A practical method for incorporating scatter in a projector-backprojector for accurate scatter compensation in SPECT

A projector-backprojector pair has been developed that models attenuation and the spatially variant collimator and scatter response functions in a uniformly attenuating object for single photon emission computed tomography (SPECT). The scatter response function (SRF) is modeled using a scheme based on the scatter responses of point sources in a large slab phantom. This scheme, slab derived scatter estimation, allows efficient and accurate modeling of the asymmetric and spatially variant properties of the scatter response during the projection and backprojection operations. The scatter model is verified by comparison of scatter line source response functions, scatter/primary ratios, and projection data from extended source distributions obtained using this method and direct Monte Carlo simulations. Combined with iterative reconstruction techniques, this projector-backprojector provides a practical and accurate means for scatter compensation in SPECT. Preliminary results of combining this projector-backprojector with the maximum-likelihood-expectation-maximization algorithm show a significant increase in quantitative accuracy as compared to compensation for only attenuation and the spatially variant collimator response function