AMENDED AND RESTATED NOTE AND EQUITY PURCHASE AGREEMENT

Exhibit 10.3.4

AMENDMENT NO. 3

to the

AMENDED AND RESTATED

NOTE AND EQUITY PURCHASE AGREEMENT

by and among

IST ACQUISITIONS, LLC.

IMAGING AND SENSING TECHNOLOGY CORPORATION AND
CERTAIN OF THE SUBSIDIARIES OF
IMAGING AND SENSING TECHNOLOGY CORPORATION

AS LOAN PARTIES

AND

AMERICAN CAPITAL FINANCIAL SERVICES, INC.

AS AGENT

and

THE PURCHASERS IDENTIFIED ON
ANNEX A HERETO

May 16, 2006

AMENDMENT NO. 3
to the
AMENDED AND RESTATED
NOTE AND EQUITY PURCHASE AGREEMENT

     THIS AMENDMENT NO. 3, dated May 16, 2006 (this “ Amendment ”), amends THE AMENDED AND RESTATED NOTE AND EQUITY PURCHASE AGREEMENT (as amended to date, the “ Agreement ”), dated as of October 29, 2004, and is by and among IST ACQUISITIONS, LLC. (successor by conversion to IST Acquisitions, Inc.), a Delaware corporation (“ Parent ”), IMAGING AND SENSING TECHNOLOGY CORPORATION, a New York corporation (“ Borrower ”), IST CONAX NUCLEAR, INC., a New York corporation, IMAGING AND SENSING TECHNOLOGY INTERNATIONAL CORP., a New York corporation, IST INSTRUMENTS, INC., a New York corporation, QUADTEK, INC., a Washington corporation (each a “ Subsidiary ” and collectively the “ Subsidiaries ” and together with Borrower and Parent, the “ Loan Parties ”), the securities purchasers that are now and hereafter at any time parties hereto and are listed in Annex A, (or any amendment or supplement thereto) attached hereto (each a “Purchases?’ and collectively, “Purchasers”), and AMERICAN CAPITAL FINANCIAL SERVICES, INC., a Delaware corporation (“ ACFS ”), as administrative and collateral agent for Purchasers (in such capacity “ Agent ”).

RECITALS

     A. The parties hereto were party to a Note and Equity Purchase Agreement, dated as of May 24, 2004 (the “ Original Purchase Agreement ”);

     B. The parties hereto are party to the Agreement, pursuant to which the Original Purchase Agreement was amended and restated;

     C. The Loan Parties, Purchasers and the Agent have agreed to enter into this Amendment to amend the Agreement, in order to amend of certain terms of the Agreement.

     NOW, THEREFORE, the parties hereto, in consideration of the foregoing premises and their mutual covenants and agreements herein set forth and intending to be legally bound hereby, covenant and agree as follows:

1. Definitions . Capitalized terms used and not defined elsewhere in this Amendment are as defined in the Agreement.

2. Amendments . Section 2.3(a) of the Agreement is hereby amended and restated in its entirety as follows:

“(a) Subject to the terms and conditions set forth in this Agreement, on or after the Closing Date and to, but excluding, May 24, 2008 (the “ Revolving Loan Termination ”), Purchasers shall, severally, on a pro rata basis based on the percentages specified to Agent, make loans and advances to the Loan Parties on a revolving credit basis (collectively, the “ Revolving Loans ”) in an aggregate amount outstanding at any time up to the Revolving Loan Commitment Amount. From and after the

Closing