Evaluating collimator designs for nuclear breast imaging with High-Purity Germanium detectors

Nuclear breast imaging with specifically designed semiconductor gamma cameras can improve breast cancer detection. One benefit of semiconductor-based imaging systems is their superior Energy Resolution (ER). In previous simulation work, we observed that the superior ER of High-Purity Germanium (HPGe) could offer potential improvements in sensitivity and scatter rejection compared to Cadmium Zinc Telluride (CZT). In this work we conducted simulations with various collimation schemes to evaluate the possible imaging performance of an HPGe system with 1% ER at 140 keV. The objective was to investigate the influence of the collimation scheme on sensitivity and spatial resolution, and how these would translate to imaging performance. Using the Monte Carlo N-Particle (MCNP5) simulation package, we modeled a 10 mm thick HPGe detector with hexagonal-hole and registered square-hole collimators for the imaging of a breast/torso phantom with three spherical tumors. Simulated energy spectra were generated, and images were created with a ±1.25% energy window around the 140 keV photopeak. Scatter and torso fractions were calculated along with tumor contrast and relative sensitivity. Our results agree with previous literature suggesting that utilizing registered collimators yields large increases in sensitivity with similar resolutions and image quality to standard hexagonal-hole collimators.