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                                                                    EXHIBIT 10.4

                                                               EXECUTION VERSION

                         STOCKHOLDERS SUPPORT AGREEMENT

            STOCKHOLDERS SUPPORT AGREEMENT, dated as of March 18, 2005 (this
"Stockholders Agreement"), among SIEMENS MEDICAL SOLUTIONS USA, INC., a Delaware
corporation ("Parent"), MI MERGER Co., a Delaware corporation and a wholly owned
subsidiary of Parent ("Purchaser"), and each of the stockholders whose names
appear on the signature pages of this Stockholders Agreement (each, a
"Stockholder" and, collectively, the "Stockholders").

            WHEREAS, as of the date hereof each Stockholder owns of record and
beneficially and has good, valid and marketable title to, free and clear of any
Lien, proxy, voting restriction, limitation on disposition, adverse claim of
ownership or use or encumbrance of any kind, other than pursuant to this
Stockholders Agreement, and has the sole power to vote and full right, power and
authority to sell, transfer and deliver, the number of shares of common stock,
par value $0.01 per share ("Company Common Stock"), of CTI Molecular Imaging,
Inc., a Delaware corporation (the "Company"), as set forth opposite such
Stockholder's name on Exhibit A hereto (all such shares of Company Common Stock
and any shares of Company Common Stock of which ownership of record or the power
to vote is hereafter acquired by any of the Stockholders prior to the
termination of this Stockholders Agreement being referred to herein as the
"Shares"); and

            WHEREAS, Parent, Purchaser and the Company propose to enter into,
simultaneously herewith, an Agreement and Plan of Merger (the "Merger
Agreement"; except as otherwise noted herein, terms used but not defined in this
Stockholders Agreement shall have the meanings ascribed to them in the Merger
Agreement), a draft of which has been made available to each Stockholder, which
provides, upon the terms and subject to the conditions thereof, for the merger
of Purchaser with and into the Company (the "Merger") following the consummation
of a cash tender offer by Purchaser to acquire all the issued and outstanding
shares of Company Common Stock (the "Offer").

            NOW, THEREFORE, in consideration of the foregoing and the mutual
covenants and agreements contained herein and in the Merger Agreement, and
intending to be legally bound hereby, the Stockholders hereby agree as follows:

            1. Tender of Shares. Each Stockholder hereby agrees that such
Stockholder (a) shall tender, or cause to be tendered, in the Offer, as promptly
as practicable, but in any event no later than five business days after the date
of commencement of the Offer, all of his or its Shares pursuant to the terms of
the Offer and (b) shall neither withdraw, nor cause to be withdrawn, such
Shares.

            2. Grant of Proxy. Each Stockholder, by this Stockholders Agreement,
with respect to his or its Shares, hereby grants an irrevocable proxy to Parent
(and agrees to execute such documents or certificates evidencing such proxy as
Parent may reasonably request) to vote, at any meeting of the stockholders of
the Company, and in any action by written consent of the

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stockholders of the Company, all of such Stockholder's Shares (a) in favor of
the approval and adoption of the Merger Agreement and approval of the Merger and
all other transactions contemplated by the Merger Agreement and this
Stockholders Agreement, (b) against any action, agreement or transaction (other
than the Merger Agreement or the transactions contemplated thereby) or proposal
(including any Competing Transaction) that would result in a breach of any
covenant, representation or warranty or any other obligation or agreement of the
Company under the Merger Agreement or that could result in any of the conditions
to the Company's obligations under the Merger Agreement not being fulfilled, and
(c) in favor of any other matter necessary to the consummation of the
transactions contemplated by the Merger Agreement and considered and voted upon
by the stockholders of the Company. Each Stockholder further agrees to cause
such Stockholder's Shares to be voted in accordance with the foregoing. THIS
PROXY IS IRREVOCABLE AND COUPLED WITH AN INTEREST. Each Stockholder hereby
acknowledges receipt and review of a copy of the Merger Agreement.

            3. Transfer of Shares. Each Stockholder agrees that he or it shall
not, directly or indirectly, (a) sell, assign, transfer (including by operation
of law), lien, pledge, dispose of or otherwise encumber any of the Shares or
otherwise agree to do any of the foregoing, (b) deposit any Shares into a voting
trust or enter into a voting agreement or arrangement or grant any proxy or
power of attorney with respect thereto that is inconsistent with this
Stockholders Agreement, (c) enter into any contract, option or other arrangement
or undertaking with respect to the direct or indirect acquisition or sale,
assignment, transfer (including by operation of law) or other disposition of any
Shares or (d) take any action that would make any representation or warranty of
such Stockholder herein untrue or incorrect in any material respect or have the
effect of preventing or disabling the Stockholder from performing his or its
obligations hereunder.

            4. No Solicitation of Transactions. None of the Stockholders shall,
directly or indirectly, through any agent or otherwise, (a) solicit, initiate or
encourage (including by way of furnishing nonpublic information), or take any
other action to facilitate, any inquiries or the making of any proposal or offer
(including, without limitation, any proposal or offer to any other stockholders
of the Company) that constitutes, or may reasonably be expected to lead to, any
Competing Transaction, or (b) enter into or maintain or continue discussions or
negotiations with any person in furtherance of such inquiries or to obtain a
proposal or offer for a Competing Transaction, or (c) agree to, approve, endorse
or recommend any Competing Transaction or enter into any letter of intent or
other contract, agreement or commitment contemplating or otherwise relating to
any Competing Transaction; provided, however, that nothing in this Section 4
shall prevent any Stockholder, in his capacity as a director or executive
officer of the Company from engaging in any activity permitted pursuant to
Section 6.05(b) or Section 6.05(c) of the Merger Agreement. Each Stockholder
shall, and shall direct or cause his or its representatives and agents to,
immediately cease and cause to be terminated all existing discussions or
negotiations with any parties conducted heretofore with respect to a Competing
Transaction. Each Stockholder shall notify Parent as promptly as practicable
(and in any event within one day after such Stockholder attains knowledge
thereof), orally and in writing, if any proposal or offer, or any inquiry or
contact with any person with respect thereto, regarding a Competing Transaction
is made, specifying the material terms and conditions thereof and the identity
of the party making such proposal or offer or inquiry or contact (including
material amendments or proposed material amendments).

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            5. Information for Offer Documents and Proxy Statement; Disclosure.
Each Stockholder represents and warrants to Parent and Purchaser that none of
the information relating to such Stockholder and his or its affiliates provided
by or on behalf of such Stockholder or his or its affiliates for inclusion in
the Schedule TO, Schedule 14D-9, Offer Documents, or Proxy Statement will, at
the respective times the Schedule TO, Schedule 14D-9, Offer Documents, or Proxy
Statement are filed with the SEC or are first published, sent or given to
stockholders of the Company, contain any untrue statement of material fact or
omit to state any 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. Each Stockholder authorizes and agrees to permit
Parent and Purchaser to publish and disclose in the Offer Documents and the
Proxy Statement and related filings under the securities laws such Stockholder's
identity and ownership of Shares and the nature of his or its commitments,
arrangements and understandings under this Agreement and any other information
required by applicable Law.

            6. Termination. The obligations of each Stockholder under this
Stockholders Agreement shall terminate upon the termination of the Merger
Agreement pursuant to Section 8.01 of the Merger Agreement. Nothing in this
Section 6 shall relieve any party of liability for any breach of this
Stockholders Agreement.

            7. Non-Competition/Non-Solicitation Agreement. (a) During the period
beginning at the Effective Time and ending on the third anniversary thereof, no
Stockholder shall, and shall not permit any of his or its agents (collectively,
the "Stockholder Parties") to, directly or indirectly, as principal for their
own account or jointly with others, or as an equity holder in any person, engage
in, distribute products for, or own, manage, operate, or control, or participate
in the ownership, management or control of, or have (or acquire) an interest in
or assets of, any person, enterprise or business that engages in:

            (i) the design, development, manufacture, assembly, distribution or
      sale of any (A) positron emission tomographs, including non-human animal
      positron emission tomographs, (either standalone or in combination with
      any other modalities, such as computed tomography, magnetic resonance, or
      near-infrared imaging or designed for dual modality imaging
      simultaneously) or components (including software, tools, procedures and
      protocols) for the assembly of, incorporation into or use with any
      positron emission tomographs (either standalone or in combination with any
      other modalities, such as computed tomography, magnetic resonance, or
      near-infrared imaging or designed for dual modality imaging
      simultaneously), including, without limitation, probes for the detection
      of positron emitters, ring tomographs (emission computerized axial
      tomography image devices) and other positron imaging devices; (B) positron
      emission tomography biomarkers, tracers, compounds, precursor agents or
      other positron emission tomography radiopharmaceuticals or (C) cyclotrons,
      cyclotron target, chemistry boxes, microfluidic chips or related tools and
      equipment used for the production of positron emission tomography
      radiopharmaceuticals and radionuclides that can be used for positron
      emission tomography;

            (ii) the design, development, manufacture, assembly, distribution or
      sale of detector materials for use in the items described in clause (i)(A)
      above;

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            (iii) the design, development, manufacture, assembly, distribution
      or sale of radioactive sources used for calibration and quality control
      and/or attenuation correction of positron emission tomographs;

            (iv) the design, development, manufacture, assembly, distribution or
      sale of computer workstations and software for the creation, display and
      analysis of molecular images;

            (v) internet hosting services to connect physicians,
      radiopharmacies, patients and positron emission tomography providers; or

            (vi) the provision of services, including, without limitation,
      technical services, training services, maintenance and repair services,
      site planning and installation services, radioactive materials licensing,
      and application services with respect to any of the foregoing (all of the
      businesses referred to in clauses (i) through (vi), inclusive, the
      "Restricted Business");

            provided, however, that the foregoing shall not prohibit any
Stockholder Party from being the passive owner of not more than 5% of any class
of capital stock of any person which is publicly traded on a national securities
exchange or in the over-the-counter market in the United States or on a foreign
securities exchange.

            (b) Each of the Stockholders agrees that for a period of three years
from the Effective Time, he or it shall not, and shall cause his or its
respective Stockholder Parties not to, in any manner, directly or indirectly,
(i) induce or attempt to induce any individual that has been an employee of the
Company at any time between October 1, 2004 and the Effective Time, to leave the
employ of the Company or to violate the terms of his or her contract, or any
employment arrangements, with the Company, (ii) except in response to a good
faith request by a person that has not been an employee with the Company since
October 1, 2004 for a recommendation regarding the employment qualifications of
such employee, recommend to any other person that they employ any such employee,
(iii) interfere with or attempt to interfere with any officers, employees,
representatives or agents of the Company, or (iv) hire any such employee, unless
such employee has not been an employee of the Company at least for a period of
eighteen consecutive months.

            (c) Each of the Stockholders agrees that for a period of three years
from the Effective Time, such Stockholder shall not, and shall cause his or its
respective Stockholder Parties not to, in any manner, directly or indirectly,
(i) solicit the business, with respect to the provision of products or services
provided by the Company to such person, of any person known by such Stockholder
to be a customer of the Company or seek to induce any such person to reduce or
refrain from doing business with any of Parent, Purchaser, the Company or any of
their respective affiliates, or (ii) disparage (including by relative
comparison) Parent, Purchaser, the Company or any of their respective affiliates
or any of their respective products or activities in the Restricted Business.

            (d) Each Stockholder hereby acknowledges that this Section 7
constitutes an independent covenant and shall not be affected by performance or
nonperformance of any other

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provision of this Stockholders Agreement by any party hereto. Each Stockholder
hereby acknowledges that the covenants of each Stockholder set forth in this
Section 7 are an essential element of this Stockholders Agreement and an
inducement for Parent and Purchaser to enter the Merger Agreement and that, but
for the agreement of each Stockholder to comply with these covenants, neither
Parent nor Purchaser would have entered into the Merger Agreement. Each party
hereto agrees that money damages would be an inadequate remedy for any breach of
this Section 7. Therefore, in the event of a breach or threatened breach of this
Section 7, Parent, Purchaser and/or any Surviving Corporation may, in addition
to other rights and remedies existing in its favor, apply to any court of
competent jurisdiction for specific performance and/or injunctive or other
relief in order to enforce, or prevent any violations of, the provisions
thereof. Each Stockholder hereby acknowledges that such Stockholder has
independently consulted with counsel and after such consultation agrees that the
covenants set forth in this Section 7 are intended to be reasonable and proper
in scope, duration and geographical area and in all other respects. If any such
covenant is found to be invalid, void or unenforceable in any situation in any
jurisdiction by a final determination of a court or any other Governmental
Authority of competent jurisdiction, each Stockholder, Parent and Purchaser
agree that: (i) such determination shall not affect the validity or
enforceability of (A) the offending term or provision in any other situation or
in any other jurisdiction or (B) the remaining terms and provisions of this
Section 7 in any situation in any jurisdiction; (ii) the offending term or
provision shall be reformed rather than voided and the court or Governmental
Authority making such determination shall have the power to reduce the scope,
duration or geographical area of any invalid or unenforceable term or provision,
to delete specific words or phrases, or to replace any invalid or enforceable
term or provision with a term or provision that is valid and enforceable and
that comes closest to expressing the intention of the invalid or unenforceable
provision, in order to render the restrictive covenants set forth in this
Section 7 enforceable to the fullest extent permitted by applicable Law; and
(iii) the restrictive covenants set forth in this Section 7 shall be enforceable
as so modified.

            (e) Notwithstanding the termination of this Stockholders Agreement
for any reason, and irrespective of the time, manner or cause of termination, if
Purchaser purchases shares pursuant to the Offer, the Stockholders' obligations
under this Section 7 shall survive and remain in full force and effect for the
periods therein provided, and the provisions for equitable relief against each
of the Stockholders shall continue in full force and effect.

            (f) In the event of any apparent or actual conflicts or
inconsistencies between or among the terms of this Section 7 and the terms of
that certain Employment Agreement, dated as of June 30, 2004, by and between CTI
Molecular Imaging, Inc. and Robert E. Nutt (the "Employment Agreement"), the
specific terms of this Stockholders Agreement shall prevail and govern over the
terms of any such other agreement.

            8. Representations and Warranties of Stockholder. Each Stockholder
hereby represents and warrants, jointly and severally, to Parent and Purchaser
as follows:

            (a) (i) Each Stockholder that is an individual has full legal right
and capacity to execute and deliver this Stockholder Agreement, to perform his
obligations hereunder and to consummate the transactions contemplated hereby,
and (ii) each Stockholder that is not an individual is duly organized, or
formed, as applicable, validly existing and in good standing

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under the laws of its jurisdiction of organization or formation, as applicable,
has the requisite power and authority to carry on its business as it is now
being conducted and has all necessary power and authority to execute and deliver
this Stockholders Agreement, to perform its obligations hereunder and to
consummate the transactions contemplated hereby. This Agreement has been duly
executed and delivered by each Stockholder and, assuming the due authorization,
execution and delivery by Parent and Purchaser, constitutes the legal, valid and
binding obligation of such Stockholder, enforceable against such Stockholder in
accordance with its terms. The failure of a Stockholder's spouse, if any, to be
a party or signatory to this Stockholder Agreement shall not (A) prevent such
Stockholder from performing such Stockholder's obligations and consummating the
transactions contemplated hereunder or (B) prevent this Stockholder Agreement
from constituting the legal, valid and binding obligation of such Stockholder,
enforceable against such Stockholder in accordance with its terms.

            (b) The execution and delivery of this Stockholder Agreement by each
Stockholder do not, and the performance of this Stockholder Agreement by such
Stockholder will not (i) conflict with or violate any organizational or
formation document of any Stockholder, (ii) assuming that all consents,
approvals, authorizations and other actions described in Section 8(d) have been
obtained and all filings and obligations described in Section 8(d) have been
made, conflict with or violate any law, rule, regulation, order, judgment or
decree applicable to any Stockholder or by which any property or asset of any
Stockholder is bound or affected, (iii) result in any breach of or constitute a
default (or an event which, with notice or lapse of time or both, would become a
default) under, or give to others any right of termination, amendment,
acceleration or cancellation of, or result in the creation of a Lien or other
encumbrance on the Shares or any other property or asset of any Stockholder
pursuant to, any note, bond, mortgage, indenture, contract, agreement, lease,
license, permit, franchise or other instrument or obligation or (iv) violate any
applicable Law.

            (c) Each Stockholder owns of record and beneficially and has good,
valid and marketable title to, free and clear of any Lien, proxy, voting
restriction, limitation on disposition, adverse claim of ownership or use or
encumbrance of any kind, other than pursuant to this Stockholder Agreement, and
has the sole power to vote and full right, power and authority to sell, transfer
and deliver, the Shares (as set forth on Exhibit A).

            (d) The execution and delivery by any Stockholder of this
Stockholders Agreement do not, and the performance by Parent and Purchaser of
this Stockholders Agreement, will not, require any consent, approval,
authorization or permit of, or filing with or notification to, any Governmental
Authority.

            (e) Each Stockholder has had access, prior to the execution of this
Stockholder Agreement, to the information he or it felt he or it needed and
desired in connection with his or its evaluation of this Stockholder Agreement
and the Merger Agreement and the transactions contemplated hereby and thereby
and has had, prior to the execution of this Stockholder Agreement, the
opportunity to ask questions of, and receive answers from, the Company and legal
counsel concerning the terms and conditions of the transactions contemplated by
this Stockholder Agreement and the Merger Agreement and to obtain additional
information necessary to assess the transactions contemplated hereby and
thereby.

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            9. Representations and Warranties of Stockholder's Spouse. The
spouse of Robert E. Nutt (the "Spouse") hereby represents and warrants to Parent
and Purchaser as follows: (a) the Spouse shall not assert or enforce, and does
hereby waive, any rights granted under any community property statute with
respect to the Shares held by Robert E. Nutt that would adversely affect the
covenants made by Robert E. Nutt pursuant to this Stockholders Agreement or the
sale and transfer of such Shares to Parent or Purchaser pursuant to the terms of
this Stockholders Agreement; provided, however, that the Spouse shall not be
prohibited from asserting any rights the Spouse may have against the
consideration received by Robert E. Nutt in exchange for such Shares; (b) the
Spouse hereby acknowledges receipt and review of a copy of the Merger Agreement
and this Stockholders Agreement.

            10. Miscellaneous. Except as otherwise provided herein, all costs
and expenses incurred in connection with this Stockholders Agreement and the
transactions contemplated hereby shall be paid by the party incurring such costs
and expenses, whether or not the transactions contemplated hereby are
consummated; all notices, requests, claims, demands and other communications
hereunder shall be in writing and shall be given (and shall be deemed to have
been duly given upon receipt) by delivery in person, by telecopy or e-mail or by
registered or certified mail (postage prepaid, return receipt requested) to the
respective parties at their addresses as specified on the signature page(s) of
this Stockholders Agreement; if any term or other provision of this Stockholders
Agreement is invalid, illegal or incapable of being enforced by any rule of law
or public policy, all other conditions and provisions of this Stockholders
Agreement shall nevertheless remain in full force and effect so long as the
economic or legal substance of the transactions contemplated hereby is not
affected in any manner materially adverse to any party; this Stockholders
Agreement and the Merger Agreement constitute the entire agreement among the
parties with respect to the subject matter hereof and supersede all prior
agreements and undertakings, both written and oral, among the parties, or any of
them, with respect to the subject matter hereof; this Stockholders Agreement
shall not be assigned (whether pursuant to a merger, by operation of law or
otherwise), except that Parent may assign all or any of its rights and
obligations hereunder to any affiliate of Parent and Parent may assign all or
any of its rights under Section 7 of this Stockholders Agreement to any person
who purchases any or all of the assets or business units of the Company or the
Subsidiaries; provided that no such assignment shall relieve Parent of its
obligations hereunder if such assignee does not perform such obligations; this
Stockholders Agreement shall be binding upon and inure solely to the benefit of
each party hereto, and nothing in this Stockholders Agreement, express or
implied, is intended to or shall confer upon any other person any right, benefit
or remedy of any nature whatsoever under or by reason of this Stockholders
Agreement; the parties hereto agree that irreparable damage would occur in the
event any provision of this Stockholders Agreement was not performed in
accordance with the terms hereof and that the parties shall be entitled to
specific performance of the terms hereof, in addition to any other remedy at law
or in equity; this Stockholders Agreement shall be governed by, and construed in
accordance with, the laws of the State of New York applicable to contracts
executed in and to be performed in that State; this Stockholders Agreement may
be executed and delivered (including by facsimile transmission) in one or more
counterparts, and by the different parties hereto in separate counterparts, each
of which when executed shall be deemed to be an original but all of which taken
together shall constitute one and the same agreement; from time to time, at the
request of Parent, in the case of any Stockholder, or at the request of the
Stockholders, in the case of Parent and Purchaser, and without further
consideration, each party shall execute and deliver or cause to be executed and

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delivered such additional documents and instruments and take all such further
action as may be reasonably necessary or desirable to consummate the
transactions contemplated by this Stockholders Agreement; EACH OF THE PARTIES
HERETO HEREBY WAIVES TO THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW ANY RIGHT
IT MAY HAVE TO A TRIAL BY JURY WITH RESPECT TO ANY LITIGATION DIRECTLY OR
INDIRECTLY ARISING OUT OF, UNDER OR IN CONNECTION WITH THIS STOCKHOLDERS
AGREEMENT OR THE TRANSACTIONS CONTEMPLATED HEREBY.

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            IN WITNESS WHEREOF, the parties have executed, or have caused to be
executed, this Stockholders Agreement as of the date first written above.

                                             SIEMENS MEDICAL SOLUTIONS USA, INC.

                                             /s/ Dr. Hermann Requardt
                                             -------------------------------
                                             Name: Dr. Hermann Requardt
                                             Title: Executive Vice President
                                             Address: Heukestr. 127
                                                   D-91050 Erlangen

                                             /s/ James R. Ruger
                                             -------------------------------
                                             Name: James R. Ruger
                                             Title: Corporate Secretary
                                             Address: 51 Valley Stream Pky.
                                                    Malvern, PA 19355

                                             MI MERGER CO.

                                             /s/ Dr. Hermann Requardt
                                             -------------------------------
                                             Name: Dr. Hermann Requardt
                                             Title: Executive Vice President
                                             Address: Heukestr. 127
                                                    D-91050 Erlangen

                                             /s/ James R. Ruger
                                             -------------------------------
                                             Name: James R. Ruger
                                             Title: Corporate Secretary
                                             Address: 51 Valley Stream Pky.
                                                    Malvern, PA 19355

<PAGE>

                                             /s/ Robert E. Nutt
                                             -------------------------------
                                             Robert E. Nutt
                                             Address:

                                             ROBERT E. NUTT IRREVOCABLE TRUST
                                             By: Danielle C. Nutt, Trustee

                                             /s/ Danielle C. Nutt
                                             -------------------------------
                                             Address:

<PAGE>

                                                                       EXHIBIT A

                              LIST OF STOCKHOLDERS

<TABLE>
<CAPTION>
                                                 Number of Shares of Company
                                                    Common Stock Owned
       Name of Stockholder                       Beneficially and of Record
       -------------------                       ---------------------------
<S>                                              <C>
         Robert E. Nutt                                    123,486
Robert E. Nutt Irrevocable Trust                           263,745
</TABLE><PAGE>

                                                                   EXHIBIT 10.5

                               AMENDMENT NO. 1 TO

                           CHANGE IN CONTROL AGREEMENT

                  THIS AMENDMENT NO. 1 TO CHANGE IN CONTROL AGREEMENT (this
Amendment") is made and entered into as of March 18, 2005, by and between CTI
Molecular Imaging, Inc. (the "Company") and R. Gregory Brophy ("Executive") and
amends that certain Change in Control Agreement, dated as of December 17, 2002,
by and between the Company and Executive (the "Agreement").

                                    PREAMBLE:

                  WHEREAS, pursuant to Section 13(a) thereof, the Agreement may
be amended or modified only by a written agreement executed by the parties
thereto or their respective successors and legal representatives; and

                  WHEREAS, the Board of Directors of the Company (the "Board")
has determined that it is in the best interests of the Company and its
stockholders to amend the Agreement in further pursuit of obtaining the
assurance that the Company will have the continued dedication of Executive,
notwithstanding the possibility, threat or occurrence of a Change of Control of
the Company;

                  NOW, THEREFORE, in consideration of the agreements set forth
herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties agree as follows:

                  1.       The Agreement is amended by amending and restating
the last sentence in Section 13(f) in its entirety as follows:

                  "(f)     Except as otherwise provided herein, from and after
         the Effective Date, this Agreement shall supersede any other agreement
         between the parties with respect to the subject matter hereof."

                  2.       Section 13 of the Agreement is amended by renumbering
         it as Section 14.

                  3.       Section 13 of the Agreement is amended by adding the
         following:

                  "13.     Effect on Letter Agreement

                  Effective as of the Effective Date, the provisions of the
         Letter Agreement dated as of August 2, 2002, by and between the Company
         and the Executive relating to the Executive's competition and
         solicitation restrictions shall apply."

                  4.       This Amendment may be executed in two or more
counterparts, each of which shall be deemed an original, but all of which
together shall constitute one and the same instrument.

                                       1
<PAGE>

                  5.       Capitalized terms used but not defined in this
Amendment shall have the meaning assigned to them in the Agreement.

                  6.       Regardless of any conflict of law or choice of law
principles that might otherwise apply, the parties agree that this Amendment
shall be governed by and construed in all respects in accordance with the laws
of the State of Delaware.

                  7.       Except as specifically set forth in this Amendment,
the Agreement shall remain in full force and effect.

                  IN WITNESS WHEREOF, the Company and Executive have caused this
Amendment to be duly executed and delivered, as of the day and year first above
written.

                                         EXECUTIVE:

                                         By: /s/ R. Gregory Brophy
                                             ----------------------------------
                                             R. Gregory Brophy

                                         THE COMPANY:

                                         CTI MOLECULAR IMAGING, INC.

                                         By: /s/ Ronald Nutt, Ph.D.
                                             ----------------------------------
                                             Name: Ronald Nutt, Ph.D.
                                             Title: President & CEO

                                       2

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