Document:

<PAGE>

                                                                   Exhibit 10.18

THIS NOTE HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED
(THE "ACT"), OR APPLICABLE STATE LAW, AND NO INTEREST THEREIN MAY BE SOLD,
DISTRIBUTED, ASSIGNED, OFFERED, PLEDGED OR OTHERWISE TRANSFERRED EXCEPT AS
OTHERWISE SET FORTH HEREIN AND UNLESS (A) THERE IS AN EFFECTIVE REGISTRATION
STATEMENT UNDER THE ACT AND APPLICABLE STATE SECURITIES LAWS COVERING ANY SUCH
TRANSACTION, (B) THE COMPANY RECEIVES AN OPINION OF LEGAL COUNSEL FOR THE HOLDER
SATISFACTORY TO THE COMPANY STATING THAT SUCH TRANSACTION IS EXEMPT FROM
REGISTRATION OR (C) THE COMPANY OTHERWISE SATISFIES ITSELF THAT SUCH TRANSACTION
IS EXEMPT FROM REGISTRATION.

APRIL 14, 2006                                                      $15,000,000

                            IMARX THERAPEUTICS, INC.

                             SECURED PROMISSORY NOTE

     ImaRx Therapeutics, Inc., a Delaware corporation (the "COMPANY"), for value
received, promises to pay to Abbott Laboratories, an Illinois corporation
("HOLDER"), the principal sum of $15,000,000, subject to adjustment from time to
time (as adjusted from time to time, the "PRINCIPAL AMOUNT") in accordance with
the terms of this Note and that certain Asset Purchase Agreement dated as of
April 10, 2006, by and among the Company and Holder (the "ASSET PURCHASE
AGREEMENT"). Capitalized terms not defined herein shall have the meanings given
such terms in the Asset Purchase Agreement.

     The following is a statement of the rights of Holder and the conditions to
which this Note is subject, to which Holder, by the acceptance of this Note,
agrees:

     1. Principal Amount and Interest; Payment; Prepayment.

          (a) Principal Amount and Interest. Simple interest shall accrue on the
unpaid Principal Amount at the annual rate of six percent (6.0%) per annum
("INTEREST"), measured from the date set forth above. Interest will be computed
on the basis of a 365-day year. The Company will pay the Principal Amount on or
before December 31, 2007 (the "PAYMENT DATE") plus all accrued but unpaid
Interest through such date. Notwithstanding the foregoing, if an Event of
Default (as defined below) occurs, then, at the option of Holder, upon 30 days
prior written notice of default given to the Company, the unpaid Principal
Amount (as it may have been adjusted pursuant to the provisions hereof) and all
accrued and unpaid Interest thereon shall be immediately due, payable and
collectible by Holder.

          (b) Prepayment. The Company may at any time prepay in whole or in part
the Principal Amount and any accrued and unpaid Interest without penalty.

<PAGE>

          (c) Withholding. Holder acknowledges that the Company may be required
by law to withhold on payments of Interest and hereby authorizes the Company to
withhold as required by law.

          (d) Payments. All payments made hereunder shall be applied first to
accrued Interest, and thereafter to the Principal Amount. Principal and Interest
and all other amounts due hereunder (collectively, the "OBLIGATIONS") are to be
paid in lawful money of the United States of America in federal or other
immediately available funds.

     2. Security Interest. Pursuant to the terms of the Security Agreement
attached as an exhibit to the Asset Purchase Agreement (the "SECURITY
AGREEMENT"), the Company has granted a continuing, first priority security
interest to Holder in all of the Collateral (as defined in the Security
Agreement) to secure the payment of the Obligations.

     3. Transfer of Note; Restrictions on Transfer. Neither this Note nor any of
the rights, interests or obligations hereunder may be assigned in whole or in
part by the Company or Holder without the prior written consent of the other
party, which consent may not be unreasonably withheld. In addition, this Note
may be transferred only in compliance with applicable federal and state
securities laws and only upon surrender of the original Note for registration of
transfer, duly endorsed, or accompanied by a duly executed written instrument of
transfer in form satisfactory to the Company. A new Note for like Principal
Amount and Interest will be issued to, and registered in the name of, the
transferee. Interest and Principal Amount are payable only to the registered
holder of the Note.

     4. Events of Default. The term "EVENT OF DEFAULT" as used in this Note
means any of the following events:

          (a) Any breach by the Company of the obligation to pay within thirty
(30) days after the date when it is due and payable (i) any amount payable
hereunder or (ii) any amount payable under the Escrow Agreement between the
Company and the Holder of even date herewith into the Escrow Account (as defined
in the Escrow Agreement);

          (b) The Company files or is served with a petition for relief under 11
U.S.C. Section 101 et seq. or any similar federal or state statute, or an action
is commenced to appoint a receiver or trustee for all or substantially all of
the Company's property, and the Company fails to cause such proceeding to be
dismissed within ninety (90) days after it is instituted against the Company;;

          (c) The liquidation, dissolution or winding up of the Company prior to
the payment in full of all Obligations hereunder

                                      -2-

<PAGE>

          (d) The breach by the Company of any representation, warranty,
covenant or agreement in the Asset Purchase Agreement or any of the Other
Agreements (as defined in the Asset Purchase Agreement) beyond any applicable
cure period;

          (e) The entry of any judgment or order against the Company that could
reasonably be expected to have a material adverse effect on the Company's
business and which remains unsatisfied or undischarged and in effect for thirty
(30) days after such entry without a stay of enforcement or execution; or

          (f) The placement of any security interest or other lien or
encumbrance upon the Collateral which is not removed within fifteen (15) days
following notice from Holder.

     5. Effect of Event of Default. If an Event of Default described in Section
4 hereof shall occur, in addition to taking any other action permitted by law,
the Holder may, at its sole option, by written notice to the Company, declare
the Obligations hereunder immediately due and payable, without presentment,
demand, protest or further notice of any kind. The Holder may also exercise any
or all of the rights and remedies available to a secured creditor under the
Uniform Commercial Code of the applicable jurisdiction, as the same may be
amended from time to time, including without limiting the foregoing, the right
to take possession of the Collateral.

     6. Nonrecourse. This Note is a nonrecourse promissory note. Upon any
default, except as set forth in the Escrow Agreement and this Section 6,
Holder's sole recourse with respect to the Obligations under this Note shall be
to the Collateral. Holder shall have no right to recover from the Company
personally or from any of the Company's assets other than the Collateral any
deficiency with respect to the Obligations under this Note. The foregoing
limitation shall not be interpreted or construed to limit (i) the ability of
Holder to seek monetary damages from the Company with respect to any breach of
any covenant under the Security Agreement to maintain the condition of the
Collateral or (ii) the right of the Holder to the Proceeds (as defined in the
Escrow Agreement) in accordance with the provisions of the Escrow Agreement.

     7. Miscellaneous.

          (a) Remedies. The Company hereby waives notice, presentment, protest
and notice of dishonor.

          (b) Holder as Owner. The Company may deem and treat the holder of
record of this Note as the absolute owner for all purposes regardless of any
notice to the contrary.

                                      -3-

<PAGE>

          (c) No Shareholder or Ownership Rights. This Note shall not entitle
Holder to any voting rights or any other rights as a shareholder or owner of the
Company or to any other rights except the rights stated herein.

          (d) Shareholders, Affiliates, Officers and Directors Not Liable. In no
event shall any shareholder, affiliate, officer or director of the Company be
liable for any amounts due or payable pursuant to this Note.

          (e) Notices. All communications, notices and consents provided for
herein shall be in writing and be given in person or by means of telex,
facsimile or other means of wire transmission (with request for assurance of
receipt in a manner typical with respect to communications of that type), by
overnight courier or by mail, and shall become effective: (a) on delivery if
given in person; (b) on the date of transmission if sent by telex, facsimile or
other means of wire transmission; (c) one (1) business day after delivery to the
overnight service; or (d) four (4) business days after being mailed, with proper
postage and documentation, for first-class registered or certified mail,
prepaid.

     Notices shall be addressed as follows:

If to the Company, to: ImaRx Therapeutics, Inc.
                       1635 East 18th Street
                       Tucson, Arizona 85719
                       Attn: Greg Cobb
                       Facsimile Number: (520) 791-2437

       with copies to: DLA Piper Rudnick Gray Cary LLP
                       701 Fifth Avenue, Ste 700
                       Seattle, Washington 98104
                       Attn: Jeff Harmes
                       Facsimile Number: (206) 839-4801

     If to Holder, to: Abbott Laboratories
                       100 Abbott Park Road
                       Building AP6D, Department 364
                       Abbott Park, Illinois 60064-6020
                       Attn: General Counsel
                       Facsimile Number: (847) 938-6277

       with copies to: Kirkland & Ellis LLP
                       200 East Randolph Drive
                       Chicago, Illinois 60601
                       Attn: R. Scott Falk, P.C.
                       Facsimile Number: (312) 861-2200

                                      -4-

<PAGE>

provided, however, at the time of mailing or within three business days
thereafter there is or occurs a labor dispute or other event that might
reasonably be expected to disrupt the delivery of documents by mail, any
communication, notice or consent provided for herein shall be given in person or
by means of telex, facsimile or other means of wire transmission or by overnight
courier, and further provided that if any party shall have designated a
different address by notice to the others, then to the last address so
designated.

          (f) Amendments and Waivers. Any term of this Note may be amended and
the observance of any term may be waived (either generally or in a particular
instance and either retroactively or prospectively) only with the written
consent of the Company and Holder. Any amendment or waiver shall be binding on
each future Holder and the Company.

          (g) Governing Law. This Note shall be subject to the provisions of
Section 12.9 of the Asset Purchase Agreement.

          (h) Successors and Assigns. The terms and conditions of this Note
shall inure to the benefit of and be binding on the respective successors and
assigns of the parties.

          (i) Severability. If one or more provisions of this Note are held to
be unenforceable under applicable law, such provision shall be excluded from
this Note, and the balance of this Note shall be interpreted as if such
provision were so excluded and shall be enforceable in accordance with its
terms.

            [The remainder of this page is intentionally left blank.]

                                      -5-

<PAGE>

     IN WITNESS WHEREOF, the Company has caused this Secured Promissory Note to
be issued as of the date first written above.

                                        IMARX THERAPEUTICS, INC.

                                        By: /s/ Evan C. Unger
                                            ------------------------------------
                                        Name: Evan C. Unger
                                        Title: President and Chief Executive
                                               Officer

AGREED AND ACCEPTED:

ABBOTT LABORATORIES ("HOLDER")

By: /s/ Sean E. Murphy
    ----------------------------------
Name: Sean E. Murphy
Its: Vice President, Global Licensing/
     New Business Development<PAGE>
                                                                   Exhibit 10.19

                  SECOND AMENDED EXECUTIVE EMPLOYMENT AGREEMENT

      THIS SECOND AMENDED EXECUTIVE EMPLOYMENT AGREEMENT (the "Agreement") is
made and entered into as of May 15, 2006 by and between IMARX THERAPEUTICS,
INC., a Delaware corporation (the "Company"), and EVAN C. UNGER ("Executive")
and replaces the Executive Employment Agreement dated July 12, 2004 (the
"Original Agreement"), as it was previously amended on August 8, 2005 (the
"First Amended Agreement").

      WITNESSETH:

      WHEREAS, the Company desires to retain the services of Executive, and
Executive desires to be employed by the Company, on the terms and conditions of
this Agreement.

      NOW, THEREFORE, in consideration of the premises and the mutual covenants
and agreements set forth herein, the Company and Executive, intending to be
legally bound, hereby agree as follows:

      1. Employment. The Company agrees to employ Executive as President and
Chief Executive Officer of the Company, and Executive accepts such employment
and agrees to perform full-time employment services for the Company, subject to
Section 3.2 and the Fourth Amended and Restated Certificate of Incorporation and
Amended and Restated Bylaws of the Company, as amended from time to time (the
"Organizational Documents"), and the resolutions of the Board of Directors of
the Company (the "Board"), for the period and upon the other terms and
conditions set forth in this Agreement.

      2. Term. The term of Executive's employment hereunder (the "Term")
commenced upon the date of execution of the Original Agreement and shall
continue until this Agreement is terminated as set forth in Section 5 below.

      3. Position and Duties.

            3.1. Service with the Company. During the Term of this Agreement,
Executive agrees to perform the duties of the President and Chief Executive
Officer of the Company as set forth in the Organizational Documents and such
other duties as the Board may from time to time prescribe that are consistent
with the duties of a Chief Executive Officer of a company of the size and nature
of the Company. In addition, during the Term, Executive shall, if elected by the
stockholders, serve without any additional compensation on the Company's Board.
The Company agrees to nominate Executive for annual election as a member of its
Board, so long as he continues to hold the position of Chief Executive Officer.

                                       1
<PAGE>

            3.2. No Conflicting Duties. Executive hereby confirms that he is
under no contractual commitments inconsistent with his obligations set forth in
this Agreement, and that during the Term of this Agreement, he will not render
or perform services, or enter into any contract to do so, for any other
corporation, firm, entity or person that are inconsistent with the provisions of
this Agreement or Executive's fiduciary obligations to the Company. Except as
otherwise provided herein, Executive shall not serve as a director of any other
corporation (except nonprofit organizations to the extent such service does not
materially affect Executive's performance of his duties for the Company) without
the prior approval of the Board of Directors. Company acknowledges that
Executive is Professor of Radiology and Bioengineering at the University of
Arizona and furthermore approves Executive to work up to 6 days per month at the
University of Arizona (or other University) in research, administration,
teaching and/or clinical work.

      4. Compensation and Benefits.

            4.1. Base Salary. (a) As compensation for all services to be
rendered by Executive under this Agreement, the Company shall pay to Executive
during the Term an annual salary of $250,000 (the "Base Salary"). Subject to
Section 4.1(b), the Base Salary shall be reviewed at least annually and changed
at the discretion of the Board (or its Compensation Committee), provided,
however, that the Base Salary may not be decreased without the written consent
of the Executive. The Company shall pay the Base Salary to Executive in
accordance with the Company's normal payroll procedures and policies.

      (b) If Executive's Base Salary is increased at any time, it shall not
thereafter be decreased during the Term of this Agreement, unless such decrease
is the result of a general reduction (on the same percentage basis) affecting
the base salaries of all other executive officers of the Company and such
decrease does not result in a Base Salary of less than $200,000.

            4.2. Annual Bonus. With respect to each full fiscal year until the
Termination Date, Executive shall be eligible to receive an annual bonus award
of up to 50% of Base Salary, payable quarterly, as determined by annual
pre-determined milestones, the current version of which is attached as Exhibit
A, which shall be mutually agreeable to Executive and the Board (or its
Compensation Committee) in its sole discretion.

            4.3. Stock Options. (a) As of the date of the First Amended
Agreement, the Company granted (the "Original Grant") to Executive stock options
to purchase 600,000 shares of the Company's common stock (the "Shares"),
pursuant to the Company's 2000 Stock Plan (the "Plan"), generally having a term
of ten years, vesting and exercisable as hereinafter set forth, and otherwise in
the form attached hereto as Exhibit C. The Original Grant was intended, to the
extent legally permissible, to comprise "incentive stock options", with the
balance being "nonqualified stock options", and the exercise price per share was
to be based on the fair market

                                       2
<PAGE>

value of the Company's common stock at the time of grant as determined by the
Board in its good faith discretion. Subject to Executive being employed
hereunder at the time of each vesting, as applicable, the Original Grant was to
vest and become exercisable as follows: (i) 45,000 shares on each of the four
anniversary dates following July 12, 2004; and (ii) 420,000 shares according to
the milestones established in Exhibit B attached to the First Amended Agreement,
of which two milestones covering 200,000 shares have lapsed and expired and the
related 200,000 shares are not exercisable and have been returned to the Plan,
leaving a remainder of 220,000 shares subject to vesting according to Exhibit B
attached to this Agreement. After execution of the First Amended Agreement, on
December 14, 2005, the Company further granted Executive a "nonqualified stock
option" for the purchase of 65,000 shares of common stock at a price based on
the fair market value at the time of grant as determined by the Board in its
good faith discretion. As a result of the foregoing grants, vesting that has
occurred thereunder to the date of this Agreement, and the lapse of two of the
milestones described in the First Amended Agreement, the options currently held
by Executive are as follows:

<Table>
<Caption>
                    Tax                                                           Vesting Schedule       Expiration
  Grant Date     Character    No. of Shares   Exercise Price   Vesting Status      or Milestones            Date
  ----------     ---------    -------------   --------------   --------------      -------------            ----
<S>              <C>          <C>             <C>              <C>              <C>                      <C>
    8-8-05          ISO           30,303           $3.30        Fully Vested            n/a                8-8-10

                    NQO          149,697           $3.00       14,697 Vested    45,000 on 7-14 of          8-8-15
                                                                                each of 2006, 2007,
                                                                                        2008

                    NQO          220,000           $3.00         Not Vested     See Ex. B to this          8-8-15
                                                                                     Agreement

   12-14-05         NQO           65,000           $4.00         Not Vested      16,250 on 12-14 of        12-14-15
                                                                                each of 2006, 2007,
                                                                                     2008, 2009
</Table>

In addition, a portion of the unvested Options shall vest as described in
Sections 6.3 and 7 hereof. If the Company's common stock is registered under
Section 12 of the Securities Exchange Act of 1934 (the "Exchange Act"), the
Company shall use its good faith efforts to register under the Securities Act of
1933 on Form S-8 (or any successor form) all common stock issued and/or issuable
under the 2000 Stock Plan, including the Shares subject to the Original Grant
and all other stock options or incentives granted or awarded to Executive under
the 2000 Stock Plan, and its good faith efforts to qualify such common stock for
sale under such state securities or `blue sky' laws as the Company shall
determine are required to issue the shares of common stock under the 2000 Stock
Plan and for the resale of such shares by the recipients thereof, provided that
the Company shall have no obligation to qualify such stock in any particular
jurisdiction in which the Company would be required to execute a general consent
to

                                       3
<PAGE>

service of process in effecting such qualification, unless the Company is
already subject to service in such jurisdiction and except as may be required by
the Securities Act.

            4.4. Participation in Benefit Plans. Executive shall be included to
the extent eligible thereunder in any and all plans of the Company providing
general benefits for the Company's executive employees, including, without
limitation, medical, dental, vision, short and long term disability insurance,
life insurance, 401(k) plan, sick days, vacation, and holidays. Executive's
participation in any such plan or program shall be subject to the provisions,
rules, and regulations applicable thereto. In addition, during the Term of this
Agreement, Executive shall be eligible to participate in all non-qualified
deferred compensation and similar compensation, incentive, bonus, profit sharing
and stock plans offered, sponsored or established by Company on substantially
the same or a more favorable basis as any other employee of Company.

            4.5. Business Expenses. In accordance with the Company's policies
established from time to time, the Company will pay or reimburse Executive for
all reasonable and necessary out-of-pocket expenses incurred by him in the
performance of his duties under this Agreement, subject to the presentment of
appropriate supporting documentation. During the Term of this Agreement, the
Company shall at its expense provide Executive with reasonable office space and
furnishings (including without limitation desk and lap top computers) at the
Company's principal executive offices, and a cell telephone.

            4.6. Key Man Life Insurance. During the Term of this Agreement, the
Company shall have the option of purchasing and paying the premiums for a "Key
Man" life insurance policy relating to Executive in a coverage amount determined
by the Company, and the Company shall be named as the beneficiary of such
policy. Executive represents and warrants that he currently is insurable for
such policy on an unrated basis and agrees to fully cooperate with the Company
in obtaining the policy.

      5. Termination.

            5.1. Disability. At the Company's election, Executive's employment
and this Agreement shall terminate upon Executive's becoming totally or
permanently disabled for a period of ninety (90) days or more in any twelve (12)
month period. For purposes of this Agreement, the term "totally or permanently
disabled" or "total or permanent disability" means Executive's inability on
account of sickness or accident, whether or not job-related, to engage in
regularly or to perform adequately his assigned duties under this Agreement and
Executive is qualified and eligible to receive disability benefits under the
disability policies maintained by the Company for Executive.

            5.2. Death of Executive. Executive's employment and this Agreement
shall terminate immediately upon the death of Executive.

                                       4
<PAGE>

            5.3. Termination for Cause. The Company may terminate Executive's
employment and this Agreement at any time for "Cause" (as hereinafter defined)
immediately upon written notice to Executive. As used herein, the term "Cause"
shall mean that Executive shall have (i) been convicted of a felony; or (ii)
committed a single act of fraud, embezzlement, or breach of trust, or (iii)
committed an act of willful misconduct or gross negligence resulting in a
material loss to the Company, or (iv) materially violated any material written
Company policy or rules of the Company, unless cured by Executive within 30 days
following written notice thereof to Executive, or (v) refused to follow the
reasonable written directions given by the Board or its designee or materially
breached any covenant or obligation under this Agreement or other agreement with
the Company, unless cured by Executive within 30 days following written notice
thereof to Executive.

            5.4. Resignation. Executive's employment and this Agreement shall
terminate on the earlier of the date that is one (1) month following the written
submission of Executive's resignation to the Company or the date such
resignation is accepted by the Company.

            5.5. Termination Without Cause. The Company may terminate
Executive's employment and this Agreement without cause upon written notice to
Executive. Termination "without cause" shall mean termination of employment on
any basis (including no reason or no cause) other than termination of
Executive's employment hereunder pursuant to Sections 5.1, 5.2, 5.3, or 5.4.

            5.6. Surrender of Records and Property. Upon termination of his
employment with the Company, Executive shall deliver promptly to the Company all
credit cards, computer equipment, cellular telephone, records, manuals, books,
blank forms, documents, letters, memoranda, notes, notebooks, reports, data,
tables, calculations or copies thereof, that are the property of the Company and
that relate in any way to the business, strategies, products, practices,
processes, policies or techniques of the Company, and all other property, trade
secrets and confidential information of the Company, including, but not limited
to, all documents that in whole or in part contain any trade secrets or
confidential information of the Company that in any of these cases are in his
possession or under his control, and Executive shall also remove all such
information from any personal computers that he owns or controls.

      6. Compensation Upon the Termination of Executive's Employment.

            6.1. In the event that Executive's employment and this Agreement are
terminated pursuant to Section 5.1 (Disability), 5.3 (Cause), or 5.4
(Resignation), then Executive shall be entitled to receive Executive's then
current Base Salary through the date his employment is terminated, and such
other amounts that accrued prior to the termination date and are required to be
paid to him pursuant to any employee benefit plan in accordance with such plan
and/or by law, but no other compensation of any kind or amount.

                                       5
<PAGE>

            6.2. In the event Executive's employment and this Agreement are
terminated pursuant to Section 5.2 (Death), Executive's beneficiary or a
beneficiary designated by Executive in writing to the Company, or in the absence
of such beneficiary, Executive's estate, shall be entitled to receive
Executive's then current Base Salary through the end of the month in which his
death occurs, and such other amounts that accrued prior to the termination date
and are required to be paid to him pursuant to any employee benefit plan in
accordance with such plan and/or by law, but no other compensation of any kind
or amount.

            6.3. Unless Section 7 applies, in the event Executive's employment
and this Agreement are terminated by the Company pursuant to Section 5.5
(Without Cause) or by Executive for "Good Reason" (as defined below), (A) the
Company shall pay to Executive, as a severance allowance, his then current
monthly Base Salary for the six (6) month period following the date of
termination, paid on the Company's regular paydays throughout that 6-month
period, followed by a one-time lump sum payment (the "Lump Sum Payment") on the
next regular payday of an amount equal to six months of his then current monthly
Base Salary (i.e. one-half of his annual Base Salary), for a total severance
allowance equal to one (1) year of his Base Salary, and such other salary that
accrued prior to the termination date and amounts required to be paid to him
pursuant to any employee benefit plan in accordance with such plan and/or by
law; and (B) Executive shall receive accelerated vesting for twelve (12) months
from the date of Executive's termination for all stock options granted by the
Company to Executive before or after the Commencement Date and extension of the
option exercise period for an additional twelve (12) months beyond the period
set forth in Exhibit C attached hereto for such exercise, provided, however,
that such stock options shall not be extended beyond the date on which they
would have terminated had Executive continued to be employed by the Company; but
no other compensation or benefits of any kind. Executive shall be entitled to
receive these benefits and payments only if he complies with his continuing
obligations to the Company as set forth in this Agreement, provided, however,
that the Company shall not deny any such benefits unless it has provided written
notice to Executive of any claimed breach of such continuing obligations and
Executive has failed to cure each such breach within fifteen days after receipt
of such written notice of breach and the exercise period of any such options
shall be tolled during such fifteen (15) day period or any longer period
required to resolve any disputed claim of breach of such continuing obligations,
and provided, further, that the foregoing shall not limit Executive's ability to
exercise any such options that had vested prior to the date of termination of
his employment which he exercises within ninety (90) days after such termination
date.

            6.4. The provisions of Section 6 shall not affect Executive's
participation in or terminating distributions and vested rights under, any
pension, profit sharing, insurance or other employee benefit plan of the Company
to which Executive is entitled pursuant to the terms of such plans.

                                       6
<PAGE>

      7. Change in Control. In the event a Change in Control (as defined below)
occurs and, in the six month periods preceding or following the Change in
Control, Executive's employment and this Agreement are terminated by the Company
or its successor, assigns or transferee pursuant to Section 5.5 (Without Cause)
or by Executive for "Good Reason" (as defined below), then the Company shall,
within thirty (30) days after occurrence of the last of these conditions (the
"Trigger Date"), pay Executive a lump sum amount equal to one hundred percent
(100%) of Executive's then current annual Base Salary (less applicable
withholdings). In addition, one hundred percent (100%) of Executive's unvested
options (whether granted before or after the Commencement Date) as of the
Trigger Date, shall automatically vest as of the Trigger Date and the exercise
period for all such stock options shall be extended an additional twelve (12)
months.

            7.1. Definition of Change in Control. For purposes of this
Agreement, a "Change in Control" shall be deemed to have occurred if, at any
time during the Term, any of the following events occurs:

                  7.1.1. if the Company does not have a class of securities
registered under Section 12 of the Securities Exchange Act of 1934, as amended
(the "Exchange Act"):

                        7.1.1.1. any person, as that term is used in Section
                  13(d) and Section 14(d)(2) of the Exchange Act, becomes a
                  beneficial owner (as defined in Rule 13d-3 under the Exchange
                  Act or any successor rule or regulation), directly or
                  indirectly, of securities of the Company representing 50% or
                  more of the combined voting power of the Company's then
                  outstanding Voting Stock, as defined below, provided, however,
                  that for purposes of this paragraph, the term "person" shall
                  exclude (A) a trustee or other fiduciary holding securities
                  under an employee benefit plan of the Company or any of its
                  subsidiaries, (B) a person who beneficially owns 25% or more
                  of the Company's outstanding Voting Stock on the Effective
                  Date, or (C) any person who becomes such a beneficial owner in
                  connection with the Company's financing.

                        7.1.1.2. the Company is merged, consolidated or
                  reorganized into or with another corporation or other legal
                  person (an "Acquiring Person") or securities of the Company
                  are exchanged for securities of an Acquiring Person, and as a
                  result of such merger, consolidation, reorganization or
                  exchange less than a majority of the combined voting power of
                  the then outstanding securities of the Acquiring Person
                  immediately after such transaction are held, directly or
                  indirectly, in the aggregate by the holders of securities
                  entitled to vote generally in the election of directors
                  ("Voting Stock") of the Company immediately prior to such
                  transaction;

                                       7
<PAGE>

                        7.1.1.3. the Company, in any transaction or series of
                  related transactions, sells or otherwise transfers, directly
                  or indirectly, all or substantially all of its assets, on a
                  consolidated basis, to an Acquiring Person, and less than a
                  majority of the combined voting power of the then outstanding
                  securities of the Acquiring Person immediately after such sale
                  or transfer are held, directly or indirectly, in the aggregate
                  by the holders of Voting Stock of the Company immediately
                  prior to such sale or transfer; or

                        7.1.1.4. during any period of two consecutive years,
                  commencing upon the closing of the Company's private placement
                  financing and the appointment of the Board of Directors in
                  connection therewith, individuals who at the beginning of any
                  such period constitute the directors of the Company cease for
                  any reason to constitute at least a majority thereof, unless
                  the election, or the nomination for election by the Company's
                  stockholders, of each director of the Company first elected
                  during such period was approved by at least a majority vote of
                  the directors of the Company then still in office who were
                  directors of the Company at the beginning of any such period;

                     OR

                        7.1.2. if the Company has a class of securities
registered under Section 12 of the Exchange Act:

                        7.1.2.1. any person, as that term is used in Section
                  13(d) and Section 14(d)(2) of the Exchange Act, becomes, is
                  discovered to be, or files a report on Schedule 13D or 14D-1
                  (or any successor schedule, form or report) disclosing that
                  such person is, a beneficial owner (as defined in Rule 13d-3
                  under the Exchange Act or any successor rule or regulation),
                  directly or indirectly, of securities of the Company
                  representing 25% or more of the combined voting power of the
                  Company's then outstanding Voting Stock, provided, however,
                  that for purposes of this paragraph, the term "person" shall
                  exclude (A) a trustee or other fiduciary holding securities
                  under an employee benefit plan of the Company or any of its
                  subsidiaries, (B) a person who becomes such a beneficial owner
                  in connection with the Company's initial public offering of
                  common stock or (C) any person who was a shareholder of the
                  Company immediately prior to the Company's initial public
                  offering of common stock; OR

                        7.1.2.2. any of the events described in Sections
                  7.1.1.2, 7.1.1.3 or 7.1.1.4 (the latter being modified to
                  refer to such a change of a majority of the Board of Directors
                  during any one year period).

                                       8
<PAGE>

Notwithstanding the foregoing, a transaction shall not constitute a Change in
Control if its sole purpose is to change the state of the Company's
incorporation or to create a holding company that will be owned in substantially
the same proportions by the persons who held the Company's securities
immediately before such transaction.

            7.2. Definition of Good Reason. As used in this Agreement, "Good
Reason" means any of the following: (i) a material reduction in Executive's
title, status, authority, or responsibility at the Company, including without
limitation the failure of Executive to be elected to the Board of Directors of
the Company during the Term for any reason other than termination of Executive's
employment pursuant to Section 5.3; or (ii) a material reduction in the benefits
in effect for the Executive, and comparable reductions have not been made in the
benefit of the other members of senior management of the Company; or (iii)
except with Executive's prior written consent, relocation of Executive's
principal place of employment to a location more than 25 miles from the
Company's executive offices in Tucson, Arizona; or (iv) ) any breach by the
Company of its material obligations under this Agreement unless such breach is
cured within 30 days after written notice of breach from Executive.

      8. Release. As a condition precedent to the Company's obligation to
provide Executive with the amounts set forth in Section 6.3 or Section 7,
Executive must first execute and deliver to the Company a mutual legal release
in the form attached hereto as Exhibit B, with such changes as the Company deems
necessary in order to maintain the breadth of such release in the event of
changes in applicable laws, rules or regulations, it being the intent of the
parties that the release be as broad as possible.

      9. Ventures. If, during the Term of this Agreement, Executive is engaged
in or associated with the planning or implementing of any project, program, or
venture involving the Company and a third party or parties, all rights in the
project, program, or venture shall belong to the Company and shall constitute a
corporate opportunity belonging exclusively to the Company. Except as approved
in writing by the Board, Executive shall not be entitled to any interest in such
project, program, or venture or to any commission, finder's fee, or other
compensation in connection therewith other than the Base Salary to be paid to
Executive as provided in this Agreement.

      10. Restrictions.

            10.1. Definitions. For purposes of this Agreement, the following
terms shall have the following meanings:

                  10.1.1. "Trade Secrets" means information that is not
generally known about the Company or its business, including without limitation
about its products, recipes, projects, designs, developmental or experimental
work, computer programs, data bases, know-how, processes, business partners,
manufacturers, customers, suppliers, business plans,

                                       9
<PAGE>

marketing plans and strategies, financial or personnel information, and
information obtained from third parties under confidentiality agreements. "Trade
Secrets" also means formulas, patterns, compilations, programs, devices,
methods, techniques, or processes that derive independent economic value, actual
or potential, from not being generally known to the public or to other persons
who can obtain economic value from its disclosure or use, and is the subject of
efforts that are reasonable under the circumstances to maintain its secrecy. In
particular, the parties agree and acknowledge that the following list, which is
not exhaustive and is to be broadly construed, enumerates some of the Company's
Trade Secrets, the disclosure of which would be wrongful and would cause
irreparable injury to the Company: (i) pharmaceutical manufacturing; (ii)
formulation technology; (iii) pricing information; (iv) product development,
marketing, sales, customer, manufacturer and supplier information related to any
Company product or service available commercially or in any stage of development
during Executive's employment with the Company; and (v) Company marketing and
business strategies, ideas, and concepts. Executive acknowledges that the
Company's Trade Secrets were and are designed and developed by the Company at
great expense and over lengthy periods of time, are secret, confidential, and
unique, and constitute the exclusive property of the Company.

                      10.1.2. "Restricted Field" means the business of
developing, manufacturing, licensing and selling (i) treatments for vascular
thrombosis comprising thrombolytic drugs, or bubbles and ultrasound, or any
combination thereof, and (ii) oxygen delivery with bubbles or fluorocarbon
emulsions.

                  10.1.3. "Non-Competition Period" means a period of 12 months
after the termination of Executive's employment with the Company unless a court
of competent jurisdiction determines that that Period is unenforceable under
applicable law because it is too long, in which case the Non-Competition Period
shall be for the longest of the following periods that the court determines is
reasonable under the circumstances: 11 months, 10 months, 9 months, 8 months, 7
months, or 6 months after the termination of Executive's employment with the
Company.

                  10.1.4. "Business Territory" means the entire United States,
unless a court of competent jurisdiction determines that that geographic scope
is unenforceable under applicable law because it is too broad, in which case the
Business Territory shall be amended by eliminating geographical areas and states
from the following list until the Business Territory is determined to be
reasonable: Alabama, Alaska, Arizona, Arkansas, California, Colorado,
Connecticut, Delaware, District of Columbia, Florida, Georgia, Hawaii, Idaho,
Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland,
Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska,
Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North
Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina,
South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, Washington,
District of Columbia, West Virginia, Wisconsin, Wyoming, Pima County, Arizona,
Maricopa County, Arizona, Tucson, Arizona, Phoenix, Arizona. The parties
acknowledge and

                                       10
<PAGE>

agree that if any of the geographic areas or States listed above are required by
law to be eliminated, it would be fair and appropriate to do so in the inverse
order of the volume of revenue received or projected to be received by the
Company from such area or State at the time of determination.

                  10.1.5. "Non-Solicitation Period" means a period of 12 months
after the termination of Executive's employment with the Company.

            10.2. Non-Disclosure Obligations. Executive shall not at any time
during the period specified in Section 4.A. of the Invention and Confidential
Information Agreement attached hereto as Exhibit C, without the express written
consent of an officer of the Company, publish, disclose, or divulge to any
person, firm or corporation, or use directly or indirectly for the Executive's
own benefit or for the benefit of any person, firm, corporation or entity other
than the Company, any Trade Secrets of the Company.

            10.3. Non-Competition Obligations. Executive acknowledges the
substantial amount of time, money, and effort that the Company has spent and
will spend in developing its products and other strategically important
information (including Trade Secrets), and agrees that during Executive's
employment with the Company hereunder and during the Non-Competition Period,
Executive will not, alone or with others, directly or indirectly, as an
employee, agent, consultant, advisor, owner, manager, lender, officer, director,
employee, partner, stockholder, or otherwise, engage in any Restricted Field
activities in the Business Territory, nor have any such relationship with any
person or entity that engages in Restricted Field activities in the Business
Territory; provided, however, that nothing in this Agreement will prohibit
Executive from owning a passive investment of less than one percent of the
outstanding equity securities of any company listed on any national securities
exchange or traded actively in any national over-the-counter market so long as
Executive has no other relationship with such company in violation of this
Agreement. The Non-Competition Period set forth in this Section 10.3 shall be
tolled during any period in which the Executive is in breach of the restriction
set forth in this Section 10.3.

            10.4. Agreement Not to Solicit Customers. Executive agrees that
during Executive's employment with the Company hereunder and during the
Non-Solicitation Period, Executive will not, either directly or indirectly, on
Executive's own behalf or in the service or on behalf of others, solicit,
divert, or appropriate, or attempt to solicit, divert, or appropriate, to any
business that engages in Restricted Field activities in the Business Territory
(i) any person or entity whose account with the Company was sold or serviced by
or under the supervision of Executive during the twelve (12) months preceding
the termination of such employment, or (ii) any person or entity whose account
with the Company has been directly solicited at least twice by the Company
within the year preceding the termination of Executive's employment (the
"Customers"). The Non-Solicitation Period set forth in this Section 10.4 shall
be tolled during any period in which the Executive is in breach of the
restriction set forth in this Section 10.4.

                                       11
<PAGE>

            10.5. Agreement Not to Solicit Employees. Executive agrees that
during Executive's employment with the Company hereunder and during the
Non-Solicitation Period, Executive will not, either directly or indirectly, on
Executive's own behalf or in the service or on the behalf of others solicit,
divert, or hire away, or attempt to solicit, divert, or hire away any person
then employed by the Company, nor encourage anyone to leave the Company's
employ. The Non-Solicitation Period set forth in this Section 10.5 shall be
tolled during any period in which the Executive is in breach of the restriction
set forth in this Section 10.5.

            10.6. Defamatory Statements. Executive agrees that during
Executive's employment with the Company hereunder and thereafter, he will not,
either directly or indirectly, defame the reputation, character, or image of the
Company or its products, services, employees, directors, or officers.

            10.7. Reasonableness. Executive and the Company agree that the
covenants set forth in this Agreement are appropriate and reasonable when
considered in light of the nature and extent of the Company's business.
Executive further acknowledges and agrees that (i) the Company has a legitimate
interest in protecting the Company's business activities and its current,
pending, and potential Trade Secrets; (ii) the covenants set forth herein are
not oppressive to Executive and contain reasonable limitations as to time,
scope, geographical area, and activity; (iii) the covenants do not harm in any
manner whatsoever the public interest; (iv) Executive's chosen profession,
trade, or business is in manufacturing, developing, and marketing pharmaceutical
drugs, products and devices (the "Profession") (v) the Restricted Field is only
a very small or limited part of the Profession, and Executive can work in many
different jobs in Executive's Profession besides those in the Restricted Field;
(vi) the covenants set forth herein do not completely restrain Executive from
working in Executive's Profession, and Executive can earn a livelihood in
Executive's Profession without violating any of the covenants set forth herein;
(vii) Executive has received and will receive substantial consideration for
agreeing to such covenants, including without limitation the consideration to be
received by Executive under this Agreement; (viii) if Executive were to work for
a competing company that engages in activities in the Restricted Field, there
would be a substantial risk that Executive would inevitably disclose Trade
Secrets to that company; (ix) the Company competes with other companies that
engage in Restricted Field Activities in the Business Territory, and if
Executive were to engage in prohibited activities in the Restricted Field within
the Business Territory, it would harm the Company; (x) the Company expends
considerable resources on hiring, training, and retaining its employees and if
Executive were to engage in prohibited activities during the Non-Solicitation
Period, it would harm the Company; and (xi) the Company expends considerable
resources acquiring, servicing, and retaining its Customers and if Executive
were to engage in prohibited activities during the Non-Solicitation Period, it
would harm the Company.

      11. Other Agreements. Executive reaffirms Executive's obligations set
forth in the Invention and Confidential Information Agreement attached hereto as
Exhibit C, which

                                       12
<PAGE>

Executive has executed and delivered herewith. Executive further acknowledges
and agrees that he will comply with all other Company policies and procedures.

      12. Assignment. This Agreement shall not be assignable, in whole or in
part, by either party without the written consent of the other party, except
that the Company may, without the consent of Executive, assign its rights and
obligations under this Agreement to any corporation, firm or other business
entity (i) with or into which the Company may merge or consolidate, (ii) to
which the Company may sell or transfer all or substantially all of its assets or
(iii) of which at least a majority of the equity investment and of the voting
control is owned, directly or indirectly, by, or is under common ownership with,
the Company. Upon such assignment by the Company, the Company shall attempt to
obtain the assignees' written agreement enforceable by Executive to assume and
perform, from and after the date of such assignment, the terms, conditions, and
provisions imposed by this Agreement upon the Company.

      13. Other Provisions.

            13.1. Governing Law. This Agreement is made under and shall be
governed by and construed in accordance with the laws of the State of Arizona
without reference to conflicts of law provisions thereof.

            13.2. Injunctive Relief. Executive agrees that it would be difficult
to compensate the Company fully for damages for any violation of the provisions
of this Agreement. Accordingly, Executive specifically agrees that the Company
shall be entitled to temporary and permanent injunctive relief to enforce the
provisions of this Agreement. This provision with respect to injunctive relief
shall not, however, diminish the right of the Company to claim and recover
damages in addition to injunctive relief.

            13.3. Prior Agreements. This Agreement and its exhibits contain the
entire agreement of the parties relating to the subject matter hereof and
supersedes all prior agreements and understandings with respect to such subject
matter, including prior option agreements relative thereto, and the parties
hereto have made no agreements, representations, or warranties relating to the
subject matter of this Agreement which are not set forth herein.

            13.4. Withholding Taxes and Right of Offset. The Company may
withhold from all payments and benefits under this Agreement all federal, state,
city, or other taxes as shall be required pursuant to any law or governmental
regulation or ruling. Executive agrees that the Company may offset any payments
owed to Executive pursuant to this Agreement by any amounts owed by Executive to
the Company.

            13.5. Amendments. No amendment or modification of this Agreement
shall be deemed effective unless made in writing signed by Executive and the
Company.

                                       13
<PAGE>

            13.6. No Waiver. No term or condition of this Agreement shall be
deemed to have been waived nor shall there be any estoppel to enforce any
provisions of this Agreement, except by a statement in writing signed by the
party against whom enforcement of the waiver or estoppel is sought. Any written
waiver shall not be deemed a continuing waiver unless specifically stated, shall
operate only as to the specific term or condition waived, and shall not
constitute a waiver of such term or condition for the future or as to any act
other than that specifically waived.

            13.7. Severability. To the extent any provision of this Agreement
shall be invalid or unenforceable, it shall be considered deleted from this
Agreement and the remainder of such provision and of this Agreement shall be
unaffected and shall continue in full force and effect.

            13.8. Indemnification. Executive shall be entitled as an officer and
director to be indemnified by the Company under the Organizational Documents, as
set forth therein, and to receive the benefits, if any, of any director and
officer liability insurance obtained by the Company in its discretion from time
to time, subject to the terms, provisions and conditions of any such insurance.

            13.9. Headings. The headings in this Agreement are included solely
for reference purposes and shall not be considered in the interpretation or
construction of this Agreement.

            13.10. Notices. All notices, requests, demands and other
communications under this Agreement shall be in writing and shall be delivered
personally, by overnight courier or similar means, by United States certified or
registered mail, return receipt requested, postage prepaid, or sent by facsimile
transmission with written confirmation of receipt, at the addresses specified
below or such other addresses as the parties may designate by like notice. Any
such notice shall be effective upon receipt if delivered personally, by
overnight courier or by United States certified or registered mail, or on the
next business day following transmittal if sent by facsimile transmission.

         IF TO THE COMPANY:         ImaRx Therapeutics, Inc.
                                    1635 East 18th Street
                                    Tucson, AZ  85719
                                    Attn:  Chairman of the Board
                                    Telephone:  520-770-1259
                                    Facsimile:   520-791-2437

                                       14
<PAGE>

         COPY TO:                   DLA Piper
                                    701 Fifth Ave., Suite 7000
                                    Seattle, Washington 98104
                                    Attn:  John M. Steel, Esq.
                                    Telephone:  (206) 839-4800
                                    Facsimile:   (206) 839-4801

         IF TO EXECUTIVE:           Evan C. Unger, MD
                                    6227 E. Miramar Dr.
                                    Tucson, AZ 85719
                                    Telephone (520) 298-9234
                                    Facsimile (520) 298-9254

            13.11. No Mitigation Obligation. It will be difficult, and may be
impossible, for Executive to find reasonably comparable employment following the
termination of Executive's employment with the Company, and the noncompetition
covenant contained in Section 10.1 hereof will further limit the employment
opportunities for Executive. Accordingly, the parties hereto expressly agree
that the payments provided for in Section 6.3 and Section 7 by the Company to
Executive will be liquidated damages, and that Executive shall not be required
to seek other employment, or otherwise, to mitigate any payment provided for
hereunder.

            13.12. Remedies Cumulative. Remedies under this Agreement of either
party hereto are in addition to any remedy or remedies to which such party is
entitled or may become entitled at law or in equity.

            13.13. Attorneys' Fees. In the event suit is brought to enforce the
terms of this Agreement or to collect any moneys due hereunder, or to collect
money damages for breach hereof, the prevailing party shall be entitled to
recover, in addition to any other remedy, reimbursement for reasonable
attorneys' fees, court costs, costs of investigation and other related expenses
incurred in connection therewith.

            13.14. Counterparts. This Agreement may be executed in any number of
counterparts, all such counterparts shall be deemed to constitute one and the
same instrument, and each of said counterparts shall be deemed an original
hereof.

            13.15. Survivability. Sections 4.3, 6, 7, 8, 10 and 13 of this
Agreement shall survive the termination of this Agreement and the termination of
Executive's employment with the Company.

                                       15
<PAGE>

      IN WITNESS WHEREOF, the parties have executed this Agreement as of the day
and year first set forth above.

                             "COMPANY":       IMARX THERAPEUTICS, INC.

                                              ----------------------------------
                                              By: /s/ Greg Cobb
                                                 -------------------------------
                                              Name: Greg Cobb
                                                   -----------------------------
                                              Title: Chief Financial Officer
                                                    ----------------------------

                             "EXECUTIVE":     /s/ Evan C. Unger
                                              ----------------------------------
                                              EVAN C. UNGER

                                       16

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