Pixelated Parallel-hole Collimator Research Articles

Comparison of a newly-designed stack-up collimator with conventional parallel-hole collimators in pre-clinical CZT gamma camera systems: a Monte Carlo simulation study

Recently, many studies have been conducted with pixelated semiconductor detectors that use cadmium zinc telluride (CZT) because these detectors have many advantages in pre-clinical gamma imaging. Collimators play an extremely important role in the imaging performance of pixelated semiconductor gamma cameras. In our previous study, based on the pixelated semiconductor gamma camera system we recommended the use of a pixelated parallel-hole collimator with equal hole and pixel sizes; this approach improved both the sensitivity and the spatial resolution. However, the pixelated parallel-hole collimator had two major limitations: (a) Although its sensitivity was higher than that of pinhole systems, the pixelated parallel-hole collimator may have still resulted in a partial loss of sensitivity due to its small collimator hole size. (b) The pixelated parallel-hole collimator with an adequate septal height was difficult to manufacture due to its small holes. Here, we present a new design for a parallel-hole collimator, which uses the stack-up method and a CZT pixelated semiconductor gamma camera system. The purpose of this study was to compare the performances of various geometric designs of our newly-designed parallel-hole collimator with those of conventional parallel-hole collimators [low-energy high-resolution (LEHR) and low-energy high-sensitivity (LEHS)]. The detector was modeled as an eValuator-2500 (eV Microelectronics Inc., Saxonburg, PA, USA) (3-mm thick, 0.5-mm pixel size) by using a Geant4 Application for Tomographic Emission (GATE) simulation. The proposed parallel-hole collimator consisted of two overlapping parallel-hole collimators. The size of each hole in the proposed parallel-hole collimator was four times that of the hole in the pixelated parallel-hole collimator. The overlap ratios of these collimators were 1 : 1, 1 : 2, 2 : 1, 1 : 5, and 5 : 1. To evaluate and compare the performances of these systems, we evaluated the sensitivity and the spatial resolution of each system. The average sensitivities of the proposed parallel-hole collimators with overlap ratios of 1 : 1, 1 : 2 or 2 : 1, and 1 : 5 or 5 : 1 and of the LEHS conventional parallel-hole collimator were 2.17, 3.45, 13.90, and 3.68 times higher than the average sensitivities of the LEHR conventional parallel-hole collimator, respectively. The average spatial resolution also varied depending on the distance from the collimator. In conclusion, we successfully designed a novel parallel-hole collimator for pre-clinical imaging; this novel collimator employs the stack-up method with a CZT pixelated semiconductor gamma camera.

Monte carlo simulation study of a novel parallel-hole collimator with a CdTe pixelated semiconductor SPECT system

Recently, many studies have investigated the use of a pixelated semiconductor detector to improve spatial resolution. The purpose of this study was to evaluate novel parallel-hole collimator geometric designs with a CdTe pixelated semiconductor single-photon-emission computed tomography (SPECT) system. The pixelated semiconductor detector was modeled as a PID 350 detector (Ajat Oy Ltd., Finland) with small pixels (0.35 × 0.35 mm2) by using Geant4 Application for Tomographic Emission (GATE) software. We designed a novel parallel-hole collimator consisting of two overlapping parallel-hole collimators. Each hole size was four times that of the pixelated parallel-hole collimator. The overlap ratios of these collimators were 1:1, 1:2, 2:1, 1:3, 3:1, 1:4, and 4:1. To evaluate the performance of this system, we evaluated the sensitivity and the spatial resolution. The results for our new parallel-hole collimator indicated that the evaluated sensitivity averages using overlap ratios of 1:1, 1:2, 2:1, 1:3, 3:1, 1:4, and 4:1 were 4.45, 7.56, 7.51, 12.76, 12.65, 20.01, and 19.90 times higher, respectively, than those of the pixelated parallel-hole collimator. The evaluated averages of the spatial resolution varied depending on the source-to-collimator distances. In conclusion, we successfully designed a novel parallel-hole collimator with various overlap ratios of the collimator septal heights with a CdTe pixelated semiconductor SPECT system. Based on our results, we recommend using this collimator with a CdTe pixelated semiconductor SPECT system.

Optimization of the SPECT systems based on a CdTe pixelated semiconductor detector using novel parallel-hole collimators

Recently, many studies have been conducted using semiconductor materials to improve the system's sensitivity and spatial resolution. We are able to improve the spatial resolution by using a pixelated parallel-hole collimator with equal hole and pixel sizes. However, pixelated parallel-hole collimator appears to be problematic to manufacture collimator with small holes. Therefore, we presented an idea for a novel parallel-hole collimator with a cadmium telluride (CdTe) pixelated semiconductor detector. The purpose of this study was to evaluate and optimize the novel parallel-hole collimator geometric designs with CdTe pixelated semiconductor detector using GATE simulation program. This detector was modeled on PID 350 (Oy Ajat, Finland). We designed a novel parallel-hole collimator which consists of the two overlapped pixelated parallel-hole collimators. The overlap ratios of these collimators are 1:1, 1:2, 2:1, 1:3, 3:1, 1:4, and 4:1. To evaluate the performance of this system, system's sensitivity and spatial resolution were estimated. Additionally, image figure of merit (FOM) were calculated from the sensitivity and spatial resolution for the optimization of the novel parallel-hole collimator. According to the results, the measured averages of sensitivity using the 1:1, 1:2, 2:1, 1:3, 3:1, 1:4, and 4:1 ratio were 4.45, 7.56, 7.51, 12.76, 12.65, 20.01, and 19.90 times higher than that of the pixelated parallel-hole collimator, respectively, and the measured averages of spatial resolution were estimated various values depending on the source-to-collimator distances. Finally, the FOM using the pixelated parallel-hole collimator, 1:1, 1:2, 2:1, 1:3, 3:1, 1:4, and 4:1 ratio were 0.57, 0.73, 1.05, 1.13, 1.47, 1.62, 1.95, and 2.15, respectively. We designed a novel parallel-hole collimator with various ratios of collimator septal heights using a CdTe pixelated semiconductor detector. In conclusion, we successfully established a novel parallel-hole collimator, and based on our results, we recommend using 4:1 ratio with CdTe pixelated semiconductor detector in SPECT system.

The effect of high-resolution parallel-hole collimator materials with a pixelated semiconductor SPECT system at equivalent sensitivities: Monte Carlo simulation studies

In nuclear medicine, the use of a pixelated semiconductor detector with cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe) is of growing interest for new devices. Especially, the spatial resolution can be improved by using a pixelated parallel-hole collimator with equal holes and pixel sizes based on the above-mentioned detector. High-absorption and high-stopping-power pixelated parallel-hole collimator materials are often chosen because of their good spatial resolution. Capturing more gamma rays, however, may result in decreased sensitivity with the same collimator geometric designs. Therefore, a trade-off between spatial resolution and sensitivity is very important in nuclear medicine imaging. The purpose of this study was to compare spatial resolutions using a pixelated semiconductor single photon emission computed tomography (SPECT) system with lead, tungsten, gold, and depleted uranium pixelated parallel-hole collimators at equal sensitivity. We performed a simulation study of the PID 350 (Ajat Oy Ltd., Finland) CdTe pixelated semiconductor detector (pixel size: 0.35 × 0.35 mm2) by using a Geant4 Application for Tomographic Emission (GATE) simulation. Spatial resolutions were measured with different collimator materials at equivalent sensitivities. Additionally, hot-rod phantom images were acquired for each source-to-collimator distance by using a GATE simulation. At equivalent sensitivities, measured averages of the full width at half maximum (FWHM) using lead, tungsten, and gold were 4.32, 2.93, and 2.23% higher than that of depleted uranium, respectively. Furthermore, for the full width at tenth maximum (FWTM), measured averages when using lead, tungsten, and gold were 6.29, 4.10, and 2.65% higher than that of depleted uranium, respectively. Although, the spatial resolution showed little differences among the different pixelated parallel-hole collimator materials, lower absorption and stopping power materials such as lead and tungsten had relatively better characteristics at specific sensitivities.

Comparison of ultra-high-resolution parallel-hole collimator materials based on the CdTe pixelated semiconductor SPECT system

Recently, many studies have sought to improve the sensitivity and spatial resolution of pixelated semiconductor detectors. Spatial resolution can be improved by using a pinhole or pixelated parallel-hole collimator with equal hole and pixel sizes. We compared a pinhole to a pixelated parallel-hole collimator and found that the pixelated parallel-hole collimator had higher sensitivity. Additionally, collimator materials with high absorption efficiency are often used because of their high spatial resolution. The purpose of this study was to compare the quality of images generated using a pixelated semiconductor single photon emission computed tomography (SPECT) system simulated with pixelated parallel-hole collimators of lead, tungsten, gold, and depleted uranium. We performed a simulation study of the PID 350 (Ajat Oy Ltd., Finland) CdTe pixelated semiconductor detector, which consists of small pixels (0.35×0.35mm2), using a Geant4 Application for Tomographic Emission (GATE) simulation. Sensitivities and spatial resolutions were measured for the four collimator materials. To evaluate overall image performance, a hot-rod phantom was designed using GATE simulation. The results showed that with lead, sensitivity was 4.25%, 6.53%, and 10.28% higher than with tungsten, gold, and depleted uranium, respectively. Spatial resolution using depleted uranium was 3.19%, 4.19%, and 8.01% better than that of gold, tungsten, and lead, respectively. Sensitivity and spatial resolution showed little difference among the four types of collimator materials tested. It was difficult to visually distinguish between the reconstructed images of the hot-rod phantom for different collimator materials. The results are promising for notable cost reductions in collimator manufacturing while avoiding impractical and rare materials.

A Monte Carlo simulation study of the feasibility of a high resolution parallel-hole collimator with a CdTe pixelated semiconductor SPECT system

It is recommended that a pixelated parallel-hole collimator in which the hole and pixel sizes are equal be used to improve the sensitivity and spatial resolution when using a small pixel size and a single-photon emission computed tomography (SPECT) system with pixelated semiconductor detector materials (e.g., CdTe and CZT). However, some significant problems arise in the manufacturing of a pixelated parallel-hole collimator. Therefore, we sought to simulate a pixelated semiconductor SPECT system with various collimator geometric designs. The purpose of this study was to compare the quality of images generated with a pixelated semiconductor SPECT system simulated with pixelated parallel-hole collimators of various geometric designs. The sensitivity and spatial resolution of the various collimator geometric designs with varying septal heights and hole sizes were measured. Moreover, to evaluate the overall performance of the imaging system, a hot-rod phantom was designed using a Monte Carlo simulation. According to the results, the average sensitivity using a 15 mm septal height was 1.80, 2.87, and 4.16 times higher than that obtained with septal heights of 20, 25, and 30 mm, respectively. Also, the average spatial resolution using the 30 mm septal height was 44.33, 22.08, and 9.26% better than that attained with 15, 20, and 25 mm septal heights, respectively. When the results acquired with 0.3 and 0.6 mm hole sizes were compared, the average sensitivity with the 0.6 mm hole size was 3.97 times higher than that obtained with the 0.3 mm hole size, and the average spatial resolution with the 0.3 mm hole size was 45.76% better than that with the 0.6 mm hole size. We have presented the pixelated parallel-hole collimators of various collimator geometric designs and evaluations. Our results showed that the effect of various collimator geometric designs can be investigated by Monte Carlo simulation so as to evaluate the feasibility of a high resolution parallel-hole collimator with a CdTe pixelated semiconductor SPECT system.

Optimization of an ultra-high-resolution parallel-hole collimator for CdTe semiconductor SPECT system

Recently, there has been an increase in the demand for semiconductor detectors in the field of nuclear medicine imaging. The development of semiconductor detectors using materials such as CdTe that allowed for improved spatial resolution greatly advanced the field. However, the pinhole collimator that allows for high spatial resolution compromises the sensitivity due to the small size of the hole. An improvement in both sensitivity and spatial resolution may be achieved by using a pixelated parallel-hole collimator where the hole and pixel sizes are the same. The purpose of this study was to optimize the design of a detector and collimator system to achieve excellent resolution and high sensitivity for a SPECT detector based on a CdTe detector. We performed a simulation study of the PID 350 (Ajat Oy Ltd., Finland) CdTe detector by using a Geant4 Application for Tomographic Emission (GATE). In addition to the above-mentioned pixelated parallel-hole collimator, we also designed a hexagonal parallel-hole collimator with similar hole size, and we evaluated the sensitivity and spatial resolution of each to determine which set-up was optimal for the PID 350 CdTe detector. Our results indicated that the average sensitivity and spatial resolution were 33.48% and 10.97% higher for the pixelated parallel-hole collimator than for the hexagonal parallel-hole collimator, respectively. We resolved a diameter of 0.5 mm in hot-rod phantom images with the pixelated parallel-hole collimator at a distance of 2 cm. Based on our results, we recommend the pixelated parallel-hole collimator for improving the sensitivity and spatial resolution of SPECT systems with CdTe semiconductor detectors.

Optimization of a high-resolution collimator for a CdTe detector: Monte Carlo simulation studies

Photon counting detectors using cadmium zinc telluride (CZT) or cadmium telluride (CdTe) have benefits compared to conventional scintillation detectors, and CZT and CdTe have advantageous physical characteristics for nuclear medicine imaging. Recently, many studies have been conducted using these materials to improve the sensitivity and the spatial resolution of the photon counting detector. By using a pixelated parallel-hole collimator, we may be able to improve the sensitivity and the spatial resolution. The purpose of this study was to optimize the design of a collimator to achieve excellent resolution and high sensitivity for a gamma camera system based on the CdTe detector. In this study we simulated a gamma camera system with a photon counting detector based on CdTe and evaluated the system’s performance. We performed a simulation study of the PID 350 (Ajat Oy Ltd., Finland) CdTe detector by using a Geant4 Application for Tomographic Emission (GATE) simulation. This detector consists of small pixels (0.35 × 0.35 mm2). We designed two parallel-hole collimators with different shapes and verified their usefulness. One was the proposed pixelated parallel-hole collimator in which the hole size and the pixel size are the same, and the other was the hexagonal parallel-hole collimator, which had a hole size similar to that of the pixelated parallel-hole collimator. We evaluated the sensitivity, spatial resolution, and contrast resolution to determine which parallel-hole collimator was best for the PID 350 CdTe detector. The average sensitivity was 22.65% higher for the pixelated parallel-hole collimator than for the hexagonal parallel-hole collimator. Also, the pixelated parallel-hole collimator provided 10.7% better spatial resolution than the hexagonal parallel-hole collimator, and the contrast resolution was improved by 8.93%. These results reflect an improvement in sensitivity and spatial resolution, and indicate that the imaging performance of the pixelated parallel-hole collimator is better than that of the hexagonal parallel-hole collimator. In conclusion, we successfully established a high resolution gamma camera system with a pixelated parallel-hole collimator, and based on our results, we recommend using the pixelated parallel-hole collimator to improve the sensitivity and the spatial resolution of gamma camera systems with semiconductor detectors such as CdTe.