shall have determined that at
any time it (together with its affiliates, if applicable) holds or has the right
to receive Common Stock (or securities or rights, options or warrants
exercisable, exchangeable or convertible for or into Common Stock) representing
in the aggregate in excess of 19.9% of the Company's outstanding Common Stock on
a fully diluted basis (assuming the exercise, exchange or conversion of such
securities beneficially owned by EIS or its affiliates, but not the exercise,
exchange or conversion of any other similar securities) or EIS has otherwise
determined that Elan would be required to equity account for its investment in
Photogen, EIS shall have the right, in its sole discretion, rather than
acquiring such securities from the Company, to exchange such number of
securities, as are necessary so that Elan shall not have to equity account, for
non-voting, convertible preferred stock of the Company (which shall be
reasonably satisfactory to each of the Company and EIS), which equity securities
shall be entitled to all of the other rights and benefits of the Common Stock.
In the event that EIS shall undertake to exercise such right, EIS shall retain
the additional rights to (i) exchange such new class of equity security for
Common Stock, in its discretion at any time and (ii) assign all or a portion of
such new class of equity security to its affiliates, in its discretion at any
time.  Each of the Company and EIS shall use commercially reasonable effort to
effect such transactions and any required subsequent conversions or adjustments
to such securities, on a quarterly basis, within 15 business days of the end of
each of EIS' fiscal quarters.

              (c)  USE OF PROCEEDS.  The Company shall use the proceeds of (i)
the issuance and sale of the Series A Preferred Stock solely to meet its initial
capitalization obligations to Newco as described in the JDOA, and (ii) the
issuance and funding of the Note solely to meet its developmental funding
commitments to Newco, as described in the Funding Agreement; and, in each case,
for no other purpose.

              (d)  CONFIDENTIALITY; NON-DISCLOSURE.

<PAGE>

                     (i)   Subject to clauses (ii) and (iii) below, from and
       after the date hereof, neither the Company nor EIS (nor their
       respective affiliates) shall disclose to any person or entity this
       Agreement or the other Transaction Documents or the contents thereof
       or the parties thereto, except that such parties may make such
       disclosure (x) to their directors, officers, employees and advisors,
       so long as they shall have advised such persons of the obligation of
       confidentiality herein and for whose breach or default the disclosing
       party shall be responsible, (y) as required by applicable law, rule,
       regulation or judicial or administrative process, provided that the
       disclosing party uses reasonable efforts to obtain an order or ruling
       protecting the confidentiality of confidential information of the
       other party contained herein or therein or (z) to the NASDAQ Stock
       Market.  The parties shall be entitled to seek injunctive or other
       equitable relief in respect of any breach or threatened breach of the
       foregoing covenant without the requirement of posting a bond or other
       collateral.

                     (ii)   Prior to issuing any press release or public
       disclosure in respect of this Agreement or the transactions
       contemplated hereby, the party proposing such issuance, shall obtain
       the consent of the other party to the contents thereof, which consent
       shall not be unreasonably withheld or delayed; it being understood
       that if such second party shall not have responded to such consent
       request within five business days, such consent shall be deemed given.

              (e)  FURTHER ASSURANCES.  From and after the date hereof, each of
the parties hereto agree to do or cause to be done such further acts and things
and deliver or cause to be delivered to each other such additional assignments,
agreements, powers and instruments, as each may reasonably require or deem
advisable to carry into effect the purposes of this Agreement and the other
Transaction Documents.

              SECTION 5.  STANDSTILL.

              (a)  Provided that nothing contained herein will prevent or
prohibit EIS from purchasing Voting Stock (as defined below) of the Company
pursuant to subsection 5(b) or from acquiring Voting Stock pursuant to the
conversion of the Series A Preferred Stock or the Note or the exercise of the
Warrant in accordance with their respective terms, EIS will not, directly or
indirectly, without the prior consent of the Board of Directors of the Company
(the "BOARD"), (i) acquire (or offer or agree to acquire) any Voting Stock; or
(ii) enter into any merger, consolidation or similar transaction with the
Company, unless, in the case of each of (i) and (ii), such transaction has been
approved by the Board; provided, that the foregoing restrictions shall not be
applicable in the event that any unaffiliated third party takes any such actions
(in the case of share ownership, acquiring at least [****] % of the outstanding
Common Stock, directly or indirectly).  Notwithstanding the foregoing, EIS will
not be obligated to dispose of any Voting Stock it owns if its percentage
ownership is increased as a result of a decrease in the number of shares of
Voting Stock outstanding.

              (b)  The provisions of this Section 5 will terminate:  (i) if EIS
owns less than
-----------------------
[****] REPRESENTS MATERIAL WHICH HAS BEEN REDACTED PURSUANT TO A REQUEST FOR
       CONFIDENTIAL TREATMENT PURSUANT TO RULE 24B-2 UNDER THE SECURITIES ACT
       OF 1934, AS AMENDED.

<PAGE>

[****]% of the outstanding Voting Stock; (ii) if any person or group,
excluding EIS, any affiliate of Elan, or any group that includes Elan or any
such affiliate, makes a BONA FIDE offer to acquire Voting Stock which would,
if successful, result in the bidder's beneficial ownership of at least [****]
% of the then outstanding Voting Stock; or (iii) upon the second anniversary
of the date of this Agreement.

              (c)  The Company will give EIS prompt notice of the receipt by
the Company of any written notice couched in such terms as to put the Company
reasonably on notice of the likelihood that a person or group has acquired or
is proposing to acquire an aggregate position of at least [****]% of the
outstanding Voting Stock, the Company receiving any BONA FIDE offer to
purchase or acquire [****]% or more of the Voting Stock or all or
substantially all of the assets of the Company, and any Board determination
to seek an acquirer for in excess of [****]% of the Voting Stock.

              (d)  EIS will cause its affiliates and associates to comply with
the provisions of this Section 5, whether directly or indirectly, individually
or as part of a "group" (as such term is defined in Rule 13d-5 under the
Exchange Act).  When used in this Section 5, the term EIS includes EIS together
with its affiliates and associates.

              For purposes of this Section 5, the term "VOTING STOCK" means the
Common Stock and any preferred stock of the Company possessing voting rights and
eligible to participate in votes of all of the Company's shareholders pursuant
to the Company's Restated Articles of Incorporation and Nevada law, and includes
any options, convertible securities or other rights to acquire such stock.

       SECTION 6.  CERTAIN RIGHTS OF EIS.  (a)  PREEMPTIVE RIGHT.  Until the
fourth anniversary of the date hereof, EIS shall have the right (but not the
obligation) to participate in any equity, warrant, or convertible or
exchangeable for equity financing consummated by the Company, in order for EIS
to maintain its PRO RATA interest in the Company, based on the actual number of
shares of Common Stock outstanding on the date of such financing is consummated
(without, however, giving effect to the shares of Common Stock underlying the
Series A Preferred Stock); provided, however, that such right shall not apply to
any public offering, offering under an option plan, or asset or company
acquisition paid for, in whole or in part, in shares of stock. Such right shall
be exercised by EIS within 15 days of receipt of notice of such financing from
the Company.  Such participation by EIS shall be on the same terms and
conditions offered to any other potential investor in such offering.


------------------
[****] 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>

              (b)  COMPANY BOARD OF DIRECTORS. For so long as (i) EIS and/or its
affiliates or subsidiaries collectively own securities that represent ownership
of at least 10% of the Common Stock (or securities convertible, exchangeable or
exercisable for or into the Common Stock) on a fully diluted basis or (ii) until
the date that is five years after the date hereof, EIS shall be entitled to
nominate one director (the "EIS DIRECTOR") for election to the Company's Board,
which nominee shall be a member of the senior management of Elan, or otherwise
shall be acceptable to the Company.  In connection with the foregoing, the
Company will take all necessary and/or appropriate steps to effect such
appointment, including the inclusion of the designated EIS Director on the
recommended slate of directors presented at any regular or special meeting of
the stockholders of the Company at which directors of the Company are to be
elected.  Prior to such election, the designated EIS Director shall be entitled
to be an observer at the meetings of the Company's board of directors.

              (c)  CONVERSION AND EXCHANGE RIGHTS.  The Certificate of
Designations sets forth certain rights of the holders of shares of Series A
Preferred Stock to convert such shares of preferred stock into newly issued
shares of Common Stock, or to exchange such shares of Series A Preferred Stock,
subject to the provisions in Section 5 of the Certificate of Designations, for
certain shares (i) of Newco Common Stock owned by the Company or (ii) non-voting
convertible preferred stock of Newco (the "EIS EXCHANGE RIGHT"), both on the
terms and conditions set forth therein.

              SECTION 7.  PLEDGE OF NEWCO STOCK.  In order to secure the
Company's obligations pursuant to the EIS Exchange Right, the Company hereby
pledges, assigns and sets over to EIS, all of the Company's right, title and
interest in and to all shares of Newco Common Stock deliverable by the Company
upon exercise of the EIS Exchange Right (including stock distributions and
dividends thereon) (if EIS elects the option in Section 6(c)(i)) for such period
of time as the EIS Exchange Right shall be exercisable.  The Company shall cause
to be delivered to EIS all of the certificates together with duly executed stock
power in favor of EIS evidencing such shares, and cause to be filed with the
Secretary of State of Nevada an appropriate UCC-1 financing statement in respect
of such pledge, assignment or setting over, and take all other necessary,
appropriate and customary actions in connection therewith.  Such pledge shall be
governed by the applicable provisions of the Nevada Uniform Commercial Code.
Upon exercise of the EIS Exchange Right, EIS shall be entitled to keep and
retain such share certificates, which shall then be owned by EIS in accordance
with the terms thereof.  Until EIS exercises the EIS Exchange Right, the Company
shall retain all rights in and to the pledged Newco Common Stock (including
without limitation all voting, dividend, liquidation and other rights), subject
only to this pledge and the JDOA.

              SECTION 8.  SURVIVAL AND INDEMNIFICATION.  (a) SURVIVAL.  The
representations and warranties of the Company and EIS contained herein shall
survive for a period of 24 months from and after the date hereof.

              (b)  INDEMNIFICATION.  In addition to all rights and remedies
available to the parties hereto at law or in equity, the parties (each, in such
capacity, "INDEMNIFYING PARTY"; together, "INDEMNIFYING PARTIES") shall
indemnify each other as corporate entities (EIS and the Company),

<PAGE>

its stockholders, officers, directors and assigns, their affiliates, and its
affiliates' stockholders, officers, directors, employees, agents,
representatives, successors and assigns (collectively, the "INDEMNIFIED
PERSON"), and save and hold each Indemnified Person harmless from and against
and pay on behalf of or reimburse each such Indemnified Person, as and when
incurred, for any and all loss, liability, demand, claim, action, cause of
action, cost, damage, deficiency, tax, penalty, fine or expense, whether or
not arising out of any claims by or on behalf of such Indemnified Person or
any third party, including interest, penalties, reasonable attorneys' fees
and expenses and all amounts paid in investigation, defense or settlement of
any of the foregoing (collectively, "LOSSES"), that any such Indemnified
Person may suffer, sustain incur or become subject to, as a result of, in
connection with, relating or incidental to or by virtue of:

                     (i) any misrepresentation or breach of warranty on the
       part of the Indemnifying Party in the case of the Company under
       Section 2 of this Agreement or in the case of EIS under Section 3 of
       this Agreement or any of the other Transaction Documents (as limited
       thereby) (it being understood that the Company shall not be
       responsible for any such misrepresentation or breach of warranty by
       Newco); or

                     (ii) any nonfulfillment, default or breach of any
       covenant or agreement on the part of the Indemnifying Party under
       Section 4 of this Agreement or any of the other Transaction Documents.

              (c)  MAXIMUM RECOVERY.   Notwithstanding anything in this
Agreement to the contrary, in no event shall the Indemnifying Parties be liable
in the case of the Company for indemnification under this Section 8 in an amount
in excess of the aggregate of the purchase price paid for the Shares and the
Warrant and the amounts advanced and not repaid under the Note or in the case of
EIS for indemnification hereunder in an amount in excess of such same aggregate.
No Indemnified Person shall assert any such claim unless Losses in respect
thereof incurred by any Indemnified Person, when aggregated with all previous
Losses hereunder, equal or exceed U.S.$50,000, but at such time that an
Indemnified Person is entitled to assert a claim, such claim shall include all
Losses covered by this Section 8.

              (d)  EXCEPTION.  Notwithstanding the foregoing, upon judicial
determination that is final and no longer appealable, that the act or omission
giving rise to the indemnification set forth above resulted primarily out of or
was based primarily upon the Indemnified Person's negligence (unless such
Indemnified Person's negligence was based upon the Indemnified Person's reliance
in good faith upon any of the representations, warranties, covenants or promises
made by the Indemnifying Party herein) the Indemnifying Party shall not be
responsible for any Losses sought to be indemnified in connection therewith, and
the Indemnifying Party shall be entitled to recover from the Indemnified Person
all amounts previously paid in full or partial satisfaction of such indemnity,
together with all costs and expenses (including reasonable attorneys fees) of
the Indemnifying Party reasonably incurred in connection with the Indemnified
Persons claim for indemnity, together with interest at the rate per annum
publicly announced by Morgan Guaranty Trust Company as its prime rate from the
time of payment of such amounts to

<PAGE>

the Indemnified Person until repayment to the Indemnifying Party.

              (e)  INVESTIGATION.  All indemnification rights hereunder shall
survive the execution and delivery of this Agreement and the consummation of the
transactions contemplated hereby to the extent provided in Section 8(g) below,
irrespective of any investigation, inquiry or examination made for or on behalf
of, or any knowledge of the Indemnified Person or the acceptance of any
certificate or opinion.

              (f)   CONTRIBUTION.  If the indemnity provided for in this Section
8 shall be, in whole or in part, unavailable to any Indemnified Person, due to
Section 8(b) being declared unenforceable by a court of competent jurisdiction
based upon reasons of public policy, so that Section 8(b) shall be insufficient
to hold each such Indemnified Person harmless from Losses which would otherwise
be indemnified hereunder, then the Indemnifying Party and the Indemnified Person
shall each contribute to the amount paid or payable for such Loss 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 Person on the
other, but also the relative fault of the Indemnifying Party and be in addition
to any liability that the Indemnifying Party may otherwise have.  The indemnity,
contribution and expense reimbursement obligations that the Indemnifying Party
has under this Section 8 shall survive the expiration of the Transaction
Documents.  The parties hereto further agree that the indemnification and
reimbursement commitments set forth in this Agreement shall apply whether or not
the Indemnified Person is a formal party to any such lawsuit, claims or other
proceedings.

              (g)  LIMITATION.  No claim shall be brought by an Indemnified
Person in respect of any misrepresentation or breach of warranty under this
Agreement after 24 months from the date hereof; and any claim for
nonfulfillment, default or breach of any covenant or any misrepresentation shall
be brought within one year of the date of that such Indemnified Person became
aware or should have become aware of the nonfulfillment, default or breach.
Except as set forth in the previous sentence and in Section 8(c) above, this
Section 8 is not intended to limit the rights or remedies otherwise available to
any party hereto with respect to this Agreement or the Transaction Documents.

              SECTION 9.  NOTICES.  All notices, demands and requests of any
kind to be delivered to any party in connection with this Agreement shall be in
writing and shall be deemed to have been duly given if personally or hand
delivered or if sent by an internationally-recognized overnight delivery or by
registered or certified mail, return receipt requested and postage prepaid, or
by facsimile transmission addressed as follows:

                     (i) if to the Company, to:

                     Photogen Technologies, Inc.
                     7327 Oak Ridge Highway, Suite B
                     Knoxville, Tennessee  37931
                     Attention:  Chief Executive Officer
                     Facsimile:  423-769-4013

<PAGE>

                     with a copy to:

                     Grippo & Elden
                     Suite 3600
                     227 West Monroe Street
                     Chicago, IL  60606
                     Attn: Theodore Grippo, Esq.
                     Facsimile: 312-558-1195

                     (ii) if to EIS, to:

                     Elan International Services, Ltd.
                     Flatts, Smiths Parish
                     Bermuda, FL 04
                     Attention: Director
                     Facsimile:  441-292-2224

                     with a copy to:

                     Brock Silverstein LLC
                     800 Third Avenue, 21st Floor
                     New York, New York 10022
                     Attention: David Robbins, Esq.
                     Facsimile:  212-371-5500

or to such other address as the party to whom notice is to be given may have
furnished to the other party hereto in writing in accordance with provisions of
this Section 9.  Any such notice or communication shall be deemed to have been
effectively given (i) in the case of personal or hand delivery, on the date of
such delivery, (ii) in the case of an internationally-recognized overnight
delivery service, on the second business day after the date when sent, (iii) in
the case of mailing, on the fifth business day following that day on which the
piece of mail containing such communication is posted, and (iv) in the case of
facsimile transmission, on the date of telephone confirmation of receipt.

              SECTION 10.  ENTIRE AGREEMENT.  This Agreement and the other
Transaction Documents contain the entire understanding of the parties with
respect to the subject matter hereof and thereof and supersede all prior
agreements and understandings among the parties with respect thereto.

              SECTION 11.  AMENDMENTS.  This Agreement may not be modified or
amended, or any of the provisions hereof waived, except by written agreement of
the Company and EIS dated after the date hereof.

              SECTION 12.  COUNTERPARTS AND FACSIMILE.  The Transaction
Documents may be executed in any number of counterparts, and each such
counterpart hereof shall be deemed to be an original instrument, but all such
counterparts together shall constitute one agreement.  Each of

<PAGE>

the Transaction Documents may be signed and delivered to the other party by
facsimile transmission; such transmission shall be deemed a valid signature.

              SECTION 13.  HEADINGS.  The section and paragraph headings
contained in this Agreement are for reference purposes only and shall not affect
in any way the meaning or interpretation of the Agreement.

              SECTION 14.  GOVERNING LAW; ARBITRATION. This Agreement shall
be governed by and construed in accordance with the substantive (as opposed
to procedural) laws of the State of New York, without giving effect to
principles thereof relating to conflicts of laws. Any dispute under this
Agreement shall be settled by binding arbitration, conducted in accordance
with the Commercial Arbitration Rules of the American Arbitration Association
by one arbitrator appointed in accordance with said rules. Such arbitrator
shall be reasonably satisfactory to each of the parties hereto; provided,
that if the parties are unable to agree upon the identity of such arbitrator
within 15 days of demand by any party, then any party shall have the right to
petition  a presiding justice of the Supreme Court of New York, New York
County, to appoint an arbitrator. The arbitration shall be held in New York,
New York.  The arbitrator shall determine what discovery will be permitted,
consistent with the goal of limiting the cost and time which the parties must
expend for discovery; provided the arbitrator shall permit such discovery as
he deems necessary to permit an equitable resolution of the dispute.  Any
written evidence originally in a language other than English shall be
submitted in English translation accompanied by the original or a true copy
thereof.  The costs of the arbitration, including administrative and
arbitrator's fees, shall be shared equally by the parties and each party
shall bear its own costs and attorneys' and witness' fees incurred in
connection with the arbitration.  In rendering judgement, the arbitrator
shall be instructed by the parties that he shall be permitted to select
solely from between the proposals for  resolution of  the relevant issue
presented by each party, and not any other proposal. A disputed performance
or suspended performances pending the resolution of the arbitration must be
completed within 30 days following the final decision of the arbitrators or
such other reasonable period as the arbitrator determines in a written order.
The parties will co-operate and use  reasonable  efforts to ensure that any
arbitration any arbitration hereunder shall be completed swiftly and in any
event within one year from the filing of notice of a request for such
arbitration. The arbitration proceedings and the decision shall not be made
public without the joint consent of the parties and each party shall maintain
the confidentiality of such proceedings and decision unless otherwise
permitted by the other party.  The parties agree that the decision shall be
the sole, exclusive and binding remedy between them regarding any and all
disputes, controversies, claims and counterclaims presented to the
arbitrator. Application may be made to any court having jurisdiction over the
party (or its assets) against whom the decision is rendered for a judicial
recognition of the decision and an order of enforcement.

              SECTION 15.  EXPENSES.  Each of the parties shall be responsible
for its own costs and expenses incurred in connection with the transactions
contemplated hereby and by the other Transaction Documents.

<PAGE>

              SECTION 16.  ASSIGNMENTS AND TRANSFERS. This Agreement and all of
the provisions hereof shall be binding upon and inure to the benefit of the
parties hereto and their respective successors and permitted assigns. This
Agreement, the shares of Series A Preferred Stock and Common Stock being
purchased hereunder by EIS, the Warrant, the Note, and the shares of Common
Stock underlying the Series A Preferred Stock, the Warrant and the Note may be
transferred by EIS to its affiliates and subsidiaries, as well as any special
purpose financing or similar vehicle established by EIS, provided, however, that
EIS shall remain liable for its obligations hereunder after any such assignment.
Other than as set forth above, no party shall transfer or assign this Agreement,
the shares of Series A Preferred Stock and Common Stock being purchased
hereunder by EIS, the Warrant, the Note, and the shares of Common Stock
underlying the Series A Preferred Stock, the Warrant and the Note, or any
interest therein, without the prior written consent of the other party.

SECTION 17.  SEVERABILITY.  In case any provision of this Agreement shall be
invalid, illegal or unenforceable, the validity, legality and enforceability of
the remaining provisions shall not be in any way affected or impaired thereby.

<PAGE>

              IN WITNESS WHEREOF, each of the undersigned has duly executed this
Agreement as of the date first written above.

                                          PHOTOGEN TECHNOLOGIES, INC.


                                          By:     /s/ John Smolik
                                              ---------------------------------
                                                 Name:   John Smolik
                                                 Title:   President


                                          ELAN INTERNATIONAL SERVICES, LTD.


                                          By:       /s/ Kevin Insley
                                              ---------------------------------
                                                 Name: Kevin Insley
                                                 Title: President





Exhibits Submitted Separately

             Schedule 2(I)


[****]
______________

[****] 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.