Consideration of backscatter photons for edge detection in SPECT

It is important to obtain an accurate attenuation map in order to produce quantitative SPECT image. Compton scatter window (CSW) technique has been proposed to get the outline of the object in SPECT. This method requires no additional scan or transmission source and is capable to rapidly and easily estimate the edge of the object. Our goal of this study is to estimate the optimized energy window for Compton scattered photon in order to obtain the accurate edge of the object. We especially focused on the scatter photons which are scattered at the one camera and entered to the another camera (backscatter photons) for the dual-head SPECT system. In order to evaluate the effect of the backscatter photons we performed Monte-Carlo simulation. In the simulation, a circular phantom of 15 cm diameter filled with water was located between two cameras which were 25.6 cm apart each other. The radioactive source of Tc-99 m was either uniformly distributed in the phantom (the uniform phantom) or placed at the center of the phantom (the hot spot phantom). Spatial and energy distributions of the backscatter photons were examined. According to the simulation results, the optimized energy window for CSW technique was 95-123 keV and 102-112 keV for the uniform phantom and the hot spot phantom, respectively