Indirect flat-panel detector with avalanche gain: design and operation of the avalanche photoconductor

Wei Zhao; Dan Li; Alla Reznik; Brian Lui; D. C. Hunt; Kenkichi Tanioka; J. A. Rowlands

doi:10.1117/12.597295

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20 April 2005 Indirect flat-panel detector with avalanche gain: design and operation of the avalanche photoconductor

Wei Zhao, Dan Li, Alla Reznik, Brian Lui, D. C. Hunt, Kenkichi Tanioka, J. A. Rowlands

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Proceedings Volume 5745, Medical Imaging 2005: Physics of Medical Imaging; (2005) https://doi.org/10.1117/12.597295
Event: Medical Imaging, 2005, San Diego, California, United States

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 d_Se and the applied electric field E_Se. To determine the optimal design parameter and operational conditions for HARP, we measured the E_Se 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 E_Se: (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.

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Wei Zhao, Dan Li, Alla Reznik, Brian Lui, D. C. Hunt, Kenkichi Tanioka, and J. A. Rowlands "Indirect flat-panel detector with avalanche gain: design and operation of the avalanche photoconductor", Proc. SPIE 5745, Medical Imaging 2005: Physics of Medical Imaging, (20 April 2005); https://doi.org/10.1117/12.597295

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