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Proceedings Paper

An analytical model of NPS and DQE comparing photon counting and energy integrating detectors
Author(s): Raymond J. Acciavatti; Andrew D. A. Maidment
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Paper Abstract

In this work, analytical models of the optical transfer function (OTF), noise power spectra (NPS), and detective quantum efficiency (DQE) are developed for two types of digital x-ray detectors. The two detector types are (1) energy integrating (EI), for which the point spread function (PSF) is interpreted as a weighting function for counting x-rays, and (2) photon counting (PC), for which the PSF is treated as a probability. The OTF is the Fourier transform of the PSF. The two detector types, having the same PSF, possess an equivalent OTF. NPS is the discrete space Fourier transform (DSFT) of the autocovariance of signal intensity. From first principles, it is shown that while covariance is equivalent for both detector types, variance is not. As a consequence, provided the two detector types have equivalent PSFs, a difference in NPS exists such that NPSPC ≥ NPSEI and hence DQEPC ≤ DQEEI. The necessary and sufficient condition for equality is that the PSF is either zero or unity everywhere. A PSF modeled as the convolution of a Lorentzian with a rect function is analyzed in order to illustrate the differences in NPS and DQE. The Lorentzian models the blurring of the xray converter, while the rect function reflects the sampling of the detector. The NPS difference between the two detector types is shown to increase with increasing PSF width. In conclusion, this work develops analytical models of OTF, NPS, and DQE for energy integrating and photon counting digital x-ray detectors.

Paper Details

Date Published: 22 March 2010
PDF: 12 pages
Proc. SPIE 7622, Medical Imaging 2010: Physics of Medical Imaging, 76220I (22 March 2010); doi: 10.1117/12.845310
Show Author Affiliations
Raymond J. Acciavatti, The Univ. of Pennsylvania (United States)
Andrew D. A. Maidment, The Univ. of Pennsylvania (United States)

Published in SPIE Proceedings Vol. 7622:
Medical Imaging 2010: Physics of Medical Imaging
Ehsan Samei; Norbert J. Pelc, Editor(s)

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