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Proceedings Paper

Indirect flat-panel detector with avalanche gain: design and operation of the avalanche photoconductor
Author(s): Wei Zhao; Dan Li; Alla Reznik; Brian Lui; D. C. Hunt; Kenkichi Tanioka; J. A. Rowlands
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Paper Abstract

An indirect flat-panel imager (FPI) with avalanche gain is being investigated for low-dose x-ray imaging. It is made by optically coupling a structured x-ray scintillator CsI(Tl) to an amorphous selenium (a-Se) avalanche photoconductor called HARP. The final electronic image can be read out using either an array of thin film transistors (TFT) or field emitters (FE). The advantage of the proposed detector is its programmable gain, which can be turned on during low dose fluoroscopy to overcome electronic noise, and turned off during high dose radiography to avoid pixel saturation. This paper investigates the important design considerations for HARP such as avalanche gain, which depends on both the thickness dSe and the applied electric field ESe. To determine the optimal design parameter and operational conditions for HARP, we measured the ESe dependence of both avalanche gain and optical quantum efficiency of an 8 μm HARP layer. The results were applied to a physical model of HARP as well as a linear cascaded model of the FPI to determine the following x-ray imaging properties in both the avalanche and non-avalanche modes as a function of ESe: (1) total gain (which is the product of avalanche gain and optical quantum efficiency); (2) linearity; (3) dynamic range; and (4) gain non-uniformity resulting from thickness non-uniformity. Our results showed that a HARP layer thickness of 8 μm can provide adequate avalanche gain and sufficient dynamic range for x-ray imaging applications to permit quantum limited operation over the range of exposures needed for radiography and fluoroscopy.

Paper Details

Date Published: 20 April 2005
PDF: 9 pages
Proc. SPIE 5745, Medical Imaging 2005: Physics of Medical Imaging, (20 April 2005); doi: 10.1117/12.597295
Show Author Affiliations
Wei Zhao, State Univ. of New York/Stony Brook (United States)
Dan Li, State Univ. of New York/Stony Brook (United States)
Alla Reznik, Sunnybrook and Women's Health Sciences Ctr. (Canada)
Brian Lui, Sunnybrook and Women's Health Sciences Ctr. (Canada)
D. C. Hunt, Sunnybrook and Women's Health Sciences Ctr. (Canada)
Kenkichi Tanioka, Japan Broadcasting Corp. (Japan)
J. A. Rowlands, Sunnybrook and Women's Health Sciences Ctr. (Canada)


Published in SPIE Proceedings Vol. 5745:
Medical Imaging 2005: Physics of Medical Imaging
Michael J. Flynn, Editor(s)

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