Analysis of SPECT imaging simulation using the TITAN transport code

Simulation of the NCAT heart phantom has recently been done using the hybrid deterministic code TITAN. Single photon emission computed tomography (SPECT) simulation is traditionally done using Monte Carlo codes such as SIMIND. This paper analyzes and compares the results of the SIMIND and TITAN codes for an NCAT heart phantom. Since the SIMIND code does not provide statistical information, runs with varying numbers of particles were used to ensure that the solution had converged for the first energy group (source particle energy bin). SIMTND results for the lower energy groups were determined to be less accurate due to the lack of cross section data and larger statistical uncertainties. The output of the TITAN code was analyzed for the Diamond Differencing with zero fix-up (DDZ) and Directional Theta-Weighted (DTW) differencing schemes and various orders of quadrature. The DTW method was found to converge to a solution at a lower order of quadrature than DDZ. In comparison with SIMIND, the DDZ and DTW methods were found to be equally accurate. The SIMIND and TITAN solutions were in good agreement and TITAN was shown to have a much shorter run time than SIMIND.