Stephen Jeffrey Glick, Presenter: Nothing to Disclose

Xing Gong PHD, Abstract Co-Author: Nothing to Disclose

Samta Thacker, Abstract Co-Author: Nothing to Disclose

In recent years, there has been interest in exploring the feasibility of dedicated CT breast imaging using flat-panel digital detectors in a truncated cone-beam geometry. In this study, a mathematical framework used for determining optimal design and acquisition parameters for such a CT breast imaging system is described. This framework is used to investigate the performance of a large range of different x-ray beam filters.

The ideal observer SNR is used as a figure-of-merit, under the assumptions that the imaging system is linear and shift-invariant. Computation of the ideal observer SNR used a parallel-cascade model to predict signal and noise propagation through the detector, as well as a realistic model of the lesion detection task in breast imaging. Filters with Z ranging from 10 to 90, with varying thickness were evaluated for tungsten anode spectra ranging from 30 kVp to 100 kVp. For all cases, the mean glandular dose was constrained to be approximately that given in a two-view conventional mammography study. For each filter and kVp setting, the ideal observer SNR, mean x-ray fluence incident on the detector, and quantum efficiency were studied. In addition, the effect of different levels of electronic noise on SNR was examined.

For spectra of 40-100 kVp, the ideal observer SNR was observed to increase gradually with increasing Z for lower Z materials. A large decrease in SNR was observed for filters with Z around 40, followed by a peak in SNR observed for filters with Z around 50-60. The optimal kVp setting was observed to be dependent on the x-ray filter, however, filtered spectra with 40-60 kVp generally provided better performance. For CT acquisition with 300 projection angles, exposure on the detector was as low as a few micro Roentgens for some spectra. Electronic noise was seen to affect performance using spectra of 30-50 kVp.

A framework for determining optimal design and acquisition parameters in CT breast imaging has been developed and implemented to explore how x-ray filters in CT breast imaging can affect image quality.

Glick, S, Gong, X, Thacker, S, An Evaluation of X-ray beam Filters for CT Breast Imaging.  Radiological Society of North America 2005 Scientific Assembly and Annual Meeting, November 27 - December 2, 2005 ,Chicago IL. http://archive.rsna.org/2005/4411302.html