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Proceedings Paper

Multiple-gain-ranging readout method to extend the dynamic range of amorphous silicon flat-panel imagers
Author(s): Pieter G. Roos; Richard E. Colbeth; Ivan Mollov; Peter Munro; John Pavkovich; Edward J. Seppi; Edward G. Shapiro; Carlo A. Tognina; Gary F. Virshup; J. Micheal Yu; George Zentai; Wolfgang Kaissl; Evangelos Matsinos; Jeroen Richters; Heinrich Riem
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Paper Abstract

The dynamic range of many flat panel imaging systems are fundamentally limited by the dynamic range of the charge amplifier and readout signal processing. We developed two new flat panel readout methods that achieve extended dynamic range by changing the read out charge amplifier feedback capacitance dynamically and on a real-time basis. In one method, the feedback capacitor is selected automatically by a level sensing circuit, pixel-by-pixel, based on its exposure level. Alternatively, capacitor selection is driven externally, such that each pixel is read out two (or more) times, each time with increased feedback capacitance. Both methods allow the acquisition of X-ray image data with a dynamic range approaching the fundamental limits of flat panel pixels. Data with an equivalent bit depth of better than 16 bits are made available for further image processing. Successful implementation of these methods requires careful matching of selectable capacitor values and switching thresholds, with the imager noise and sensitivity characteristics, to insure X-ray quantum limited operation over the whole extended dynamic range. Successful implementation also depends on the use of new calibration methods and image reconstruction algorithms, to insure artifact free rebuilding of linear image data by the downstream image processing systems. The multiple gain ranging flat panel readout method extends the utility of flat panel imagers and paves the way to new flat panel applications, such as cone beam CT. We believe that this method will provide a valuable extension to the clinical application of flat panel imagers.

Paper Details

Date Published: 6 May 2004
PDF: 11 pages
Proc. SPIE 5368, Medical Imaging 2004: Physics of Medical Imaging, (6 May 2004); doi: 10.1117/12.535471
Show Author Affiliations
Pieter G. Roos, Varian Medical Systems, Inc. (United States)
Richard E. Colbeth, Varian Medical Systems, Inc. (United States)
Ivan Mollov, Varian Medical Systems, Inc. (United States)
Peter Munro, Varian Medical Systems, Inc. (United States)
John Pavkovich, Varian Medical Systems, Inc. (United States)
Edward J. Seppi, Varian Medical Systems, Inc. (United States)
Edward G. Shapiro, Varian Medical Systems, Inc. (United States)
Carlo A. Tognina, Varian Medical Systems, Inc. (United States)
Gary F. Virshup, Varian Medical Systems, Inc. (United States)
J. Micheal Yu, Varian Medical Systems, Inc. (United States)
George Zentai, Varian Medical Systems, Inc. (United States)
Wolfgang Kaissl, Varian Medical Systems, Inc. (Switzerland)
Evangelos Matsinos, Varian Medical Systems, Inc. (Switzerland)
Jeroen Richters, Varian Medical Systems, Inc. (Switzerland)
Heinrich Riem, Varian Medical Systems, Inc. (Switzerland)


Published in SPIE Proceedings Vol. 5368:
Medical Imaging 2004: Physics of Medical Imaging
Martin J. Yaffe; Michael J. Flynn, Editor(s)

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