**Exhibit4.6**

**FIFTH SUPPLEMENTAL INDENTURE**

This Fifth Supplemental Indenture (this “*Supplemental Indenture*”), dated as of May18, 2006, by and among **LOCKPORT MRI, LLC,**aNew York limited liability company (the “*Guaranteeing Subsidiary*”),**INSIGHT HEALTH SERVICES CORP**. (or its permitted successor), aDelaware corporation (the “*Company*”),**INSIGHT HEALTH SERVICES HOLDINGS CORP**.,a Delaware corporation, the Subsidiary Guarantors (as defined in the Indenturereferred to herein) and **U.S. BANK TRUSTNATIONAL ASSOCIATION**, a national banking association, as trusteeunder the Indenture referred to below (the “*Trustee*”).

**W I T N E S S E T H**

WHEREAS, the Company, the Guarantors and theTrustee have entered into an Indenture, dated as of October 30, 2001, assupplemented by a Supplemental Indenture dated as of February 25, 2002, aSupplemental Indenture dated as of April 2, 2003, a Third SupplementalIndenture dated as of March 8, 2004, and a Fourth Supplemental Indenture datedas of June 8, 2004 (as so supplemented, the “*Indenture*”),pursuant to which the Company issued $250,000,000 aggregate principal amount ofthe 9 7/8% Senior Subordinated Notes due 2011 (the “Notes”),

WHEREAS, the Indenture provides that undercertain circumstances the Guaranteeing Subsidiary shall execute and deliver tothe Trustee a supplemental indenture pursuant to which the GuaranteeingSubsidiary shall unconditionally guarantee all of the Company’s obligationsunder the Notes and the Indenture on the terms and conditions set forth herein(the “*Guarantee*”); and

WHEREAS, pursuant to Section 9.01 of theIndenture, the Trustee is authorized to execute and deliver this SupplementalIndenture.

NOW THEREFORE, in consideration of theforegoing and for other good and valuable consideration, the receipt of whichis hereby acknowledged, the Guaranteeing Subsidiary and the Trustee mutuallycovenant and agree for the equal and ratable benefit of the Holders of theNotes as follows:

# 1.             Capitalized Terms.  Capitalized terms used herein withoutdefinition shall have the meanings assigned to them in the Indenture.

# 2.             Agreement to Guarantee.  The Guaranteeing Subsidiary hereby agrees asfollows:

## (a)           Along with all other Guarantors, tojointly and severally Guarantee to each Holder of a Note authenticated anddelivered by the Trustee and to the Trustee and its successors and assigns,irrespective of the validity and enforceability of the Indenture, the Notes orthe obligations of the Company hereunder or thereunder, that:

#### (i)            the principal of and interest on the Notes will bepromptly paid in full when due, whether at maturity, by acceleration,redemption or otherwise, and interest on the overdue principal of and intereston the Notes, if any, if lawful, and all other 

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#### obligations of the Company to the Holders or theTrustee hereunder or thereunder will be promptly paid in full or performed, allin accordance with the terms hereof and thereof; and

#### (ii)           in case of any extension of time of payment or renewal ofany Notes or any of such other obligations, the same will be promptly paid infull when due or performed in accordance with the terms of the extension orrenewal, whether at stated maturity, by acceleration or otherwise.  Failing payment when due of any amount soguaranteed or any performance so guaranteed for whatever reason, the Guarantorsshall be jointly and severally obligated to pay the same immediately.

## (b)           The obligations hereunder shall beunconditional, irrespective of the validity, regularity or enforceability ofthe Notes or the Indenture, the absence of any action to enforce the same, anywaiver or consent by any Holder of the Notes with respect to any provisionshereof or thereof, the recovery of any judgment against the Company, any actionto enforce the same or any other circumstance that might otherwise constitute alegal or equitable discharge or defense of a guarantor.

## (c)           The following are hereby waived:  diligence, presentment, demand of payment,filing of claims with a court in the event of insolvency or bankruptcy of theCompany, any right to require a proceeding first against the Company, protest,notice and all demands whatsoever.

## (d)           This Guarantee shall not bedischarged except by complete performance of the obligations contained in theNotes and the Indenture.

## (e)           If any Holder or the Trustee isrequired by any court or otherwise to return to the Company, the Guarantors, orany Custodian, Trustee, liquidator or other similar official acting in relationto either the Company or the Guarantors, any amount paid by either to theTrustee or such Holder, this Guarantee, to the extent theretofore discharged,shall be reinstated in full force and effect.

## (f)            Such Guaranteeing Subsidiary shallnot be entitled to any right of subrogation in relation to the Holders inrespect of any obligations guaranteed hereby until payment in full of allobligations guaranteed hereby.

## (g)           As between the Guarantors, on the onehand, and the Holders and the Trustee, on the other hand, (x) the maturityof the obligations guaranteed hereby may be accelerated as provided in Article Sixof the Indenture for the purposes of the Guarantee, notwithstanding any stay,injunction or other prohibition preventing such acceleration in respect of theobligations guaranteed hereby, and (y) in the event of any declaration ofacceleration of such obligations as provided in Article Six of theIndenture, such obligations (whether or not due and payable) shall forthwithbecome due and payable by the Guarantors for the purpose of the Guarantee.

## (h)           Pursuant to Section 10.02 of theIndenture, after giving effect to any maximum amount and any other contingentand fixed liabilities that are relevant under any applicable Bankruptcy orfraudulent conveyance laws, and after giving effect to any collections 

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## from, rights to receivecontribution from or payments made by or on behalf of any other Guarantor inrespect of the obligations of such other Guarantor under Article Ten ofthe Indenture shall result in the obligations of such Guarantor under itsGuarantee not constituting a fraudulent transfer or conveyance.

# 3.             Subordination.  The Obligations of the GuaranteeingSubsidiary under its Guarantee pursuant to this Supplemental Indenture shall bejunior and subordinated to the Senior Indebtedness of such GuaranteeingSubsidiary on the same basis as the Notes are junior and subordinated to theSenior Indebtedness of the Company.  Forthe purposes of the foregoing sentence, the Trustee and the Holders shall havethe right to receive and/or retain payments by the Guaranteeing Subsidiary onlyat such time as they may receive and/or retain payments in respect of the Notespursuant to the Indenture, including Article Ten thereof.

# 4.             Execution and Delivery.  The Guaranteeing Subsidiary agrees that theGuarantee shall remain in full force and effect notwithstanding any failure toendorse on each Note a notation of such Guarantee.

# 5.             Guaranteeing Subsidiary MayConsolidate, Etc., on Certain Terms.

Except as otherwise provided inSection 11.05 of the Indenture, a Subsidiary Guarantor may not consolidatewith or merge with or into any other Person or convey, sell, assign, transfer,lease or otherwise dispose of its properties and assets substantially as anentirety to any other Person (other than the Company or another SubsidiaryGuarantor) unless:

##### (i)            subject to the provisions of the following paragraph, thePerson formed by or surviving such consolidation or merger (if other than suchSubsidiary Guarantor) or to which such properties and assets are transferredassumes all of the obligations of such Subsidiary Guarantor under the Indentureand its Guarantee, pursuant to a supplemental indenture in form and substancesatisfactory to the Trustee;

##### (ii)           immediately after giving effect to such transaction, noDefault or Event of Default has occurred and is continuing; and

##### (iii)          the Subsidiary Guarantor delivers, or causes to bedelivered, to the Trustee, in form and substance reasonably satisfactory to theTrustee, an Officers’ Certificate and an Opinion of Counsel, each stating thatsuch transaction complies with the requirements of the Indenture.

For purposes of the foregoing, the transfer(by lease, assignment, sale or otherwise, in a single transaction or series oftransactions) of all or substantially all of the properties or assets of one ormore Restricted Subsidiaries, the Capital Stock of which constitutes all orsubstantially all of the properties and assets of the Company, shall be deemedto be the transfer of all or substantially all of the properties and assets ofthe Company.

In case of any such consolidation, merger,sale or conveyance and upon the assumption by the successor Person, bysupplemental indenture, executed and delivered to the Trustee and reasonablysatisfactory in form to the Trustee, of the Guarantee endorsed upon the Notesand the due and punctual performance of all of the covenants and conditions ofthe 

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Indenture to be performed bya Guarantor, such successor Person shall succeed to and be substituted for aGuarantor with the same effect as if it had been named herein as aGuarantor.  Such successor Personthereupon may cause to be signed any or all of the Guarantees to be endorsedupon all of the Notes issuable hereunder which theretofore shall not have beensigned by the Company and delivered to the Trustee.  All the Guarantees so issued shall in allrespects have the same legal rank and benefit under the Indenture as theGuarantees theretofore and thereafter issued in accordance with the terms ofthe Indenture as though all of such Guarantees had been issued at the date ofexecution hereof.

# 6.             Releases.

### (a)           A Subsidiary Guarantor will be deemedautomatically and unconditionally released and discharged from all of itsobligations under its Guarantee without any further action on the part of theTrustee or any Holder of the Notes upon a sale or other disposition to a Personnot an Affiliate of the Company of all of the Capital Stock of, or all orsubstantially all of the assets of, such Subsidiary Guarantor, by way ofmerger, consolidation or otherwise, which transaction is carried out inaccordance with Section 4.10 of the Indenture; *provided* that any such termination shall occur (x) onlyto the extent that all obligations of such Subsidiary Guarantor under all ofits guarantees of, and under all of its pledges of assets or other securityinterests which secure any Indebtedness of the Company shall also terminateupon such sale, disposition or release and (y) only if the Trustee isfurnished with written notice of such release together with an Officers’Certificate from such Subsidiary Guarantor to the effect that all of theconditions to release in this Section 6 have been satisfied.

### (b)           Any Guarantor not released from itsobligations under its Guarantee shall remain liable for the full amount ofprincipal of and interest on the Notes and for the other obligations of anyGuarantor under the Indenture as provided in Article Eleven of the Indenture.

# 7.             No Recourse Against Others.  No director, officer, employee, incorporatoror stockholder of the Parent, the Company or any Subsidiary Guarantor, as suchshall have any liability for any obligations of the Parent, the Company or theSubsidiary Guarantors under the Notes, the Indenture, the Guarantees or for anyclaim based on, in respect of, or by reason of, such obligations or theircreation.  Each Holder of Notes, byaccepting a Note, waives and releases all such liability.  The waiver and release are part of theconsideration for issuance of the notes. The waiver may not be effective to waive liabilities under the federalsecurities laws.

# 8.             NEW YORK LAW TO GOVERN.  THE INTERNAL LAW OF THE STATE OF NEW YORKSHALL GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE BUT WITHOUTGIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THATTHE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

# 9.             Counterparts.  The parties may sign any number of copies ofthis Supplemental Indenture.  Each signedcopy shall be an original, but all of them together represent the sameagreement.

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# 10.           Effect of Headings.  The Section headings herein are forconvenience only and shall not affect the construction hereof.

# 11.           Trustee.  The Trustee shall not be responsible in anymanner whatsoever for or in respect of the validity or sufficiency of thisSupplemental Indenture or for or in respect of the recitals contained herein,all of which recitals are made solely by the Guaranteeing Subsidiary and theCompany.

# [Remainderof Page Left Intentionally Blank]

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IN WITNESS WHEREOF, the parties hereto havecaused this Supplemental Indenture to be duly executed and attested, all as ofthe date first above written.
| Dated: May 18, 2006 |                          |                                      |
|---------------------|-------------------------------|-------------------------------------------|
|                |                          |                                      |
|                | LOCKPORT MRI, LLC             |
|                |                          |
|                | By:                           | InSight Health Corp., as the sole manager |
|                |                          | and the sole member                       |
|                |                          |                                      |
|                |                          |                                      |
|                | By:                           |                                      | /s/ Mitch C. Hill |   |
|                | Name:                         |                                      | Mitch C. Hill |
|                | Title:                        |                                      | Executive Vice President and |
|                |                          |                                      | Chief Financial Officer |
|                |                          |                                      |   |
|                |                          |                                      |   |
|                | INSIGHT HEALTH SERVICES CORP. |
|                |                          |
|                |                          |
|                | By:                           |                                      | /s/ Mitch C. Hill |   |
|                | Name:                         |                                      | Mitch C. Hill |
|                | Title:                        |                                      | Executive Vice President and |
|                |                          |                                      | Chief Financial Officer |
|                |                          |                                      |   |
|                |                          |                                      |   |
|                | INSIGHT HEALTH SERVICES       |
|                | HOLDINGS CORP.                |
|                |                          |
|                |                          |
|                | By:                           |                                      | /s/ Mitch C. Hill |   |
|                | Name:                         |                                      | Mitch C. Hill |
|                | Title:                        |                                      | Executive Vice President and |
|                |                          |                                      | Chief Financial Officer |
|                |                          |                                      |   |
|                |                          |                                      |   |
|                | WILKES-BARRE IMAGING, L.L.C.  |
|                |                          |
|                | By:                           |                                      | InSight Health Corp., as the sole member  and sole manager |
|                |                          |                                      |   |
|                |                          |                                      |   |
|                | By:                           |                                      | /s/ Mitch C. Hill |   |
|                | Name:                         |                                      | Mitch C. Hill |
|                | Title:                        |                                      | Executive Vice President and |
|                |                          |                                      | Chief Financial Officer |

 

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|        | MRI ASSOCIATES, L.P.                              |
|--------|---------------------------------------------------|
|   |                                              |
|   | By:                                               |   | InSight Health Corp., as the |
|   |                                              |   | general partner |
|   |                                              |   |   |
|   | By:                                               |   | /s/ Mitch C. Hill |   |
|   | Name:                                             |   | Mitch C. Hill |
|   | Title:                                            |   | Executive Vice President and |
|   |                                              |   | Chief Financial Officer |
|   |                                              |   |   |
|   |                                              |   |   |
|   | VALENCIA MRI, LLC                                 |
|   | ORANGE COUNTY REGIONAL PET CENTER -   IRVINE, LLC |
|   | SAN FERNANDO VALLEY REGIONAL PET  CENTER, LLC     |
|   |                                              |
|   | By:                                               |   | InSight Health Corp., as the sole member |
|   |                                              |   |   |
|   | By:                                               |   | /s/ Mitch C. Hill |   |
|   | Name:                                             |   | Mitch C. Hill |
|   | Title:                                            |   | Executive Vice President and |
|   |                                              |   | Chief Financial Officer |
|   |                                              |   |   |
|   |                                              |   |   |
|   | PARKWAY IMAGING CENTER, LLC                       |
|   |                                              |
|   |                                              |
|   | By:                                               |   | /s/ Mitch C. Hill |   |
|   | Name:                                             |   | Mitch C. Hill |
|   | Title:                                            |   | Manager |

 

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|        | INSIGHT HEALTH CORP.                               |
|--------|----------------------------------------------------|
|   | OPEN MRI, INC.                                     |
|   | MAXUM HEALTH CORP.                                 |
|   | MAXUM HEALTH SERVICES CORP.                        |
|   | RADIOSURGERY CENTERS, INC.                         |
|   | DIAGNOSTIC SOLUTIONS CORP.                         |
|   | MAXUM HEALTH SERVICES OF                           |
|   | NORTH TEXAS, INC.                                  |
|   | MAXUM HEALTH SERVICES OF DALLAS, INC.              |
|   | NDDC, INC.                                         |
|   | SIGNAL MEDICAL SERVICES, INC.                      |
|   | INSIGHT IMAGING SERVICES CORP.                     |
|   | COMPREHENSIVE MEDICAL IMAGING, INC.                |
|   | COMPREHENSIVE MEDICAL IMAGING                      |
|   | CENTERS, INC.                                      |
|   | COMPREHENSIVE MEDICAL IMAGING-                     |
|   | BILTMORE, INC.                                     |
|   | COMPREHENSIVE OPEN MRI-EAST MESA, INC.             |
|   | TME ARIZONA, INC.                                  |
|   | COMPREHENSIVE MEDICAL IMAGING-                     |
|   | FREMONT, INC.                                      |
|   | COMPREHENSIVE MEDICAL IMAGING-SAN  FRANCISCO, INC. |
|   | COMPREHENSIVE OPEN MRI-GARLAND, INC.               |
|   | IMI OF ARLINGTON, INC.                             |
|   | COMPREHENSIVE MEDICAL IMAGING-                     |
|   | FAIRFAX, INC.                                      |
|   | IMI OF KANSAS CITY, INC.                           |
|   | COMPREHENSIVE MEDICAL IMAGING-                     |
|   | BAKERSFIELD, INC.                                  |
|   |                                               |
|   |                                               |
|   | By:                                                |   | /s/ Mitch C. Hill |   |
|   | Name:                                              |   | Mitch C. Hill |
|   | Title:                                             |   | Executive Vice President and |
|   |                                               |   | Chief Financial Officer |

 

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|        | COMPREHENSIVE OPEN MRI-                        |
|--------|------------------------------------------------|
|   | CARMICHAEL/FOLSOM, LLC                         |
|   | SYNCOR DIAGNOSTICS SACRAMENTO, LLC             |
|   | SYNCOR DIAGNOSTICS BAKERSFIELD, LLC            |
|   |                                           |
|   | By:                                            | Comprehensive Medical Imaging, Inc. and  Comprehensive Medical Imaging Centers,  Inc., as the members |
|   |                                           |   |   |
|   |                                           |   |   |
|   | By:                                            |   | /s/ Mitch C. Hill |   |
|   | Name:                                          |   | Mitch C. Hill |
|   | Title:                                         |   | Executive Vice President and |
|   |                                           |   | Chief Financial Officer |
|   |                                           |   |   |
|   |                                           |   |   |
|   | PHOENIX REGIONAL PET CENTER-  THUNDERBIRD, LLC |
|   |                                           |
|   | By:                                            | Comprehensive Medical Imaging Centers,  Inc., as the sole member |
|   |                                           |   |
|   |                                           |   |
|   | By:                                            |   | /s/ Mitch C. Hill |   |
|   | Name:                                          |   | Mitch C. Hill |
|   | Title:                                         |   | Executive Vice President and |
|   |                                           |   | Chief Financial Officer |
|   |                                           |   |   |
|   |                                           |   |   |
|   | MESA MRI                                       |
|   | MOUNTAIN VIEW MRI                              |
|   | LOS GATOS IMAGING CENTER                       |
|   | WOODBRIDGE MRI                                 |
|   | JEFFERSON MRI-BALA                             |
|   | JEFFERSON MRI                                  |
|   |                                           |
|   | By:                                            | Comprehensive Medical Imaging, Inc. and |
|   |                                           | Comprehensive Medical Imaging Centers,  Inc., as the members |
|   |                                           |   |
|   |                                           |   |
|   | By:                                            |   | /s/ Mitch C. Hill |   |
|   | Name:                                          |   | Mitch C. Hill |
|   | Title:                                         |   | Executive Vice President and |
|   |                                           |   | Chief Financial Officer |

 

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|        | U.S. Bank Trust National Association, as Trustee |
|--------|--------------------------------------------------|
|   |                                             |
|   |                                             |
|   | By:                                              |   | /s/ Jean Clarke |   |
|   | Name:                                            |   | Jean Clarke |
|   | Title:                                           |   | Assistant Vice President |

 

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