Effect of scatter from radioactivity outside of the field of view in 3D PET

The contribution of the scattered events originating from Radioactivity Outside the tomograph Field of View (ROFOV) is treated differently by different scatter correction algorithms. Using measured data we have evaluated the amount of scatter originating from ROFOV, its axial and transaxial distribution in two energy windows for direct and a subset of oblique planes in 3D PET. Nonuniform distributions were observed with the total contribution found to be non negligible when the amount of ROFOV was comparable to the radioactivity in the Field of View (FOV).