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Proceedings Paper

Achieving sub-pixel resolution using CZT-based photon counting detectors for dedicated breast CT
Author(s): Andrey Makeev; John McGrath; Martin Clajus; Scott Snyder; Stephen J. Glick
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Paper Abstract

Semiconductor based photon-counting detectors for x-ray CT have a number of advantages over energy integrat­ ing detectors, including reduced electronic and Swank noise, increased dynamic range, capability of spectral CT for material decomposition, and improved SNR characteristics through energy weighting. Quite a few clinical applications could benefit from high-resolution spectral CT. For example, in breast CT the visualization of mi­ crocalcifications and assessment of tumor microvasculature after contrast enhancement require spatial resolution on the order of 100 μm or better. A straightforward approach to increasing spatial resolution by decreasing the detector pixel size, leads to two major problems: 1) fabricating circuitry with small pixels becomes very costly, and 2) inter-pixel charge spreading can obviate any improvement in spatial resolution. In this study, we have used computer simulations to investigate position estimation algorithms that utilize charge sharing to achieve sub-pixel position resolution. To study these algorithms, we model a simple detector geometry with a pixellated 5 x 5 anode array, and use conditional probability functions modeling electron-hole charge transport in CZT. We used COMSOL Multiphysics software to map the distribution of charge pulses in the detector. Performance of two x-ray interaction position estimation algorithms were evaluated: 1) method of maximum likelihood, and 2) a fast, practical algorithm that can be realistically implemented in a readout ASIC, providing identification of the quadrant of the pixel in which interaction occurred. Both methods exhibit good sub-pixel resolution performance, however their actual efficiency is limited by electronic noise.

Paper Details

Date Published: 19 March 2013
PDF: 8 pages
Proc. SPIE 8668, Medical Imaging 2013: Physics of Medical Imaging, 86680T (19 March 2013); doi: 10.1117/12.2008351
Show Author Affiliations
Andrey Makeev, Univ. of Massachusetts Medical School (United States)
John McGrath, Diamond Light Source Ltd. (United Kingdom)
Martin Clajus, NOVA R&D, Inc. (United States)
Scott Snyder, NOVA R&D, Inc. (United States)
Stephen J. Glick, Univ. of Massachusetts Medical School (United States)

Published in SPIE Proceedings Vol. 8668:
Medical Imaging 2013: Physics of Medical Imaging
Robert M. Nishikawa; Bruce R. Whiting; Christoph Hoeschen, Editor(s)

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