Effect of secondary radiations on the performance of digital radiographic detectors

Blur and noise in radiographs are caused in part by the transport of fluorescent radiation in imaging detectors. We have studied this effect using a Monte Carlo radiation transport analysis which tracks radiations associated with K, L, and M shell transitions. Energy deposition distributions are accumulated which permit computation of the large area energy absorption and noise characteristics. Additionally, the spatial distribution of deposited energy is evaluated in a manner which permits determination of the line spread function and the auto-correlation function. The frequency dependent detective quantum efficiency, DQE(E,f), is subsequently determined by Fourier analysis. This novel method is illustrated by considering the response of a selenium direct digital detector to 120 keV x-rays. It is shown that fluorescent radiations associated with the composition of glass substrates cause a frequency dependent drop in DQE(E,f)/DQE(E,O) of 10% to 22%.

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