SCATTER CORRECTION IN 3-D PET

Modern multiring positron emission tomographs allow the acquisition of 3-D data sets to increase their sensitivity. A substantial part of th is data is due to scattered radiation. We describe the experimental de pendence of point source scatter distributions on energy window settin g, source location, and scatter volume in geometries relevant for brai n studies. The point source scatter distribution was parametrized accu rately by a broad, 2-D Gaussian, which included a shift parameter to a ccount for asymmetry of the scatter medium relative to the source. Thi s parametrization was used to formulate two fast scatter correction al gorithms suitable for brain scans. In both algorithms, a 2-D subset of the measured projections was transformed into a scatter projection, A n image of the 3-D scatter distribution was reconstructed using 2-D al gorithms. It was then subtracted from the total (true + scattered) 3-D image. Both algorithms were implemented in different combinations wit h the additional attenuation correction and were tested on point sourc e and phantom measurements. It was shown that, for the situation typic al for brain scans, reconstructed scatter fractions could be reduced t o 5% or less.