Geant4 Application For Tomographic Emission Simulation Research Articles

Monte Carlo simulation of two Siemens Biograph PET/CT system using GATE: Image quality performance

The utilization of Monte Carlo simulation is a highly effective method in advancing research within the field of nuclear medicine. An important software tool for simulating and modeling cutting-edge systems for Positron Emission Tomography (PET) is the Geant4 Application for Tomographic Emission (GATE). This research specifically concentrates on two Siemens PET scanners: the Siemens Biograph True point (True V) and Siemens Biograph mcT 20 excel. Our primary objective was to validate the GATE V8.2 simulation in accordance with the NEMA (National Electrical Manufacturers Association) NU 2-2018 protocol, using a parallel computing platform on a local cluster of computers. This cluster was managed by the open-source package TORQUE version 6.1.0, which is based on the original wrapper PBS.The results of this validation process for the Siemens Biograph True point (True V) scanner were highly promising. The scatter fraction (SF), peak noise equivalent count rate (NECR), and sensitivity all demonstrated a remarkable level of agreement, with deviations within 10.02%, 5.4%, and 1.57%, respectively. Additionally, the spatial resolution was found to deviate by less than 0.59 mm. Image evaluations demonstrate high-quality results for both Siemens Biograph True point (True V) and Siemens Biograph mcT 20 excel scanners, validating the GATE simulation. The study on acquisition time provides insights into optimizing computing simulation time.This research demonstrates the effectiveness of Monte Carlo simulation, facilitated by GATE, in accurately modeling advanced PET systems. The validation results affirm the reliability of GATE V8.2 in accordance with NEMA standards for the Siemens Biograph True point (True V) scanner. The high-quality images obtained from GATE-validated scanners underscore the potential of this simulation approach in advancing nuclear medicine research. Additionally, the study on acquisition time provides valuable considerations for optimizing simulation efficiency.

Quantitative validation of Monte Carlo SPECT simulation: application to a Mediso AnyScan GATE simulation

BackgroundMonte Carlo (MC) simulations are used in nuclear medicine imaging as they provide unparalleled insight into processes that are not directly experimentally measurable, such as scatter and attenuation in an acquisition. Whilst MC is often used to provide a ‘ground-truth’, this is only the case if the simulation is fully validated against experimental data. This work presents a quantitative validation for a MC simulation of a single-photon emission computed tomography (SPECT) system.MethodsAn MC simulation model of the Mediso AnyScan SCP SPECT system installed at the UK National Physical Laboratory was developed in the GATE (Geant4 Application for Tomographic Emission) toolkit. Components of the detector head and two collimator configurations were modelled according to technical specifications and physical measurements. Experimental detection efficiency measurements were collected for a range of energies, permitting an energy-dependent intrinsic camera efficiency correction function to be determined and applied to the simulation on an event-by-event basis. Experimental data were collected in a range of geometries with ^{99text {m}}Tc for comparison to simulation. The procedure was then repeated with ^{177}Lu to determine how the validation extended to another isotope and set of collimators.ResultsThe simulation’s spatial resolution, sensitivity, energy spectra and the projection images were compared with experimental measurements. The simulation and experimental uncertainties were determined and propagated to all calculations, permitting the quantitative agreement between simulated and experimental SPECT acquisitions to be determined. Statistical agreement was seen in sinograms and projection images of both ^{99text {m}}Tc and ^{177}Lu data. Average simulated and experimental sensitivity ratios of (0.991 pm 0.011) were seen for emission and scatter windows of ^{99text {m}}Tc, and (0.897 pm 0.014) and (0.839 pm 0.014) for the 113 and 208 keV emissions of ^{177}Lu, respectively.ConclusionsMC simulations will always be an approximation of a physical system and the level of agreement should be assessed. A validation method is presented to quantify the level of agreement between a simulation model and a physical SPECT system.

Dosimetric Analysis of Rhizophora-based Phantom Material in Radiation Therapy Applications Using Monte Carlo GATE Simulation.

This study aims to determine the percentage depth dose (PDD) of a phantom material made from soy-lignin bonded Rhizophora spp. particleboard coated with a gloss finish by using Monte Carlo Geant4 Application for Tomographic Emission (GATE) simulation. The particleboard was fabricated using a hot pressing technique at target density of 1.0 g·cm-3 and the elemental fraction was recorded for the simulation. The PDD was simulated in the GATE simulation using the linear accelerator Elekta Synergy model for the water phantom and Rhizophora phantom, and the results were compared with the experimental PDD performed by several studies. Beam flatness and beam symmetry were also measured in this study. The simulated PDD for Rhizophora and water was in agreement with the experimental PDD of water with overall discrepancies of 0% to 8.7% at depth ranging from 1.0 to 15.0 cm. In the GATE simulation, all the points passed the clinical 3%/3 mm criterion in comparison with water, with the final percentage of 2.34% for Rhizophora phantom and 2.49% for the water phantom simulated in GATE. Both the symmetries are all within the range of an acceptable value of 2.0% according to the recommendation, with the beam symmetry of the water phantom and Rhizophora phantom at 0.58% and 0.28%, respectively. The findings of this study provide the necessary foundation to confidently use the phantom for radiotherapy purposes, especially in treatment planning.

Correlation between X-ray tube current exposure time and X-ray photon number in GATE.

X-ray image quality relies heavily on the emitted X-ray photon number which depends on X-ray tube current and exposure time. To accurately estimate the absorbed dose in an imaging protocol, it is better to simulate the X-ray imaging with a Monte Carlo platform such as GATE (Geant4 Application for Tomographic Emission). Although input of GATE is the X-ray photon number of the simulated X-ray tube, it lacks a good way to setup the photon number for a desired X-ray tube current setting. To provide a method to correlate the experimental X-ray tube current exposure time and the X-ray photon number in GATE. The accumulated radiation dose of a micro-computed tomography (CT) X-ray tube was recorded at different current exposure times with a general-purpose ion chamber. GATE was used to model the experimental microCT imaging system and calculate the total absorbed dose (cGy) in the sensitive volume of the ion chamber with different X-ray photon numbers. Linear regression models are used to establish a correlation between the estimated X-ray photon number and the X-ray tube settings. At first, one model establishes the relationship between the experimentally measured dose and the X-ray tube setting. Then, another model establishes a relationship between the simulated dose and the X-ray number in GATE. At last, by correlating these two models, a regression model to estimate the X-ray output number from an experimental X-ray tube setting (mAs) is obtained. For a typical micro-CT scan, the X-ray tube is operated at 50 kVp and 0.5 mA for a 500 ms exposure time per projection (0.25 mAs). For these X-ray imaging parameters, the X-ray number per projection is estimated to be 3.613×106 with 1.0 mm Al filter. The findings of this work provide an approach to correlate the experimental X-ray tube current exposure time to the X-ray photon number in the GATE simulation of the X-ray tube to more accurately determine radiation dose for an imaging protocol.

Utilization of an energy-resolving detection system for mammography applications: A preliminary study

Abstract Breast cancer remains one of the major causes of mortality among female cancer patients. This fact caused a spark in the medical field, which in turn helped to improve the diagnostic and treatment of breast cancer patients over the years making this field always active with new ideas and innovative methods. In our study, a new method was explored using an energy-resolving detection system made from a NaI (Tl) scintillation detector to detect the gamma photons from an Am-241 radiation source to try and construct an image by scanning the American College of Radiology (ACR) mammography phantom. In addition to the experimental work, a Geant4 Application for Tomographic Emission (GATE) toolkit was used to investigate more complex options to improve the image quality of mammographic systems, which is limited by the experimental setup. From the experimental setup, the researchers were able to construct an image using the 26.3 keV and the 59.5 keV energy photons, to show the largest size tumour (12 mm) in the ACR phantom. With an improved setup in the simulation environment, the majority of the ACR phantom tumours was visible using both energy windows from the 26.3 keV and the 59.5 keV, where the 26.3 keV yielded better quality images showing four tumours compared to three when using 59.5 keV. The simulation results were promising; however, several improvements need to be incorporated into the experimental work so that the system can generate high-resolution mammographic images similar to the ones obtained by the GATE simulation setup.

High-resolution and high-sensitivity PET for quantitative molecular imaging of the monoaminergic nuclei: A GATE simulation study.

Quantitative in vivo molecular imaging of fine brain structures requires high-spatial resolution and high-sensitivity. Positron emission tomography (PET) is an attractive candidate to introduce molecular imaging into standard clinical care due to its highly targeted and versatile imaging capabilities based on the radiotracer being used. However, PET suffers from relatively poor spatial resolution compared to other clinical imaging modalities, which limits its ability to accurately quantify radiotracer uptake in brain regions and nuclei smaller than 3 mm in diameter. Here we introduce a new practical and cost-effective high-resolution and high-sensitivity brain-dedicated PET scanner, using our depth-encoding Prism-PET detector modules arranged in a conformal decagon geometry, to substantially reduce the partial volume effect and enable accurate radiotracer uptake quantification in small subcortical nuclei. Two Prism-PET brain scanner setups were proposed based on our 4-to-1 and 9-to-1 coupling of scintillators to readout pixels using mm3 and mm3 crystal columns, respectively. Monte Carlo simulations of our Prism-PET scanners, Siemens Biograph Vision, and United Imaging EXPLORER were performed using Geant4 application for tomographic emission (GATE). National Electrical Manufacturers Association (NEMA) standard was followed for the evaluation of spatial resolution, sensitivity, and count-rate performance. An ultra-micro hot spot phantom was simulated for assessing image quality. A modified Zubal brain phantom was utilized for radiotracer imaging simulations of 5-HT1A receptors, which are abundant in the raphe nuclei (RN), and norepinephrine transporters, which are highly concentrated in the bilateral locus coeruleus (LC). The Prism-PET brain scanner with 1.5 mm crystals is superior to that with 1 mm crystals as the former offers better depth-of-interaction (DOI) resolution, which is key to realizing compact and conformal PET scanner geometries. We achieved uniform 1.3 mm full-width-at-half-maximum (FWHM) spatial resolutions across the entire transaxial field-of-view (FOV), a NEMA sensitivity of 52.1 kcps/MBq, and a peak noise equivalent count rate (NECR) of 957.8 kcps at 25.2 kBq/mL using 450-650 keV energy window. Hot spot phantom results demonstrate that our scanner can resolve regions as small as 1.35 mm in diameter at both center and 10 cm away from the center of the transaixal FOV. Both 5-HT1A receptor and norepinephrine transporter brain simulations prove that our Prism-PET scanner enables accurate quantification of radiotracer uptake in small brain regions, with a 1.8-fold and 2.6-fold improvement in the dorsal RN as well as a 3.2-fold and 4.4-fold improvement in the bilateral LC compared to the Biograph Vision and EXPLORER, respectively. Based on our simulation results, the proposed high-resolution and high-sensitivity Prism-PET brain scanner is a promising cost-effective candidate to achieve quantitative molecular neuroimaging of small but important brain regions with PET clinicallyviable.

Preliminary results of a single photon emission computed tomography (SPECT) detector for inspection of spent fuel assembly

SPECT systems are being used by international safeguards organizations for the measurement for structural evaluation of spent fuel assemblies. However, the low sensitivity still limits the verification of spent fuel assemblies within a short measurement time (1–2 h per assembly). In this study, the SPECT detector was optimized and evaluated to identify the structure of spent fuel. The detector module consists of 64 one-dimensional (1-D) multi-slit collimators and 1-D pixelated scintillators coupled to SiPMs. We evaluated and optimized the light collection efficiency and energy resolution according to the shape of scintillator (Trapezoid, Rectangular), and reflector materials (Paint, Teflon tape, BaSO4) by Geant4 Application for Tomographic Emission (GATE) simulation and experiment. As a result, the trapezoidal scintillator coated with BaSO4 showed the highest light collection efficiency among the six models in GATE simulation and in experiments. The spent fuel rods were imaged using trapezoidal scintillator coated with BaSO4, and 1-D projections and line profiles were obtained in order to distinguish the source location. In this study, the scintillator structure and reflector material variables were optimized using Monte Carlo simulation to measure 662 keV gamma-ray of 137Cs for inspection of spent fuel assembly using the SPECT system. In order to confirm the imaging potential of the spent fuel assembly, the detector performance was evaluated using unused fuel rods for testing. The performance of the detector for fuel rod identification has been proven, and we expect that the optimized detector module will contribute to the rapid verification of the spent fuel assembly compared to conventional systems.

Prediction of Absorbed Dose to Normal Organs with Endocrine Tumors for I-131 by use of 99mTC Single Photon Emission Computed Tomography/Computed Tomography and Geant4 Application for Tomographic Emission Simulation.

Introduction:This study aimed to predict the dose absorbed by normal organs with neuroendocrine tumors for 131I using single photon emission computed tomography/computed tomography (SPECT/CT) images and Geant4 application for tomographic emission (GATE) simulation.Materials and Methods:Four to 5 whole-body planar scan series, along with one SPECT/CT image, were taken from four patients following 99mTc-hynic-Tyr3-octreotide radiotracer injection. After image quantification, the residence time of each organ was calculated using the image analysis and the activity time curves. The energy deposit and dose conversion (S-value) were extracted from the GATE simulation for the target organs of each patient. Using the residence times and S-values, the mean absorbed dose for the target organs of each patient was calculated and compared with the data obtained from the standard method.Results:Very close agreement was obtained between the S-value of the self–organ irradiation. The mean percentage difference between the two methods (i.e. GATE and Medical Internal Radiation Dose [MIRD]) was 1.8%, while a weak agreement was observed for cross-organ irradiation. The percentage difference between the total absorbed doses by the organs was 2%. The percentage difference between the absorbed doses obtained for tumors and three considered normal organs estimated by the GATE method was slightly higher than the MIRD method (about 11% on average for tumors).Conclusion:Regardless of the small difference between the obtained results for the organs and absorbed doses of the tumors in the present study, patient-specific dosimetry by the GATE methods is useful and essential for therapeutic radionuclides such as 131I due to high cross-dose effects, especially for young adult patients, to ensure the radiation safety and increase the effectiveness of the treatment.

Development of a Gamma Camera with a Diverging Collimator Using DMLS 3D Printing

The purpose of this study is to use a Monte Carlo simulation to derive optimal values for collimator design variables and to produce an optimized collimator for a gamma camera using a 3D printing direct metal laser sintering (DMLS) technique. For the optimization studies, GATE (Geant4 application for tomographic emission) simulation was used, and we tested lead, tungsten, and a full absorber. A total of 15 design variables were simulated using hole sizes of 0.5 mm, 0.7 mm, and 1.0 mm and slat heights from 10 mm to 20 mm at intervals of 2.5 mm. The scintillator used GAGG (gadolinium aluminum gallium garnet) and was set to a size of 25.8 × 25.8 mm². The radiation of the source used in the simulation was 37 MBq, and the source was a 140 keV point source. To obtain the diverging collimator optimization design variables, the point source was detected and an image was acquired to analyze the sensitivity and spatial resolution values. As a result, tungsten, which has good hardness, was used. If the source is located in the center of the diverging collimator, the FWHM is limited to 3.0 mm or less. The optimization value is obtained by considering the permeability, sensitivity, and spatial resolution at a height of 15 mm or higher. The results obtained by moving the source were also similar to those obtained when the source was located at the center. Based on the values of the optimized design variables, this study designed and produced a collimator using DMLS, which is a 3D printing technique. We believe this process can be applied in various fields, such as medical and industrial sectors; optimized collimators can be produced for different purposes while maintaining high precision.

GEANT4/GATE Simulation Studies in the Emission Tomography

Radiotracer imaging studies for a small field, high resolution ∞-Camera system and a clinical system for Positron Emission Tomography (PET) by means of GATE (GEANT4 Application for Tomographic Emission) simulations are presented in this work. In a validation phase, which preceded the main study, experimentally obtained results for planar images with the existing ∞-Camera system were directly compared to simulated data. A simple phantom structure, consisting of four parallel capillaries filled with 99mTc water solution, was imaged by the γ-Camera system for several phantom-collimator distances and the measured and Monte-Carlo calculated spatial projections were compared. The major objective of this validation study was the optimal description of the most important components, the hexagonal, parallel-hole Pb-collimator and the pixelated CsI scintillation crystal of the γ-imaging system in terms of GATE components. In the main study, a GATE simulation setup for this ∞-Camera detector is used and Monte-Carlo data are accumulated for simple geometrical phantoms with different monophotonic radiotracer energies and relative intensities. In parallel, a commercially available cylindrical shaped PET scanner ring, consisting of 32 sectors with 4 x 6 x 6 LSO scintillation crystals, has been constructed in the GATE environment. Simulation data are obtained for the most usual positron emitters (18F, 11C and 15O) and for several phantom geometries. The spatial resolution of both systems and their overall performance is presented and discussed in this study.

Monte Carlo simulations of an innovative molecular breast imaging system for the small breast cancer diagnosis using GATE

ABSTRACTThis paper draws attention to the study of performance of a new Molecular Breast Imaging (MBI) device, whose purpose is the early diagnosis of breast cancer, using Monte Carlo simulations. MBI provides functional and specific information that are more appropriated to dense breasts. Two asymmetric heads with different types of collimators, facing each other in anti-parallel viewing direction, characterize the system. Detectors and phantoms, together with the data taking procedure, are shortly reported. Monte Carlo simulations using the GATE (GEANT4 Application for Tomographic Emission) simulation toolkit have been implemented to evaluate the optimal detector configuration, in terms of sensitivity and spatial resolution, and also to reproduce the real experimental data. The device can be used both in spot compression and in Limited Angle Tomography (LAT); in the latter configuration one detector head with pinhole collimator is able to rotate around the breast in order to diagnose and localized the small tumors.

Image Optimization of Fast Non Local Means Noise Reduction Algorithm using Various Filtering Factors with Human Anthropomorphic Phantom : a Simulation Study

In this study we analyzed the tendency of the image characteristic by changing filtering factor for the proposed fast non local means (FNLM) noise reduction algorithm with designed Male Adult mesh (MASH) phantom through Geant4 application for tomographic emission (GATE) simulation program. To accomplish this purpose, MASH phantom for human copy was designed through the GATE simulation program. In addition, we acquired degraded image by adding Gaussian noise with a value of 0.005 using the MATALB program in MASH phantom. Moreover, in degraded image, the FNLM noise reduction algorithm was applied by changing the filtering factors, which set to 0.005, 0.01, 0.05, 0.1, 0.5, and 1.0 value, respectively. To quantitatively evaluate, the coefficient of variation (COV), signal to noise ratio (SNR), and contrast to noise ratio (CNR) were calculated in reconstructed images. Results of the COV, SNR and CNR were most improved in image with a filtering factor of 0.05 value. Especially, the COV was decreased with increasing filtering factor, and showed nearly constant values after 0.05 value of the filtering factor. In addition, SNR and CNR were showed that improvement with increasing filtering factor, and deterioration after 0.05 value of the filtering factor. In conclusion, we demonstrated the significance of setting the filtering factor when applying the FNLM noise reduction algorithm in degraded image.

Characterization of three layer depth of interaction PET detectors for small animal imaging

High sensitivity and spatial resolution are two main parameters of each small animal imaging system. Multi-layers phoswich detectors have been developed to measure the depth of interaction and to improve system spatial resolution. In the past, efforts have been made to develop these kinds of detectors with different crystal materials and lengths. In this work, three layers phoswich detectors based on GE Healthcare eXplore VISTA PET scanner geometry composing LYSO, GSO and BGO scintillators with different crystal orders and lengths were investigated to find the optimum case with the highest sensitivity and uniform spatial resolution. All simulations were performed using the Monte Carlo simulation tool, the Geant4 Application for Tomographic Emission (GATE). In order to validate GATE simulation package, the GE eXplore VISTA small animal PET system was modeled and output results were compared with the experimental data. The length of each of the three layers varied, while the total length (LYSO + GSO + BGO) was fixed at 15 mm. The order of these crystal layers was also changed, so that totally we have considered 55 × 6 = 330 different configurations. Using three layer phoswich detector, a 25%–68% improvement in the sensitivity at central slice was found compared to the dual layer VISTA PET scanner, dependent on different detector configurations. In this study, among all posible configurations, detector length permutations with higher efficiency values (12 × 6 = 72 cases) were choosen to evaluate spatial resolution. The radial and tangential spatial resolutions were markedly improved for all studied different detector configurations compared to the VISTA PET scanner. Among all the possible selected detector configurations, LYSO (4 mm) + GSO (4 mm) + BGO (7 mm) and BGO (5 mm) + LYSO (5 mm) + GSO (5 mm) cases gave the best DOI radial and tangential resolutions for an energy threshold of 250 keV, respectively. In the LYSO (4 mm) + GSO (4 mm) + BGO (7 mm) scanner configuration, the radial resolution was kept below 1.154 mm, over 25 mm field of view (FOV). The tangential resolution variations were minimized to less than 1.029 mm, over 25 mm FOV, using the BGO (5 mm) + LYSO (5 mm) + GSO (5 mm) detector type. As a result, our new designed three layers phoswich detectors with excellent DOI resolution will lead to small animal PET scanners with higher sensitivity and uniform spatial resolution across the FOV.

Feasibility of gamma camera system with CdWO4 detector for quantitation of yttrium-90 bremsstrahlung imaging: Monte Carlo simulation study

Yttrium-90 (Y-90) has attracted great attention as a therapeutic radionuclide because of higher emitted particle energy and pure beta emitter. In Y-90 bremsstrahlung imaging, NaI(Tl) and GSO detectors are widely used in detecting photon but these detectors cannot be easily applied to this imaging because of relatively low sensitivity. Among detector candidates, cadmium tungstate (CdWO4) can acquire high detection efficiency due to the high density and good light yield. The purpose of this study was to evaluate the feasibility of gamma camera system with CdWO4 detector for quantitation of Y-90 bremsstrahlung imaging using a Geant4 Application for Tomographic Emission (GATE). To evaluate performance of the imaging system, a Y-90 point source was designed in GATE simulation. These detectors using CdWO4, NaI(Tl), and GSO were equipped with low energy general purpose (LEGP), medium energy general purpose (MEGP), and high energy general purpose (HEGP) parallel-hole collimators. According to the results, the average sensitivities of the CdWO4 detector with LEGP, MEGP, and HEGP were 43.76, 37.16, and 28.22cps/MBq, respectively. In addition, the sensitivity was higher for CdWO4 detector system than for NaI(Tl) or GSO detector systems for all parallel-hole collimator system with 55–285keV energy window. However, differences of scatter fraction for three detectors were very similar. Our results showed that the effect and feasibility of CdWO4 detector for Y-90 bremsstrahlung imaging can be investigated by a GATE simulation. In conclusion, the results of this study suggest that CdWO4 detector can be achieved improved performance of Y-90 bremsstrahlung imaging.

GATE simulation of a LYSO-based SPECT imager: Validation and detector optimization

This paper presents a small animal SPECT system that is based on cerium doped lutetium–yttrium oxyorthosilicate (LYSO) scintillation crystal, position sensitive photomultiplier tubes (PSPMTs) and parallel hole collimator. Spatial resolution test and animal experiment were performed to demonstrate the imaging performance of the detector. Preliminary results indicated a spatial resolution of 2.5mm at FWHM that cannot meet our design requirement. Therefore, we simulated this gamma camera using GATE (GEANT 4 Application for Tomographic Emission) aiming to make detector spatial resolution less than 2mm. First, the GATE simulation process was validated through comparison between simulated and experimental data. This also indicates the accuracy and effectiveness of GATE simulation for LYSO-based gamma camera. Then the different detector sampling methods (crystal size with 1.5, and 1mm) and collimator design (collimator height with 30, 34.8, 38, and 43mm) were studied to figure out an optimized parameter set. Detector sensitivity changes were also focused on with different parameters set that generated different spatial resolution results. Tradeoff curves of spatial resolution and sensitivity were plotted to determine the optimal collimator height with different sampling methods. Simulation results show that scintillation crystal size of 1mm and collimator height of 38mm, which can generate a spatial resolution of ~1.8mm and sensitivity of ~0.065cps/kBq, can be an ideal configuration for our SPECT imager design.

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.

Design of a high-resolution small-animal SPECT-CT system sharing a CdTe semiconductor detector

A single photon emission computed tomography (SPECT) system with a co-registered X-y computed tomography (CT) system allows the convergence of functional information and morphologic information. The localization of radiopharmaceuticals on a SPECT can be enhanced by combining the SPECT with an anatomical modality, such as X-ray CT. Gamma-ray imaging for nuclear medicine devices and X-ray imaging systems for diagnostics has recently been developed based on semiconductor detectors, and semiconductor detector materials such as cadmium telluride (CdTe) or cadmium zinc telluride (CZT) are available for both X-ray and gamma-ray systems for small-animal imaging. CdTe or CZT detectors provide strong absorption and high detection efficiency of high energy X-ray and gamma-ray photons because of their large atomic numbers. In this study, a pinhole collimator SPECT system sharing a cadmium telluride (CdTe) detector with a CT was designed. The GEANT4 application for tomographic emission (GATE) v.6.1 was used for the simulation. The pinhole collimator was designed to obtain a high spatial resolution of the SPECT system. The acquisition time for each projection was 40 seconds, and 60 projections were obtained for tomographic image acquisition. The reconstruction was performed using ordered subset expectation maximization (OS-EM) algorithms. The sensitivity and the spatial resolution were measured on the GATE simulation to evaluate the system characteristics. The spatial resolution of the system calculated from the FWHM of Gaussian fitted PSF curve was 0.69 mm, and the sensitivity of the system was measured to be 0.354 cps/kBq by using a Tc-99m point source of 1 MBq for 800 seconds. A phantom study was performed to verify the design of the dual imaging modality system. The system will be built as designed, and it can be applied as a pre-clinical imaging system.

Development and Validation of a GATE Simulation Model for the LabPET Scanner

A three-dimensional (3D) model of the LabPET™ scanner has been newly developed by means of GATE (Geant4 application for tomographic emission) with the purpose of carrying out a detailed study of the system’s performance and validating at the same time the potential of GATE for the simulation of PET (positron emission tomography) scanners. The accuracy of this model was examined by comparing simulated, theoretical and experimental results obtained with LabPET for different performance features including detection efficiency, sensitivity, count rates, photoelectric probability, phoswich detector energy resolution and intrinsic spatial resolution. An agreement of 95% for singles count rates, 96% for detection efficiency, and 90% for absolute sensitivity was obtained between simulations and measurements. Also, an agreement of ≫97% for photoelectric fraction, ≫96% for radial intrinsic resolution, ≫93% for axial intrinsic resolution, and 91% for detection efficiency was obtained between simulations and the theoretical calculations. In conclusion, the achieved results support the accurate modeling of LabPET with GATE.

HIGH-RESOLUTION L(Y)SO DETECTORS USING PMT-QUADRANT-SHARING FOR HUMAN & ANIMAL PET CAMERAS.

We developed high resolution L(Y)SO detectors for human and animal PET applications using Photomultiplier-quadrant-sharing (PQS) technology. The crystal sizes were 1.27 × 1.27 × 10 mm(3) for the animal PQS-blocks and 3.25 × 3.25 × 20 mm(3) for human ones. Polymer mirror film patterns (PMR) were placed between crystals as reflector. The blocks were assembled together using optical grease and wrapped by Teflon tape. The blocks were coupled to regular round PMT's of 19/51 mm in PQS configuration. List-mode data of Ga-68 source (511 KeV) were acquired with our high yield pileup-event recovery (HYPER) electronics and data acquisition software. The high voltage bias was 1100V. Crystal decoding maps and individual crystal energy resolutions were extracted from the data. To investigate the potential imaging resolution of the PET cameras with these blocks, we used GATE (Geant4 Application for Tomographic Emission) simulation package. GATE is a GEANT4 based software toolkit for realistic simulation of PET and SPECT systems. The packing fractions of these blocks were found to be 95.6% and 98.2%. From the decoding maps, all 196 and 225 crystals were clearly identified. The average energy resolutions were 14.0% and 15.6%. For small animal PET systems, the detector ring diameter was 16.5 cm with an axial field of view (AFOV) of 11.8 cm. The simulation data suggests that a reconstructed radial (tangential) spatial resolution of 1.24 (1.25) mm near the center is potentially achievable. For the wholebody human PET systems, the detector ring diameter was 86 cm. The simulation data suggests that a reconstructed radial (tangential) spatial resolution of 3.09(3.38) mm near the center is potentially achievable. From this study we can conclude that PQS design could achieve high spatial resolutions and excellent energy resolutions on human and animal PET systems with substantially lower production costs and inexpensive readout devices.