Investigation of scatter in SPECT transmission studies

In simultaneous emission/transmission, scans photons spilling over from the higher to the lower energy window (cross-talk) are observed. We have evalu ated the amount of cross talk scatter using data from several phantom and p atient studies for different strengths of the Profile attenuation source. T he quality of the resulting attenuation maps was assessed. In all studies t he number of scattered photons which need to be subtracted from the transmi ssion window by the cross-talk correction is 2 to 4 times larger than the n umber of true transmission photons. Using simulations we have studied the a mount of scattered photons in transmission studies for different transmissi on source collimations, scan geometries and window energies. Although the t otal number of scattered transmission photons for 2D collimation, ranges fr om 5% to 26% of the primary photons for angles 1 to 10 degrees, their contr ibution to any particular energy window is much smaller, usually less then 1-2%. Our conclusion from this study is that in order to minimize the cross -talk effect in simultaneous emission/transmission studies the energy of th e transmission isotope should be higher than that of the emission isotope.