Document:

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                                                                Exhibit 10.12(a)

                            MASTER SECURITY AGREEMENT
                    dated as of OCTOBER 4, 2001 ("AGREEMENT")

          THIS AGREEMENT is between GENERAL ELECTRIC CAPITAL CORPORATION
   (together with its successors and assigns, if any, "SECURED PARTY") and
   ALLIANCE MEDICAL CORPORATION ("DEBTOR"). Secured Party has an office at 401
   Merritt 7 Suite 23, Norwalk, CT 06851. Debtor is a corporation organized and
   existing under the laws of the state of Delaware. Debtor's mailing address
   and chief place of business is 10232 S 51st street, Phoenix, AZ 85044.

   1.    CREATION OF SECURITY INTEREST.

         Debtor grants to Secured Party, its successors and assigns, a security
   interest in and against all property listed on any collateral schedule now or
   in the future annexed to or made a part of this Agreement ("COLLATERAL
   SCHEDULE"), and in and against all additions, attachments, accessories and
   accessions to such property, all substitutions, replacements or exchanges
   therefor, and all insurance and/or other proceeds thereof (all such property
   is individually and collectively called the "COLLATERAL"). This security
   interest is given to secure the payment and performance of all debts,
   obligations and liabilities of any kind whatsoever of Debtor to Secured
   Party, now existing or arising in the future, including but not limited to
   the payment and performance of certain Promissory Notes from time to time
   identified on any Collateral Schedule (collectively "NOTES" and each a
   "NOTE"), and any renewals, extensions and modifications of such debts,
   obligations and liabilities (such Notes, debts, obligations and liabilities
   are called the "INDEBTEDNESS"). Unless otherwise provided by applicable law,
   notwithstanding anything to the contrary contained in this Agreement, to the
   extent that Secured Party asserts a purchase money security interest in any
   items of Collateral ("PMSI COLLATERAL"): (i) the PMSI Collateral shall secure
   only that portion of the Indebtedness which has been advanced by Secured
   Party to enable Debtor to purchase, or acquire rights in or the use of such
   PMSI Collateral (the "PMSI INDEBTEDNESS"), and (ii) no other Collateral shall
   secure the PMSI Indebtedness.

   2.    REPRESENTATIONS, WARRANTIES AND COVENANTS OF DEBTOR.

         Debtor represents, warrants and covenants as of the date of this
   Agreement and as of the date of each Collateral Schedule that:

         (a)Debtor's exact legal name is as set forth in the preamble of this
   Agreement and Debtor is, and will remain, duly organized, existing and in
   good standing under the laws of the State set forth in the preamble of this
   Agreement, has its chief executive offices at the location specified in the
   preamble, and is, and will remain, duly qualified and licensed in every
   jurisdiction wherever necessary to carry on its business and operations;

         (b)Debtor has adequate power and capacity to enter into, and to perform
   its obligations under this Agreement, each Note and any other documents
   evidencing, or given in connection with, any of the Indebtedness (all of the
   foregoing are called the "DEBT DOCUMENTS");

         (c)This Agreement and the other Debt Documents have been duly
   authorized, executed and delivered by Debtor and constitute legal, valid and
   binding agreements enforceable in accordance with their terms, except to the
   extent that the enforcement of remedies may be limited under applicable
   bankruptcy and insolvency laws;

         (d)No approval, consent or withholding of objections is required from
   any governmental authority or instrumentality with respect to the entry into,
   or performance by Debtor of any of the Debt Documents, except any already
   obtained;

         (e)The entry into, and performance by, Debtor of the Debt Documents
   will not (i) violate any of the organizational documents of Debtor or any
   judgment, order, law or regulation applicable to Debtor, or (ii) result in
   any breach of or constitute a default under any contract to which Debtor is a
   party, or result in the creation of any lien, claim or encumbrance on any of
   Debtor's property (except for liens in favor of Secured Party) pursuant to
   any indenture, mortgage, deed of trust, bank loan, credit agreement, or other
   agreement or instrument to which Debtor is a party;
<PAGE>   2

         (f)There are no suits or proceedings pending in court or before any
   commission, board or other administrative agency against or affecting Debtor
   which could, in the aggregate, have a material adverse effect on Debtor, its
   business or operations, or its ability to perform its obligations under the
   Debt Documents, nor does Debtor have reason to believe that any such suits or
   proceedings are threatened;

         (g)All financial statements delivered to Secured Party in connection
   with the Indebtedness have been prepared in accordance with generally
   accepted accounting principles, and since the date of the most recent
   financial statement, there has been no material adverse change in Debtors
   financial condition;

         (h)The Collateral is not, and will not be, used by Debtor for personal,
   family or household purposes;

         (i)The Collateral is, and will remain, in good condition and repair and
   Debtor will not be negligent in its care and use;

         (j)Debtor is, and will remain, the sole and lawful owner, and in
   possession of, the Collateral, and has the sole right and lawful authority to
   grant the security interest described in this Agreement; and

         (k)The Collateral is, and will remain, free and clear of all liens,
   claims and encumbrances of any kind whatsoever, except for (i) liens in favor
   of Secured Party, (ii) liens for taxes not yet due or for taxes being
   contested in good faith and which do not involve, in the judgment of Secured
   Party, any risk of the sale, forfeiture or loss of any of the Collateral, and
   (iii) inchoate materialmen's, mechanic's, repairmen's and similar liens
   arising by operation of law in the normal course of business for amounts
   which are not delinquent (all of such liens are called "PERMITTED LIENS").

   3.    COLLATERAL.

         (a)Until the declaration of any default, Debtor shall remain in
   possession of the Collateral; except that Secured Party shall have the right
   to possess (i) any chattel paper or instrument that constitutes a part of the
   Collateral, and (ii) any other Collateral in which Secured Party's security
   interest may be perfected only by possession. Secured Party may inspect any
   of the Collateral during normal business hours after giving Debtor reasonable
   prior notice. If Secured Party asks, Debtor will promptly notify Secured
   Party in writing of the location of any Collateral.

         (b)Debtor shall (i) use the Collateral only in its trade or business,
   (ii) maintain all of the Collateral in good operating order and repair,
   normal wear and tear excepted, (iii) use and maintain the Collateral only in
   compliance with manufacturers recommendations and all applicable laws, and
   (iv) keep all of the Collateral free and clear of all liens, claims and
   encumbrances (except for Permitted Liens).

         (c)Secured Party does not authorize and Debtor agrees it shall not (i)
   part with possession of any of the Collateral (except to Secured Party or for
   maintenance and repair), (ii) remove any of the Collateral from the
   continental United States, or (iii) sell, rent, lease, mortgage, license,
   grant a security interest in or otherwise transfer or encumber (except for
   Permitted Liens) any of the Collateral.

         (d)Debtor shall pay promptly when due all taxes, license fees,
   assessments and public and private charges levied or assessed on any of the
   Collateral, on its use, or on this Agreement or any of the other Debt
   Documents. At its option, Secured Party may discharge taxes, liens, security
   interests or other encumbrances at any time levied or placed on the
   Collateral and may pay for the maintenance, insurance and preservation of the
   Collateral and effect compliance with the terms of this Agreement or any of
   the other Debt Documents. Debtor agrees to reimburse Secured Party, on
   demand, all costs and expenses incurred by Secured Party in connection with
   such payment or performance and agrees that such reimbursement obligation
   shall constitute Indebtedness.

         (e)Debtor shall, at all times, keep accurate and complete records of
   the Collateral, and Secured Party shall have the right to inspect and make
   copies of all of Debtor's books and records relating to the Collateral during
   normal business hours, after giving Debtor reasonable prior notice.

         (f)Debtor agrees and acknowledges that any third person who may at any
   time possess all or any portion of the Collateral shall be deemed to hold,
   and shall hold, the Collateral as the agent of, and as pledge holder for,
   Secured Party. Secured Party may at any time give notice to any third person
   described in the preceding sentence that such third person is holding the
   Collateral as the agent of, and as pledge holder for, the Secured Party.

   4.    INSURANCE.

         (a)Debtor shall at all times bear the entire risk of any loss, theft,
   damage to, or destruction of, any of the Collateral from any cause
   whatsoever.
<PAGE>   3

         (b)Debtor agrees to keep the Collateral insured against loss or damage
   by fire and extended coverage perils, theft, burglary, and for any or all
   Collateral which are vehicles, for risk of loss by collision, and if
   requested by Secured Party, against such other risks as Secured Party may
   reasonably require. The insurance coverage shall be in an amount no less than
   the full replacement value of the Collateral, and deductible amounts,
   insurers and policies shall be acceptable to Secured Party. Debtor shall
   deliver to Secured Party policies or certificates of insurance evidencing
   such coverage. Each policy shall name Secured Party as a loss payee, shall
   provide for coverage to Secured Party regardless of the breach by Debtor of
   any warranty or representation made therein, shall not be subject to
   co-insurance, and shall provide that coverage may not be canceled or altered
   by the insurer except upon thirty (30) days prior written notice to Secured
   Party. Debtor appoints Secured Party as its attorney-in-fact to make proof of
   loss, claim for insurance and adjustments with insurers, and to receive
   payment of and execute or endorse all documents, checks or drafts in
   connection with insurance payments. Secured Party shall not act as Debtor's
   attorney-in-fact unless Debtor is in default. Proceeds of insurance shall be
   applied, at the option of Secured Party, to repair or replace the Collateral
   or to reduce any of the Indebtedness.

   5.    REPORTS.

         (a)Debtor shall promptly notify Secured Party of (i) any change in the
   name of Debtor, (ii) any change in the state of its incorporation or
   registration, (iii) any relocation of its chief executive offices, (iv) any
   relocation of any of the Collateral, (v) any of the Collateral being lost,
   stolen, missing, destroyed, materially damaged or worn out, or (vi) any lien,
   claim or encumbrance other than Permitted Liens attaching to or being made
   against any of the Collateral.

         (b)Debtor will deliver to Secured Party Debtor's complete financial
   statements, certified by a recognized firm of certified public accountants,
   within ninety (90) days of the close of each fiscal year of Debtor. If
   Secured Party requests, Debtor will deliver to Secured Party copies of
   Debtor's quarterly financial reports certified by Debtor's chief financial
   officer, within ninety (90) days after the close of each of Debtor's fiscal
   quarter. Debtor will deliver to Secured Party copies of all Forms 10-K and
   10-Q, if any, within 30 days after the dates on which they are filed with the
   Securities and Exchange Commission.

   6.    FURTHER ASSURANCES.

         (a)Debtor shall, upon request of Secured Party, furnish to Secured
   Party such further information, execute and deliver to Secured Party such
   documents and instruments (including, without limitation, Uniform Commercial
   Code financing statements) and shall do such other acts and things as Secured
   Party may at any time reasonably request relating to the perfection or
   protection of the security interest created by this Agreement or for the
   purpose of carrying out the intent of this Agreement. Without limiting the
   foregoing, Debtor shall cooperate and do all acts deemed necessary or
   advisable by Secured Party to continue in Secured Party a perfected first
   security interest in the Collateral, and shall obtain and furnish to Secured
   Party any subordinations, releases, landlord waivers, lessor waivers,
   mortgagee waivers, or control agreements, and similar documents as may be
   from time to time requested by, and in form and substance satisfactory to,
   Secured Party.

         (b)Debtor authorizes Secured Party to file a financing statement and
   amendments thereto describing the Collateral and containing any other
   information required by the applicable Uniform Commercial Code. Debtor
   irrevocably grants to Secured Party the power to sign Debtor's name and
   generally to act on behalf of Debtor to execute and file applications for
   title, transfers of title, financing statements, notices of lien and other
   documents pertaining to any or all of the Collateral; this power is coupled
   with Secured Party's interest in the Collateral. Debtor shall, if any
   certificate of title be required or permitted by law for any of the
   Collateral, obtain and promptly deliver to Secured Party such certificate
   showing the lien of this Agreement with respect to the Collateral. Debtor
   ratifies its prior authorization for Secured Party to file financing
   statements and amendments thereto describing the Collateral and containing
   any other information required by the Uniform Commercial Code if filed prior
   to the date hereof.

         (c)Debtor shall indemnify and defend the Secured Party, its successors
   and assigns, and their respective directors, officers and employees, from and
   against all claims, actions and suits (including, without limitation, related
   attorneys' fees) of any kind whatsoever arising, directly or indirectly, in
   connection with any of the Collateral.

   7.    DEFAULT AND REMEDIES.

         (a)Debtor shall be in default under this Agreement and each of the
other Debt Documents if:

            (i) Debtor breaches its obligation to pay when due any installment
   or other amount due or coming due under any of the Debt Documents;
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            (ii)Debtor, without the prior written consent of Secured Party,
   attempts to or does sell, rent, lease, license, mortgage, grant a security
   interest in, or otherwise transfer or encumber (except for Permitted Liens)
   any of the Collateral;

            (iii) Debtor breaches any of its insurance obligations under Section
   4;

            (iv)Debtor breaches any of its other obligations under any of the
   Debt Documents and fails to cure that breach within thirty (30) days after
   written notice from Secured Party;

            (v) Any warranty, representation or statement made by Debtor in any
   of the Debt Documents or otherwise in connection with any of the Indebtedness
   shall be false or misleading in any material respect;

            (vi)Any of the Collateral is subjected to attachment, execution,
   levy, seizure or confiscation in any legal proceeding or otherwise, or if any
   legal or administrative proceeding is commenced against Debtor or any of the
   Collateral, which in the good faith judgment of Secured Party subjects any of
   the Collateral to a material risk of attachment, execution, levy, seizure or
   confiscation and no bond is posted or protective order obtained to negate
   such risk;

            (vii) Debtor breaches or is in default under any other agreement
   between Debtor and Secured Party;

            (viii) Debtor or any guarantor or other obligor for any of the
   Indebtedness (collectively "GUARANTOR") dissolves, terminates its existence,
   becomes insolvent or ceases to do business as a going concern;

            (ix)If Debtor or any Guarantor is a natural person, Debtor or any
   such Guarantor dies or becomes incompetent;

            (x) A receiver is appointed for all or of any part of the property
   of Debtor or any Guarantor, or Debtor or any Guarantor makes any assignment
   for the benefit of creditors;

            (xi)Debtor or any Guarantor files a petition under any bankruptcy,
   insolvency or similar law, or any such petition is filed against Debtor or
   any Guarantor and is not dismissed within forty-five (45) days;

            (xii) Debtor's improper filing of an amendment or termination
   statement relating to a filed financing statement describing the Collateral;
   or

         (b)If Debtor is in default, the Secured Party, at its option, may
   declare any or all of the Indebtedness to be immediately due and payable,
   without demand or notice to Debtor or any Guarantor. The accelerated
   obligations and liabilities shall bear interest (both before and after any
   judgment) until paid in full at the lower of eighteen percent (18%) per annum
   or the maximum rate not prohibited by applicable law.

         (c)After default, Secured Party shall have all of the rights and
   remedies of a Secured Party under the Uniform Commercial Code, and under any
   other applicable law. Without limiting the foregoing, Secured Party shall
   have the right to (i) notify any account debtor of Debtor or any obligor on
   any instrument which constitutes part of the Collateral to make payment to
   the Secured Party, (ii) with or without legal process, enter any premises
   where the Collateral may be and take possession of and remove the Collateral
   from the premises or store it on the premises, (iii) sell the Collateral at
   public or private sale, in whole or in part, and have the right to bid and
   purchase at said sale, or (iv) lease or otherwise dispose of all or part of
   the Collateral, applying proceeds from such disposition to the obligations
   then in default. If requested by Secured Party, Debtor shall promptly
   assemble the Collateral and make it available to Secured Party at a place to
   be designated by Secured Party which is reasonably convenient to both
   parties. Secured Party may also render any or all of the Collateral unusable
   at the Debtor's premises and may dispose of such Collateral on such premises
   without liability for rent or costs. Any notice that Secured Party is
   required to give to Debtor under the Uniform Commercial Code of the time and
   place of any public sale or the time after which any private sale or other
   intended disposition of the Collateral is to be made shall be deemed to
   constitute reasonable notice if such notice is given to the last known
   address of Debtor at least five (5) days prior to such action.

         (d)Proceeds from any sale or lease or other disposition shall be
   applied: first, to all costs of repossession, storage, and disposition
   including without limitation attorneys', appraisers', and auctioneers' fees;
   second, to discharge the obligations then in default; third, to discharge any
   other Indebtedness of Debtor to Secured Party, whether as obligor, endorser,
   guarantor, surety or indemnitor; fourth, to expenses incurred in paying or
   settling liens and claims against the Collateral; and lastly, to Debtor, if
   there exists any surplus. Debtor shall remain fully liable for any
   deficiency.
<PAGE>   5

         (e)Debtor agrees to pay all reasonable attorneys' fees and other costs
   incurred by Secured Party in connection with the enforcement, assertion,
   defense or preservation of Secured Party's rights and remedies under this
   Agreement, or if prohibited by law, such lesser sum as may be permitted.
   Debtor further agrees that such fees and costs shall constitute Indebtedness.

         (f)Secured Party's rights and remedies under this Agreement or
   otherwise arising are cumulative and may be exercised singularly or
   concurrently. Neither the failure nor any delay on the part of the Secured
   Party to exercise any right, power or privilege under this Agreement shall
   operate as a waiver, nor shall any single or partial exercise of any right,
   power or privilege preclude any other or further exercise of that or any
   other right, power or privilege. SECURED PARTY SHALL NOT BE DEEMED TO HAVE
   WAIVED ANY OF ITS RIGHTS UNDER THIS AGREEMENT OR UNDER ANY OTHER AGREEMENT,
   INSTRUMENT OR PAPER SIGNED BY DEBTOR UNLESS SUCH WAIVER IS EXPRESSED IN
   WRITING AND SIGNED BY SECURED PARTY. A waiver on any one occasion shall not
   be construed as a bar to or waiver of any right or remedy on any future
   occasion.

         (g)DEBTOR AND SECURED PARTY UNCONDITIONALLY WAIVE THEIR RIGHTS TO A
   JURY TRIAL OF ANY CLAIM OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF THIS
   AGREEMENT, ANY OF THE OTHER DEBT DOCUMENTS, ANY OF THE INDEBTEDNESS SECURED
   HEREBY, ANY DEALINGS BETWEEN DEBTOR AND SECURED PARTY RELATING TO THE SUBJECT
   MATTER OF THIS TRANSACTION OR ANY RELATED TRANSACTIONS, AND/OR THE
   RELATIONSHIP THAT IS BEING ESTABLISHED BETWEEN DEBTOR AND SECURED PARTY. THE
   SCOPE OF THIS WAIVER IS INTENDED TO BE ALL ENCOMPASSING OF ANY AND ALL
   DISPUTES THAT MAY BE FILED IN ANY COURT. THIS WAIVER IS IRREVOCABLE. THIS
   WAIVER MAY NOT BE MODIFIED EITHER ORALLY OR IN WRITING. THE WAIVER ALSO SHALL
   APPLY TO ANY SUBSEQUENT AMENDMENTS, RENEWALS, SUPPLEMENTS OR MODIFICATIONS TO
   THIS AGREEMENT, ANY OTHER DEBT DOCUMENTS, OR TO ANY OTHER DOCUMENTS OR
   AGREEMENTS RELATING TO THIS TRANSACTION OR ANY RELATED TRANSACTION. THIS
   AGREEMENT MAY BE FILED AS A WRITTEN CONSENT TO A TRIAL BY THE COURT.

   8.    MISCELLANEOUS.

         (a)This Agreement, any Note and/or any of the other Debt Documents may
   be assigned, in whole or in part, by Secured Party without notice to Debtor,
   and Debtor agrees not to assert against any such assignee, or assignee's
   assigns, any defense, set-off, recoupment claim or counterclaim which Debtor
   has or may at any time have against Secured Party for any reason whatsoever.
   Debtor agrees that if Debtor receives written notice of an assignment from
   Secured Party, Debtor will pay all amounts payable under any assigned Debt
   Documents to such assignee or as instructed by Secured Party. Debtor also
   agrees to confirm in writing receipt of the notice of assignment as may be
   reasonably requested by Secured Party or assignee.

         (b)All notices to be given in connection with this Agreement shall be
   in writing, shall be addressed to the parties at their respective addresses
   set forth in this Agreement (unless and until a different address may be
   specified in a written notice to the other party), and shall be deemed given
   (i) on the date of receipt if delivered in hand or by facsimile transmission,
   (ii) on the next business day after being sent by express mail, and (iii) on
   the fourth business day after being sent by regular, registered or certified
   mail. As used herein, the term "business day" shall mean and include any day
   other than Saturdays, Sundays, or other days on which commercial banks in New
   York, New York are required or authorized to be closed.

         (c)Secured Party may correct patent errors and fill in all blanks in
   this Agreement or in any Collateral Schedule consistent with the agreement of
   the parties.

         (d)Time is of the essence of this Agreement. This Agreement shall be
   binding, jointly and severally, upon all parties described as the "Debtor"
   and their respective heirs, executors, representatives, successors and
   assigns, and shall inure to the benefit of Secured Party, its successors and
   assigns.

         (e)This Agreement and its Collateral Schedules constitute the entire
   agreement between the parties with respect to the subject matter of this
   Agreement and supersede all prior understandings (whether written, verbal or
   implied) with respect to such subject matter. THIS AGREEMENT AND ITS
   COLLATERAL SCHEDULES SHALL NOT BE CHANGED OR TERMINATED ORALLY OR BY COURSE
   OF CONDUCT, BUT ONLY BY A WRITING SIGNED BY BOTH PARTIES. Section headings
   contained in this Agreement have been included for convenience only, and
   shall not affect the construction or interpretation of this Agreement.

         (f)This Agreement shall continue in full force and effect until all of
   the Indebtedness has been indefeasibly paid in full to Secured Party or its
   assignee. The surrender, upon payment or otherwise, of any Note or any of the
   other documents evidencing any of the Indebtedness shall not affect the right
   of Secured Party to retain the Collateral for such other Indebtedness as may
   then exist or as it may be reasonably contemplated will exist in the future.
   This Agreement shall automatically be reinstated if Secured Party is ever
   required to return or restore the payment of all or any portion of the
   Indebtedness (all as though such payment had never been made).
<PAGE>   6

         (g)THIS AGREEMENT AND THE RIGHTS AND OBLIGATIONS OF THE PARTIES
   HEREUNDER SHALL IN ALL RESPECTS BE GOVERNED BY AND CONSTRUED IN ACCORDANCE
   WITH, THE INTERNAL LAWS OF THE STATE OF CONNECTICUT (WITHOUT REGARD TO THE
   CONFLICT OF LAWS PRINCIPLES OF SUCH STATE), INCLUDING ALL MATTERS OF
   CONSTRUCTION, VALIDITY AND PERFORMANCE, REGARDLESS OF THE LOCATION OF THE
   EQUIPMENT.

         IN WITNESS WHEREOF, Debtor and Secured Party, intending to be legally
  bound hereby, have duly executed this Agreement in one or more counterparts,
  each of which shall be deemed to be an original, as of the day and year first
  aforesaid.

  SECURED PARTY:                                                     DEBTOR:

  GENERAL ELECTRIC CAPITAL CORPORATION    ALLIANCE MEDICAL CORPORATION

By: /s/ Thomas Annino                 By: /s/ Tim Einwechter

Name:   Thomas Annino                 Name:   Tim Einwechter

Title:                                Title:  CFO

<PAGE>   7
                                    AMENDMENT

         THIS AMENDMENT is made as of the 4th day of October, 2001, between
General Electric Capital Corporation ("Secured Party") and Alliance Medical
Corporation ("Debtor") in connection with that certain Master Security
Agreement, dated or dated as of October 4, 2001 ("Agreement"). The terms at this
Amendment are hereby incorporated into the Agreement as though fully set forth
therein. Section references below refer to the section numbers of the Agreement.
The Agreement is hereby amended as follows:

         2.       REPRESENTATIONS, WARRANTIES AND COVENANTS OF DEBTOR.

         Subsection (f) is hereby amended and replaced with the following:

                  As of the date of this Agreement, except as previously
                  disclosed to the Secured Party, there are no suits or
                  proceedings pending in court or before any commission, board
                  or other administrative agency against or affecting Debtor
                  which could, in the aggregate, have a material adverse effect
                  on Debtor, its business or operations, or its ability to
                  perform its obligations under the Debt Documents, nor does
                  Debtor have reason to believe that any such suits or
                  proceedings are threatened;

         6.       FURTHER ASSURANCES.

         Subsection (c) is hereby amended and replaced with the following:

                  Debtor shall indemnify and defend the Secured Party, its
                  successors and assigns, and their respective directors,
                  officers and employees, from and against all claims, actions
                  and suits (including, without limitation, related attorneys'
                  fees) of any kind whatsoever arising, directly or indirectly,
                  in connection with any of the Collateral, excluding all
                  claims, actions and suits of any kind whatsoever arising from
                  the Secured Party's, its successors and assigns, and their
                  respective directors, officers and employees, willful
                  misconduct and gross negligence.

         7.       DEFAULT AND REMEDIES.

         Subsection (ix) is intentionally omitted.

         TERMS USED, BUT NOT OTHERWISE DEFINED HEREIN SHALL HAVE THE MEANINGS
GIVEN TO THEM IN THE AGREEMENT. EXCEPT AS EXPRESSLY AMENDED HEREBY, THE
AGREEMENT SHALL REMAIN IN FULL FORCE AND EFFECT. IF THERE IS ANY CONFLICT
BETWEEN THE PROVISIONS OF THE AGREEMENT AND THIS AMENDMENT, THEN THIS AMENDMENT
SHALL CONTROL.

         IN WITNESS WHEREOF, the parties hereto have executed this Amendment
simultaneously with the Agreement by signature of their respective authorized
representative set forth below.

GENERAL ELECTRIC CAPITAL CORPORATION         ALLIANCE MEDICAL CORPORATION

By: /s/ Thomas Annino                        By:/s/ Tim Einwechter
    --------------------------------------      -------------------------------

Name: Thomas Annino                          Name:  Tim Einwechter
      ------------------------------------        -----------------------------

Title:                                       Title: CFO
      ------------------------------------        ------------------------------<PAGE>   1
                                                                EXHIBIT 10.12(b)

                                 PROMISSORY NOTE

                              --------------------
                                     (DATE)

FOR VALUE RECEIVED, Alliance Medical Corporation, a Delaware corporation located
at the address stated below ("MAKER") promises, jointly and severally if more
than one, to pay to the order of GENERAL ELECTRIC CAPITAL CORPORATION or any
subsequent holder hereof (each, a "PAYEE") at its office located at 401 MERRITT
7 2ND FLOOR, NORWALK, CT 06856 or at such other place as Payee or the holder
hereof may designate, the principal sum of ____________________ DOLLARS
($____________________), with interest on the unpaid principal balance, from the
date hereof through and including the dates of payment, at a fixed interest rate
of ____________________ percent (____________________%) per annum, to be paid in
lawful money of the United States, in ____________________
(____________________) consecutive _______________ installments of principal and
interest as follows:

          Periodic

         Installment               Amount

each ("Periodic Installment") and a final installment which shall be in the
amount of the total outstanding principal and interest. The first Periodic
Installment shall be due and payable on ____________________ and the following
Periodic Installments and the final installment shall be due and payable on the
same day of each succeeding _______________ (each, a "Payment Date"). Such
installments have been calculated on the basis of a 360 day year of twelve
30-day months. Each payment may, at the option of the Payee, be calculated and
applied on an assumption that such payment would be made on its due date.

The acceptance by Payee of any payment which is less than payment in full of all
amounts due and owing at such time shall not constitute a waiver of Payee's
right to receive payment in full at such time or at any prior or subsequent
time.

The Maker hereby expressly authorizes the Payee to insert the date value is
actually given in the blank space on the face hereof and on all related
documents pertaining hereto.

This Note may be secured by a security agreement, chattel mortgage, pledge
agreement or like instrument (each of which is hereinafter called a "SECURITY
AGREEMENT").

Time is of the essence hereof. If any installment or any other sum due under
this Note or any Security Agreement is not received within ten (10) days after
its due date, the Maker agrees to pay, in addition to the amount of each such
installment or other sum, a late payment charge of five percent (5%) of the
amount of said applicable late payment, but not exceeding any lawful maximum. If
(i) Maker fails to make payment of any amount due hereunder within ten (10) days
after the same becomes due and payable; or (ii) Maker is in default under, or
fails to perform under any term or condition contained in any Security
Agreement, then the entire principal sum remaining unpaid, together with all
accrued interest thereon and any other sum payable under this Note or any
Security Agreement, at the election of Payee, shall immediately become due and
payable, with interest thereon at the lesser of eighteen percent (18%) per annum
or the highest rate not prohibited by applicable law from the date of such
accelerated maturity until paid (both before and after any judgment).

The Maker may prepay in full, but not in part, its entire indebtedness hereunder
upon payment of the entire indebtedness plus an additional sum as a premium of
the original principal balance.

It is the intention of the parties hereto to comply with the applicable usury
laws; accordingly, it is agreed that, notwithstanding any provision to the
contrary in this Note or any Security Agreement, in no event shall this Note or
any Security Agreement require the payment or permit the collection of interest
in excess of
<PAGE>   2
the maximum amount permitted by applicable law. If any such excess
interest is contracted for, charged or received under this Note or any Security
Agreement, or if all of the principal balance shall be prepaid, so that under
any of such circumstances the amount of interest contracted for, charged or
received under this Note or any Security Agreement on the principal balance
shall exceed the maximum amount of interest permitted by applicable law, then in
such event (a) the provisions of this paragraph shall govern and control, (b)
neither Maker nor any other person or entity now or hereafter liable for the
payment hereof shall be obligated to pay the amount of such interest to the
extent that it is in excess of the maximum amount of interest permitted by
applicable law, (c) any such excess which may have been collected shall be
either applied as a credit against the then unpaid principal balance or refunded
to Maker, at the option of the Payee, and (d) the effective rate of interest
shall be automatically reduced to the maximum lawful contract rate allowed under
applicable law as now or hereafter construed by the courts having jurisdiction
thereof. It is further agreed that without limitation of the foregoing, all
calculations of the rate of interest contracted for, charged or received under
this Note or any Security Agreement which are made for the purpose of
determining whether such rate exceeds the maximum lawful contract rate, shall be
made, to the extent permitted by applicable law, by amortizing, prorating,
allocating and spreading in equal parts during the period of the full stated
term of the indebtedness evidenced hereby, all interest at any time contracted
for, charged or received from Maker or otherwise by Payee in connection with
such indebtedness; provided, however, that if any applicable state law is
amended or the law of the United States of America preempts any applicable state
law, so that it becomes lawful for the Payee to receive a greater interest per
annum rate than is presently allowed, the Maker agrees that, on the effective
date of such amendment or preemption, as the case may be, the lawful maximum
hereunder shall be increased to the maximum interest per annum rate allowed by
the amended state law or the law of the United States of America.

The Maker and all sureties, endorsers, guarantors or any others (each such
person, other than the Maker, an "OBLIGOR") who may at any time become liable
for the payment hereof jointly and severally consent hereby to any and all
extensions of time, renewals, waivers or modifications of, and all substitutions
or releases of, security or of any party primarily or secondarily liable on this
Note or any Security Agreement or any term and provision of either, which may be
made, granted or consented to by Payee, and agree that suit may be brought and
maintained against any one or more of them, at the election of Payee without
joinder of any other as a party thereto, and that Payee shall not be required
first to foreclose, proceed against, or exhaust any security hereof in order to
enforce payment of this Note. The Maker and each Obligor hereby waives
presentment, demand for payment, notice of nonpayment, protest, notice of
protest, notice of dishonor, and all other notices in connection herewith, as
well as filing of suit (if permitted by law) and diligence in collecting this
Note or enforcing any of the security hereof, and agrees to pay (if permitted by
law) all expenses incurred in collection, including Payee's actual attorneys'
fees. Maker and each Obligor agrees that fees not in excess of twenty percent
(20%) of the amount then due shall be deemed reasonable.

THE MAKER HEREBY UNCONDITIONALLY WAIVES ITS RIGHTS TO A JURY TRIAL OF ANY CLAIM
OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF, DIRECTLY OR INDIRECTLY, THIS
NOTE, ANY OF THE RELATED DOCUMENTS, ANY DEALINGS BETWEEN MAKER AND PAYEE
RELATING TO THE SUBJECT MATTER OF THIS TRANSACTION OR ANY RELATED TRANSACTIONS,
AND/OR THE RELATIONSHIP THAT IS BEING ESTABLISHED BETWEEN MAKER AND PAYEE. THE
SCOPE OF THIS WAIVER IS INTENDED TO BE ALL ENCOMPASSING OF ANY AND ALL DISPUTES
THAT MAY BE FILED IN ANY COURT (INCLUDING, WITHOUT LIMITATION, CONTRACT CLAIMS,
TORT CLAIMS, BREACH OF DUTY CLAIMS, AND ALL OTHER COMMON LAW AND STATUTORY
CLAIMS.) THIS WAIVER IS IRREVOCABLE MEANING THAT IT MAY NOT BE MODIFIED EITHER
ORALLY OR IN WRITING, AND THE WAIVER SHALL APPLY TO ANY SUBSEQUENT AMENDMENTS,
RENEWALS, SUPPLEMENTS OR MODIFICATIONS TO THIS NOTE, ANY RELATED DOCUMENTS, OR
TO ANY OTHER DOCUMENTS OR AGREEMENTS RELATING TO THIS TRANSACTION OR ANY RELATED
TRANSACTION. IN THE EVENT OF LITIGATION, THIS NOTE MAY BE FILED AS A WRITTEN
CONSENT TO A TRIAL BY THE COURT.

This Note and any Security Agreement constitute the entire agreement of the
Maker and Payee with respect to the subject matter hereof and supercedes all
prior understandings, agreements and representations, express or implied.

No variation or modification of this Note, or any waiver of any of its
provisions or conditions, shall be valid unless in writing and signed by an
authorized representative of Maker and Payee. Any such waiver, consent,
modification or change shall be effective only in the specific instance and for
the specific purpose given.
<PAGE>   3
Any provision in this Note or any Security Agreement which is in conflict with
any statute, law or applicable rule shall be deemed omitted, modified or altered
to conform thereto.

                                           DRAFT COPY

 _____________________________          By:  ___________________________________
 (Witness)
 _____________________________          Name:
 (Print name)
 _____________________________          Title:
 (Address)
                                        Federal Tax ID #:_______________________

                                        Address: 10232 South 51st Street,
                                                 Phoenix, Arizona 85044

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