AMENDMENT NO. 1 TO AMENDED AND RESTATED NOTE AND EQUITY PURCHASE AGREEMENT

Exhibit 10.3.1

AMENDMENT NO. 1
TO
AMENDED AND RESTATED NOTE AND EQUITY PURCHASE AGREEMENT

BY AND AMONG

IST ACQUISITIONS, INC.

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

and

AMERICAN CAPITAL STRATEGIES, LTD.,

ACS FUNDING TRUST I

and

AMERICAN CAPITAL FINANCIAL SERVICES, INC.

Date of Amendment No. 1: May 24, 2005
Original Date: October 29, 2004

AMENDMENT NO. 1
TO
AMENDED AND RESTATED NOTE AND EQUITY PURCHASE AGREEMENT

$15,000,000 Aggregate Principal Amount of Senior Term A Notes Due May 24, 2009

$7,500,000 Aggregate Principal Amount of Senior Term B Notes Due May 24, 2010

$4,000,000 Aggregate Principal Amount of Senior Term C Notes Due October 29, 2011

$7,500,000 Aggregate Principal Amount of Senior Subordinated Notes Due May 24, 2011

$1,250,000 Aggregate Principal Amount of Junior Subordinated Notes Due May 24, 2012

$5,250,000 Revolving Loan Facility

22,000 Shares Preferred Stock of Parent

10,000 Shares of Class B Common Stock of Parent

Warrants to Purchase 83,458 Shares
of Class B Common Stock of Parent

     THIS AMENDMENT NO. 1 TO THE AMENDED AND RESTATED NOTE AND EQUITY PURCHASE AGREEMENT (this “ Amendment ”), dated as of May 24, 2005, is by and among 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 ”), AMERICAN CAPITAL STRATEGIES, LTD., a Delaware corporation (“ ACAS ”), ACS FUNDING TRUST I, a Delaware statutory trust (“ AFT, ” and with ACAS, each a “ Purchaser ” 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 Loan Parties and ACAS entered into an Amended and Restated Note and Equity Purchase Agreement, dated as of October 29, 2004 (the “ Agreement ”),

pursuant to which ACAS advanced certain sums to the Loan Parties and purchased from the Loan Parties certain Notes and Warrants to purchase Common Stock. As of the date hereof, ACAS has sold or contributed certain of such Notes to AFT.

     B. The parties wish to amend the Agreement in certain respects.

     C. Capitalized terms used herein and not otherwise defined shall have the meaning assigned to such term as set forth in the Agreement.

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

ARTICLE I
THE AMENDMENT

     1.1 Amendment to Section 2.3(a) Revolving Loans . Section 2.3(a) of the