SUPPLEMENTAL
INDENTURE

     

    Supplemental
Indenture
(this “Supplemental
Indenture”), dated as of January 10, 2011 among Imaging On Call, LLC, a
New York limited liability company (the “Guaranteeing Subsidiary”), a
subsidiary of RadNet, Inc. (or its permitted successor), a Delaware corporation
(“Parent”), Radnet
Management, Inc., a California corporation (the “Issuer), the other Guarantors
(as defined in the Indenture referred to herein) and U.S. Bank National
Association, as trustee under the Indenture referred to below (the “Trustee”).

     

    WITNESSETH

     

    WHEREAS,
the Issuer has heretofore executed and delivered to the Trustee an indenture
(the “Indenture”),
dated as of April 6, 2010, providing for the issuance of 103⁄8% Senior Notes due
2018 (the “Notes”);

     

    WHEREAS,
the Indenture provides that under certain circumstances the Guaranteeing
Subsidiary shall execute and deliver to the Trustee a supplemental indenture
pursuant to which the Guaranteeing Subsidiary shall unconditionally guarantee
all of the Issuer’s Obligations under the Notes and the Indenture on the terms
and conditions set forth herein (the “Note Guarantee”);
and

     

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

     

    NOW,
THEREFORE, in consideration of the foregoing and for other good and valuable
consideration, the receipt of which is hereby acknowledged, the Guaranteeing
Subsidiary and the Trustee mutually covenant and agree for the equal and ratable
benefit of the Holders of the Notes as follows:

     

    1.           Capitalized
Terms.  Capitalized
terms used herein without definition shall have the meanings assigned to them in
the Indenture.

     

    2.           Agreement
to
Guarantee.  The
Guaranteeing Subsidiary hereby agrees to provide an unconditional Guarantee on
the terms and subject to the conditions set forth in the Note Guarantee and in
the Indenture including but not limited to Article 10 thereof.

     

    4.           No
Recourse
Against
Others.  No
director, officer, employee, stockholder, general or limited partner or
incorporator of the Issuers or any Guarantor, as such, shall have any liability
for any obligations of the Issuers or the Guarantors under the Notes, this
Indenture, the Note Guarantees or the note documents or for any claim based on,
in respect of, or by reason of, such obligations or their creation. Each Holder
of Notes by accepting a Note waives and releases all such liability. The waiver
and release are part of the consideration for issuance of the Notes. The waiver
may not be effective to waive liabilities under the federal securities
laws.

     

    5.           NEW
YORK LAW TO GOVERN.  THE INTERNAL LAW OF THE STATE OF NEW YORK SHALL
GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE WITHOUT GIVING EFFECT
TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION
OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

     

    6.           Counterparts.  The
parties may sign any number of copies of this Supplemental
Indenture.  Each signed copy shall be an original, but all of them
together represent the same agreement.

     

    7.           Effect
of
Headings.  The
Section headings herein are for convenience only and shall not affect the
construction hereof.

     

    8.           The
Trustee.  The
Trustee shall not be responsible in any manner whatsoever for or in respect of
the validity or sufficiency of this Supplemental Indenture or for or in respect
of the recitals contained herein, all of which recitals are made solely by the
Guaranteeing Subsidiary and the Issuer.


    
      
         


      

      
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    IN
WITNESS WHEREOF, the undersigned have executed this Supplemental Indenture as of
the date first set forth above.

     

    
      
        
          
            	
                    IMAGING
      ON CALL, LLC

                  
	 
      	 
      
	
                    By:  

                  	
                    /S/
      HOWARD G. BERGER, M.D.

                  
	 
      	
                    Name:

                  	
                      Howard
      G. Berger, M.D.

                  
	 
      	
                    Title:

                  	
                      Manager,
      President and Chief Financial 

                      Officer

                  


          

        

      

    

    


    
      
        
          	
                  PARENT,
      ISSUER AND OTHER GUARANTORS

                
	 
      	 
      
	
                  By:  

                	
                  /S/
      HOWARD G. BERGER, M.D.

                
	 
      	
                  Name:

                	
                    Howard
      G. Berger, M.D.

                
	 
      	
                  Title:

                	
                    Authorized
      Officer of Parent, Issuer and the 

                    other
      Guarantors

                


        

      

    

    


    [Signature
Page to Supplemental Indenture - Imaging On Call, LLC] 

    
      
         


      

      
         


        
          

        

      

      
         


      

    

     

    
      
        
          	
                  U.S.
      BANK NATIONAL ASSOCIATION,

                  as
      Trustee

                
	 
      	 
      
	
                  By:  

                	
                  /S/
      GEORGINA THOMAS

                
	 
      	
                  Name:

                	
                    Georgina
      Thomas

                
	 
      	
                  Title:

                	
                    Trust
      Officer

                


        

      

    

     

    [Signature Page to
Supplemental Indenture - Imaging On Call, LLC]