A SIMIND Monte Carlo Simulation Study on CdTe and NaI (Tl) Thickness as Detectors of a Small Animal SPECT System

Purpose: Micro Single Photon Emission Computed Tomography (Micro-SPECT) system has recently been introduced on nuclear medicine in the preclinical and research in which NaI (Tl) and Cadmium Telluride (CdTe) are used as the gamma-ray detectors with more generally use of NaI (Tl). The present study aimed to evaluate different thicknesses of the NaI (Tl) and (CdTe) detectors on functional parameters of a micro-SPECT system. Materials and Methods: A Micro-SPECT system with CdTe semiconductor detector and a hexagonal parallel hole collimator with a hole diameter of 0.11 mm, high of 24.05 mm, and septal thickness of 0.016 mm was simulated by Simulating Medical Imaging Nuclear Detectors (SIMIND) Monte Carlo program. The system performance was assessed by comparing the functional parameters, including system efficiency, sensitivity, energy and spatial resolution with the NaI (Tl) detector. The simulated scans of a 99mTc point source, a digital micro-Jacszack phantom, and a voxelized MOBY mouse phantom with the system were prepared to evaluate image quality. Results: The functional parameters; sensitivity, efficiency, planar spatial resolution, and image contrast of CdTe detector were determined 1.4, 1.2, 1.7, and 1.8 times higher than those of NaI (Tl), respectively. Moreover, the calculated energy resolution of CdTe and NaI (Tl) detectors was obtained 6.2% and 10.2% at 141 KeV, respectively. In the filtered back projection (FBP) reconstructed images of the micro-Jacszack phantom, minimum detectable size of the cold rods with CdTe and NaI (Tl) detectors were obtained 0.79 mm and 0.95 mm, respectively. Conclusion: The imaging system with a 5.5 mm thickness CdTe detector provided better image quality and showed considerable efficiency.