Optimization of a rotating modulation collimator for neutron stimulated emission computed tomography (NSECT) imaging

A high-energy gamma camera design is being developed for use with neutron simulated emission computed tomography (NSECT). NSECT is a spectroscopic imaging technique that measures elemental concentrations in vivo through neutron interrogation and collection of the subsequent prompt characteristic gamma emission. NSECT operates in an energy range above that of typical nuclear medicine gamma cameras (0.3 - 2 MeV), and requires high-resolution gamma spectroscopy. We are developing a camera using a rotating modulation collimator (RMC) placed in front of a high purity germanium (HPGe) detector. The RMC consists of a pair of parallel slat collimators rotating in unison and as it rotates it modulates the number of incident gammas. Counting the number of incident gammas at each angle provides spatial information and allows reconstruction of images. There are six parameters in the camera system that can be optimized to improve image quality. A preliminary experiment was performed to determine the six parameters´ relationship to each other and to image quality. Four subsequent experiments were performed based on the preliminary data to optimize the camera configuration. Results of these experiments found a tradeoff between system efficiency and spatial resolution, much like that for high-energy gamma collimation for standard gamma cameras. Point source reconstructions are provided to illustrate this tradeoff.