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Proceedings Paper

Detective quantum efficiency of direct flat-panel x-ray imaging detectors for fluoroscopy
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Paper Abstract

Our goal is to develop a large area, flat panel solid-state detector for fluoroscopy. The detector employs a layer of photoconductor to convert incident x-rays directly to a charge image, which is then read out in real-time using a two dimensional array of thin film transistors (TFTs), or 'active matrix.' In order to guide the design of an optimum fluoroscopic flat-panel detector, a cascaded linear systems model was developed, from which the spatial frequency dependent detective quantum efficiency [DQE(f)] can be obtained. Then DQE(f) was calculated as a function of different detector design parameters, e.g. pixel fill-factor, x-ray exposure, Swank factor, electronic noise, and the calculation was performed for three different x-ray photoconductors: amorphous selenium (a-Se), cadmium zinc telluride (CZT), and lead iodide (PbI2). A critical comparison was made of the advantages and disadvantages of each photoconductor. The results showed that the DQE(0) of all direct detectors has a linear dependence on the pixel fill- factor. For an a-Se layer with an electric field of 10 V/micrometer, DQE(f) is significantly degraded by the electronic noise of the detector, especially at very low x-ray exposure rates (e.g. 0.1 (mu) R/frame). With CZT and PbI2, the detector is more tolerant of electronic noise because of the larger number of charge generated for each absorbed x-ray. We have applied our cascaded linear systems model of the direct, flat-panel detector to fluoroscopy. The theoretical predictions of DQE(f) for different detector parameters, e.g. the type of x-ray photoconductor, fill-factor, and electronic noise, provide a guideline for an optimum detector design for fluoroscopy.

Paper Details

Date Published: 24 July 1998
PDF: 10 pages
Proc. SPIE 3336, Medical Imaging 1998: Physics of Medical Imaging, (24 July 1998); doi: 10.1117/12.317041
Show Author Affiliations
Dylan C. Hunt, Sunnybrook Health Science Ctr./Univ. of Toronto (Canada)
Wei Zhao, Sunnybrook Health Science Ctr./Univ. of Toronto (Canada)
John A. Rowlands, Sunnybrook Health Science Ctr./Univ. of Toronto (Canada)

Published in SPIE Proceedings Vol. 3336:
Medical Imaging 1998: Physics of Medical Imaging
James T. Dobbins; John M. Boone, Editor(s)

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