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 attenuat ion and the spatially variant collimator and scatter response function s in a uniformly attenuating object for single photon emmission comput ed tomography (SPECT). In particular, the scatter response function (S RF) is modeled using a scheme based on the scatter responses of point sources in a large, slab phantom. This scheme, slab derived scatter es timation, allows efficient and accurate modeling of the asymmetric and spatially variant properties of the scatter response during the proje ction and backprojection operations. The scatter model has been verifi ed by comparison of scatter line source response functions, scatter/pr imary ratios, and projection data from extended source distributions o btained using this method and direct Monte Carlo (MC) simulations. It eliminates the need for extensive MC simulations for each object image d and the extremely large memory required to store the resulting SRFs for every pixel and view during the projection and backprojection proc ess. While the computational requirements of this method we substantia l, they are significantly less than those required for MC simulations. Combined with iterative reconstruction techniques, this projector-bac kprojector provides a practical and accurate means for scatter compens ation in SPECT. Preliminary results of combining this projector-backpr ojector with the maximum likelihood-expectation maximization algorithm show a significant increase in quantitative accuracy as compared to c ompensation for only attenuation and the spatially variant collimator response function.