New Concept of Irregular Stack-Up Parallel-Hole Collimators with Photon Counting Gamma Camera System: Monte Carlo Simulation Study
The potential of room temperature photon counting detector (PCD) based on semiconductor materials is recognized in many nuclear medicine fields. In this study, the PCD using cadmium telluride (CdTe) was modeled as a PID 350 (Ajat Oy Ltd., Finland) with small pixels (0.35 × 0.35 mm2) using Geant4 Application for Tomographic Emission (GATE) simulation. In addition, a new concept of parallel-hole collimators with irregular stack-up method based on CdTe photon counting gamma camera system is proposed. Above-mentioned parallel-hole collimator is composed of three layers of tungsten plates stacked directly above each other with different ratio of septal height. The first layer is composed of fourfold increase in hole diameter compared to a pixel-matched parallel-hole collimator with an equal hole and pixel size. The second and third layers are composed of double increase in hole diameter compared to a pixel-matched parallel-hole collimator. The first layer functions to increase sensitivity due to large hole size and the third layer plays an role for a pixel-matched parallel-hole collimator. The aim of this study was the design and evaluation of the new concept of parallel-hole collimators with CdTe PCD. To estimate performance of the imaging system, spatial resolution and sensitivity were measured with various collimator geometric designs using 99mTc point source with different source-to-collimator distances. According to the results, the measured averages of spatial resolution and sensitivity varied depending on the collimator geometric designs and source-to-collimator distances. In conclusion, we successfully designed a new concept of parallel-hole collimator with various collimator geometric designs with a CdTe photon counting gamma camera system.
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