Accelerated simulation of cone beam X-ray scatter projections

Monte Carlo (MC) methods can accurately simulate scatter in X-ray imaging. However, when low noise scatter projections have to be simulated these MC simulations tend to be very time consuming. Rapid computation of scatter estimates is essential for several applications. The aim of the work presented in this paper is to speed up the estimation of noise-free scatter projections while maintaining their accuracy. Since X-ray scatter projections are often rather smooth, an approach is chosen whereby a short MC simulation is combined with a data fitting program that is robust to projection truncation and noise. This method allows us to estimate the smooth scatter projection rapidly. The speed-up and accuracy achieved by using the fitting algorithm were validated for the projection simulation of a small animal X-ray CT system. The acceleration that can be obtained over standard MC simulations is typically two orders of magnitude, depending on the accuracy required. The proposed approach may be useful for rapid simulation of patient and animal studies and for correction of the image-degrading effects of scatter in tomography.