| Summary: | 碩士 === 國立中央大學 === 光電科學與工程學系 === 101 === High resolution pinhole-SPECT systems are generally applied to small-animal nuclear medicine imaging, but the small acceptant solid angle of the single pinhole will limit the sensitivity. Therefore, multi-pinhole apertures are introduced into the micro-SPECT system developed in our group to raise the sensitivity. This study aims to design the multi-pinhole configuration that optimizes the spatial resolution and the sensitivity simultaneously.
The design procedure starts from deciding the multi-pinhole pattern. First, we choose the system magnification based on the predetermined field-of-view (FOV) and the criterion of using maximum detector area. Second, we choose the number of pinholes and the pinhole locations by setting an upper bound for the multiplexing factor and avoiding truncated projections. Third, we choose the pinhole size to have comparable spatial resolution among candidate pinhole patterns, where the sensitivity and resolution are preliminary evaluated by analytical models. After implementing the procedure, we obtain six single- and multi-pinhole patterns and their corresponding system magnifications.
The next step is to model the designed pinhole patterns in GATE Monte-Carlo simulations to generate the imaging system matrices. The final step is to compare the Area-Under-Curve (AUC) values, the sensitivities and the spatial resolutions of the designed pinhole patterns. The AUC values are evaluated with their respective imaging system matrices through signal detection tasks. The sensitivities are calculated during the generation of the system matrices as the ratio of detected counts divided by the number of emitted photons. The spatial resolutions are calculated by the Fourier crosstalk approach and visualized by reconstruction images of a hot-rod phantom. According to the resulting AUC, sensitivity and spatial resolution, the four-pinhole pattern with 20% multiplexing, 0.6-mm pinhole diameter, and 1.52 times system magnification is the optimized configuration for our micro-SPECT system with a camera face of 49 × 49 mm2 and a spherical FOV of 14-mm diameter. The corresponding system resolution is 1.0 mm, and the sensitivity is 2.2 ×10-4.
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