Monte Carlo study of scattered radiation in variable resolution X-ray CT scanner

Variable resolution x-ray (VRX) CT is a newly introduced CT scanner that provides increased spatial resolution. Compton scatter poses a significant threat to VRX CT, bringing cupping and streak artifacts. Appropriate compensation of scattered radiation in VRX CT needs accurate estimation of Compton scattering. The aim of this study is to assess the magnitude and spatial distribution of scattered radiation in a one-dimensional VRX CT. To fulfill this aim, a model based on an actual VRX CT scanner was developed in GATE Monte Carlo and scatter-to primary ratio was measured as a function of field of view (FOV). The magnitude of scatter-to primary ratio of the system increased from less than 0.001% at FOV of 1 cm (minimum FOV) to more than 5% at FOV of 36 cm (maximum FOV). The spatial distribution of the scatter-to primary ratio was different at each FOV because of angulation of the detector. Increasing the x-ray tube voltage 20% more than its experimental value increased slightly the magnitude of scatter-to primary ratio of the system at FOVs of 1 cm to 22 cm. On the other hand, increased x-ray tube voltage reduced the scatter-to primary ratio up to 0.5% at FOVs of 22 cm to 36 cm.