Search

Positron emission tomography (PET) can be utilized in particle beam therapy to verify the dose distribution of the target volume as well as the accuracy of the treatment. We present an in-beam PET scanner that can be integrated into a particle beam therapy system. The proposed PET scanner consisted of 14 detector modules arranged in a C-shape to avoid blockage of the particle beam line by the detector modules. Each detector module was composed of a 9×9 array of 4.0 mm×4.0 mm×20.0 mm LYSO crystals optically coupled to four 29-mm-diameter PMTs using the photomultiplier-quadrant-sharing (PQS) technique. In this study, a Geant4 Application for Tomographic Emission (GATE) simulation study was conducted to design a C-shaped PET scanner and then experimental evaluation of the proposed design was performed. The spatial resolution and sensitivity were measured according to NEMA NU2-2007 standards and were 6.1 mm and 5.61 cps/kBq, respectively, which is in good agreement with our simulation, with an error rate of 12.0%. Taken together, our results demonstrate the feasibility of the proposed C-shaped in-beam PET system, which we expect will be useful for measuring dose distribution in particle therapy. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, there has been an increasing interest in the magnetic resonance (MR)-compatible positron emission tomography (PET) scanners for both clinical and preclinical practice. The aim of this study was to design a novel PET detector module using a segmented block crystal readout with an array of multi-pixel photon counters (MPPCs). A 16.5×16.5×10.0mm3 LSO block was segmented into an 11×11 array, and reflective material was used to fill in the cuts to optically isolate the elements. The block was attached to a 4×4 MPPC array (Hamamatsu S11064) of 3.0×3.0mm2 detectors to give a total effective area of 144mm2. To visualize all the individual detector elements in this 11×11 detector module, the depth of the cuts was optimized by DETECT2000 simulations. The depth of the cuts determines the spread of scintillation light onto the MPPC array. The accuracy of positioning was evaluated by varying the depth of the cuts from 0.0 to 10.0mm in steps of 0.5mm. A spatial resolution of 1.5mm was achieved using the optimized partially segmented block detector. The simulation results of this study can be used effectively as a guide for parameter optimization for the development of a partially segmented block detector for high-resolution MR-compatible PET scanners. [Copyright &y& Elsevier]

Abstract: In recent years, small-animal PET scanners with depth of interaction (DOI) capability have been developed for molecular imaging research. The aim of this study is to perform simulations to design a high performance small-animal PET, called TraPET. TraPET has an inner diameter of 76.21mm with 6 dual-layer phoswich detector modules. Each module is composed of a 5.0-mm-thick trapezoidal-monolithic-LSO crystal with a front face (surface facing toward the inside of the scanner) of 44.0×44.0mm2 and a back face of 50.0×50.0mm2 and a 25×25 array of LuYAP crystals with a 2.0×2.0mm2 sensitive area with a 15.0mm thickness. DOI information is extracted by a pulse shape discrimination method. The ability of event positioning in the trapezoidal-monolithic-LSO was evaluated by modeling the light distribution in the crystal using DETECT2000 and a 16×16 array of silicon photo-multipliers (SiPMs), with a 3.0mm pixel size, selected as the photo-sensor. Also, the sensitivity and gap filling effect between modules were simulated using the Monte Carlo code, GATE. The new detector showed higher and more uniform sensitivity, as compared to scanners with rectangular-shaped detectors, because the trapezoidal-monolithic-LSO minimizes the dead space within the detector ring. In conclusion, our new detector proved to be a reliable design for small-animal PET with high spatial resolution by DOI information, and high sensitivity by high filling fraction. [Copyright &y& Elsevier]

Abstract: We have built a four-layer detector to obtain depth of interaction (DOI) information in which all four layers have a relative offset of half a crystal pitch with each other. The main characteristics of the detector, especially the energy and spatial resolutions, strongly depend on the crystal surface treatments. As a part of the development of an animal PET, we have investigated the effect of crystal surface treatment on detector performances using Monte Carlo simulations in order to optimize the surface conditions of crystals composing a four-layer detector. The proposed detector consists of four LYSO layers with crystal dimensions of 1.5×1.5×7.0 and 1.5×1.5×5.0mm3. A simulation tool (DETECT2000) was used and validated against the experimental results; flood images were acquired by a prototype module. Flood images were simulated by varying the surface treatment of the crystals. The optimal surface conditions of the four-layer crystals were derived for a small animal PET with a view towards achieving high sensitivity, as well as high and uniform radial resolution. [ABSTRACT FROM AUTHOR]

Abstract: In our previous work, the new detector module with depth of interaction (DOI) based on a quasi-monolithic crystal array and maximum-likelihood position-estimation (MLPE) algorithm was designed and the methodology for 3D event positioning in the detector was established by using Monte Carlo simulation. The aim of this study was to evaluate the performance of our detector module experimentally. The detector module consisted of a 1D array of eight LYSO crystals of 20.0(X)×2.0(Y)×10.0(Z)mm3, optically coupled to a Hamamatsu H7546B position sensitive photomultiplier tube (PSPMT). The PSPMT was read out using a resistive charge divider, which multiplexes 64 anodes into 8(X)+8(Y) channels. Gaussian-based MLPE methods have been implemented using experimentally measured detector response functions (DRFs). The results demonstrated that the detector module could identify the position of the gamma ray interaction inside the crystal in all three directions. The new DOI detector for a small animal PET was developed and verified experimentally with a view towards achieving high sensitivity as well as high and uniform radial resolution. [ABSTRACT FROM AUTHOR]

Abstract: We report a new design of a detector module with depth of interaction (DOI) based on a quasi-monolithic LSO crystal, a multi-channel sensor, and maximum-likelihood position-estimation (MLPE) algorithm. Light transport and detection were modeled in a quasi-monolithic crystal using DETECT2000 code, with lookup tables (LUTs) built by simulation. Events were well separated by applying the MLPE method within 2.0mm spatial resolution in both trans-axial and DOI directions. These results demonstrate that the proposed detector provides dependable positioning capability for small animal positron emission tomography (PET). [Copyright &y& Elsevier]

Abstract: The NAA#3 irradiation hole in the 30MW HANARO research reactor of the Korea Atomic Energy Research Institute (KAERI), with a thermal neutron flux of 1.26×1014 cm−2 s−1, has been regarded as suitable for the application of k 0-based neutron activation analysis (k 0-NAA). The objectives of the present work were: (a) to characterize the NAA#3 irradiation hole via the determination of the neutron spectrum parameters required for the method, (b) to calibrate the HPGe gamma-ray spectrometer system via establishing the detection efficiency curves and (c) to assess the quality of the k 0-NAA method by the analysis of six certified reference materials, three of which were of biological nature and three of environmental origin. The results obtained indicated that, by using the k 0-NAA method, approximately 25 or 35 elements could be quantitatively determined in the biological and environmental samples, respectively. The deviations between the experimental and the certified values for the determined elements were generally within 12% with u-scores mostly below 2. The results prove that the k 0-NAA method, implemented in the HANARO research reactor, is applicable for multi-element analysis in biological and environmental samples with a rather high analytical performance and that the method is available for further practical applications. [Copyright &y& Elsevier]

Abstract: In recent years, there has been a growing interest in compact and high resolution small gamma cameras for the early detection of breast cancer and thyroid diseases. We proposed a new detector consisting of a trapezoidal-shaped crystal and a position-sensitive photomultiplier tube (PSPMT) to reduce the edge effect. In this study, the imaging performance of the proposed detector was evaluated by DETECT2000 simulation. Trapezoidal-shaped NaI(Tl) and CsI(Tl) crystals were modeled and the 2-dimensional event positions were calculated using Anger-logic. 99mTc (140keV) and 131I (364keV) gamma rays were generated on evenly spaced points with 3.0mm spacing in the X–Y plane starting 1.0mm away from the corner surface and 10,000 gamma events were simulated at each location. The simulated results demonstrated that all the 99mTc and 131I point sources were clearly identified in the NaI(Tl) crystal. CsI(Tl) crystal could image 131I sources without edge effect but did not distinguish 99mTc points at the periphery region due to low light yield. In conclusion, our new detector with an enlarged FOV without increasing crystal size could be a useful tool in breast as well as thyroid imaging. [Copyright &y& Elsevier]

Abstract: A range verification method plays an important role in the quality assurance of the proton therapy offering the high conformity and reduction in radiation dose. To localize the distal falloff of the dose distribution, secondary particles (C-11, O-15, and N-13) produced by the proton interaction within the patient body can be used as a measure of the beam range. We proposed a multi-modality imaging system for X-ray and gamma-ray coincidence imaging using CdZnTe detectors to measure proton range verification. The detector system consists of two parallel planes of detectors and an X-ray generator. An X-ray image is acquired using one detector for the verification of 2-dimensional anatomical structure of the patient, and the paired gamma rays from the annihilation are imaged with two modules to determine the maximum range of proton penetration. Image registration is intrinsic because the X-ray and gamma ray images are acquired in the same geometry. 110 and 140MeV proton beam, a cylindrical tissue phantom, and two rectangular CdZnTe detectors were modeled, and the imaging performance of this system was evaluated using GATE simulation. The results showed the potential benefits of an X-ray/gamma-ray imaging with photon counting detectors for range verification in proton therapy. [Copyright &y& Elsevier]

Abstract: LSO/LuYAP phoswich detectors for small animal PET were developed to measure the depth of interaction (DOI), and to improve the spatial resolution at the edge of the field of view (FOV). The aim of this study was to optimize the optical coupling conditions between the crystal and photomultiplier tube (PMT) to maximize the light-collection efficiency, and to develop a method for rejecting scatter events by applying an equal energy window in each crystal layer. The light yields of the phoswich detector were estimated by changing the refractive index of the optical coupling material using a DETECT simulation. The accuracy of the DOI measurement on the phoswich detector, using an optical coupling material with the optimal light yield, were evaluated experimentally and compared with the air condition. The energy window for the photopeak events cannot be applied properly because the light outputs of LSO and LuYAP are different. The LSO/LuYAP photopeaks need to be superposed in order to effectively discriminate the scattered events by applying an equal energy window. The photopeaks of the LSO and LuYAP can be superposed by inserting a reflecting material between the crystals. The optimal coverage ratio of the inserting material was derived from a DETECT simulation, and its performance was investigated. In the simulation result, optimal refractive index of the optical coupling material was 1.7. The average DOI measurement errors of the LSO/LuYAP were 0.6%/3.4% and 4.9%/41.4% in the phoswich detector with and without an optical coupling material, respectively. The photopeaks of the LSO and LuYAP were superposed by covering 75% of the contact surface between the crystals with white Teflon. The DOI measurement errors of the LSO/LuYAP were 0.2%/2.4%. In this study, the optimal condition of the optical coupling material inserted between the crystal and PMT was derived to improve the accuracy of DOI measurement, and a photopeak superposition method of the LSO and LuYAP was developed in order to reject scatter events. [Copyright &y& Elsevier]

Abstract: A new concept of dual-energy X-ray beam generation and acquisition of dual-energy security radiography is proposed. Erbium (Er) and rhodium (Rh) with a copper filter were positioned in front of X-ray tube to generate low- and high-energy X-ray spectra. Low- and high-energy X-rays were guided to separately enter into two parallel detectors. Monte Carlo code of MCNPX was used to derive an optimum thickness of each filter for improved dual X-ray image quality. It was desired to provide separation ability between organic and inorganic matters for the condition of 140kVp/0.8mA as used in the security application. Acquired dual-energy X-ray beams were evaluated by the dual-energy Z-map yielding enhanced performance compared with a commercial dual-energy detector. A collimator for the parallel dual-energy X-ray beam was designed to minimize X-ray beam interference between low- and high-energy parallel beams for 500mm source-to-detector distance. [Copyright &y& Elsevier]

We developed a depth of interaction (DOI) positron emission tomography (PET) detector using depth-dependent reflector patterns in a discrete crystal array. Due to the different reflector patterns at depth, light distribution was changed relative to depth. As a preliminary experiment, we measured DOI detector module crystal identification performance. The crystal consisted of a 9×9 array of 2 mmx2 mmx20 mm lutetium-yttrium oxyorthosilicate (LYSO) crystals. The crystal array was optically coupled to a 64-channel position-sensitive photomultiplier tube with a 2 mmx2 mm anode size and an 18.1 mmx18.1 mm effective area. We obtained the flood image with an Anger-type calculation. DOI layers and 9×9 pixels were well distinguished in the obtained images. Preclinical PET scanners based on this detector design offer the prospect of high and uniform spatial resolution. [ABSTRACT FROM AUTHOR]

Muon tomography is a technique for monitoring special nuclear material, such as uranium, inside the shielding material. It is a 3D imaging system capable of identifying atomic number (Z) using muon particles, high energy natural radiation. The following technique shows an advantage in no radiation exposure due to its usage of naturally occurring cosmic ray muons. In this study, a prototype muon tomography system was developed using four muon detectors in top and bottom structures. The four muon detectors based on a plastic scintillator and WLS fibers were implemented in the previous study. Two detectors above the target object and the other two below the target object measure a muon's incoming and outgoing trajectories, respectively. Four detectors constituting the prototype were connected by coincidence to confirm the muon detection. The purpose of this study was to develop the prototype muon tomography system and to reconstruct the image of the high-Z material, such as lead and uranium. The performance of the prototype was confirmed by imaging under various conditions, such as measurement time, position, and thickness changes, using lead blocks. In addition, the feasibility of the prototype was verified by performing imaging using three materials with different atomic numbers, such as lead, iron, and aluminum. [ABSTRACT FROM AUTHOR]

Abstract: Recently, monitoring nuclear materials to avoid nuclear terrorism has become an important area of national security. It can be difficult to detect gamma rays from nuclear material because they are easily shielded by shielding material. Muon tomography using multiple -Coulomb scattering derived from muons can be utilized to detect special nuclear materials (SNMs) such as uranium-235 and plutonium-239. We designed a muon tomography system composed of four detector modules. The incident and scattered muon tracks can be calculated by two top and two bottom detectors, respectively. 3D tomographic images are obtained by extracting the crossing points of muon tracks with a point-of-closest-approach algorithm. The purpose of this study was to optimize the muon tomography system using Monte Carlo simulation code. The effects of the geometric parameters of the muon tomography system on material Z-discrimination capability were simulated and evaluated. [Copyright &y& Elsevier]

Abstract: The purpose of this study was to develop and evaluate a gamma camera with a newly designed diverging collimator for monitoring radiation fields in nuclear medicine. Simulations using the Geant4 Application for Tomographic Emission (GATE) were performed to model the gamma camera system designed to monitor Tc-99m radioactive isotopes usually used in nuclear medicine. A gamma camera consists of a diverging collimator, a CsI(Na) scintillation crystal with dimensions of 50.0mm×50.0mm×6.0mm and Hamamatsu H8500 PSPMT. The diverging collimator is composed of two layers of diverging slats stacked directly above each other, and the front layer is rotated by 90° with respect to the back layer. The point source at different positions was simulated, and the optimal slat thickness and slat height were determined by evaluating the spatial resolution and sensitivity. The slat thickness is 1.0mm, the slat height is 40.0mm and the angle of slats ranges from 0 to 22.5°. The front and back layers are composed of 40 and 18 slats, respectively, to achieve equal spatial resolution in the x and y directions. The diverging collimator improves the uniformity of the spatial resolution and sensitivity across the field of view and the count rate better than the pinhole collimator. Experimental measurements were performed, and the results agreed well with simulations in terms of spatial resolution and sensitivity. The results demonstrated that the two-layer diverging-slat collimator is suitable for large area monitoring of the radiation fields. [Copyright &y& Elsevier]

Abstract: The application of hadrons such as carbon ions is being developed for the treatment of cancer. The effectiveness of such a technique is due to the eligibility of charged particles in delivering most of their energy near the end of the range, called the Bragg peak. However, accurate verification of dose delivery is required since misalignment of the hadron beam can cause serious damage to normal tissue. PET scanners can be utilized to track the carbon beam to the tumor by imaging the trail of the hadron-induced positron emitters in the irradiated volume. In this study, we designed and evaluated (through Monte Carlo simulations) an in-beam PET scanner for monitoring patient dose in carbon beam therapy. A C-shaped PET and a partial-ring PET were designed to avoid interference between the PET detectors and the therapeutic carbon beam delivery. Their performance was compared with that of a full-ring PET scanner. The C-shaped, partial-ring, and full-ring scanners consisted of 14, 12, and 16 detector modules, respectively, with a 30.2cm inner diameter for brain imaging. Each detector module was composed of a 13×13 array of 4.0mm×4.0mm×20.0mm LYSO crystals and four round 25.4mm diameter PMTs. To estimate the production yield of positron emitters such as 10C, 11C, and 15O, a cylindrical PMMA phantom (diameter, 20cm; thickness, 20cm) was irradiated with 170, 290, and 350AMeV 12C beams using the GATE code. Phantom images of the three types of scanner were evaluated by comparing the longitudinal profile of the positron emitters, measured along the carbon beam as it passed a simulated positron emitter distribution. The results demonstrated that the development of a C-shaped PET scanner to characterize carbon dose distribution for therapy planning is feasible. [Copyright &y& Elsevier]

Abstract: Presently, the gamma camera system is widely used in various medical diagnostic, industrial and environmental fields. Hence, the quantitative and effective evaluation of its imaging performance is essential for design and quality assurance. The National Electrical Manufacturers Association (NEMA) standards for gamma camera evaluation are insufficient to perform sensitive evaluation. In this study, modulation transfer function (MTF) and normalized noise power spectrum (NNPS) will be suggested to evaluate the performance of small gamma camera with changeable pinhole collimators using Monte Carlo simulation. We simulated the system with a cylinder and a disk source, and seven different pinhole collimators from 1- to 4-mm-diameter pinhole with lead. The MTF and NNPS data were obtained from output images and were compared with full-width at half-maximum (FWHM), sensitivity and differential uniformity. In the result, we found that MTF and NNPS are effective and novel standards to evaluate imaging performance of gamma cameras instead of conventional NEMA standards. [Copyright &y& Elsevier]

Abstract: Neutron-induced prompt gamma-ray analysis method was evaluated for the detection of explosives by measuring the H, C(C/H), and N(N/H) concentrations of samples at a research nuclear reactor. The hydrogen concentration was measured from the calibration curves obtained from various samples which contained hydrogen, and the detection limit for the determination of hydrogen in the samples was estimated. Standard reference materials (NIST SRMs) were used as analytical controls. The γ-spectra obtained here will be directly used for further studies as a training set for a pattern recognition to develop suitable discriminant classes with which explosives can be distinguished from innocuous materials. [Copyright &y& Elsevier]

Small-animal positron emission tomography (PET) systems are useful functional imaging systems for pathology and pharmacology research. However, conventional small-animal PET systems show degradation with regard to spatial resolution and sensitivity when small objects are image with a scanner having large diameter. In this study, to overcome this limitation, we propose a small-animal PET using an adjustable gantry and a depth-of-interaction (DOI) detector. The adjustable gantry allows the field of view (FOV) to be changed depending on object size to increase the solid-angle coverage and improve sensitivity. In addition, detector modules are arranged in a square shape to fill gaps between the detector module as well as in the corners to achieve higher sensitivity. To overcome the parallax error that occurs in the square-shaped gantry with long and thin crystal elements, a DOI detector is employed using a depth-dependent reflector pattern. The adjustable-gantry PET (AGPET) system is designed by GATE Monte Carlo simulation and evaluated by comparison with conventional small-animal PET systems, such as Inveon and PETbox, in terms of spatial resolution and sensitivity. The DOI detector blocks were composed of two 8 × 8 SiPM arrays coupled to two blocks of 12 × 12 lutetium-yttrium oxyorthosilicate (LYSO) crystals of size 2.1 × 2. 1 × 20 mm3. The signals of the detector blocks are fed to a data acquisition system based on field-programmable gate array, and the position, energy, and time information were recorded. The detector module performance is analyzed by the peak-to-valley ratio (PVR), distance-to-width ratio (DWR), energy resolution, and timing resolution. The results demonstrate that the proposed AGPET potentially provide higher sensitivity and resolution for small animal imaging. • Development of small animal PET system with adjustable gantry. • Investigation of the depth of interaction method using depth-dependent reflector. • Evaluation of small animal PET system using Monte Carlo simulation. [ABSTRACT FROM AUTHOR]

Abstract: The gamma camera system was designed for monitoring the medical fields such as a radiopharmaceutical preparation lab or a patient waiting room (after source injection) in the division of nuclear medicine. However, gamma cameras equipped with a large-angle pinhole collimator and a thick monolithic crystal suffer from the degradation of the spatial resolution at the periphery region due to parallax error by obliquely incident photons. To improve the uniformity of the spatial resolution across the field of view (FOV), we proposed a three-layer crystal detector with a maximum-likelihood position-estimation (MLPE) method, which can measure depth-of-interaction (DOI) information. The aim of this study was to develop and evaluate the performance of new detector experimentally. The proposed detector employed three layers of monolithic CsI(Tl) crystals, each of which is 50.0×50.0×2.0mm3, and a large-angle pinhole collimator with an acceptance angle of 120°. The bottom surface of the third layer was directly coupled to an 8×8 channel position-sensitive photomultiplier tube (PSPMT, Hamamatsu H8500C). The PSPMT was read out using a resistive charge divider, which multiplexes 64 anodes into 8(X)+8(Y) channels. Gaussian-based MLPE method has been implemented using experimentally measured detector response functions (DRFs). Tc-99m point source was imaged at different positions with and without DOI measurements. Experimental results showed that the spatial resolution was degraded gradually as the source moved from the center to the periphery of the FOV without DOI information but the DOI detector showed the marked improvement in the spatial resolution, especially at off-center by correcting the parallax error. In this paper, our new detector with DOI capability proved to characterize reliably the gamma event position with the high and uniform spatial resolution, so that the large-angle pinhole gamma camera could be a useful tool in contamination monitoring. [Copyright &y& Elsevier]

Abstract: In recent years, there has been a growing interest in developing small gamma cameras dedicated to breast imaging. We designed a new detector with trapezoidal shape to expand the field of view (FOV) of camera without increasing its dimensions. To find optimal parameters, images of point sources at the edge area as functions of the angle and optical treatment of crystal side surface were simulated by using a DETECT2000. Our detector employs monolithic CsI(Tl) with dimensions of 48.0×48.0×6.0mm coupled to an array of photo-sensors. Side surfaces of crystal were treated with three different surface finishes: black absorber, metal reflector and white reflector. The trapezoidal angle varied from 45° to 90° in steps of 15°. Gamma events were generated on 15 evenly spaced points with 1.0mm spacing in the X-axis starting 1.0mm away from the side surface. Ten thousand gamma events were simulated at each location and images were formed by calculating the Anger-logic. The results demonstrated that all the 15 points could be identified only for the crystal with trapezoidal shape having 45° angle and white reflector on the side surface. In conclusion, our new detector proved to be a reliable design to expand the FOV of small gamma camera for breast imaging. [Copyright &y& Elsevier]