Monte Carlo studies on the amorphous silicon based digital X-ray imagers

Results of Monte Carlo simulations on amorphous silicon based X-ray imaging arrays are described. In order to investigate the characteristics of amorphous silicon X-ray imaging devices and to provide the optimum design parameters, Monte Carlo simulations were performed. Monte Carlo simulation codes for the authors´ purpose were developed and various combinations of X-ray peak voltages, aluminum filter thicknesses, CsI(Tl) thicknesses, and amorphous silicon photodiode pixel sizes were tested in connection with detection efficiency and spatial resolution of the amorphous silicon based X-ray imager. With usual CsI(Tl) thickness of 300 μm~500 μm, detection efficiency was in the range of 70%~95% and energy absorption efficiency was in the range of 40%~70% for 60 kVp~120 kVp X-rays. From the simulations it was found that amorphous silicon pixel size and CsI(Tl) thickness were the most important parameters which determine the resolution of the imager. By use of the authors´ simulation results they could provide proper combinations of CsI(Tl) thicknesses and pixels sizes for optimum sensitivity and resolution