A SCATTER MODEL FOR PARALLEL AND CONVERGING BEAM SPECT BASED ON THE KLEIN-NISHINA FORMULA

In this study, a scatter model is proposed for parallel-, fan-, and co ne-beam SPECT imaging. In this model, a photon is allowed to be scatte red only once, and the probability of scatter for given angle and ener gy is computed by using the Klein-Nishina formula. The detector is ass umed to have perfect energy resolution. The scatter counts are compute d for every projection bin. From the scatter counts, the scatter line source response function and scatter-to-primary ratio (SPR) are obtain ed. They agree well with those from Monte Carlo (MC) simulation includ ing only single scattering, but deviate from those from full MC simula tion including both single and multiple scattering. The deviation depe nds on the source depth within the medium. For a source depth of 6 cm, the difference of the scatter-to-primary ratio between the model and full MC simulation is less than 7%, while for a 21.6 cm source depth, the difference goes up to 27% for parallel-beam geometry and 32% for c one-beam geometry. Since scatter accounts for 20-40% of the total coun ts in most clinical studies, the scatter model yields a SPR accuracy t hat ranges from 3% to 12%. The scatter model provides an effective mea ns to estimate the scatter response with reasonable accuracy, and can be used in developing scatter compensation techniques in parallel- and converging-beam SPECT.