Abstract
Background: Monte Carlo N-Particle code, version 5 (MCNP5) is a generalpurpose Monte Carlo code and it can be used for the design of imaging systems. In this paper, a realistic single photon emission computed tomography (SPECT) model was developed referred to the SIEMENS Symbia T imaging system. Methods: The most important components of the SPECT camera were modeled, especially a low-energy highresolution collimator with hexagonalhole was simulated as closely as possible to its shape and dimensions. The photoelectric effect, Compton and coherent scattering were included in the gamma transport process. In order to validate the SPECT model, specifications in terms of intrinsic spatial resolution, energy resolution, sensitivity, system spatial resolution, and tomography spatial resolution were calculated in comparison with experimental data. Results: Overall results showed good agreements between the simulations and experimental results provided by SIEMENS. The simulated intrinsic resolution and energy resolution matched well with experimental data. The sensitivity measurements from simulation data yielded higher values. For the system spatial resolution, it differed about 3% compared with the experimental result. The tomographic results showed differences of 5.9%, 5.6%, 0.3%, 10.7%, and 0.2% for the five average resolutions, respectively. Conclusion: In summary, the results demonstrated the flexibility and accuracy of MCNP5 to simulate the basic features of SIEMENS Symbia T SPECT Camera and exemplified its potential benefits in protocol optimization and in system design.

Key words: Monte Carlo simulation, MCNP5, SPECT.