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                                                                   Exhibit 10.31

THIS WARRANT AND THE STOCK ISSUABLE UPON THE EXERCISE HEREOF HAVE NOT BEEN
REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT"), AND CAN BE
TRANSFERRED ONLY IN COMPLIANCE WITH THE ACT AND APPLICABLE STATE SECURITIES
LAWS. THIS WARRANT AND SUCH SECURITIES MAY NOT BE SOLD, TRANSFERRED OR ASSIGNED
IN THE ABSENCE OF AN EFFECTIVE REGISTRATION STATEMENT, UNLESS, IN THE OPINION OF
COUNSEL FOR THE COMPANY OR COUNSEL FOR THE REGISTERED HOLDER (WHICH SHALL BE IN
FORM AND FROM SUCH COUNSEL AS SHALL BE REASONABLY SATISFACTORY TO THE COMPANY),
SUCH REGISTRATION IS NOT THEN REQUIRED.

                           MOBILE P.E.T. SYSTEMS, INC.
                          COMMON STOCK PURCHASE WARRANT

                  1. ISSUANCE. In consideration of good and valuable
consideration, the receipt of which is hereby acknowledged by MOBILE P.E.T.
SYSTEMS, INC., a Delaware corporation (the "Company"), York, LLC, a Cayman
Islands limited liability company, or registered assigns (the "Holder") is
hereby granted the right to purchase at any time until 5:00 P.M., Pacific Coast
time, on September 30, 2005 (the "Expiration Date"), Fifty Thousand (50,000)
fully paid and nonassessable shares of the Company's Common Stock, no par value
per share (the "Common Stock") at an exercise price of $3.00 per share (the
"Exercise Price") subject to further adjustment as set forth in Section 6
hereof.

                  2. EXERCISE OF WARRANTS. This Warrant is exercisable in whole
or in part for whole shares of the Company's Common Stock at the Exercise Price
per share of Common Stock payable hereunder, payable in cash or by certified or
official bank check. In lieu of paying cash to exercise this Warrant, the Holder
may, by designating a "cashless" exercise on the Notice of Exercise Form,
acquire a number of whole shares of the Company's Common Stock equal to (a) the
difference between (i) the Market Value of the Company's Common Stock and (ii)
the Exercise Price, multiplied by (b) the number of shares of Common Stock
purchasable under the portion of the Warrant tendered to the Company, divided by
(c) the Market Value of the Company's Common Stock. Upon surrender of this
Warrant Certificate with the annexed Notice of Exercise Form duly executed,
together with payment of the Exercise Price for the shares of Common Stock
purchased, the Holder shall be entitled to receive a certificate or certificates
for the shares of Common Stock so purchased. For the purposes of this Section 2,
"Market Value" shall be an amount equal to the average closing bid price of a
share of Common Stock for the five (5) business days immediately preceding the
Company's receipt of the Notice of Exercise Form duly executed.

                  3. RESERVATION OF SHARES. The Company hereby agrees that at
all times during the term of this Warrant there shall be reserved for issuance
upon exercise of this Warrant such number of shares of its Common Stock as shall
be required for issuance upon exercise of this Warrant (the "Warrant Shares").

                  4. MUTILATION OR LOSS OF WARRANT. Upon receipt by the Company
of evidence satisfactory to it of the loss, theft, destruction or mutilation of
this Warrant, and (in the case of loss,

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theft or destruction) receipt of reasonably satisfactory indemnification, and
(in the case of mutilation) upon surrender and cancellation of this Warrant, the
Company will execute and deliver a new Warrant of like tenor and date and any
such lost, stolen, destroyed or mutilated Warrant shall thereupon become void.

                  5. RIGHTS OF THE HOLDER. The Holder shall not, by virtue
hereof, be entitled to any rights of a stockholder in the Company, either at law
or equity, and the rights of the Holder are limited to those expressed in this
Warrant and are not enforceable against the Company except to the extent set
forth herein.

                  6. ADJUSTMENTS TO EXERCISE TERMS.

                     If the Company at any time prior to the full execution of
this Warrant shall, by subdivision, combination, merger, spin-off,
re-classification or like capital adjustment of the securities, change any of
the securities to which purchase rights under this Warrant exist into the same
or different number of securities of any class or classes, this Warrant shall
thereafter entitle the Holder to acquire such number and kind of securities as
would have been issuable as a result of such change with respect to the
securities acquirable immediately prior to such transaction. If shares of the
securities acquirable upon exercise of this Warrant are subdivided into a
greater number of securities, including any stock dividend, or if such
securities are combined into a lesser number of securities, then the purchase
price for the securities acquirable upon exercise of this Warrant and the
securities acquirable pursuant to this Warrant shall be proportionately and
equitably adjusted.

                  7. TRANSFER TO COMPLY WITH THE SECURITIES ACT; REGISTRATION
RIGHTS.

                  (a) This Warrant has not been registered under the Securities
Act of 1933, as amended, (the "Act") and has been issued to the Holder for
investment and not with a view to the distribution of either the Warrant or the
Warrant Shares. Neither this Warrant nor any of the Warrant Shares or any other
security issued or issuable upon exercise of this Warrant may be sold,
transferred, pledged or hypothecated in the absence of an effective registration
statement under the Act and applicable state securities laws relating to such
security, unless in the opinion of counsel satisfactory to the Company, such
registrations are not required under the Act. Each certificate for the Warrant,
the Warrant Shares and any other security issued or issuable upon exercise of
this Warrant shall contain a legend on the face thereof, in form and substance
satisfactory to counsel for the Company, setting forth the restrictions on
transfer contained in this Section.

                  (b) The Company agrees to file a registration statement, which
shall include the Warrant Shares, on Form SB-2 or another available form (the
"Registration Statement"), pursuant to the Act, pursuant to a Registration
Rights Agreement between the Company and Holder dated as of the date hereof (the
"Registration Rights Agreement").

                  8. NOTICES. Any notice or other communication required or
permitted hereunder shall be in writing and shall be delivered personally,
telegraphed, telexed, sent by facsimile transmission or sent by certified,
registered or express mail, postage pre-paid. Any such notice shall

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be deemed given when so delivered personally, telegraphed, telexed or sent by
facsimile transmission, or, if mailed, two days after the date of deposit in the
United States mails, as follows:

                           (i)      if the to Company, to:

                                    Mobile P.E.T. Systems, Inc.
                                    2240 Shelter Island Drive
                                    San Diego, CA  92106
                                    ATTN: CEO
                                    Telephone No.: (619) 226-6738
                                    Telecopier No.: (619) 226-6889

                           (ii)     if to the Holder, to:

                                    c/o Thomson Kernaghan & Co.
                                    365 Bay Street, Suite 1000, 10th Fl.
                                    Toronto, Ontario M5H 2V2
                                    Telephone No.: (416) 860-4160
                                    Telecopier No.: (416) 860-8313

Any party may be notice given in accordance with this Section to the other
parties designate another address or person for receipt of notices hereunder.

                  9. SUPPLEMENTS AND AMENDMENTS; WHOLE AGREEMENT. This Warrant
may be amended or supplemented only by an instrument in writing signed by the
parties hereto. This Warrant contains the full understanding of the parties
hereto with respect to the subject matter hereof and thereof and there are no
representations, warranties, agreements or understandings other than expressly
contained herein and therein.

                  10. GOVERNING LAW. This Warrant shall be deemed to be a
contract made under the laws of the State of California and for all purposes
shall be governed by and construed in accordance with the laws of such State
applicable to contracts to be made and performed entirely within such State.

                  11. DESCRIPTIVE HEADINGS. Descriptive headings of the several
Sections of this Warrant are inserted for convenience only and shall not control
or affect the meaning or construction of any of the provisions hereof.

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         IN WITNESS WHEREOF, the parties hereto have executed this Warrant as of
the 21st day of September 2000.

                             MOBILE P.E.T. SYSTEMS, INC., a Delaware corporation

                             By:   /s/ Paul Crowe
                                ------------------------------------------------
                                Name:  PAUL CROWE
                                Title: CEO

Attest:

/s/ Thomas G. Brown
------------------------
Name:  Thomas G. Brown
Title: Secretary

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                                                                   Exhibit 10.32

                          CONTINUING CORPORATE GUARANTY

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PRINCIPAL AMOUNT:          Four Hundred Thirty-Five thousand One Hundred Dollars
                           ($435,100.00)

DEBTOR:                    London Radiosurgical Centres, Ltd.
                           154 Harley Street
                           London
                           United Kingdom

GUARANTOR:                 Neurotechnologies International, Inc.
                           2540 Shelter Island Drive, Suite F
                           San Diego, CA  92106

CREDITOR:                  Mobile PET Systems, Inc.
                           2540 Shelter Island Drive, Suite F
                           San Diego, CA  92106

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

         For valuable consideration, Guarantor unconditionally guarantees and
promises to pay Creditor, its successors or assigns, on demand in lawful U.S.
currency, all debt of Debtor to Creditor, including that debt in the amount
referred to above, as follows:

         1.       MAXIMUM LIABILITY. Guarantor's liability shall include all
debt and obligations owed by Debtor to Creditor, including (a) the Principal
Amount set forth above; (b) all extensions and advances of principal or other
sums to Debtor by Creditor (c) all interest owed by Debtor on the foregoing; (d)
all Creditor's costs, expenses and attorneys fees, including any on appeal, in
connection with the collection of the debt or the collection or sale of any
collateral, whether there is a lawsuit; and (e) all other sums and obligations
due to Creditor from Debtor. This limitation on liability is not a restriction
on the amount of the debt of Debtor to Creditor either in the aggregate or at
one time. If Creditor presently holds one or more guaranties from Guarantor of
the debt of Debtor, the rights of Creditor under all guaranties shall be
cumulative. Guarantor's liability will be the total of all sums due under all
unterminated guaranties.

         2.       DEBT. "DEBT" is used in its most comprehensive sense and
includes all advances, debts, obligations, judgments and liabilities of Debtor,
or any one or more of them, whenever made, incurred or created, whether
voluntarily or however arising, whether due, absolute, contingent, liquidated or
determined, whether Debtor may be liable individually, jointly with others,
primarily, secondarily or as Guarantor, whether recovery on such debt may be or
become barred by any statute of limitations, whether such debt may be or become
otherwise unenforceable and whether such debt arises from transactions which may
be voidable on account of infancy, insanity, ULTRA VIRES or otherwise.

         3.       NATURE OF GUARANTORS UNDERTAKING. Guarantor's liability shall
be open and continuous for so long as this Guaranty is in force. Guarantor
intends to guarantee at all times the performance of all obligations of Debtor
to Creditor referred to herein. Guarantor's liability will be enforceable
against both the separate and community property of Guarantor whether now owned
or hereafter acquired.

         4.       CREDITOR'S DEALING WITH DEBTOR. Guarantor authorizes Creditor
to deal with Debtor and Debtors sureties, endorsers and any other Guarantor(s),
in any manner in which Creditor sees fit in connection with any debt of Debtor
to Creditor, now or hereafter created, without any further consent or

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authorization from Guarantor. Creditor may make secured or unsecured loans to
Debtor, Creditor may extend the terms for payment, or alter the terms relating
to the manner of payment, of any debt of Debtor; release any collateral given to
Creditor by Debtor, with or without the substitution of new collateral; release
or agree not to sue Debtors sureties, endorsers or other Guarantor on any terms
it chooses; sue or fail to sue Debtor on any overdue debt or may realize or
neglect to realize on any collateral held in connection therewith; all of the
foregoing without the necessity of any notice to or consent from Guarantor and
all without affecting Guarantor's liability hereunder.

         5.       DURATION OF GUARANTY. This Guaranty will take effect when
received by Creditor, without the, necessity of any acceptance by Creditor, and
will continue in full force until such time as all debt and obligations of
Debtor to Creditor and all debt and obligations of Guarantor hereunder are paid
in full. This Guaranty shall bind Guarantors estate as to debt created both
before and after Guarantor's death or incapacity.

         6.       CREDITOR'S RIGHTS. Guarantor expressly waives presentment,
protest, demand or notice of any kind, including notice of nonpayment of any of
Debtor's debt or of any collateral thereto and notice of any action or inaction
on the part of Debtor, Creditor or any surety, endorser or other Guarantor. On
any default of Debtor on any obligation to Creditor, Creditor may, at its
option, demand and be entitled to payment from Guarantor of the full amount of
any part of the amount of Debtors debt to Creditor, and all sums due hereunder.
If Guarantor shall not pay the sum demanded to Creditor, Creditor may proceed
directly and at once against Guarantor to collect such sum without first
proceeding against Debtor, or any surety, endorser or other Guarantor and
without foreclosing on or selling or otherwise disposing of any collateral
Creditor may have as security for any of Debtors debt. Creditors failure to make
such demand at such time or so to proceed shall not relieve Guarantor of its
obligations hereunder or in any sense constitute a waiver. Creditor shall have
the right to demand and collect from Guarantor all or part of Debtors debt and
failure of Creditor at any time to demand from Guarantor or to proceed to
collect from Guarantor the full amount of Debtor's debt from Guarantor shall not
preclude Creditor from later demanding or proceeding to collect from Guarantor
any remaining debt of Debtor to Creditor covered by this Guaranty. In any action
or suit against Guarantor to enforce this Guaranty, Creditor shall be entitled
to recover from Guarantor, in addition to costs and disbursements allowed by
law, a reasonable amount for Creditors attorneys' fees in such action or suit of
appeal therefrom. Guarantor waives any applicable statute of limitations to the
fullest extent permitted by law. If payment is made by Debtor on a debt
guaranteed hereby and thereafter Creditor is forced to remit the amount of that
payment to the Debtors trustee in bankruptcy or similar person under any federal
or state bankruptcy law or law for the relief of debtors, the Debtor's debt
shall be considered unpaid for the purpose of enforcement of this Guaranty.
Guarantor waives any right to participate in any collateral, until all debt of
Debtor to Creditor shall have been paid in full.

                  6.1.     In addition to all liens on, and rights of setoff
against the moneys, securities or other property of Guarantor given to Creditor
by law, Creditor shall have a security interest in and a right of setoff against
all moneys, securities and other property of Guarantor now or hereafter in
Creditors possession, whether held in a general or special account or deposit,
or for safekeeping or otherwise. Every such security interest and right of
setoff may be exercised without demand on or notice to Guarantor. No security
interest or right of setoff shall be deemed to have been waived by any act or
conduct on Creditor's part, or by any neglect to exercise such right of setoff
or to enforce such security interest, or by any delay in so doing. Every right
of setoff and security interest shall continue in full force and effect until
such right of setoff or security interest is specifically waived or released by
an instrument in writing executed by Creditor.

                  6.2.     If any one or more of Debtors or Guarantor are
corporations or partnerships, it is not necessary for Creditor to inquire into
the powers of Debtors or Guarantor or the officers, directors,

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partners or agents acting or purporting to act on their behalf, and any debt
made or created in reliance on the professed exercise of such powers shall be
guaranteed hereunder.

         7.       SUBORDINATION. The debt of Debtor to Creditor, whether now
existing or hereafter created, shall be prior to any claim that Guarantor may
now have or later acquire against Debtor, whether Debtor becomes insolvent, and
Guarantor expressly subordinates any such claim Guarantor may have against
Debtor, on any account whatsoever, to any claim that Creditor may now or
hereafter have against debtor. Guarantor waives any defense arising by reason
son of any disability or other defense of Debtor or by reason of the cessation
of Debtors liability for any reason. Guarantor shall not have any right of
subrogation until all debt of Debtor to Creditor shall have been paid in full.
In the event of insolvency and consequent liquidation of the assets of Debtor,
through bankruptcy, an assignment for the benefit of creditors, voluntary
liquidation or otherwise, the assets of Debtor applicable to the payment of the
claims of both Creditor and Guarantor shall be paid to Creditor and shall be
first applied by Creditor to the debt of Debtor to Creditor. Guarantor hereby
assigns to Creditor all claims which it may have or acquire against Debtor or
any assignee or trustee in bankruptcy of Debtor.

         8.       ASSIGNMENT OF GUARANTY Assignment by Creditor of all or part
of the debt shall transfer to the assignee all benefits of this Guaranty as to
the portion of the debt assigned. This Guaranty shall remain in effect in favor
of the Creditor as to the portion of the debt not assigned.

         9.       GUARANTOR. "GUARANTOR" includes all persons executing this
Guaranty. The liability of all Guarantors shall be joint and several.

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

         If any one or more provisions of this Agreement be determined to be
illegal or unenforceable, all other provisions shall nevertheless remain
effective. This Agreement shall inure to the benefit of and bind, as the case
may require, Creditor, its successors and assigns, including the assignees of
any credit guaranteed hereby, and Guarantees representatives, successors and
assigns.

 THE UNDERSIGNED SPECIFICALLY ACKNOWLEDGES READING ALL TERMS OF THIS CONTINUING
              CORPORATE GUARANTY AND RECEIPT OF A TRUE COPY OF IT.

"GUARANTOR"

/s/ Paul Crowe
----------------------------------
PAUL J. CROWE                                          DATED: July 1, 2000

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