Investigation of scatter in singles-based PVI transmission imaging

Singles-based positron volume imaging (PVI) transmission scans can provide measured 3D attenuation correction factors (ACFs) while requiring relatively short scan times (4-5 minutes). The main concern associated with singles-based transmission measurements is bias in the ACFs caused by scattered events in the transmission data. The magnitude and spatial characteristics of this scatter were investigated through computer simulation. Objects simulated include right circular cylinders of varying diameters, a 32 cm by 24 cm right elliptical cylinder, and the voxel.man digital phantom. Results indicated that scatter is very object dependent. For all objects simulated single scatter events comprised at least 70% of the total detected scatter. Furthermore, the shape of the scatter distribution was primarily determined by the single scatter events. Because the scatter distribution is very object dependent it is unlikely that simple correction techniques (e.g. fitting scatter tails or convolution subtraction) will prove effective. On the other hand because most of the detected scatter are single scatters, analytical methods which can accurately model single scatter events should provide the basis for an accurate scatter correction.