Validation of a new deterministic transport code for SPECT simulation

The simulation of single photon emission computed tomography (SPECT) has traditionally been done using Monte Carlo methods. However, the hybrid deterministic transport code TITAN is being benchmarked for the simulation of SPECT. The TITAN code is referred to as “hybrid” because it uses a discrete ordinates method in the phantom and a simplified ray-tracing algorithm in the air outside of the phantom. The TITAN code has been compared with the results of the SIMIND Monte Carlo code and experimental data of a myocardial perfusion phantom. In comparison with SIMIND, TITAN projection images were found to be in good visual agreement. However, maximum relative differences ranging from 13% to 26% were found when the projection images were compared numerically. These are believed to be the result of different cross-section information used in the codes and differences in how the codes represent collimation. A computation time comparison showed the advantage of the TITAN code over SIMIND when an increasing number of projection images are generated. The comparison with experimental data also resulted in excellent visual agreement with numerical differences of 21% to 30%, which are at least partially due to limitations of the experiment.