A : Significant progress has been achieved in the design of pixelated CZT detectors dedicated to cardiac and breast SPECT imaging. However, their detector geometry and associated collimators' design have limited their clinical use. The aim of this work is to determine the best combination between a large pixelated CZT detector and parallel-hole collimator that can provide high spatial resolution at low injected activity with low-energy radiotracers. Our proposed combination resulted in the design of a novel four-hole matched pixel detector (4-HMPD) configuration. Our novel 4-HMPD design based on large pixelated CZT detector was firstly compared to the standard one-hole matched pixel detector (1-HMPD) configuration using Monte Carlo simulation. We have also predicted the influence of pixel size, interpixel gap and source-to-collimator distance on the basis of resulting spatial resolution, sensitivity and crosstalk events fraction for three collimator hole lengths for Tc-99m (140 keV). Thereafter, we used the same detector and collimator settings of the 1-HMPD configuration as constructed with the D-SPECT camera module (Redlen Technologies, BC, Canada) for our 4-HMPD design to compare the performance of the two configurations. Our preliminary results showed that a large pixel size, a small interpixel gap and a small collimator hole length increased significantly the sensitivity at the detriment of spatial resolution. The performance comparison between the 4-HMPD and the 1-HMPD configurations demonstrated an improved reconstructed spatial resolution (by a factor two), higher contrast with the large sphere of the modified Jaszczak phantom (from 63.1% to 39.1%), clear appearance of cold spheres (> 14 mm diameter) and the cold cylinders (> 11.1 mm diameter). The crosstalk events fraction varied from 8.5% to 12.8%. Our novel detector/collimator combination allows less electronic readout complexity, less crosstalk events between pixels and twofold increase in septal thickness resulting in low septal penetration compared to the classical 1-HMPD configuration. It also showed the highest enhancement in terms of spatial resolution even in cases of low sensitivity with less injected activity, and outperformed the performance of existing conventional NaI (TI) crystal-based systems.
Purpose: Current hole matching pixel detector (HMPD) collimators for SPECT imaging exist in two configurations: one hole per pixel (1HMPD) or four holes per pixel (4HMPD). The aim of this study was to assess the performance of a dual-layer collimator made by stacking up these two collimator types (1H/4HMDP) for low- and medium-energy gamma emitters. Method: Analytical equations describing geometrical efficiency and full width at half maximum (FWHM) of the 1H/4HMDP collimator were derived. In addition, a fast dedicated Monte Carlo (MC) code neglecting scattering and designed for the collimator geometry was developed to assess the collimator’s point spread function (PSF) and to simulate planar and SPECT acquisitions. Results: A relative agreement between analytical equations and MC simulations better than 3% was observed for the efficiency and for the FWHM. The length of the two layers was optimized to get the best spatial resolution while keeping the geometrical efficiency equal to that of the 45mm-length 1HMPD collimator. An optimized combination of the 1H/4HMPD configuration with respective hole lengths of 20mm and 13mm has been derived. For source-collimator distances above 5 cm and equal collimator geometrical efficiency, the spatial resolution of this optimal 1H/4HMDP collimator supersedes that of the 45mm-le-ngth 1HMPD collimator, and that of the 19.1mm-length 4HMPD collimator. This improvement was observed in simulations of bar phantom planar images and of hot rods phantom SPECT. Remarkably, the spatial resolution was preserved along the whole radial range within the Jaszczak phantom. Conclusion: The 1H/4HMDP collimator is a promising solution for CZT SPECT imaging of low- and medium-energy emitters.
Current hole matching pixel detector (HMPD) collimators for SPECT imaging exist in two configurations: one hole per pixel (1HMPD) or four holes per pixel (4HMPD). The aim of this study was to assess the performance of a dual-layer collimator made by stacking up these two collimator types (1H/4HMDP) for low and medium-energy gamma emitters. Analytical equations describing 1H/4HMDP collimator geometrical efficiency and full width at half maximum (FWHM) were derived. In addition, a fast dedicated gamma ray-tracing Monte Carlo (MC) code was developed to assess the collimator’s point spread function (PSF) and to simulate planar and SPECT acquisitions. A relative agreement between analytical equations and MC simulations better than 3% was observed for the efficiency and better than 1% for the FWHM. The length of the two layers was optimized to get the best spatial resolution while keeping the geometrical efficiency equal to that of the 45mm-length 1HMPD collimator. An optimized combination of the 1H/4HMPD configuration with respective hole lengths of 20mm and 12.95mm has been derived. For source-collimator distances above 5 cm and equal collimator geometrical efficiency, the spatial resolution of this optimal 1H/4HMDP collimator supersedes that of the 45mm-length 1HMPD collimator, and that of the 19.1mm-length 4HMPD collimator. This improvement was observed in simulations of bar phantoms planar images and of hot rods phantom SPECT. Remarkably, the spatial resolution was preserved along the depth of the Jaszczak phantom slices. The 1H/4HMDP collimator is a promising solution for CZT SPECT imaging of low- and medium-energy emitters.
Current hole matching pixel detector (HMPD) collimators for SPECT imaging exist in two configurations: one hole per pixel (1HMPD) or four holes per pixel (4HMPD). The aim of this study was to assess the performance of a dual-layer collimator made by stacking up these two collimator types (1H/4HMDP) for low and medium-energy gamma emitters. Analytical equations describing 1H/4HMDP collimator geometrical efficiency and full width at half maximum (FWHM) were derived. In addition, a fast dedicated gamma ray-tracing Monte Carlo (MC) code was developed to assess the collimator’s point spread function (PSF) and to simulate planar and SPECT acquisitions. A relative agreement between analytical equations and MC simulations better than 3% was observed for the efficiency and better than 1% for the FWHM. The length of the two layers was optimized to get the best spatial resolution while keeping the geometrical efficiency equal to that of the 45mm-length 1HMPD collimator. An optimized combination of the 1H/4HMPD configuration with respective hole lengths of 20mm and 12.95mm has been derived. For source-collimator distances above 5 cm and equal collimator geometrical efficiency, the spatial resolution of this optimal 1H/4HMDP collimator supersedes that of the 45mm-length 1HMPD collimator, and that of the 19.1mm-length 4HMPD collimator. This improvement was observed in simulations of bar phantoms planar images and of hot rods phantom SPECT. Remarkably, the spatial resolution was preserved along the depth of the Jaszczak phantom slices. The 1H/4HMDP collimator is a promising solution for CZT SPECT imaging of low- and medium-energy emitters.
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