Energy window optimization in simultaneous SPECT(Tl-201)/TCT(Tc-99m) data acquisition

In simultaneous SPECT(Tl-201)/TCT(Tc-99m) data acquisition, emission and transmission images are degraded by both scatter photons and cross-contamination between emission and transmission photons. In this work, the authors aim to reduce these image degradations by optimizing the position and width of the energy window in a triple-camera fan-beam SPECT system. A statistical criterion based on maximizing the Figure-of-Merit (FOM) was used in the optimization by determining a compromise between increased detection efficiency of primary photons and reduced scatter and contamination photons. Scatter events were modeled using Monte Carlo (MC) simulation method. Experimental studies were performed to verify the simulations and to estimate the lead X-rays and scatter in the collimator which were not modeled in the MC program. Results suggest that cross-contamination degrades the emission and transmission data. However, they do not significantly alter the optimal energy window settings which centered at 75 keV with a window width of 30-35% for detecting the Tl emission photons, and centered at 140 keV with a window width of 15~20% for detecting the Tc transmission photons