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24 July 1998 Digital radiology using amorphous selenium and active-matrix flat-panel readout: photoconductive gain and gain fluctuations
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New radiological imaging techniques have to be capable of high image quality, high acquisition speed, compactness, and versatility in operation. We have been investigating a flat panel imager based on the direct conversion of x-ray energy to an electric charge signal in a layer of amorphous selenium (a- Se) and an active matrix real-time self scanning read out, that is expected to achieve these goals. Although prototype imagers have demonstrated both real-time acquisition and the quality necessary for radiography, systematic investigations of the photoconductive properties of a-Se were undertaken to understand and extend the photoconductor range of operation and facilitate the designs for specialized radiological applications, such as fluoroscopy. The method of pulse height spectroscopy was adapted to accurately measure the reciprocal photoconductive gain W+/- (eV/e-h+) as a function of the incident photon energy (epsilon) and the applied field E. Improvements were taken until spectral peaks could be well resolved. The accuracy of the measurements was increased by calibration with a Si-PIN diode with a known W+/- . The measured values of W+/- showed that gain increases of a factor of 2.6 could be realized at the highest fields. The spectral widths were corrected to give the gain fluctuations and then used to calculate the contribution to imaging noise, i.e. the Swank factor. The imaging noise contribution was shown to be negligible, in agreement with previous calculations. The data suggests a new model of charge recombination in low mobility semiconductors which can be used to calculate W+/- at different fields and x-ray spectra for the full range of radiological applications.
© (1998) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Ira M. Blevis, Dylan C. Hunt, and John A. Rowlands "Digital radiology using amorphous selenium and active-matrix flat-panel readout: photoconductive gain and gain fluctuations", Proc. SPIE 3336, Medical Imaging 1998: Physics of Medical Imaging, (24 July 1998);

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