<PAGE>
                                                                   EXHIBIT 10.13



                            MASTER PURCHASE AGREEMENT


         This Agreement effective as of this first day of September 1999, by and
between CTI PET SYSTEMS, INC., a Tennessee Corporation with offices at 810
Innovation Drive, Knoxville, TN 37932-2571, USA (hereinafter "Buyer") and
PHOTONIS with offices at Avenue Roger Roncier, BP520, 19106 BRIVE Cedex, FRANCE
(hereinafter "Seller").

                                   WITNESSETH:

         WHEREAS, Buyer desires to purchase and Seller desires to sell certain
products either distributed by or for Seller or designated or manufactured by or
for the Seller as of the date hereof, or developed for manufacture or sale by or
for Seller in the future, and all supplies and services necessary in relation
hereto as set forth herein.

         NOW, THEREFORE, in consideration of the foregoing and the mutual
covenants and agreements set forth herein, the parties agree as follows:

1.       EFFECTIVE DATE AND CONTRACT TERM.

         This Agreement shall be effective on the day and year first above
         written and shall continue until September 1, 2004.

         1.1.     SUPERCESSION OF PREVIOUS AGREEMENT.

                  None.

         1.2.     PRODUCTS

                  Subject to the terms and conditions hereof, Buyer from time to
                  time may purchase and Seller agrees to sell such products as
                  are identified in Exhibit A attached hereto.

         1.3.     SPECIFICATIONS FOR PRODUCTS.

                  All products supplied by Seller here under shall be furnished
                  in accordance with all terms and conditions of this agreement,
                  as well as all specifications set forth in Exhibit A attached
                  hereto or any subsequent engineering change orders relating
                  thereto and approved by Buyer consistent with the terms and
                  conditions of the Agreement.

2.       PURCHASE OF PRODUCTS.

         2.1.     EXCLUSIVE METHOD.

                  No products shall be purchased or sold by virtue of execution
                  of this Agreement alone, but shall require the issuance of one
                  or more purchase orders by the Buyer's Purchasing Department.
                  Such purchase orders shall reference this Agreement and shall
                  make it a part thereof.




<PAGE>

         2.2.     DELIVERY DATE.

                  On each purchase order submitted to Seller, Buyer shall
                  specify one or more delivery dates. The parties shall agree on
                  such delivery dates in advance of Buyer's issuance of such
                  purchase orders. Seller agrees to ship all products ordered
                  here under, so that such products will be delivered to Buyer's
                  specified location on the delivery dates specified in Buyer's
                  purchase orders indicated as PTA (Promised to Arrive Date -
                  (-5, +2 days)). Delivery shall not be accelerated or delayed
                  by Seller without the prior written consent of Buyer's
                  Purchasing Department.

         2.2.1    LATE DELIVERY

                  If Seller fails to meet the scheduled date of delivery and
                  such failure is not cured within ten (10) business days, Buyer
                  may, in lieu of actual damages, require Seller to pay to Buyer
                  as liquidated damages the amount of one percent (1 %) of the
                  value of the delayed order for each calendar day of delay, up
                  to a maximum aggregated payment per order of ten percent (10
                  %) of the value of the delayed order.

                  If more than fifty percent (50%) of PMTs delivered during one
                  calendar quarter are more than ten (10) business days late in
                  meeting the scheduled PTA, then, notwithstanding the above
                  liquidated damages, Buyer may elect to:

                  1.       cancel, the order(s) experiencing the delay as well
                           as any other pending order(s).

                  2.       terminate this Agreement for Default,

                  3.       claim for damages suffered.

3.       PRICE AND PAYMENT TERMS.

         3.1.     PRICES

                  Prices for the products are set forth in Exhibit "B" of this
                  Agreement.

         3.2.     NO ADDITIONAL CHARGES

                  Unless otherwise expressly provided herein, Buyer shall not be
                  responsible for any additional charges of any kind, unless
                  Buyer's Purchasing Department specifically agrees in writing
                  and in advance to incur liability for any such additional
                  charges.




                                       2
<PAGE>


         3.3.     INVOICING AND PAYMENT

                  Seller will issue an invoice for each shipment on or after the
                  day of shipment. Each invoice shall reference the applicable
                  Purchase Order number. Invoices shall be mailed to: CTI Inc.,
                  Accounts Payable Department, 810 Innovation Drive, Knoxville,
                  TN 37932.

                  Unless otherwise agreed in writing, all payments due hereunder
                  shall be due net (30) thirty days from invoice date.

                  Credits due to rejection of product within 30 days of receipt,
                  or discrepancies on payment shall be deducted from subsequent
                  payments.

4.       SCHEDULING AND RESCHEDULING OF ORDERS

         4.1.     PROCEDURE.

                  The Buyer will purchase PMTs from the Seller upon
                  qualification of the product over the period set by this
                  contract (see Exhibit B). These tubes will be released under
                  separate purchase orders according to this Master Purchase
                  Agreement. Buyer reserves the option to reschedule quantities
                  of any products on order. Buyer shall give Seller sixty (60)
                  days written notice prior to the Promise to Arrive Date (PTA).

5.       LIMITATIONS OF LIABILITY.

         5.1.a. SELLER WILL NOT UNDER ANY CIRCUMSTANCES, WHETHER AS A RESULT OF
         BREACH OF CONTRACT, BREACH OF WARRANTY, TORT OR OTHERWISE BE LIABLE FOR
         CONSEQUENTIAL, INCIDENTAL, SPECIAL, OR EXEMPLARY DAMAGES INCLUDED, BUT
         NOT LIMITED TO, LOSS OF PROFITS OR REVENUES, LOSS OF USE OR DAMAGE TO
         ANY ASSOCIATED EQUIPMENT, COST OF CAPITAL, COST OF SUBSTITUTE PRODUCTS,
         FACILITIES OR SERVICES, DOWNTIME COSTS, OR CLAIMS OF BUYER'S CUSTOMERS.

         5.1.b. SELLER'S LIABILITY ON ANY CLAIM OF ANY KIND FOR ANY LOSS OR
         DAMAGE ARISING OUT OF, RESULTING FROM, OR CONCERNING ANY ASPECT OF THIS
         AGREEMENT OR FROM THE GOODS OR SERVICES FURNISHED TO BUYER SHALL NOT
         EXCEED THE PRICE OF THE SPECIFIC PRODUCT WHICH GIVES RISE TO THE CLAIM.

         5.1.c. SELLER WILL NOT BE SUBJECTED TO ANY LIABILITY, WHETHER IN
         CONTRACT, WARRANTY, TORT OR OTHERWISE, ON ANY CLAIM FOR LOSS OR DAMAGE
         CONCERNING PRODUCTS, PARTS, ADVICE, ASSISTANCE OR SERVICE WHICH SELLER




                                       3
<PAGE>

         FURNISHED TO BUYER AS A BUSINESS COURTESY, BUT ARE NOT REQUIRED HERE
         UNDER.

         5.1.d. THE WARRANTIES AND REMEDIES SET FORTH HEREIN DO NOT APPLY TO
         GOODS WHICH HAVE BEEN MISUSED, INADEQUATELY MAINTAINED OR STORED, OR
         INCORRECTLY OR NEGLIGENTLY INSTALLED OR SERVICED.

         5.2. IN NO EVENT SHALL BUYER BE LIABLE FOR ANTICIPATED PROFITS
         INDIRECT, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES. BUYERS
         LIABILITY ON ANY CLAIM OF ANY KIND FOR ANY LOSS OR DAMAGE ARISING OUT
         OF THIS AGREEMENT OR ANY PERFORMANCE HERE UNDER, SHALL IN NO CASE
         EXCEED THE PRICE ALLOCABLE TO THE GOODS OR SERVICES OR UNIT THEREOF
         WHICH GIVES RISE TO THE CLAIM.

6.       CHANGES

         6.1.     BUYER CHANGES.

                  Upon written notice to Seller, Buyer from time to time may
                  direct changes in design specifications, or manufacturing
                  processes relating to any order for product(s) placed
                  thereunder. Within 30 days of receipt of Buyer's change
                  notice, Seller shall deliver to Buyer a quotation (or a
                  request for an extension beyond 30 days) detailing the impact
                  of such change, if any, on price, lead-times, and ability to
                  manufacture the product (s). Buyer retains the right to accept
                  or reject any such quotation. Rejection of any such quotation
                  shall have the effect of suspending Buyer's change notice. All
                  quotations required of Seller under this paragraph 6.1 shall
                  include only those net cost increases made necessary because
                  of Buyer's changes. All cost savings resulting from buyer's
                  changes shall be shared equally by Buyer and Seller for 12
                  months. After 12 months all cost savings resulting from
                  Buyer's changes will be passed on to the Buyer.

         6.2.     SELLER CHANGES.

                  Seller hereby represents and warrants that it shall not change
                  the design of the product(s) affecting form, fit, function,
                  spares, specifications, or manufacturing processes specified
                  with respect to the manufacture of any product(s), which
                  changes shall or may have an adverse impact on the
                  manufacturing or performance specifications for the
                  product(s), without the prior written consent of the
                  Purchasing Department of Buyer.

         6.3      NEW PRODUCTS

                  If Seller starts marketing new generation products which are
                  to replace products hereunder, Buyer shall have the right to
                  either





                                       4
<PAGE>

                  replace products by such new products or add such new products
                  to this Agreement

7.       SHIPPING

                  All prices are DDP Shipping Point. Seller shall ensure product
                  is shipped on a timely basis to meet all Promise to Arrive
                  commitments. Should Seller fail to ship on said basis, Seller
                  shall bear the cost of all premium freight required to meet
                  Buyer's immediate delivery requirements.

8.       WARRANTY.

                  Seller's Standard Warranty applies. See Exhibit C.

         8.1.     TERMS OF WARRANTY.

                  The warranty period for newly manufactured items shall extend
                  fifteen (15) months from the actual date of delivery or twelve
                  (12) months from the date of installation at Buyer's customer,
                  whichever is earlier. All warranty periods identified in this
                  Paragraph 8.1 shall be suspended in the event of downtime
                  caused by or relating to defects in the products or component
                  parts thereof and such warranty periods shall resume only upon
                  repair or replacement of such products or component parts
                  thereof. Suspension of the warranty period will only become
                  effective upon return of the defective item to Seller.

         8.2.     INVENTORY.

                  Seller agrees to maintain a target minimum finished goods
                  inventory of 3 weeks for the product identified in Exhibit A
                  based on the forecasted delivery rate at that time. Such
                  material may be used to temporarily replace defective product
                  or to support accelerated production requirements. The amount
                  so quoted is a target, which Seller will use reasonable
                  efforts to meet. Failure to meet these targets during any
                  period of the contract shall not constitute a basis for
                  termination of contract.

9.       PATENT AND OTHER PROPRIETARY RIGHTS INDEMNIFICATION.

         Seller will defend, indemnify and hold Buyer and its customers harmless
         against all liability and expenses arising from actual or claimed
         infringement of any domestic or foreign patent, trademark copyright or
         other rights, misappropriation of trade secrets or breach of
         confidential relationship with respect to the goods or services covered
         by this Agreement. If use of product sold here under is enjoined as a
         result of any claimed infringement, Seller will, without in any way
         limiting the foregoing, and at its expense,

                  (a) procure for Buyer the right to continue using the product;
         or,



                                       5
<PAGE>


                  (b) replace or modify the product so that it becomes
         non-infringing; or

                  (c) remove the product and refund the Buyer all monies paid
         therefore and release Buyer from any further liability under this
         Agreement.

         To the extent that the items ordered are manufactured to designs,
         drawings and specifications or instructions furnished by Buyer, Buyer
         agrees to indemnify and hold the Seller harmless from any expense,
         loss, cost, damage or liability of any kind which may be incurred
         because of any infringement or alleged infringement of domestic and
         foreign patent rights with respect to such items of the use of such
         items in combination with other items and to defend, as its own cost
         and expense, any action or claim in which such infringement is alleged.
         Buyer shall promptly notify Seller of any such action and shall provide
         Seller an opportunity, at Seller's option, to participate in any
         defense of such action or claim at Seller's own expense. The terms of
         this section shall survive the termination of this Agreement for a
         period of ten (10) years.

10.      INDEMNITIES.

         10.1.    INDEMNITY.  (Products and Completed Operations).

                  Seller agrees to indemnify, hold harmless and defend Buyer,
                  its successors and assigns for all losses, claims, and defense
                  costs for injury, death, or property damage to the extent
                  caused by the negligence or strict liability of Seller in the
                  manufacture or design of products supplied to Buyer's selling
                  chain. The terms of this paragraph shall survive the
                  expiration or termination of this Agreement.

         10.2.    INDEMNITY.  (Products and Completed Operations).

                  Buyer agrees to indemnify, hold harmless and defend Seller,
                  its successors and assigns for all losses, claims, and defense
                  costs for injury, death, or property damage to the extent
                  caused by the negligence or strict liability of Buyer in the
                  manufacture or design of products supplied to Buyer's selling
                  chain. The terms of this paragraph shall survive the
                  expiration or termination of this Agreement.

11.      TERMINATION.

         Each of the following events shall constitute a default hereunder and
         either party may terminate this Agreement if the other Party defaults
         in any obligation hereunder for a period of 30 days following written
         notice and failure to correct that default;

                  1.) Files a voluntary petition in bankruptcy, which is not
                  discharged within 90 days;




                                       6
<PAGE>

                  2.) Is adjudged bankrupt;

                  3.) Has a court assume jurisdiction of its assets under a
                  Federal Reorganization Act;

                  4.) Has a trustee or receiver appointed by court for all or a
                  substantial portion of its assets;

                  5.) Becomes insolvent or suspends business; or

                  6.) Makes an assignment of its assets for the benefit of its
                  creditors.

                  Buyer may by 90 days written notice of default to Seller
                  terminate this Agreement, or any purchase order placed here
                  under, if Seller:

                  1.) consistently fails to deliver in accordance with the
                  delivery dates specified in any order placed hereunder, or

                  2.) consistently fails to replace or correct defective or
                  non-conforming product in accordance with the terms and
                  requirements of this Agreement, or

                  3.) consistently fails to perform any of the other significant
                  obligations of this Agreement, and does not correct such
                  failure within a commercially reasonable time after receipt of
                  written notice from Buyer specifying such failure. Said notice
                  shall include a reasonably detailed description of any such
                  failures.

                  4.) Failure by Seller to meet required FDA Good Manufacturing
                  Practices may constitute cause for default if Seller does not
                  implement mutually agreed upon and verified corrective action
                  within a reasonable amount of time (30 days unless otherwise
                  agreed to by the parties).

12.      SPARE AND REPLACEMENT PARTS.

         12.1.    AVAILABILITY OF PARTS.

                  For a period of two (2) years from the date of the last
                  delivery of products under this Agreement, Seller shall
                  maintain in inventory a sufficient stock of spare and
                  replacement parts and accessories to permit complete, prompt,
                  competent and efficient repair and maintenance of the
                  products. In the event Seller or its suppliers, or both,
                  should stop doing business or should terminate the manufacture
                  or distribution of such components, subassemblies, spare
                  parts, or replacement parts, Seller will notify Buyer with 12
                  months notice of termination or obsolescence of the product
                  and offer the Buyer the right to make a reasonable all-time
                  final purchase.

         12.2.    DELIVERY OF SPARE AND REPLACEMENT PARTS.

                  Seller shall fill Buyer's orders for spare and replacement
                  parts and shall ship the same to Buyer within ten (10) working
                  days of receiving Buyer's order. In the event Seller is unable
                  to ship





                                       7
<PAGE>

                  ten (10) working days, both parties shall mutually agree to
                  negotiate new ship dates.

         12.3.    MAINTENANCE AND REPAIR.

                  Repairs and replacements provided by Seller are to be
                  completed by Seller and returned to Buyer within forty (40)
                  working days of receipt of product by Seller.

         12.3.    REPAIRS/REVISION LEVEL.

                  All Seller repairs will be completed to the revision level
                  currently on order unless that revision level makes the part
                  incompatible with lower revision. Any questions associated
                  with revisions will be addressed in writing to the Buyer's
                  representative as shown in section 17.

13.      QUALITY ASSURANCE

                  It is understood and agreed that the quality of all items to
                  be delivered under Buyer's Purchase Orders shall be in
                  conformance with the standards set forth in Buyer's product
                  specifications. Seller is responsible, and will ensure that
                  all Products conform to such quality standards. Buyer retains
                  the right to inspect items to be purchased hereunder to assure
                  conformance with such Product specification.

                  Seller shall have and maintain ISO 9001 certification and
                  agrees to notify Buyer promptly (within 15 calendar days) and
                  in writing in the event of any change in Seller's status as it
                  relates to quality assurance such as, but not limited to, ISO
                  certification, FDA audit, or items of a similar nature.

                  All work performed in conjunction with this Agreement shall be
                  in compliance with the most current and relevant ISO 9001 as
                  it pertains to suppliers. Specifically that (a) Seller
                  documents and is able to verify that it follows its own
                  manufacturing, test, and inspection processes; (b) that any
                  discrepancies to these processes are identified, corrected,
                  and verified; (c) that all required manufacturing test and
                  inspection records, complaints, RMAs, corrective actions, and
                  variance reports are retained for a minimum of 10 years and
                  made readily available to Buyer for review during that period;
                  (d) that all manufacturing test and inspection equipment is
                  maintained properly and calibrated as required; and (e) that
                  the manufacturing, test, and inspection processes are adequate
                  to ensure that all product specifications provided by Buyer
                  are met. Seller's Quality Assurance shall maintain compliance
                  of final production through vigilant monitoring of all phases
                  of production.




                                       8
<PAGE>

                  Seller shall utilize statistical process control (SPC)
                  throughout the production cycle as verification of process
                  control. The resultant data shall be made available to Buyer
                  upon request.

                  During Seller's performance of any Purchase Order or contract
                  which incorporates this Agreement, Seller agrees to allow and
                  to cooperate with Buyer to periodically review, verify, and
                  perform analysis of Seller's quality control and assurance
                  systems and manufacturing processes for the purpose of
                  confirming compliance to the ISO 9001.

                  Workmanship standards, in order of precedence, shall be: (1)
                  Buyer product specifications and purchase order; (2) Seller
                  specifications, (3) Seller workmanship standards.

                  Seller agrees to notify Buyer promptly and in writing if
                  Seller determines or has any reason to believe it has
                  delivered a defective product to Buyer and to identify that
                  product to the maximum practical extent.

                  In case of a serial defect in PMTs, Seller shall, at Buyer's
                  option, be obliged either to supply new PMTs free of such
                  serial defect or refund the full purchase price paid for such
                  defective PMTs. A serial defect shall be presumed if more than
                  five percent (5%) of the PMTs supplied under a single purchase
                  order show the same defect. In this case, the Buyer may elect
                  to return the entire lot to Seller for evaluation and
                  appropriate action(s). Notwithstanding the foregoing, if
                  Seller is unable to timely remedy the serial defect, by
                  supplying PMTs free of such defect, Buyer may terminate this
                  Agreement as per Section 11.

                  ANSI/ASQC Z1.4-1993 shall apply where sample auditing is
                  performed.

                  Seller is expected to deliver products with acceptance rates
                  of 99% or better. It is understood that there will be a
                  learning curve on new products; however, higher reject rates
                  will not be tolerated in the long term.

                  Seller shall conduct inspection and testing of the completed
                  product to assure compliance with all Buyer specifications.
                  Seller shall maintain inspection and test data for a minimum
                  period of 10 years.

                  Seller shall provide a Certificate of Conformance (C of C)
                  with each delivery, which includes the serial number of each
                  product in the shipment. The C of C shall warrant that the
                  product was produced in accordance with Seller's ISO 9001
                  Quality System, and that all






                                       9
<PAGE>

                  Purchase Order requirements and Product Specifications have
                  been met. The C of C shall be signed by appropriate
                  individuals and dated.

                  At some point the Buyer may choose to "validate" the Seller
                  for a particular product. This internal process consists of
                  having the Seller submit a certain quantity of certified
                  product and verifying that all specifications have been met
                  and all documentation is in order. Once a product/supplier is
                  validated, that product is received directly into CPS
                  production with no incoming inspection required. It is
                  imperative that all incoming products and documentation are
                  100% correct for every shipment. Buyer's decision not to
                  inspect or test product at incoming does not release the
                  Seller of its responsibilities to deliver conforming product.
                  Seller is responsible for nonconforming product found in
                  process, at point of consumption, or at higher levels of
                  product completion.

14.      FORCE MAJEURE.

                  Force Majeure shall mean act of God, acts, regulation or
                  decrees of any Government (de facto or de jure), natural
                  phenomena such as earthquake, floods, fires, riots, wars,
                  shipwrecks, strikes, freight embargoes, lockouts, and other
                  causes similar to the foregoing which are beyond the
                  reasonable control of the parties and which prevent either or
                  both parties from performing their respective obligations
                  under this Agreement in whole or in part. In the event of
                  force majeure, the party affected shall notify the other
                  within seven (7) days thereof, specifying the event and the
                  probable consequences thereof. In the event that performance
                  of substantially all obligations herein, cannot be restored
                  within a mutually agreeable time frame, then this Agreement
                  may be terminated by ten (10) days notice without further
                  liability of either party for damages on account of such
                  termination. In the event this Agreement is not terminated
                  under this Paragraph 16.2, the parties will cooperate with
                  each other to restore as promptly as possible full and
                  complete performance here under and all rights and obligations
                  of the parties shall remain in force and enforceable, with
                  reasonable revisions to delivery schedules as may be mutually
                  agreed.

15.      PROPRIETARY INFORMATION

                  Buyer and Seller agree to keep in confidence and not disclose
                  to others all knowledge, information and data furnished to it
                  by the other and claimed by either to be proprietary, provided
                  such proprietary information is given in writing and such
                  writing is marked to indicate the confidential nature of the
                  information and the disclosing party's claim of ownership.
                  Buyer and Seller agree that





                                       10
<PAGE>

                  neither shall use or reproduce for use in any way any
                  proprietary information of the other except in furtherance of
                  the relationship set forth in this Agreement. Buyer and Seller
                  agree to protect the proprietary information with the same
                  standard of care and procedures which each uses to protect its
                  own proprietary information. This paragraph shall not be
                  applicable and shall impose no obligation on either party with
                  respect to any portion of proprietary information which:

                  A.) Was at the time received or which thereafter becomes,
                  through no act or failure on the part of either party,
                  generally known or available to the public;

                  B.) Is known to either party at the time of receiving such
                  information as evidenced by documentation then rightfully in
                  the possession of either party;

                  C.) Is furnished by either party to a third party without
                  restriction by that third party on disclosure;

                  D.) Is thereafter rightfully furnished to either party by
                  third party without restriction by that third party on
                  disclosure; or

                  E.) Is released from restrictions imposed hereunder by written
                  release given by the owner of the information.

                  G.) In the event a dispute hereunder must be resolved by
                  litigation, the prevailing party shall be entitled to receive
                  reimbursement for all associated costs.

                  H.) This Agreement is intended for the benefit of the parties
                  hereto and their permitted assigns, and no other person shall
                  be entitled to rely upon this Agreement or be entitled to any
                  benefits under this Agreement. This Agreement shall not be
                  assignable by either Party without the prior written consent
                  of the other Party hereto.

                  I.) Each party agrees that information to be furnished to the
                  other hereunder will, to the best of its knowledge and belief,
                  be correct. Each party agrees to notify the other promptly in
                  the event that information provided by the supplying party
                  contains an error or omission at such time that the furnishing
                  party modifies such information in any respect.

                  J.) Neither party shall, for any purpose, be deemed to be an
                  agent of the other party and the relationship between the
                  parties shall only be that of independent contractors.




                                       11
<PAGE>

                  K.) Any tool or special equipment furnished by the Buyer to
                  Seller or acquired by Seller exclusively for use in connection
                  here with shall remain the property of the Buyer. All other
                  tooling remains the property of the Seller. Seller agrees to
                  use such tools and equipment only in the manufacture, testing,
                  or installation of the products for Buyer or for Buyer's
                  customers or end users, and Seller agrees to return such tools
                  and equipment to Buyer at Buyer's expense immediately upon any
                  request by Buyer to do so. If Buyer provides tooling, the
                  Buyer will mark it as their property.

                  L.) For this Agreement, "in writing" shall mean written either
                  on paper and faxed or mailed, or written electronically and
                  sent via e-mail.

                  M.) The headlines contained in this Agreement are for the
                  convenience of reference only and shall not be considered in
                  construing this Agreement.

                  N.) Seller shall not, and shall require that its
                  subcontractors and suppliers of any tier shall not cause or
                  permit to be released any publicity, advertisement, news
                  release, public announcement, or denial or confirmation of
                  same, in whatever form, regarding any aspect of this Agreement
                  or the products or program to which they pertain without
                  Buyer's prior written approval.

                  O.) Any notice in connection with this Agreement must be made
                  in writing and if by mail, by certified mail, return receipt
                  requested, and shall be deemed to be given and received on the
                  date of actual receipt by the addressee at the address listed
                  below:

                  All technical data, hardware, and intellectual property
                  including, but not limited to, designs, engineering and
                  manufacturing drawings, specifications, standards, process
                  information, manuals, technical reports, computer software and
                  related information, tooling, fixtures, test equipment and
                  other hardware purchased and/or furnished by Buyer and bills
                  of material first produced and/or uniquely resulting from the
                  performance of this Agreement shall be the sole property of
                  Buyer. Seller shall not use any such items for any purpose
                  other than the performance of this Agreement without express
                  written permission of Buyer.

16.      GENERAL

                  A) This Agreement may be amended upon the mutual written
                  consent of the parties hereto. No modification, termination,
                  extension, renewal or waiver of any provision of this
                  Agreement





                                       12
<PAGE>

                  shall be binding upon either party unless made in writing and
                  signed by an authorized officer of both parties.

                  B) This Agreement supersedes all proposals, oral or written,
                  and all negotiations, conversations or discussions heretofore
                  had between the parties hereto as to the subject matter
                  hereof.

                  C) This Agreement shall govern all Purchase Orders, which
                  contain a reference to this Agreement, and the terms, and
                  conditions herein shall take precedence over any conflicting
                  terms of any such Purchase Order. Any conflicts which might
                  exist between this Agreement and Purchase Order terms and
                  conditions referencing this Agreement shall be resolved in
                  this order: 1) this Agreement; 2) front side of Purchase
                  Order; 3) back side of Purchase Order; 4) Seller's proposal.

                  D) If any clause, term or provision of this Agreement shall be
                  judged invalid by any court or administrative agency having
                  jurisdiction over performance of the Agreement, such
                  invalidity shall not affect the validity or operation of any
                  other clause, term or provision; and such invalid clause, item
                  or provision shall be deemed to have been deleted from this
                  Agreement.

                  E) This Agreement and its performance shall be governed by,
                  subject to, and construed in accordance with the laws of the
                  State of Tennessee, U.S.A.

                  F) If a dispute arises out of or relates to this Agreement or
                  the breach thereof, the Parties agree that in the first
                  instance they shall enter into good faith negotiations to
                  resolve such dispute by mutual agreement.

                  P) The failure of any party hereto at any time to require
                  performance by the other party of any of its obligations
                  hereunder shall not in any way affect the full right to
                  require such performance at any time thereafter. The waiver by
                  either party of any remedy with respect to any breach of any
                  particular provision(s) does not constitute a waiver of any
                  other breach of other provisions.

17.      NOTICES.

                  Any notice or other communication required or permitted to be
                  given hereunder shall be effective only when received and
                  shall be directed to the following parties:




                                       13
<PAGE>

                  a.  If to Buyer                  b.  If to Seller
                      CTI PET Systems, Inc.            PHOTONIS
                      810 Innovation Drive             Avenue Roger Roncier
                      Knoxville, TN 37932-2571         BP520 - 19106 BRIVE Cedex
                      USA                              FRANCE

                      Attn: Mr. Juel Hensley           Attn: Mr. Rene Dupont
                            Purchasing Manager               General Manager

18.      AUTHORITY TO EXECUTE AGREEMENT

                  In executing this Agreement, the undersigned hereby represents
                  that they have read carefully, the foregoing terms of this
                  Agreement on behalf of their respective interests, that they
                  have the authority to execute this Agreement and that they
                  have signed the same as their own respective free acts and
                  with the expressed authority to do so on behalf of their
                  respective interests.


CTI PET Systems, Inc.                       PHOTONIS

       /s/ Ronald Nutt                          /s/ Rene Dupont
------------------------------------        -------------------------------
By:    Dr. Ronald Nutt                      By:   Rene Dupont
       Executive Vice President                   General Manager,


Date:                                       Date:






                                       14
<PAGE>



                                    EXHIBIT A


<Table>
<Caption>
PHOTONIS                  CTI
PART #                    PART #                          REVISION          DESCRIPTION
--------                  ------                          --------          -----------
<S>                       <C>                             <C>               <C>
XP 1912/FLB               5410009-00 C                    C                 19mm round fast PMT
XP3102/FLB                To Be Determined                                  25mm round fast PMT
XP5292/SO                 To Be Determined                                  2" square assembly
</Table>


For Pricing, see Exhibit B and Purchase Orders which reference this Agreement.

Rejection Criteria:

o    PMT which fails to meet CTI or Photonis' specifications .

o    Failure or intermittent failure due to internal shorts

o    PMTs which are unfit for use due to failure to meet workmanship standards
     of Seller. (e.g., tinned leads which snap off at the bulb as a result of
     normal handling at CPS during the course of mounting bleeder networks.)

o    Failure to meet CPS standard stability monitoring criteria

PMTs which are rejected by CPS shall be processed as follows:

o    CPS purchasing will notify Seller of the quantity and cause of rejection
     and request return authorization.

o    Seller will issue a return authorization number to CPS

o    CPS will return rejected PMTs to Seller at Seller's expense

o    Seller will evaluate rejected PMTs, prepare a disposition and send report
     along with corrective action as appropriate to Buyer's representative
     within 30 days (see section 17) and issue appropriate credit

o    Seller will replace PMTs on the appropriate purchase order and line and
     re-invoice

o    Any dispute regarding rejected PMTs will be resolved between CPS purchasing
     and the Sellers designated representative.



<PAGE>


                                    EXHIBIT C

                       WARRANTY FOR PHOTOMULTIPLIER TUBES


Unless otherwise agreed, the Seller (PHOTONIS) guarantees to the original Buyer
to refund the price paid for, or at the Seller's discretion, to repair or
replace, those tubes which proved to the Seller's reasonable satisfaction not to
conform to the published specifications at the time of receipt of materials by
the Buyer or to have failed by reason of faulty design or workmanship during a
period of twelve months.

This guarantee is subject to the following provisions:

1.       Claims for damage in transit will be considered only if the Buyer
         promptly notifies the Seller upon receipt of the tubes.

2.       The guarantee shall not extend to failures by reason of defects which
         ought reasonably to have been discovered by the Buyer upon inspection
         and testing of the tubes and were not reported to the Seller within
         thirty days.

3.       The Buyer informs the Seller promptly on discovery of any alleged
         defect and, if and when requested, returns the tubes, (cost of shipping
         to be born by the Seller), as the Seller directs with a full written
         report of the defect.

4.       The tubes have been stored, installed, maintained, and used properly,
         having regard in particular to the applicable specifications and
         instructions for use as published by the Seller.

5.       The Seller's liability in the case of tubes or components not of the
         seller's manufacture shall in no circumstances extend beyond any
         corresponding liability to the Seller of the manufacturer of such tubes
         or components.

All expressed and implied conditions, warranties and other liabilities arising
under common law or status are expressly excluded.


<PAGE>


                                    EXHIBIT B

                        PRICING FOR PHOTOMULTIPLIER TUBES


Pricing will be as shown below for the time period September 1, 1999 through
Aug. 31, 2001. Pricing for the three years beginning September 1, 2001 will be
the price from the previous year adjusted only * For example, if the volume of
19mm tubes in year two was * and in year three, the volume is *, the price will
be:
(*
.. *  The decrease in price due to volume factor

*

<Table>
<S>                              <C>                         <C>                           <C>
Pricing:                                                      *                              *

XP1912 (19mm)                    5410009-00                   *                              *
                                                              *                              *
                                                              *                              *
XP3102 (1")                      TBD                          *                              *
                                                              *                              *
                                                              *                              *
                                                              *                              *
XP5292 (2")                      TBD                          *                              *
                                                              *                              *
                                                              *                              *
                                                              *                              *
</Table>

Note: the 2" pricing to be re-negotiated after production volumes reach *
pieces.


*Omitted information is the subject of a request for confidential treatment
pursuant to Rule 406 under the Securities Act of 1933 and has been filed
separately with the Securities and Exchange Commission.