ENERGY WINDOW OPTIMIZATION IN SIMULTANEOUS TC-99M TCT AND THALLIUM-2O1 SPECT DATA-ACQUISITION

In simultaneous Tc-99m TCT and Tl-201 SPECT data acquisition, the emis sion images are degraded by not only scatter from the emission source, but also cross-contamination from the transmission photons. Also, the transmission images are degraded by scatter from the transmission sou rce and cross-contamination from the emission photons. In this work, a criterion based on maximizing a Figure-of-Merit (FOM) was used to red uce image degradations by optimizing the position and width of the ene rgy windows used in the data acquisition in a triple-camera fan-beam S PECT system. The FOM determines a compromise between increased detecti on efficiency of primary photons and reduction of scatter and cross-co ntamination photons. Scatter in the projection data was modeled using Monte Carlo (MC) simulation methods, Experimental studies were perform ed to verify the simulations and to estimate the amount of Pb x-rays a nd scatter in the collimator which were not modeled in the MC program. Results suggest that cross-contamination degrades the emission and tr ansmission data. However, the contamination does not significantly alt er the optimal energy window settings, which should be centered at sim ilar to 77 keV with a window width of similar to 34% for detecting the Tl emission photons, and centered at 140 keV with a window width of s imilar to 20% for detecting the Tc transmission photons.