David Leong, Presenter: Employee, Analogic Corporation Stockholder, General Electric Company

Patrick C. Brennan PhD, Abstract Co-Author: Nothing to Disclose

By first measuring the system HVL, the RQA beam qualities can be generated by simple use of a lookup table to determine the filter necessary. Since for most testing the initial system HVL is measured, this eliminates the need to measure and adjust the filtration to achieve the desired target. The use of copper also reduces the amount of Al requires to levels that make it easy to work with. We selected steps of 0.5 mm Al as tradeoff between target value accuracy and simplicity; however the method could be extended to 0.1 mm Al for improved accuracy. This method has been tested clinically and found to have good results on a limited sample set.

Radiography system calibration and testing requires the beam quality defined in IEC 61267. To produce the RQA series of beam qualities with the IEC procedure, 99.9% pure Aluminum (Al) is needed, which is very difficult to access and procedural steps that are not well suited for the clinical environment must be performed. This paper shows how a combination of Copper (Cu) and off the shelf Alloy 1100 Al can be used develop these beam qualities with a simpler procedure.

Beam spectrum simulation using IDL 7.0 (ITT Visual Solutions, Boulder, Colorado) was performed for each RQA setting. The simulated X-ray beam spectrum was first filtered with Cu and then Alloy 1100 Al. To achieve a specific target Half Value Layer (HVL), a range of initial system HVL was determined. Al filters were incremented in thickness of 0.5 mm and 0.25 mm for Cu. A table was constructed to reference the desired RQA level with the initial system HVL and list the filter required to achieve each target. The developed procedure was tested on several systems to confirm simulation accuracy.

For the RQA5 beam quality, simulation shows that if the system HVL is between 1.02 and 3.82, a 0.5 mm Cu filter and an Al in the range of 0 to 4 mm would produce an HVL with a maximum deviation of 0.025 or 0.36% from the target of 6.8. For instance, if a system had an system HVL of 2.11 a filter of 0.5 mm Cu with 3 mm Al would produce an acceptable HVL of 6.78 which is slightly less than the target of 6.8.

Leong, D, Brennan, P, How to Use Alloy 1100 Aluminum with Copper to Produce RQA5 Beam Quality.  Radiological Society of North America 2009 Scientific Assembly and Annual Meeting, November 29 - December 4, 2009 ,Chicago IL. http://archive.rsna.org/2009/8013262.html