The problem of scatter correction in positron volume imaging

Thin, dense interslice septa have long been used to reduce the scattered radiation collected in positron emission tomography (PET). These septa prevent the acquisition of coincident gamma rays that are oblique to the scanning planes. Several volume imaging systems that acquire oblique rays have been built. The reasons why the scatter fraction is intrinsically higher in these systems are discussed, and two different scatter compensation techniques are compared. The comparison uses Monte Carlo simulations to generate average profiles and spectra for typical phantoms and scanning geometries. Comparison results indicate that deconvolution of the total event profiles with a filter adjusted to the object size and good energy discrimination provide an excellent scatter estimate as long as the object's diameter is less than the detector's radius. The profiles derived from a second, lower, energy window are always much flatter than the scattered counts in a window covering the photopeak. They do not match the scattered event profile and are less reliable, being based on a lower number of counts.