Nicole T. Ranger MSc, Presenter: Nothing to Disclose

Ehsan Samei PhD, Abstract Co-Author: Nothing to Disclose

James Talmage Dobbins PhD, Abstract Co-Author: Nothing to Disclose

Carl Eric Ravin MD, Abstract Co-Author: Nothing to Disclose

In October 2003, the International Electrotechnical Commission (IEC) published Standard 62220-1: Characteristics of digital X-ray imaging devices - Part 1: Determination of the detective quantum efficiency, specifying how the DQE should be measured and computed. Most notably, it requires that measurements be performed using x-ray beam conditions specified in IEC 61267, which require the use of ultra-high purity aluminum filtration (>99.9% purity) to achieve the specified beam qualities. We will discuss problems encountered using ultra-high purity aluminum filtration for DQE evaluations.

We purchased scientific-grade ultra-high purity aluminum (99.999% and 99.99% pure) and low-purity aluminum (99.0% pure) filters from two well-known, specialty metals suppliers. All imaging tests were performed on a prototype amorphous silicon digital detector using the RQA5 beam quality.

Qualitative evaluation of flat field images acquired with of ultra-high purity aluminum filtration (99.999% pure) demonstrated a low frequency mottle which was not observed when the measurement was repeated with low-purity aluminum (99.0% pure) filtration. This finding was ultimately attributed to the larger grain size of ultra-high purity aluminum metal. This low frequency mottle significantly overestimates the NPS at low frequencies, which in turn will cause an under-estimation of the low frequency DQE. An evaluation of ultra-high purity aluminum purchased from a second source (99.99% pure) suggested that reduced grain size can be achieved by the process of annealing. However, images acquired with this sample demonstrated striated defects attributed to the manufacturing method, which would preclude its use in radiographic imaging applications.

Our observations suggest that the non-uniformity of filter materials should be evaluated when measuring the DQE. We recommend that the IEC 61267 and 62220-1 committees revisit their recommendation of using aluminum with a minimum purity of 99.9%, until it can be established that there is a supply of aluminum at this purity that would be appropriate for DQE measurements

Ranger, N, Samei, E, Dobbins, J, Ravin, C, Hot Topic: DQE Measurements According to the New International Standard (IEC 62220-1): Problems with the Required Aluminum Filtration.  Radiological Society of North America 2004 Scientific Assembly and Annual Meeting, November 28 - December 3, 2004 ,Chicago IL. http://archive.rsna.org/2004/4418659.html