Fast GATE fan beam SPECT projector

Fan beam collimation offers a higher sensitivity than parallel beam collimation at the cost of a reduced field of view. The spatially varying collimator-detector response has so far been studied analytically and with Monte Carlo simulations in order to improve reconstruction quality. Similarly to parallel beam collimation, it may be possible to improve the reconstruction quality further by using accurate Monte Carlo-based scatter estimates. In this work, we have developed a fast hybrid CPU-GPU accelerated Monte Carlo projector for fan beam collimation that can be used for this purpose. A pre-simulated collimator-detector response was combined with a parallelized GEANT4 implementation and GPU accelerated convolution-based forced detection. Our method was validated with a GATE model of the Prism 3000XP equiped with low energy high resolution fan beam collimators. Projections of an image quality phantom showed an excellent agreement with GATE. Almost noiseless projections can be obtained in under 30 seconds.