Feasibility of Ultra-High-Resolution Photon Counting Gamma Camera System with Different Types of Filtered Backprojection: Monte Carlo Simulation Study

The utilization of a photon counting single photon emission computed tomography (SPECT) system with cadmium zinc telluride (CZT) detector is of growing interest for new devices in the field of nuclear medicine. In SPECT system, the reconstruction with projections is essential for acquiring image. Among the reconstruction methods, the filtered backprojection (FBP) is most widely used in the field of the nuclear medicine imaging. The purpose of this study was to confirm feasibility of the eValuator-2500 (eV Microelectronics Inc., Saxonburg, PA, USA) CZT photon counting SPECT system using a pixelated parallel-hole collimator for ultra-high-resolution with FBP reconstruction methods. The three reconstruction methods using Ram-lak, Cosine, and Hann filter were carried out in this study. For that purpose, we evaluated the sensitivity, the spatial resolution, and the coefficient of variation (COV) using Geant4 Application for Tomographic Emission (GATE) simulation. According to the results, 0.0204 cps/kBq of sensitivity was acquired and the evaluated spatial resolution using a Ram-lak filter was 2.3 and 11.3% higher than that of the Cosine and the Hann filters, respectively. In addition, the evaluated COV using a Hann filter was 7.3 and 22.1% higher than that of the Cosine and Ram-lak filters, respectively. We have presented the performances of the imaging system using a pixelated parallel-hole collimator SPECT system with three FBP reconstruction methods. Our results showed that the effect of various reconstruction methods can be investigated by GATE simulation so as to evaluate the feasibility of an ultra-high-resolution parallel-hole collimator with a CZT photon counting SPECT system.