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25 April 2000 Experimentally validated theoretical model of avalanche multiplication x-ray noise in amorphous selenium
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We are investigating active matrix flat panel x-ray detectors for real-time operation in the fluoroscopic exposure range. The typical exposure range for fluoroscopy is low, (0.1 - 10 (mu) R/frame). Hence the flat panel must be very sensitive to produce quantum noise limited images. The application of avalanche multiplication in amorphus selenium, ((alpha) -Se) is examined. Avalanche multiplication, M, can be used to increase signal size, potentially eliminating the quantum sink at low exposure levels. However, M greater than 1 also causes an overall degradation of DQE due to the addition of a new source of gain fluctuation noise. Using a linear cascaded systems model, this noise can be expressed as an additional avalanche Swank factor A(alpha ) in the expression for DQE(0) equals (eta) AsA(alpha ) where (eta) is the quantum efficiency, AS is the conventional conversion gain Swank factor. Depending upon the parameters, the value of A(alpha ) can vary from unity to less than 0.2. Our model was in agreement with experimentally observed values of A(alpha ) obtained using an imaging system (HARP) with (alpha) -Se layers capable of avalanche multiplication. The results indicate that a balance must be maintained between the improvement from avalanche multiplication to the amplifier noise limited part of the image, and the degradation effect it has on the quantum noise limited parts of the image. It also suggests that proper engineering of the avalanche layer can minimize, and perhaps eliminate, the additional noise fluctuations arising from avalanche multiplication of x-ray signals.
© (2000) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Dylan C. Hunt, Brian Lui, and John A. Rowlands "Experimentally validated theoretical model of avalanche multiplication x-ray noise in amorphous selenium", Proc. SPIE 3977, Medical Imaging 2000: Physics of Medical Imaging, (25 April 2000);


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