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. The authors have evaluated the amount of cross talk scatter using data from several phantom and patient studies for different strengths of the Profile attenuation source. The quality of the resulting attenuation maps was assessed. In all studies the number of scattered photons which need to be subtracted from the transmission window by the cross-talk correction is 2 to 4 times larger than the number of true transmission photons. Using simulations the authors have studied the amount of scattered photons in transmission studies for different transmission source collimations, scan geometries and window energies. Although the total number of scattered transmission photons for 2D collimation, ranges from 5% to 26% of the primary photons for angles 1 to 10 degrees, their contribution to any particular energy window is much smaller, usually less then 1-2%. The authors' conclusion from this study is that in order to minimize the cross-talk effect in simultaneous emission/transmission studies the energy of the transmission isotope should be higher than that of the emission isotope.