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The jPET-D4 is a brain positron emission tomography (PET) scanner that we have developed to meet user demands for high sensitivity and high spatial resolution. For this scanner, we developed a four-layer depth-of-interaction (DOI) detector. The four-layer DOI detector is a key component for the jPET-D4, its performance has great influence on the overall system performance. Previously, we reported the original technique for encoding four-layer DOI. Here, we introduce the final design of the jPET-D4 detector and present the results of an investigation on uniformity in performance of the detector. The performance evaluation was done over the 120 DOI crystal blocks for the detectors, which are to be assembled into the jPET-D4 scanner. We also introduce the crystal assembly method, which is simple enough, even though each DOI crystal block is composed of 1,024 crystal elements. The jPET-D4 detector consists of four layers of 16 × 16 Gd2SiO5 (GSO) crystals and a 256-channel flat-panel position-sensitive photomultiplier tube (256ch FP-PMT). To identify scintillated crystals in the four-layer DOI detector, we use pulse shape discrimination and position discrimination on the two-dimensional (2D) position histogram. For pulse shape discrimination, two kinds of GSO crystals that show different scintillation decay time constants are used in the upper two and lower two layers, respectively. Proper reflector arrangement in the crystal block then allows the scintillated crystals to be identified in these two-layer groupings with two 2D position histograms. We produced the 120 DOI crystal blocks for the jPET-D4 system, and measured their characteristics such as the accuracy of pulse shape discrimination, energy resolution, and the pulse height of the full energy peak. The results show a satisfactory and uniform performance of the four-layer DOI crystal blocks; for example, misidentification rate in each GSO layer is

We are developing a small animal PET scanner, "jPET-RD" to achieve high sensitivity as well as high spatial resolution by using four-layer depth-of-interaction (DOI) detectors. The jPET-RD is designed with two detector rings. Each detector ring is composed of six DOI detectors arranged hexagonally. The diameter of the field-of-view (FOV) is 8.8 cm, which is smaller than typical small animal PET scanners on the market now. Each detector module consists of a crystal block and a 256-channel flat panel position-sensitive photomultiplier tube. The crystal block, consisting of 32 x 32 x 4 crystal (4096 crystals, each 1.46 mm x 1.46 mm x 4.5 mm) and a reflector, is mounted on the 256ch FP-PMT. \nIn this study, we evaluated the spatial resolution of reconstructed images with the evaluation system of two four-layer DOI detectors which consist of 32 x 32 x 4 LYSO (Lu: 98%, Y: 2%) crystals coupled on the 256ch FP-PMT by using RTV rubber. The spatial resolution of 1.5 mm was obtained at the center of the FOV by the filtered back projection. The spatial resolution, better than 2 mm in the whole FOV, was also achieved with DOI while the spatial resolution without DOI was degraded to 3.3 mm.

The non-collinearity of electron-positron annihilation radiation from in vivo 18FDG was determined for the first time by the conversion from the measured Doppler effect in the energy spectrum into the angle difference from 180 degrees. The distribution was a Gaussian centered at 0 degree and the FWHM was 0.54 +/- 0.02 degrees, which is about 15% larger value than that have reported for pure water. Some polarized groups and ions may suppress the formation of positronium, and the pure water is not good quantitative approximation of the human body about the angular distribution. Since the value is determined under the same condition as a clinical 18FDG-PET scan, it can be used reliably for simulations, system designs, image reconstructions, etc.

第３回日韓医学物理学術大会

jPET-RD (for Rodents with depth of interaction (DOI) detectors) is the small animal PET scanner which is under development at the National Institute of Radiological Sciences in Japan. High sensitivity is expected without degradation of the spatial resolution by the use of four-layer DOI detectors in the scanner. The detector consists of four-layers of scintillation crystal array optically coupled to a position sensitive photo-detector and scintillation light controlled by a proper reflector arrangement in the crystal array provides information for the crystal of detection. A basic study such as the validation of the four-layer DOI encoding method and detector parameter optimization has been carried out with a subset of the crystal arrays; a 10 X 10 X 4 array of Lu2(1-x)Y2xSiO5 (LYSO, x=0.02). We determined detector parameters through the basic study and will compose the full-size detector with a 32 X 32 X 4 LYSO crystal array. In this paper, we introduce the jPET-RD system, detector design and its performance. The subset of crystal array in optimal design showed enough crystal identification performance and 12-17% energy resolutions for all layer crystals. The results confirm the expectation of the same level performance on the full-size detector., World Congress on Medical Physics and Biomedical Engineering 2006

Depth-of-interaction (DOI) PET detectors possess three-dimensional information on the interaction point of annihilation radiation and a scintillator crystal. The information has been used for improving PET spatial resolution especially at the edge of field-of-view. In this paper, DOI information is used for improving timing resolution of scintillation detectors. The annihilation radiation travels at the light speed, c, while scintillation photon travels at the speed of c/n in medium, where n is the refractive index. The difference in the propagation speed causes timing error which depends on the DOI. Given that the total length of the scintillator is 3.0 cm and the refractive index is 1.8, the error is estimated to be 80 ps or longer. We experimentally evaluated the timing error as the function of the DOI by using Pseudo-four-layer DOI detector and a fast digital oscilloscope. The detector was composed of an LYSO scintillator crystal and 255 dummy crystals made of silica. As the result, the error was estimated to be about 100 ps. Timing correction using DOI information would be an important technique when constructing high timing resolution PET detectors, especially ones for time-of-flight PET., IEEE 2007 Nuclear Science Symposium and Medical Imaging Conference

We are developing jPET-RD designed as a small animal PET scanner to achieve high sensitivity as well as high spatial resolution by the use of four-layer depth of interaction (DOI) information of the detector. jPET-RD has five detector rings composed of six DOI detectors arranged hexagonally and the ring diameter of the field of vies is 8.8 mm smaller than typical small animal PET scanners. Each detector module consists of a 32 X 32 X 4 LYSO (Lu: 98%, Y: 2%) crystal array and a 256-channel flat panel position sensitive photomultiplier tube. The size of each crystal element is 1.46 mm X 1.46 mm X 4.5 mm. The crystal block (46.5 mm X 11.6 mm X 18.0 mm) is placed on the central area of a 256ch FP-PMT (49 mm X 49 mm useful area) and coupled with silicone rubber. In the previous study, we succeeded at crystal identification for the detector module composed of the four layer crystal array and achieved the good performance as a detector for a small animal PET with a 32 X 8 X 4 LYSO array corresponding with a quarter of the full size crystal array. We evaluated the spatial resolution of reconstructed images with the one pair system of the two 4-Layer DOI detectors for jPET-RD. The spatial resolutions of smaller than 2 mm in whole field of view by FBP algorithm were achieved. In addition, the spatial resolution of 1.5mm at the center of FOV was achieved., IEEE 2006 Nuclear Science Symposium and Medical Imaging Conference

To avoid loss of data sampling and sensitivity between detectors in a PET system, it is necessary to fill up scintillation crystals in the region between two PMTs, PMT blind region, and recognize gamma-ray detected location by a special crystal identification technique for the region. We have developed a 2-layer depth of interaction (DOI) detector for the PMT blind. The detector is composed of two layers of scintillation crystal array standing over two PMTs without a light guide plate. Crystal identification, that is 2-layer DOI encoding, is performed by Anger-type calculation of the PMT signals. Because all upper layer crystals and lower crystals in the PMT blind region are not coupled directory to the PMTs, materials between crystals must be chosen to guide scintillation light appropriately from the crystal of detection to the PMT useful area. Not only reflectors, air gap and the translucent film that is expected to pass scintillation light much more than reflector but less than air gap can be the candidates of the material. The basic study to determine proper reflector arrangement was carried out on one position sensitive PMT (PS-PMT) with using distant anodes instead of preparing two PMTs. Lu2(1-x)Y2xSiO5 (LYSO) in dimensions of 1.46 mm x 1.46 mm x 4.5 mm was used as the crystal element and a 256ch flat panel PS-PMT (FP-PMT) was done as the PS-PMT. The FP-PMT has 16 x 16 multi-anodes with 3.04 mm interval. It has 52 mm x 52 mm opening area and 89% of useful area. Since the reflector arrangement was optimized through the basic study, we measured the 2-layer DOI detector performance in the more realistic system with the existence of the PMT blind region made by two FP-PMTs., World Congress on Medical Physics and Biomedical Engineering 2006

Objectives: jPET-RD a small animal PET scanner which is under development at our institute. Its capability of 4-layer DOI encoding in the detector allows closer detector setting to a subject for keeping large axial view that is greatly advantageous in terms of high sensitivity but, at the same time, causes significant parallax error in non-DOI detector systems. At the present stage, we developed an experimental system which replicates detector geometry in the jPET-RD. With a pair of prototype jPET-RD detectors, we measured spatial resolution in the system to show the effects of the 4-layer DOI encoding on uniformity in the resolution. Methods: The jPET-RD detector is designed to have a 256ch flat panel position sensitive PMT (FP-PMT) and 4096 Lu2(1-x)Y2xSiO5 (LYSO) crystal elements, which arranged in four layers of 32 x 32 arrays. Each crystal size is 1.46 mm x 1.46 mm x 4.5 mm. 6 detectors form one detector ring of 8.8 cm diameter. The prototype detector we developed has full 32 x 4 crystal elements in transaxial and depth but 8 crystal alignments in axial direction. A 68Ge-68Ga line source of 1.65 mm in diameter is first placed at the center of the field of view (FOV) and coincidence events are measured at all detector pair positions on the experimental system. Signals from FP-PMT anodes are reduced to 8 signals by a resistor-chain in each prototype detector and provided to the coincidence circuit of the system. Measurements are performed with the source positions of every 0.5 cm steps from the center till 4.0 cm off-center. Point spread functions (PSFs) are measured as FWHM of the image reconstructed by filtered backprojection. Results: PSFs at the center and at the 4.0 cm off-center source positions were measured to be 2.2 mm and 2.5 mm in FWHM, respectively. The average of all 9 source positions was 2.5 mm. Without DOI information, these spatial resolutions degraded to 2.6 mm (center), 5.0 mm (4.0 cm off-center) and 3.3 mm (average). Intrinsic spatial resolutions of 1.46 mm (center) and 1.88 mm (4.0 cm off-center) with DOI information are estimated by deconvoluting the source distribution, with the assumption that the source distribution is a Gaussian function of 1.65 mm FWHM. Conclusions: Almost uniform spatial resolution from the center to the top face of detectors was obtained by the jPET-RD experimental system., 第５３回米国核医学会

jPET-RD is designed to achieve high sensitivity as well as high spatial resolution by the use of four-layer depth of interaction (DOI) information of the detector. We have previously proposed the DOI encoding method that enables four layers DOI identification using only single kind crystal elements. The basic idea was tested by using Gd2SiO5, and the first prototype detector was developed using Lu2(1-x)Y2xSiO5 (LYSO). In this work, we measured response functions of a jPET-RD prototype detector composed of four layers of a 32 (axial) x 8 (transaxial) LYSO (Lu: 98%, Y: 2%) crystal block with 511 keV gamma rays to estimate resolution performance. The size of each crystal element is 1.44 mm x 1.44 mm x 4.5 mm. The crystal block (46.5 mm x 11.6 mm x 18.0 mm) is placed on the central area of a 256-channel flat panel position sensitive photomultiplier tube (49 mm x 49 mm useful area) and coupled with silicone rubber. As a result, the averaged FWHM of response functions was 1.56 mm in axial and 4.51 mm in depth direction. The energy resolution of all events was 14.7% and the time resolution was found to be 0.66 ns. The experimental results promise excellent performance of a jPET-RD detector., Nuclear Science Symposium & Medical Imaging Conference

An 8-layer depth of interaction (DOI) detector was designed on the basis of the technique we have developed for 4-layer DOI detectors. It attains 8-layer encoding by pulse shape discrimination (2-layer DOI encoding) and the proper reflector arrangement in a 3-dimmensional crystal array (4-layer DOI encoding). Its capability was proved with an 8 layers of 10 x 10 Gd2SiO5 (GSO) crystal array coupled to a 256-channel flat panel position sensitive photomultiplier tube (256ch FP-PMT). The dimensions of a crystal element are 2.90 mm x 2.90 mm x 3.75 mm and intervals of 16 x 16 multi-anodes in the 256ch FP-PMT are 3.04 mm. Two kinds of GSO were used to make pulse shape discrimination; GSOs of 0.5 mol% and 1.5 mol% Ce dopants that show 60 ns and 35 ns scintillation decay times, respectively. In the crystal array, the layer-1, the farthest from the 256ch FP-PMT, layer-3, -5 and -7 were composed of 0.5 mol% GSO: Ce crystals and 1.5 mol% GSO: Ce crystals were in other layers. Performance of the 8-layer DOI detector was evaluated by irradiating 662 keV uniform gamma-rays. The results indicate capability of 8-layer DOI encoding. To prove the validity of the layer encoding, fan-beam of 662 keV gamma-rays are irradiated onto the side face of each layer. The obtained 2D histograms show the right structure in each corresponding layer clearly. In this measurement, the pulse height distribution of a central crystal in each layer suggests the minimum light output of 0.62 to the maximum and about 15% energy resolutions for all layers., Medical Image Conference

In this work, an 8-layer depth of interaction (DOI) encoding was newly achieved. We have already proposed a 4-layer DOI detector that is composed of 3-dimensinal crystal array with all the same crystal material. In this DOI detector, the proper reflector arrangement controls light path in the crystal array and makes 4-layer DOI detection. It is expected that the use of two kinds of crystal elements should enhance the 4-layer DOI detection capability to 8-layer with pulse shape discrimination. A prototype DOI detector was composed of 8 layers of 10 by 10 Gd2SiO5 (GSO) crystal array and a 256-channel flat panel position sensitive photomultiplier tube (256ch FP-PMT) which has 16 by 16 multi anodes at the intervals of 3.04 mm. The size of the crystal element is 2.90 mm by 2.90 mm by 3.75 mm. Two kind GSO crystals were used; GSO crystals of 0.5 mol% Ce dopant were in the 1st, the furthest from the FP-PMT, 3rd, 5th and 7th layers and crystals of 1.5 mol% Ce dopant were in other layers. Performance of the 8-layer DOI detector was evaluated by irradiating 662 keV uniform gamma rays. In this measurement, it is found that all crystals could be identified clearly., 第４回日韓合同医学物理学会

We are now planning a small animal PET scanner named jPET-RD (for rodent with depth of interaction (DOI) detector), which meets the demand for high sensitivity and high spatial resolution. We have previously proposed the four-layer DOI encoding method using only single kind crystal elements. In this work, we measured the energy resolution, the timing resolution and response functions of a jPET-RD prototype detector composed of four layers of a 32 (axial) x 8 (transaxial) LYSO (Lu: 98%, Y: 2%) crystal block with 511 keV gamma rays to estimate resolution performance. The size of each crystal element is 1.44 mm x 1.44 mm x 4.5 mm. The crystal block is placed on the central area of a 256-channel flat panel position sensitive photomultiplier tube (49 mm x 49 mm useful area) and coupled with silicone rubber. The averaged FWHM of response functions was 1.56 mm in axial and 4.51 mm in depth direction. The energy resolution of all events was 14.7% and the time resolution was found to be 0.66 ns. The experimental results promise excellent performance of a jPET-RD detector., 第４回日韓合同医学物理学会

For research studies in biomedical sciences, small animal PET scanners should be highly sensitive to allow the clarification of vital functions at the molecular level and imaging of gene expression. We are planning to develop a small animal PET scanner with a large solid angle, jPET-RD (for Rodents with DOI detectors). The jPET-RD is designed to achieve high sensitivity as well as high spatial resolution by the use of four-layer depth of interaction (DOI) information. Lu2(1-x)Y2xSiO5 (LYSO) is chosen as scintillator to get higher count rate and detection efficiency. In this paper, we evaluate energy, timing, and spatial resolution of a jPET-RD prototype detector., 52nd Annual Meeting

2004 IEEE Nuclear Science Symposium Medical Imaging Conference

51th Society of Nuclear Medicine Annual Meeting

Medical Imaging Conference

Medical Imaging Conference

2002 IEEE Nuc. Sci. Sympo. & Med. Imag. Conf.

第３回日韓医学物理学術大会

Small animal positron emission tomography (PET) scanners and positron emission mammography (PEM) scanner require not only high spatial resolution but also high scanner sensitivity. One of methods to achieve high scanner sensitivity is to move gamma ray detectors closer to objects. However it increases the gamma rays entering to the detector obliquely. Therefore, spatial resolution of reconstructed images is degraded. The solution of the degradation is using depth-of-interaction (DOI) detectors which can measure interaction positions of depth directions in scintillation crystals. We are developing a small bore PET scanner to achieve high sensitivity as well as high spatial resolution by the use of four-layer DOI information of the detector. We constructed and tested the prototype scanner of the four-layer DOI detectors. The prototype system consists of the six DOI detectors arranged hexagonally. The distance between the opposed DOI detectors is 9.2 cm and a field-of-view (FOV) is 8.8 cm. The DOI detectors consist of a 32 (transaxial) x 32 (axial) x 4 (depth) array of LGSO crystals and a 256ch FP-PMT. The size of each crystal element is 1.46 mm x 1.46 mm x 4.5 mm. In the presentation, the experimental data, especially the evaluation of the spatial resolution and sensitivity of the scanner, are presented., 2008 Nuclear Science Symposium, Medical Imaging Conference