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 which are oblique to the scanning planes. Several volume imaging systems which acquire oblique rays have now been built. This paper discusses why the scatter fraction is intrinsically higher in these systems, and then compares two different scatter compensation techniques. The comparison is done using Monte Carlo simulation to generate average profiles and spectra for typical phantoms and scanning geometries. On the basis of this study, deconvolution of the total event profiles with a filter adjusted to the object size, and good energy discrimination provides 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 did not match the scattered event profile, and were less reliable, being based on a lower number of counts.