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 emmission computed tomography (SPECT). In particular, 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 has been 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 (MC) simulations. It eliminates the need for extensive MC simulations for each object imaged and the extremely large memory required to store the resulting SRFs for every pixel and view during the projection and backprojection process. While the computational requirements of this method we substantial, they are significantly less than those required for MC 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.