<PAGE>
                                                                   EXHIBIT 10.49

         NEITHER THIS WARRANT NOR THE SHARES OF STOCK ISSUABLE UPON EXERCISE
         HEREOF HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933, AS
         AMENDED (THE "ACT") OR ANY STATE SECURITIES LAWS. NO SALE, TRANSFER OR
         OTHER DISPOSITION OF THIS WARRANT OR SAID SHARES MAY BE EFFECTED
         WITHOUT (I) AN EFFECTIVE REGISTRATION STATEMENT RELATED THERETO, (II)
         AN OPINION OF COUNSEL FOR THE PURCHASER SATISFACTORY TO THE COMPANY
         THAT SUCH REGISTRATION IS NOT REQUIRED OR (III) RECEIPT OF A NO-ACTION
         LETTER FROM THE SECURITIES AND EXCHANGE COMMISSION TO THE EFFECT THAT
         REGISTRATION UNDER THE ACT IS NOT REQUIRED.


                                    CTI, INC.

                        Warrant to Purchase Common Stock

         CTI, INC., a Tennessee corporation (the "Company"), hereby certifies
that, for value received, Mr. Gene McGrevin (the "Purchaser"), is entitled,
subject to the terms set forth herein, to purchase from the Company upon
surrender of this Warrant, at any time or times but not after 5:00 P.M., Eastern
Standard Time, on the Expiration Date (as defined below), TWO THOUSAND FIVE
HUNDRED (2,500) shares of Common Stock (as defined below) of the Company (the
"Warrant Shares") (as adjusted from time to time as provided in this Warrant),
at an initial purchase price of $10.50 per share in lawful money of the United
States.

                                   DEFINITIONS

                  SECTION 1. (a) Definitions. The following words and terms as
used in this Warrant shall have the following meanings:

                  "Affiliate" means, with respect to a Person, any other Person
that, directly or indirectly through one or more intermediaries, controls, or is
controlled by, or is under common control with, such first Person.

                  "Business Day" means a day other than a Saturday, a Sunday, a
day on which banking institutions in the State of Tennessee are authorized or
obligated by law or required by executive order to be closed.

                  "Common Stock", when used with reference to stock of the
Company, means all shares now or hereafter authorized of any class of the common
equity of the Company, whether with or without par value, and stock of any other
class into which such shares may hereafter have been changed and other rights or
securities convertible into shares of common stock of the Company.


<PAGE>

                  "Consulting Agreement" means that certain Consulting and Sales
Agency Agreement to be entered into by the Company, P.E.T. Net Pharmaceuticals,
Inc., and the Purchaser as contemplated in that certain Letter of Intent between
the parties dated February 7, 2002.

                  "Convertible Securities" mean any securities issued by the
Company or an Affiliate which are convertible into or exchangeable for, directly
or indirectly, shares of Common Stock.

                  "Exchange Act" means the Securities and Exchange Act of 1934,
as amended, and the rules and regulations promulgated thereunder.

                  "Expiration Date" means March 22, 2007.

                  "Person" means an individual or corporation, partnership,
trust, incorporated or unincorporated association, joint venture, joint stock
company, government (or any agency or political subdivision thereof) or other
entity of any kind.

                  "Securities Act" means the Securities Act of 1933, as amended,
and the rules and regulations promulgated thereunder.

                  "Warrant Exercise Price" means $10.50 per share and may be
adjusted from time to time as provided in this Warrant.

                  SECTION 2. Exercise of Warrant. Subject to the terms and
conditions hereof, this Warrant may be exercised, in whole or in part, at any
time during normal business hours on or after the date hereof and prior to 5:00
P.M., Eastern Standard Time, on the Expiration Date. The rights represented by
this Warrant may be exercised by the Purchaser, in whole or from time to time in
part (except that this Warrant shall not be exercisable as to a fractional
share) by (i) delivery of a written notice of such Purchaser's election to
exercise this Warrant, which notice shall specify the number of Warrant Shares
to be purchased, (ii) payment to the Company of an amount equal to the Warrant
Exercise Price multiplied by the number of Warrant Shares as to which the
Warrant is being exercised in cash or by certified or official bank check or by
net issue election, (iii) surrender of this Warrant, properly endorsed, at the
principal office of the Company (or at such other agency or office of the
Company as the Company may designate by notice to the Purchaser), and (iv)
delivery to the Company by the Purchaser of a letter in the form of Exhibit A
hereto. In the event of any exercise of the rights represented by this Warrant,
a certificate or certificates for the Warrant Shares so purchased, registered in
the name of the Purchaser, shall be delivered to such Purchaser within 15
calendar days after such rights shall have been so exercised. Unless the rights
represented by this Warrant shall have expired or have been fully exercised, the
Company shall issue a new Warrant identical in all respects to the Warrant
exercised, except that it shall represent rights to purchase the number of
Warrant Shares purchasable immediately prior to such exercise under the Warrant
exercised, less the number of Warrant Shares with respect to which such Warrant
was exercised. The entity in whose name any certificate for Warrant Shares is
issued upon the exercise of this Warrant shall for all purposes be deemed to
have become the holder of record of such Warrant Shares


                                      -2-
<PAGE>

immediately prior to the close of business on the date on which the Warrant was
surrendered and payment of the amount due in respect of such exercise and any
applicable taxes was made, irrespective of the date of delivery of such share
certificate, except that, if the date of such surrender and payment is a date
when the stock transfer books of the Company are properly closed, such person
shall be deemed to have become the holder of such Warrant Shares at the opening
of business on the next succeeding date on which the stock transfer books are
open.

                  SECTION 3. Covenants as to Common Stock. The Company covenants
and agrees that all Warrant Shares which may be issued upon the exercise of the
rights represented by this Warrant will, upon issuance, be validly issued, fully
paid and nonassessable, free and clear of all liens, claims and encumbrances.
The Company further covenants and agrees that, during the period within which
the rights represented by this Warrant may be exercised, the Company will at all
times have authorized and reserved a sufficient number of shares of Common Stock
to provide for the exercise of the rights then represented by this Warrant.

                  SECTION 4. Adjustments to the Warrant Shares.

                  (a)      Stock Dividends, Splits, Etc. In case the Company
shall at any time subdivide its outstanding shares of Common Stock into a
greater number of shares or issue a stock dividend or make a distribution with
respect to outstanding shares of Common Stock or Convertible Securities payable
in Common Stock or in Convertible Securities which are convertible with no
additional consideration into shares of Common Stock, then, upon exercise of
this Warrant, for each Warrant Share acquired, Purchaser shall receive, without
additional cost to Purchaser, the total number and kind of securities to which
the Purchaser would have been entitled if it had held the Common Stock issuable
upon the exercise hereof immediately prior to such subdivision, dividend or
distribution.

                  (b)      Reorganization, Reclassification, Exchange or
Substitution. In case of any capital reorganization, or of any reclassification
of the capital stock, of the Company (other than a change in par value or from
par value to no par value or from no par value to par value or as a result of a
split-up or combination) this Warrant shall, after such capital reorganization
or reclassification of capital stock, entitle the Purchaser to purchase the kind
and number of shares of stock or other securities or property of the Company, or
of the corporation resulting from such consolidation, to which the Purchaser
would have been entitled if it had held the Common Stock issuable upon the
exercise hereof immediately prior to such capital reorganization,
reclassification of capital stock, consolidation, merger or sale, and in any
such case appropriate provision shall be made with respect to the rights and
interests of the Purchaser of this Warrant to the end that the provisions hereof
(including without limitation provisions for adjustment of the Warrant Exercise
Price and of the number of shares purchasable upon the exercise of this Warrant)
shall thereafter be applicable, as nearly as may be in relation to any shares of
stock, securities or assets thereafter deliverable upon the exercise of the
rights represented hereby.


                                      -3-
<PAGE>

                  (c)      Combinations, Etc. In case the Company shall at any
time combine or consolidate, by reclassification or otherwise, the outstanding
shares of Common Stock into a smaller number of shares, the Warrant Exercise
Price in effect immediately prior to such combination shall be proportionately
increased.

                  (d)      Merger or Consolidation. If at any time there shall
be a merger or consolidation of the Company with or into another corporation
when the Company is not the surviving corporation, then, as part of such merger
or consolidation, lawful provision shall be made so that the holder of the
Warrant evidenced hereby shall thereafter be entitled to receive upon exercise
of rights herein granted, during the period specified herein and upon payment of
the aggregate Warrant Exercise Price, the number of shares of stock or other
securities or property of the successor corporation resulting from such merger
or consolidation, to which a holder of the stock deliverable upon exercise of
the rights granted in this Warrant would have been entitled in such merger or
consolidation if such rights had been exercised immediately before such merger
or consolidation. In any such case, appropriate adjustment shall be made in the
application of the provisions of this Warrant Agreement with respect to the
rights and interests of the holder after the merger or consolidation.

                  SECTION 5. Notice of Adjustment. Upon any adjustment of the
Warrant Exercise Price and/or the number of shares which may be subscribed for
and purchased upon exercise of this Warrant, the Company shall give notice
thereof to the Purchaser, which notice shall state the Warrant Exercise Price in
effect after such adjustment and the increase, or decrease, if any, in the
number of shares purchasable at the Warrant Exercise Price upon the exercise of
this Warrant, setting forth in reasonable detail the method of calculation and
the facts upon which such calculation is based.

                  SECTION 6. Computation of Adjustments. Upon each computation
of an adjustment in the Warrant Exercise Price and the number of shares which
may be subscribed for and purchased upon exercise of this Warrant, the Warrant
Exercise Price shall be computed to the nearest cent (i.e., fractions of .5 of a
cent, or greater, shall be rounded to the next highest cent) and the shares
which may be subscribed for and purchased upon exercise of this Warrant shall be
calculated to the nearest whole share (i.e., fractions of one half of a share,
or greater, shall be treated as being a whole share). No such adjustment shall
be made, however, if the change in the Warrant Exercise Price would be less than
$.01 per share, but any such lesser adjustment shall be made at the time of, and
together with, the next subsequent adjustment which, together with any
adjustments carried forward, shall amount to a change in the Warrant Exercise
Price of $.01 per share or more.

                  SECTION 7. Net Issue Exercise. Notwithstanding any provisions
herein to the contrary, if the fair market value of one share of Common Stock is
greater than the Warrant Exercise Price (at the date of exercise of the Warrant
as set forth below), in lieu of exercising the Warrant by payment of cash, the
Purchaser may elect to receive shares equal to the value (as determined below)
of the Warrant (or portion thereof being canceled) by surrender of the Warrant
at the principal office of the Company together with the duly executed Notice of
Exercise in which event the Company


                                      -4-
<PAGE>

shall issue to the Purchaser a number of shares of the Common Stock computed
using the following formula:

                                  X = Y(A - B)
                                      --------
                                        A

                  WHERE X = the number of shares of Common Stock to be issued to
                  the Purchaser;

                  Y = the number of shares of the Common Stock purchasable under
                  the Warrant or, if only a portion of the Warrant is being
                  exercised, the number of shares underlying the Warrant to the
                  extent exercised (at the date of such exercise);

                  A = the fair market value of one share of Common Stock (at the
                  date of such calculation); and

                  B = Warrant Exercise Price (at the date of such calculation).

For purposes of the above calculation, fair market value of one share of Common
Stock shall be equal to the closing sale price of the Common Stock on the day
immediately prior to the date the Notice of Exercise is tendered to the Company.
If the Common Stock is not traded on NASDAQ or other national stock exchange,
the fair market value of one share of Common Stock shall be determined by the
Board of Directors in good faith.

                  SECTION 8. Notice of Certain Events. In case at any time:

                  (a) the Company shall pay any dividend upon, or make any
distribution in respect of, its Common Stock;

                  (b) the Company shall offer for subscription pro rata to the
holders of its Common Stock any additional shares of stock of any class or other
rights;

                  (c) there shall be any capital reorganization, or
reclassification of the capital stock, of the Company; or

                  (d) there shall be a voluntary or involuntary dissolution,
liquidation or winding up of the Company;

then, in any one or more said cases, the Company shall give notice to the
Purchaser of the date on which (i) the books of the Company shall close or a
record shall be taken for such dividend, distribution or subscription rights, or
(ii) such reorganization, reclassification, involuntary dissolution, liquidation
or winding up shall take place, as the case may be. Such notice shall be given
not less than ten (10) days prior to the record date or the date on which the
transfer books of the


                                      -5-
<PAGE>

Company are to be closed in respect thereto in the case of an action specified
in clause (i) and at least thirty (30) days prior to the action in question in
the case of an action specified in clause (ii).

                  SECTION 9. Taxes. The Purchaser shall pay any tax or taxes
attributable to the initial issuance of the Warrant Shares, and the Company
shall not be required to pay any tax or taxes levied or assessed with respect to
any transfer of any Warrant Shares.

                  SECTION 10. Warrant Purchaser Not Deemed a Shareholder. The
Purchaser shall not be entitled to vote or receive dividends or be deemed a
shareholder of the Company for any purpose, nor shall anything contained in this
Warrant be construed to confer upon the Purchaser any of the rights of a
shareholder of the Company or any right to vote, give or withhold consent to any
corporate action (whether any reorganization, issuance of stock,
reclassification of stock, consolidation, merger, conveyance or otherwise),
receive notice of meetings, receive dividends or subscription rights, or
otherwise, prior to the issuance of record to the Purchaser of the Warrant
Shares which it is then entitled to receive upon the due exercise of this
Warrant.

                  SECTION 11. No Limitation on Corporate Action. No provisions
of this Warrant and no right or option granted or conferred hereunder shall in
any way limit, affect or abridge the exercise by the Company of any of its
corporate rights or powers to recapitalize, amend its Articles of Incorporation,
reorganize, consolidate or merge with or into another corporation, or transfer
all or any part of its property or assets, or the exercise of any other of its
corporate rights and powers.

                  SECTION 12. Accredited Investor; Restrictive Legends.

                  (a) The issuance of this Warrant is conditioned upon, and by
its acceptance hereof Purchaser hereby confirms, represents and warrants that,
this Warrant and the shares of Common Stock or other securities issuable upon
exercise hereof are being acquired for the account of Purchaser for investment
and not with a view to, or for sale in connection with, any distribution thereof
(or any portion thereof) and with no present intention of offering and
distributing such securities or any portion thereof, except under circumstances
that will not result in a violation of the Securities Act and any applicable
state securities laws. Upon exercise of this Warrant, Purchaser shall confirm in
writing, in a letter in the form of Exhibit A hereto, that the Warrant Shares so
purchased are being acquired solely for the account of Purchaser for investment
and not with a view to, or for sale in connection with, any distribution thereof
(or portion thereof) and with no present intention of offering and distributing
such securities or any portion thereof, except under circumstances that will not
result in a violation of the Securities Act and any applicable state securities
laws. Purchaser agrees that it will comply with all applicable provisions of
state and federal securities laws. Purchaser acknowledges to the Company that
the Warrant Shares will have restrictions upon resale imposed by state and
federal securities laws. Purchaser also confirms, represents and warrants to the
Company that it is an "accredited investor" as defined in Rule 501 of Regulation
D promulgated under the Securities Act.


                                      -6-
<PAGE>

                  (b) The certificates evidencing the Warrant Shares shall bear
a legend in substantially the following form:

         THIS SECURITY HAS NOT BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
         AS AMENDED (THE "ACT") OR ANY STATE SECURITIES LAWS. NO SALE, TRANSFER
         OR OTHER DISPOSITION OF THIS SECURITY MAY BE EFFECTED WITHOUT (I) AN
         EFFECTIVE REGISTRATION STATEMENT RELATED THERETO, (II) AN OPINION OF
         COUNSEL FOR THE PURCHASER SATISFACTORY TO THE COMPANY THAT SUCH
         REGISTRATION IS NOT REQUIRED OR (III) RECEIPT OF A NO-ACTION LETTER
         FROM THE SECURITIES AND EXCHANGE COMMISSION TO THE EFFECT THAT
         REGISTRATION UNDER THE ACT IS NOT REQUIRED.

together with any legend required under applicable State securities laws.

                  SECTION 13. Lost, Stolen, Mutilated or Destroyed Warrant. If
this Warrant is lost, stolen, mutilated or destroyed, the Company shall, on such
terms as to indemnity or otherwise as it may in its discretion impose (which
shall, in the case of a mutilated Warrant, include the surrender thereof), issue
a new warrant of like denomination and tenor as the Warrant so lost, stolen,
mutilated or destroyed.

                  SECTION 14. Notice. All notices, demands and other
communications under this Warrant shall be in writing (which shall include
communications by telecopy) and shall be either (a) delivered in person, or by
hand, courier or overnight delivery service, (b) mailed by first class
registered or certified mail, postage prepaid, return receipt requested, or sent
by prepaid telecopier, and (c) be given at the following respective addresses
and telecopier numbers and to the attention of the following Persons:

                  (i)      if to the Company, to:

                           CTI, Inc.
                           810 Innovation Drive
                           Knoxville, Tennessee  37932-2571
                           Attn:  Terry D. Douglass
                           Telecopier No.:  (865) 218-3001


                                      -7-
<PAGE>


                  with a copy (which shall not constitute notice) to:

                           Alston & Bird LLP
                           One Atlantic Center
                           1201 West Peachtree Street
                           Atlanta, Georgia  30309-3424
                           Attn:  R. Gregory Brophy, Esq.
                           Telecopier No.:  (404) 881-7777

                  (ii)     if to the Purchaser hereof, to:

                           Mr. Gene McGrevin

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

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

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

                           with a copy (which shall not constitute notice) to:

                           Womble Carlyle Sandridge & Rice LLC
                           1201 West Peachtree Street, Suite 3500
                           Atlanta, Georgia  30309
                           Attn:  G. Donald Johnson, Esq.
                           Telecopier No.:  (404) 870-4878

or at such other address or telecopier number, or to the attention of such other
person, as the party to whom such information pertains may hereafter specify for
the purpose in a notice to the other specifically captioned "Notice of Change of
Address", and (d) be effective or deemed delivered or furnished (i) if given by
mail, on the third Business Day after such communication is deposited in the
mail, addressed as above provided, (ii) if given by telecopier, when such
communication is transmitted to the appropriate number determined as above
provided and the appropriate confirmation of transmission is received or receipt
is otherwise acknowledged, and (iii) if given by hand delivery or overnight
delivery service, when left at the address of the addressee addressed as above
provided, except that notices of a change of address or telecopier number shall
not be deemed furnished until received.

                  SECTION 15. Miscellaneous. This Warrant and any term hereof
may be changed, waived, discharged, or terminated only by an instrument in
writing signed by the party or holder hereof against whom enforcement of such
change, waiver, discharge or termination is sought. The headings in this Warrant
are for purposes of reference only and shall not limit or otherwise affect the
meaning hereof.

                  SECTION 16. Fractional Shares. No certificates representing
fractional


                                      -8-
<PAGE>

shares of Common Stock will be issued upon exercise of this Warrant.
In lieu of the issuance of fractional shares, a cash adjustment (without
interest) will be paid to the Purchaser for any fraction of a share that would
be otherwise issuable. The amount of any such cash payment shall be determined
by multiplying the fractional interest due to the Purchaser times the fair
market value of one share of Common Stock as determined in accordance with
Section 7 hereof.

                  SECTION 17. Void after Expiration Date. This Warrant shall in
all events be wholly void and of no effect after 5:00 P.M., Eastern Standard
Time, on the Expiration Date, except that notwithstanding any other provisions
hereof, the provisions of Section 13(a) shall continue in full force and effect
after such date as to any Warrant Shares or other securities issued upon the
exercise of this Warrant.

         IN WITNESS WHEREOF, the Company has caused this Warrant to be executed
by its duly authorized officers and its seal to be hereunto affixed as of the
27th day of March, 2002.


                                  CTI, INC.



                                  By:      /s/ Terry D. Douglass
                                      ------------------------------------------
                                           Name:  Terry D. Douglass
                                           Title:    President



                                      -9-
<PAGE>

                                    EXHIBIT A

                               Notice of Exercise


                                     [Date]


CTI, Inc.
810 Innovation Drive
Knoxville, Tennessee  37932-2571
Attn:  Terry D. Douglass

                             Re: Exercise of Warrant


         Pursuant to the provisions of that certain Warrant to Purchase Common
Stock (the "Warrant") of CTI, INC., a Tennessee corporation (the "Company"),
dated March __, 2002, Mr. Gene McGrevin (the "Purchaser"), hereby represents,
warrants, covenants and agrees with the Company as follows:

                  The shares of common stock of the Company being acquired by
         Purchaser pursuant to this exercise of the Warrant (the "Warrant
         Shares") will be acquired for its own account without the participation
         of any other person, with the intent of holding the Warrant Shares for
         investment and without the intent of participating, directly or
         indirectly, in a distribution of the Warrant Shares and not with a view
         to, or for resale in connection with, any distribution of the Warrant
         Shares, nor is Purchaser aware of the existence of any distribution of
         the Warrant Shares;

                  Purchaser is not acquiring the Warrant Shares based upon any
         representation, oral or written, by any person with respect to the
         future value of, or income from, the Warrant Shares but rather upon an
         independent examination and judgment as to the prospects of the
         Company;

                  The Warrant Shares were not offered to Purchaser by means of
         publicly disseminated advertisements or sales literature;

                  Purchaser is able to bear the economic risks of the investment
         in the Warrant Shares, including the risk of a complete loss of
         Purchaser's investment therein;

                  Purchaser understands and agrees that the Warrant Shares will
         be issued and sold to Purchaser in reliance upon an exemption from, and
         without registration under, any state law relating to the registration
         of securities for sale, and will be issued and sold in reliance on the
         exemptions from registration under the Securities Act of 1933 (the
         "Securities Act"), provided by Sections 3(b) and/or 4(2) thereof,
         Regulation D thereunder, and the other rules and regulations
         promulgated thereunder;


<PAGE>

                  The Warrant Shares cannot be offered for sale, sold or
         transferred by Purchaser other than pursuant to: (i) either (A) an
         effective registration under the Securities Act, (B) an opinion of
         counsel for Purchaser satisfactory to the Company that such
         registration is not required, or (C) receipt of a no-action letter from
         the Securities and Exchange Commission to the effect that such
         registration is not required, and (ii) evidence satisfactory to the
         Company of compliance with the applicable securities laws of other
         jurisdictions. The Company shall be entitled to rely upon an opinion of
         counsel satisfactory to it with respect to compliance with the above
         laws;

                  The Company will be under no obligation to register the
         Warrant Shares or to comply with any exemption available for sale of
         the Warrant Shares without registration or filing, and the information
         or conditions necessary to permit routine sales of securities of the
         Company under Rule 144 of the Securities Act are not now available and
         no assurance has been given that it or they will become available. The
         Company is under no obligation to act in any manner so as to make Rule
         144 available with respect to the Warrant Shares;

                  Purchaser is familiar with the business and affairs of the
         Company. Purchaser realizes that the purchase of the Warrant Shares is
         a speculative investment and that any possible profit therefrom is
         uncertain;

                  Purchaser has had the opportunity to ask questions of and
         receive answers from the Company and any person acting on its behalf
         and to obtain all material information reasonably available with
         respect to the Company and its affairs. Purchaser has received all
         information and data with respect to the Company which it has requested
         and which it has deemed relevant in connection with the evaluation of
         the merits and risks of its investment in the Company;

                  Purchaser has such knowledge and experience in financial and
         business matters that it is capable of evaluating the merits and risks
         of the purchase of the Warrant Shares hereunder, and it is able to bear
         the economic risk of such purchase; and

                  The agreements, representations, warranties, and covenants
         made by Purchaser herein extend to and apply to all of the Warrant
         Shares. Acceptance by Purchaser of the certificate representing such
         Warrant Shares shall constitute a confirmation by Purchaser that all
         such agreements, representations, warranties and covenants made herein
         are true and correct at that time.

                  Purchaser understands that the certificates representing the
         Warrant Shares shall bear a legend referring to the foregoing
         covenants, representations, warranties and restrictions on transfer,
         and agrees that a legend to that effect may be placed on any
         certificate which may be issued to Purchaser as a substitute for the
         certificates representing the Warrant Shares.


                                      -2-

<PAGE>
                                             Very truly yours,



                                             By:
                                                --------------------------------
                                             Name:
                                                  ------------------------------


AGREED TO AND ACCEPTED:


CTI, INC.


By:
   -----------------------------------------
Title:
      --------------------------------------


Number of Shares
as to which Warrant
is being Exercised:
                    -------------------------------


Number of Shares
Remaining:                                              Date:
           ---------------------------------                 ------------


                                      -3-