Realistic Monte Carlo simulation of Ga-67 SPECT imaging

Describes a comprehensive Monte Carlo program tailored for efficient simulation of realistic Ga-67 SPECT imaging through the entire range of photon emission energies. The authors' approach incorporates several new features developed by them and by others. It is now being used to optimize and evaluate the performance of various methods of compensating for photon scatter, attenuation, and nonstationary distance- and energy-dependent detector resolution. Improvements include (1) the use of a numerical torso phantom with accurate organ source and attenuation maps obtained by segmenting CT images of a Radiology Support Devices anthropormorphic heart/thorax phantom, modified to include eight axillary lymph nodes; (2) accelerated photon propagation through the attenuator using a variant of the maximum rectangular region algorithm of Suganuma and Ogawa (1999); and (3) improved variance reduction using modified spatial sampling for simulation of large-angle collimator penetration, scatter and lead X-rays. Very-high-count projections were simulated in 55 energy windows spaced irregularly in the range 60-370 keV; these essentially noise-free images were used as a basis for generating Poisson noise realizations characteristic of 72-h postinjection Ga-67 studies. Comparisons of spatial and energy distributions demonstrated good agreement between data experimentally measured from the RSD phantom and those simulated from the mathematical segmentation of the same phantom.