Estimate of the scatter component in SPECT

Analytical expressions that describe the dependence of slopes and amplitudes of the scatter distribution functions (SDF) on source depth and media density are used to estimate a scatter component in SPECT projection data. Since the ratio of detected scattered to total photons (S/T), SDF amplitude and slope depend strongly on line source length (SL) used to obtain SDFs, we compared estimated scattered components using SDFs, obtained for lengths of 2-21 cm. At 10 cm source depth, S/T changes from 0.19 to 0.36 when SL changes from 2 to 21 cm. Scatter amplitude's dependence on source depth (d) in water was described by 6.38e/sup -0.186d/ for a 2 cm and 16.15e/sup -0.129d/ for a 21 cm SL. Slope was described by 0.292d/sup -0.601/ for a 21 cm SL, and by 0.396d/sup -0.82/ for a 21 cm SL. The estimated scatter components are compared with simulated SPECT projection data obtained with Monte Carlo modeling of six hot spheres placed in a cylindrical water filled phantom. The comparison of estimated with simulated total counts/projection shows very good agreement when approaching SDF for point source (the % difference varied from 2 to 13% for 2 cm SL). Significant overestimate is seen when source length increases.