Fast simulation of micro-pinhole imaging by mixing Monte Carlo and analytical modeling

The aim of the present work is to accelerate Monte Carlo (MC) simulations of micro-pinhole SPECT projections. To this end, forced detection (FD), a commonly used acceleration technique, is replaced by a kernel-based forced detection (KFD) step. In KFD, instead of tracing individual photons from the source or last scatter position to the detector, a position dependent point spread function (PSF) modeling a channel edge pinhole aperture is projected. The speed-up and accuracy achieved by using KFD were validated by means of digital phantoms. MC simulations with FD and with KFD converge to almost identical projections. However, KFD converges to an equal noise level in the projections one up to four orders of magnitude faster than FD, depending on the number of photons simulated.