Monte Carlo simulations of sodium iodide detector modules for a cylindrical SPECT system

Monte Carlo simulation methods are used to investigate the light output characteristics and energy resolution of detector modules that consist of long, narrow bars of sodium iodide crystals. These modules are designed to be components of a proposed modular cylindrical single photon emission computed tomography system suitable for cardiac imaging. The simulations are used to investigate the effects of crystal geometry and detector surface reflection properties on the total light output and energy resolution of the detector modules. The simulations include the effects on scintillation photons due to internal photon absorption at the crystal and light guide surfaces, partial (Fresnel) reflections and total internal reflections at the crystal/quartz exit window interface, refraction in the light guide, and finite quantum efficiency of photomultiplier tubes. For the imaging of 140-keV gamma rays, modules with 3-mm wide crystals and diffusely-reflecting surfaces are expected to have total light output of about 12.1% and energy resolution of about 10.9%. Modules with 4-mm wide crystals are expected to have total light output of about 13.9% and energy resolution of about 9.9%