Simulation study of patient and crystal scatter in 3D PET for various crystals

The main objective of this study is to understand by means of simulations which patient scatter order is significantly predominating in the photopeak window. A second goal was to qualify the difference between phantom and crystal scatter influences. Since this is dependent of the photoelectric fraction (ratio of the number of detections in the photopeak window after photo-electric effect to the total of the photopeak detections including multiple Compton and photo-electric events), several crystal materials were investigated: GSO, LSO, BGO. We also included two innovative materials: LaBr₃ and LUI₃. Simulation studies showed that only first order patient scatter is significantly degrading PET image quality. The effect of higher order scatter in the photopeak window is negligible. For crystal scatter we propose to realistically simulate the generalized natural pixel matrix in order to incorporate the aforementioned degrading factor. It was shown that this improves the image resolution.