Development and validation of a Monte Carlo simulation tool for multi-pinhole microSPECT

The purpose of this study is to develop and validate a Monte Carlo simulation (MCS) tool for investigation and evaluation of multi-pinhole microSPECT imaging. This simulation tool is based on a combination of SimSET and MCNP-4b Monte Carlo codes. It allows accurate simulation of a great range of physical factors, especially the pinhole collimator-detector response with specific photon energy, material, and geometry (such as knife and keel edge, size of the aperture, and orientation of the pinhole axis.) Point response functions (PRFs) and detection efficiencies (DEs) of 99mTC point sources obtained from MCS were verified through physical experiments using both a single-pinhole and a 4-pinhole collimator and also with theoretical predictions. Further evaluation involved simulations of a newly developed 4D digital mouse phantom using 3 multi-pinhole collimator configurations with 1, 4, and 5 pinholes. The simulated projection data were reconstructed using a 3D multi-pinhole OSEM algorithm. Good agreement was found between the MCS, experimental and theoretical results indicating the accuracy of the simulation method. The simulated mouse data demonstrated the application of the MCS. We concluded that we have developed and validated a special MCS tool, and illustrated its values in investigating and evaluating multi-pinhole collimator designs, data acquisition methods, and pinhole SPECT image reconstructions and correction techniques, which are crucial in the development of small animal imaging.