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                                                                  Exhibit 4.5(A)

THE SECURITIES REPRESENTED BY THIS WARRANT HAVE NOT BEEN REGISTERED UNDER THE
SECURITIES ACT OF 1933, AS AMENDED, OR APPLICABLE STATE SECURITIES LAWS. THE
SECURITIES HAVE BEEN ACQUIRED FOR INVESTMENT AND MAY NOT BE OFFERED FOR SALE,
SOLD, TRANSFERRED OR ASSIGNED IN THE ABSENCE OF AN EFFECTIVE REGISTRATION
STATEMENT FOR THE SECURITIES UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR
APPLICABLE STATE SECURITIES LAWS, OR AN OPINION OF COUNSEL IN FORM, SUBSTANCE
AND SCOPE REASONABLY ACCEPTABLE TO THE ISSUER THAT REGISTRATION IS NOT REQUIRED
UNDER SAID ACT OR APPLICABLE STATE SECURITIES LAWS OR UNLESS SOLD PURSUANT TO
RULE 144 UNDER SAID ACT. ANY SUCH OFFER, SALE, ASSIGNMENT OR TRANSFER MUST ALSO
COMPLY WITH THE APPLICABLE STATE SECURITIES LAWS.

                          ALLIANCE MEDICAL CORPORATION

                             STOCK PURCHASE WARRANT

Date of Issuance:  July 1, 1999                         Number of Shares 37,500


            For value received, Alliance Medical Corporation, a Delaware
corporation (the "Company") hereby grants to Marquette Venture Partners III,
L.P. or its registered assigns (the "Registered Holder") the right to purchase
from the Company a number of shares of the Company's Common Stock (the "Common
Stock") at a price per share equal to $0.01 (the "Exercise Price").

            This Warrant is subject to the following provisions:

            Section 1. Exercise of Warrant.

            1A. Exercise Period. The Registered Holder may exercise, in whole or
in part, the purchase rights represented by this Warrant at any time and from
time to time after the Date of Issuance until the fifth anniversary of the date
hereof (the "Exercise Period").

            1B. Exercise Procedure.

            (i) This Warrant shall be deemed to have been exercised when the
Company has received all of the following items (the "Exercise Time"):

                        (a) a completed Exercise Agreement, as described in
            Section 1C below, executed by the Person exercising all or part of
            the purchase rights represented by this Warrant (the "Purchaser");

                        (b) this Warrant;
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                        (c) if this Warrant is not registered in the name of the
            Purchaser, an Assignment or Assignments in the form set forth in
            Exhibit II hereto evidencing the assignment of this Warrant to the
            Purchaser; and

                        (d) a check payable to the Company in an amount equal to
            the product of the Exercise Price multiplied by the number of shares
            of Common Stock being purchased upon such exercise (the "Aggregate
            Exercise Price").

            (ii) A certificate for shares of Common Stock purchased upon
exercise of this Warrant shall be delivered by the Company to the Purchaser
within ten business days after the date of the Exercise Time. Unless this
Warrant has expired or all of the purchase rights represented hereby have been
exercised, the Company shall prepare a new Warrant, substantially identical
hereto, representing the rights formerly represented by this Warrant which have
not expired or been exercised and shall, within such ten-day period, deliver
such new Warrant to the Person designated for delivery in the Exercise
Agreement.

            (iii) The Common Stock issuable upon the exercise of this Warrant
shall be deemed to have been issued to the Purchaser at the Exercise Time, and
the Purchaser shall be deemed for all purposes to have become the record holder
of such Common Stock at the Exercise Time.

            (iv) The issuance of certificates for shares of Common Stock upon
exercise of this Warrant shall be made without charge to the Registered Holder
or the Purchaser for any issuance tax in respect thereof or other cost incurred
by the Company in connection with such exercise and the related issuance of
shares of Common Stock. Each share of Common Stock issuable upon exercise of
this Warrant shall, upon payment of the Exercise Price therefor, be fully paid
and nonassessable and free from all liens and charges with respect to the
issuance thereof.

            (v) The Company shall not close its books against the transfer of
this Warrant or of any share of Common Stock issued or issuable upon the
exercise of this Warrant in any manner which interferes with the timely exercise
of this Warrant, except as required in order to comply with applicable federal
and state securities laws. The Company shall from time to time take all such
action as may be necessary to assure that the par value per share of the
unissued Common Stock acquirable upon exercise of this Warrant is at all times
equal to or less than the Exercise Price then in effect.

            (vi) The Company shall assist and cooperate with any Registered
Holder or Purchaser required to make any governmental filings or obtain any
governmental approvals prior to or in connection with any exercise of this
Warrant (including, without limitation, making any filings required to be made
by the Company), except that this subsection (vi) will not require the Company
to register the sale of the Common Stock underlying this Warrant under any
federal or state securities laws.

            (vii) Notwithstanding any other provision hereof, if an exercise of
any portion of this Warrant is to be made in connection with a registered public
offering or the sale of the Company, the exercise of any portion of this Warrant
may, at the election of the holder hereof, be

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conditioned upon the consummation of the public offering or sale of the Company
in which case such exercise shall not be deemed to be effective until the
consummation of such transaction.

            (viii) The Company shall at all times reserve and keep available out
of its authorized but unissued shares of Common Stock solely for the purpose of
issuance upon the exercise of the Warrants, such number of shares of Common
Stock issuable upon the exercise of all outstanding Warrants. All shares of
Common Stock which are so issuable shall, when issued, be duly and validly
issued, fully paid and nonassessable and free from all taxes, liens and charges.
The Company shall take all such actions as may be necessary to assure that all
such shares of Common Stock may be so issued without violation of any applicable
law or governmental regulation or any requirements of any domestic securities
exchange upon which shares of Common Stock may be listed (except for official
notice of issuance which shall be immediately delivered by the Company upon each
such issuance). The Company shall not take any action which would cause the
number of authorized but unissued shares of Common Stock to be less than the
number of such shares required to be reserved hereunder for issuance upon
exercise of the Warrant.

            (ix) If the shares of Common Stock issuable by reason of exercise of
this Warrant are convertible into or exchangeable for any other stock or
securities of the Company, the Company shall, at the exercising holder's option
and upon surrender of this Warrant by such holder as provided above together
with any notice, statement or payment required to effect such conversion or
exchange of Common Stock, deliver to such holder (or as otherwise specified by
such holder) a certificate or certificates representing the stock or securities
into which the shares of Common Stock issuable by reason of such conversion are
convertible or exchangeable, registered in such name or names and in such
denomination or denominations as such holder has specified.

            1C. Exercise Agreement. Upon any exercise of this Warrant, the
Exercise Agreement shall be substantially in the form set forth in Exhibit I
hereto, except that if the shares of Common Stock are not to be issued in the
name of the Person in whose name this Warrant is registered, the Exercise
Agreement shall also state the name of the Person to whom the certificates for
the shares of Common Stock are to be issued, and if the number of shares of
Common Stock to be issued does not include all the shares of Common Stock
purchasable hereunder, it shall also state the name of the Person to whom a new
Warrant for the unexercised portion of the rights hereunder is to be delivered.
Such Exercise Agreement shall be dated the actual date of execution thereof.

            Section 2.

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            2A. Subdivision or Combination of Common Stock. If the Company at
any time subdivides (by any stock split, stock dividend, recapitalization or
otherwise) one or more classes of its outstanding shares of Common Stock into a
greater number of shares, the Exercise Price in effect immediately prior to such
subdivision shall be proportionately reduced (but not below its par value) and
the number of shares of Common Stock obtainable upon exercise of this Warrant
shall be proportionately increased. If the Company at any time combines (by
reverse stock split or otherwise) one or more classes of its outstanding shares
of Common Stock into a smaller number of shares, the Exercise Price in effect
immediately prior to such combination shall be proportionately increased and the
number of shares of Common Stock obtainable upon exercise of this Warrant shall
be proportionately decreased.

            2B. Reorganization, Reclassification, Consolidation, Merger, or
Sale. Any recapitalization, reorganization, reclassification, consolidation,
merger, sale of all or substantially all of the Company's assets, or other
transaction, which in each case is effected in such a way that the holders of
Common Stock are entitled to receive (either directly or upon subsequent
liquidation) stock, securities, or assets with respect to or in exchange for
Common Stock is referred to herein as "Organic Change." Prior to the
consummation of any Organic Change, the Company shall make appropriate provision
(in form and substance satisfactory to the Registered Holders of the Warrants
representing a majority of the Common Stock obtainable upon exercise of all
Warrants then outstanding) to insure that each of the Registered Holders of the
Warrants shall thereafter have the right to acquire and receive, in lieu of or
addition to (as the case may be) the shares of Common Stock immediately
theretofore acquirable and receivable upon the exercise of such holder's
Warrant, such shares of stock, securities or assets as may be issued or payable
with respect to or in exchange for the number of shares of Common Stock
immediately theretofore acquirable and receivable upon exercise of such holder's
Warrant had such Organic Change not taken place. In any such case, the Company
shall make appropriate provision (in form and substance satisfactory to the
Registered Holders of the Warrants representing a majority of the Common Stock
obtainable upon exercise of all Warrants then outstanding) with respect to such
holders' rights and interests to insure that the provisions of this Section 2
and Section 4 hereof shall thereafter be applicable to the Warrants (including,
in the case of any such consolidation, merger or sale in which the successor
entity or purchasing entity is other than the Company, an immediate adjustment
of the Exercise Price to the value for the Common Stock reflected by the terms
of such consolidation, merger or sale, and a corresponding immediate adjustment
in the number of shares of Common Stock acquirable and receivable upon exercise
of the Warrants). The Company shall not effect any such consolidation, merger or
sale, unless prior to the consummation thereof, the successor entity (if other
than the Company) resulting from consolidation or merger or the entity
purchasing such assets assumes by written instrument (in form and substance
satisfactory to the Registered Holders of Warrants representing a majority of
the Common Stock obtainable upon exercise of all of the Warrants then
outstanding), the obligation to deliver to each such holder such shares of
stock, securities, or assets as, in accordance with the foregoing provisions,
such holder may be entitled to acquire.

            2C. Notices.

            (i) The Company shall give written notice to the Registered Holder
at least 20 days prior to the date on which the Company closes its books or
takes a record (A) with respect to

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any pro rata subscription offer to holders of Common Stock or (B) for
determining rights to vote with respect to any Organic Change, dissolution, or
liquidation.

            (ii) The Company shall also give written notice to the Registered
Holders at least 20 days prior to the date on which any Organic Change,
dissolution, or liquidation shall take place.

            Section 3. Purchase Rights. If at any time on or after the date this
Warrant becomes exercisable the Company grants, issues or sells any Options,
Convertible Securities, or rights to purchase stock, warrants, securities, or
other property pro rata to the record holders of any class of Common Stock (the
"Purchase Rights"), then the Registered Holder of this Warrant shall be entitled
to acquire, upon the terms applicable to such Purchase Rights, the aggregate
Purchase Rights which such holder could have acquired if such holder had held
the number of shares of Common Stock acquirable upon complete exercise of this
Warrant immediately before the date on which a record is taken for the grant,
issuance or sale of such Purchase Rights, or, if no such record is taken, the
date as of which the record holders of Common Stock are to be determined for the
grant, issue or sale of such Purchase Rights; provided that if the Purchase
Rights involve voting securities, the Company shall make available to the
Registered Holder of this Warrant, at such holder's request, Purchase Rights
involving securities (except as otherwise required by law) which are otherwise
identical to the Purchase Rights involving voting securities.

            Section 4. Definitions. The following terms have meanings set forth
below:

            "Common Stock" means the Company's Common Stock, par value $0.001
per share and any capital stock of any class of the Company hereafter authorized
which is not limited to a fixed sum or percentage of par or stated value in
respect to the rights of the holders thereof to participate in dividends or in
the distribution of assets upon any liquidation, dissolution or winding up of
the Company.

            "Convertible Securities" means any stock or securities (directly or
indirectly) convertible into or exchangeable for Common Stock.

            "Options" means any rights or options to subscribe for or purchase
Common Stock or Convertible Securities.

            "Person" means an individual, a partnership, a joint venture, a
corporation, a limited liability company, a trust, an unincorporated
organization and a government or any department or agency thereof.

            Section 5. No Voting Rights; Limitations of Liability. This Warrant
shall not entitle the holder hereof to any voting rights or other rights as a
stockholder of the Company. No provision hereof, in the absence of affirmative
action by the Registered Holder to purchase Common Stock, and no enumeration
herein of the rights or privileges of the Registered Holder shall give rise to
any liability of such holder for the Exercise Price of Common Stock acquirable
by exercise hereof or as a stockholder of the Company.

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            Section 6. Warrant Transferable. Subject to the transfer conditions
referred to in the legend endorsed hereon, this Warrant and all rights hereunder
are transferable, in whole or in part, without charge to the Registered Holder,
upon surrender of this Warrant with a properly executed Assignment (in the form
of Exhibit II hereto) at the principal office of the Company, subject to
compliance with applicable federal and state securities laws.

            Section 7. Warrant Exchangeable for Different Denominations. This
Warrant is exchangeable, upon the surrender hereof by the Registered Holder at
the principal office of the Company, for new Warrants of like tenor representing
in the aggregate the purchase rights hereunder, and each of such new Warrants
shall represent such portion of such rights as is designated by the Registered
Holder at the time of such surrender; provided that, as long as any Subject
Shares remain outstanding, this Warrant shall only be exchangeable in connection
with the exchange of the certificate representing such Subject Shares pursuant
to the Company's Certificate of Incorporation. The date the Company initially
issues this Warrant shall be deemed to be the "Date of Issuance" hereof
regardless of the number of times new certificates representing the unexpired
and unexercised rights formerly represented by this Warrant shall be issued. All
Warrants representing portions of the rights hereunder are referred to herein as
the "Warrants."

            Section 8. Replacement. Upon receipt of evidence reasonably
satisfactory to the Company (an affidavit of the Registered Holder shall be
satisfactory) of the ownership and the loss, theft, destruction or mutilation of
any certificate evidencing this Warrant, and in the case of any such loss, theft
or destruction, upon receipt of indemnity reasonably satisfactory to the Company
(provided that if the holder is a financial institution or other institutional
investor its own agreement shall be satisfactory), or, in the case of any such
mutilation upon surrender of such certificate, the Company shall (at its
expense) execute and deliver in lieu of such certificate a new certificate of
like kind representing the same rights represented by such lost, stolen,
destroyed or mutilated certificate and dated the date of such lost, stolen,
destroyed or mutilated certificate.

            Section 9. Notices. Except as otherwise expressly provided herein,
all notices referred to in this Warrant shall be in writing and shall be
delivered personally, sent by reputable overnight courier service (charges
prepaid) or sent by registered or certified mail, return receipt requested,
postage prepaid and shall be deemed to have been given when received (if hand
delivered) or five days after delivered, sent or deposited in the U.S. Mail or
by overnight courier (i) to the Company, at its principal executive offices and
(ii) to the Registered Holder of this Warrant, at such holder's address as it
appears in the records of the Company (unless otherwise indicated by any such
holder).

            Section 10. Amendment and Waiver. Except as otherwise provided
herein, the provisions of the Warrants may be amended and the Company may take
any action herein prohibited, or omit to perform any act herein required to be
performed by it, only if the Company has obtained the written consent of the
Registered Holders of Warrants representing a majority of the shares of Common
Stock obtainable upon exercise of the Warrants; provided that no such action may
change the Exercise Price of the Warrants or the number of shares or class of
stock obtainable upon exercise of each Warrant without the written consent of
Registered Holders beneficially owning a majority of the subject Shares.

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            Section 11. Descriptive Headings; Governing Law. The descriptive
headings of the several Sections and paragraphs of this Warrant are inserted for
convenience only and do not constitute a part of this Warrant. The corporation
laws of the State of Arizona shall govern all issues concerning the relative
rights of the Company and its stockholders. All other questions concerning the
construction, validity, enforcement and interpretation of this Warrant shall be
governed by the internal law of the State of Arizona, without giving effect to
any choice of law or conflict of law provision or rule (whether of the State of
Arizona or any other jurisdictions) that would cause the application of the laws
of any jurisdictions other than the State of Arizona.

            IN WITNESS WHEREOF, the Company has caused this Warrant to be signed
and attested by its duly authorized officers under its corporate seal and to be
dated the Date of Issuance hereof.

                                           ALLIANCE MEDICAL CORPORATION

                                           By____________________________

                                           Its_____________________________

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                                                                       EXHIBIT I

                               EXERCISE AGREEMENT

To:                                                           Dated:

            The undersigned, pursuant to the provisions set forth in the
attached Warrant, hereby agrees to subscribe for the purchase of ______ shares
of the Common Stock covered by such Warrant and makes payment herewith in full
therefor at the price per share provided by such Warrant.

                                                 Signature ____________________

                                                 Address ______________________

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                                                                      EXHIBIT II

                                   ASSIGNMENT

            FOR VALUE RECEIVED, _____________________________ hereby sells,
assigns and transfers all of the rights of the undersigned under the attached
Warrant with respect to the number of shares of the Common Stock covered thereby
set forth below, unto:

Names of Assignee                  Address                  No. of Shares



Dated:                                 Signature        _______________________

                                                        _______________________


                                       Witness          _______________________

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