A scatter reduction method for In-111 scintigrams using five energy windows

Measurements from water-filled phantoms were used to adapt the dual photopeak window scatter correction method to In-111 imaging. The ratio of the counts in a 226-246-keV window to those in a 247-274-keV window was found to correlate well (r=0.99) with a scatter fraction measure for a 226-274-keV window. To apply this dual photopeak window method to the 171-keV peak, the scatter spill-down from the 247-keV peak was estimated using an image recorded with a 195-225-keV window. This image was blurred and scaled to estimate more accurately the spill-down into each of the two 171 -keV photopeak windows, the scaling and blurring being estimated using Monte Carlo simulations for average scatter and blurring conditions. These estimated spill-down images were subtracted from the two 171-keV photopeak windows (160-170 and 171-184 keV, respectively). The ratio of the remaining counts in the 160-170 keV window to those in the 171-184 keV window correlated well. (r=0.975) with a scatter fraction measure in the 171-keV peak. Pixel-by-pixel application of the method to point source images reduced global measures of the scatter fraction magnitude by an average factor of 6.8 for the 171-keV photopeak and by an average factor of 5.7 for the 247-keV photopeak.<>