Monte Carlo simulation study of optimization for ultra-high-resolution parallel-hole collimator using detective quantum efficiency (DQE) with CdTe pixelated semiconductor-based gamma ray photon imaging system
In recent years, the pixelated semiconductor radiation detector (SRD) has been studied for single- or multi-energy gamma ray imaging. In previous research, to improve not only sensitivity but also spatial resolution, we proposed utilization of ultra-high-resolution parallel-hole collimator with pixel matched method based on cadmium telluride (CdTe) SRD. However, appropriate level of sensitivity and spatial resolution is needed before modelling of parallel-hole collimator geometric designs. The detective quantum efficiency (DQE) is a concept which takes both the sensitivity and spatial resolution into account to provide an overall measure and may be better suited for optimization. The purpose of this study was to evaluate and optimize the ultra-high-resolution parallel-hole collimator using DQE concept to determine the best image performance of CdTe semiconductor gamma camera system using a Geant4 Application for Tomographic Emission (GATE) simulation. To evaluate the modulation transfer function (MTF) and sensitivity, the collimator septal heights were varied from 15 to 30 mm at 5 mm intervals and source-to-collimator distances were 4, 5, 6, and 7 cm. Then, we calculated DQE to optimize the collimator geometric designs using evaluated MTF and sensitivity. The MTF decreased with increasing source-to-collimator distance and decreasing septal height. The DQE decreased with increasing source-to-collimator distance and septal height. We have presented the evaluation results of ultra-high-resolution parallel-hole collimators with various geometric designs. In conclusion, we successfully optimized the ultra-high-resolution parallel-hole collimator using DQE concept, and based on our results, we recommended using lower septal height with smaller source-to-collimator distance with CdTe semiconductor gamma camera system.
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