A slice-by-slice blurring model and kernel evaluation using the Klein-Nishina formula for 3D scatter compensation in parallel and converging beam SPECT

Converging collimation increases the geometric efficiency for imaging small organs, such as the heart, but also increases the difficulty of correcting far the physical effects of attenuation, geometric response and scatter in SPECT. In this paper, 3D first-order Compton scatter in non-uniform scatte ring media is modelled by using an efficient slice-by-slice incremental blu rring technique in both parallel and converging beam SPECT. The scatter pro jections are generated by first forming an effective scatter source image ( ESSI), then forward-projecting the ESSI. The Compton scatter cross section described by the Klein-Nishina formula is used to obtain spatial scatter re sponse functions (SSRFs) of scattering slices which are parallel to the det ector surface. Two SSRFs of neighbouring scattering slices are used to comp ute two small orthogonal 1D blurring kernels used for the incremental blurr ing from the slice which is further from the detector surface to the slice which is closer to the detector surface. First-order Compton scatter point response functions (SPRFs) obtained using the proposed model agree well wit h those of Monte Carlo (MC) simulations for both parallel and fan beam SPEC T. Image reconstruction in fan beam SPECT MC simulation studies shows incre ased left ventricle myocardium-to-chamber contrast (LV contrast) and slight ly improved image resolution when performing scatter compensation using the proposed model. Physical torso phantom fan beam SPECT experiments show inc reased myocardial uniformity and image resolution as well as increased LV c ontrast. The proposed method efficiently models the 3D first-order Compton scatter effect in parallel and converging beam SPECT.