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This study aimed to develop a new system, named CD-Well, for mouse PET dynamic study. CD-Well allows the determination of time-activity curves(TACs) for arterial whole blood and plasma using 2-3 muL of blood per sample;the minute sample size is ideal for studies in small animals. The system has the following merits: (1)measures volume and radioactivity of whole blood and plasma separately; (2) allows measurements at 10 s intervals to capture initial rapid changes in the TAC; and (3) is compact and easy to handle, minimizes blood loss from sampling, and delay and dispersion of the TAC. CD-Well has 36 U-shaped channels. A drop of blood is sampled into the opening of the channel and stored there. After serial sampling is completed, CD-Well is centrifuged and scanned using a flatbed scanner to define the regions of plasma and blood cells. The length measured is converted to volume because the channels have a precise and uniform cross section. Then, CD-Well is exposed to an imaging plate to measure radioactivity. Finally, radioactivity concentrations are computed. We evaluated the performance of CD-Well in in vitro measurement and in vivo 18F-fluorodeoxyglucose and [11C]2-carbomethoxy-3beta-(4-fluorophenyl) tropane studies. In in vitro evaluation, per cent differences (mean+-SE) from manual measurement were 4.4+-3.6% for whole blood and 4.0+-3.5% for plasma across the typical range of radioactivity measured in mouse dynamic study. In in vivo studies, reasonable TACs were obtained. The peaks were captured well, and the time courses coincided well with the TAC derived from PET imaging of the heart chamber. The total blood loss was less than 200 muL, which had no physiological effect on the mice. CD-Well demonstrates satisfactory performance, and is useful for mouse PETdynamic study.

現在，異なる機能画像を同時に観測することのできるPET（Positron Emission Tomography・光CT(Computed Tomography）同時計測装置の開発が進められている。ここで，機能画像観測を行うことのできる光CT としては，発光観測によるものと蛍光観測によるものとがあるが，PET 装置と組み合わせた場合の性能などについては十分考察がなされていない。本研究では，PET 装置に光CT の機能を組み合わせた際に，発光／蛍光観測の違いが断層画像再構成に与える影響を，光拡散方程式を用いた計算機シミュレーションにより検討した。その結果，外部からの励起光照射を必要としない内部発光では，観測方向を増やすことが必ずしも空間分解能の向上に繋がらず，とくに対象部位中央付近の分解能で劣化が大きいことが明ら かになった。これに対して蛍光観察では，励起光を照射する位置を変えることで固定された検出器配置でも情報量を増やすことができ，部位中央にある蛍光でも推定可能なことを示した。

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 jPET-D4 is the first PET scanner to introduce a unique four-layer depthof- interaction (DOI) detector scheme in order to achieve high sensitivity and uniform high spatial resolution. This paper compares measurement and Monte Carlo simulation results of the static physics performance of this prototype research PET scanner. Measurement results include single and coincidence energy spectra, point and line source sensitivities, axial sensitivity profile (slice profile) and scatter fraction. We use GATE (Geant4 application for tomographic emission) as a Monte Carlo radiation transport model. Experimental results are reproduced well by the simulation model with reasonable assumptions on characteristic responses of the DOI detectors. In a previous study, the jPET-D4 was shown to provide a uniform spatial resolution as good as 3 mm (FHWM). In the present study, we demonstrate that a high sensitivity, 11.3 +/- 0.5%, is provided at the FOV centre. However, about threefourths of this sensitivity is related to multiple-crystal events, for which some misidentification of the crystal cannot be avoided. Therefore, it is crucial to develop a more efficient way to identify the crystal of interaction and to reduce misidentification in order to make use of these high performance values simultaneously. We expect that effective sensitivity can be improved by replacing the GSO crystals with more absorptive crystals such as BGO and LSO. The results we describe here are essential to take full advantage of the next generation PET systems that have DOI recognition capability.

The jPET-D4 is a novel brain PET scanner which aims to achieve not only high spatial resolution bui also high scanner sensitivity by measuring 4-layer depth-of-interaction (DOI) information. At this stage, we have developed a full-ring prototype scanner. In this work, we present software strategies for fully 3D imagereconstruction and imaging performance of the jPET-D4 prototype. The quality of reconstructed images depends on an accurate model of relationships between object space and measurement space. Therefore iterative image reconstruction methods such as ML-EM have been successfully used to improve imagequality through accurate system modeling. However it is not practical to apply these methods directly to the jPET-D4 systems since the number of detector crystal pairs increases in proportion to the square of the number of DOI layers. The process that requires the most computational time and storage space is the calculation of a huge number of system matrix elements. In order to reduce computational cost while retaining the advantages of DOI information in iterative image reconstruction, we applied the DOI compression method which reduces date dimensions with suppression of resolution loss. We also used the approximated imaging system model which enables fast system matrix calculation while preserving image quality. At this development stage, histogram-based 3D OSEM was implemented. After evaluating basic imaging performance though phantom experiments, the first human brain images were obtained. The experimental results show that almost uniform spatial resolution of 2-3 mm is obtained over the field-of-view by using the 4-layer DOI information. The human brain images show the excellent imageing performance of the jPET-D4., World Congress on Medical Physics and Biomedical Engineering 2006

PET scanner are an important component in functional brain imaging devices. Several PET scanners have been developed during the last two decades for brain research studies. We are developing a high-performance brain PET scanner, jPET-D4.This scanner is designed to achieve not only high spatial resolution but also high sensitivity using four-layered depth-of-interaction (DOI) detectors. The scanner has five block detector rings with the ring diameter of 390 mm and each blockdetector ring consists of 24 DOI detectors. In previous work, we have demonstrated that 3 mm FWHM uniform spatial resolution within the field-of-view could be realized. In this paper, we describe the jPET-D4 system and evaluate its performance. The average energy resolution for 120 DOI detectors is optimized to 16 % +/- 1.0 %. The scater fraction for this system is 40 % with an energy window of 400-600 keV. The sensitivity for the point source is 102 kcps/MBq (10.2 %) with a 400 keV LLD. Maximum noise equivalent count rate (NECR) is 154 kcps at 11 kBq/ml with a 10 ns coinsidence time window. We evaluated scatter fraction and NECR following procedures based on NEMA NU-2-1994. These first evalution measurements indicate the jPET-D4 has good performance.

the Ninth EGS4 Users' Meeting in Japan

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

[Introduction] The system for uL-ordered blood sampling and plasma radioactive concentration measurement, Microfluidic Mouse Plasma Counting System (uFmPC, patent pending), is developing. uFmPC should measure very small radioactivity concentration, from several to hundreds Bq/uL. This study aimed to investigate the accuracy on such small radioactivity concentration. [Method] In uFmPC, blood was sampled using microfluidic technique, and it was stocked in channels on a plastic disc (CD-Well). The blood was then separated by rotating the disc. Because the channels had exact cross-sectional area of 0.067 mm2, the volumes of blood and separated plasma could be derived by measurement of the length using a flatbed scanner. The amount of radioactivity was acquired by a storage phosphor screen. In the experiments, one and three uL of FDG solutions containing the radioactivity ranging from 4 to 128 Bq/uL were introduced in the channels. The radioactivity was measured using Imaging Plate (IP) and BAS-5000 (Fujifilm Corp., Japan) with 120-minute exposure. CD-Well was also scanned by GT-X970 scanner (Seiko EPSON, Japan) in 2400 dpi in order to measure the volume of solution. The activity concentration of given FDG was compared with a photo-stimulated luminescence value (PSL) derived from uFmPC. [Results and Discussion] Measured images were shown in Fig. 1: a scanned image (A) and an image from IP (B). The position of introduced FDG was detected as shown in (C) with black thick curves, and it was applied to the IP image to read out an amount of radioactivity. (D) was a superimposed image. From 120-minute exposure, the PSL was correlated with the given concentration well (y = 1.8x + 4.4 for 1 uL case and y = 2.1x + 6.6 for 3 uL case. r2=1.00 for both cases). We can conclude that the concept of uFmPC had potential to measure small radioactivity concentration., 2009 World Molecular Imaging Congress

2009 World Molecular Imaging Congress

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

Depth-of-Interaction (DOI) detectors, which can improve resolution uniformity in the field-of-view (FOV), enable high sensitivity PET scanners with small bore detector rings. We are developing a small bore PET scanner dedicated for small animals or mammography. We have proposed a DOI detector which consists of a four-layer array of 32x32 crystals (1.44mm x 1.44mm x 4.5mm) and a 256ch flat panel position sensitive photomultiplier tube (FP-PS-PMT). The FP-PS-PMT has a large effective area of 49mmx49mm and multi anodes of 16x16ch, which can be read out in parallel. In this work, we simulated following three geometries based on this detector blocks using GATE (Geant4 Application for Tomographic Emission): two rings of (A) six detector blocks arranged in a hexagonal shape (85mm diameter FOV), (B) four detector blocks arranged in a tetragonal shape (49mm diameter FOV) and (C) in overlapped tetragonal shape (38mm diameter FOV). The axial FOV for two rings of detectors is 99mm. The aim of overlapped detector arrangement in geometry C is to reduce inter-module gaps and achieve higher sensitivity. The absolute sensitivity of geometry A, B and C with non-parallel readout were approximately 19%, 23% and 29%, respectively (400-600keV). Maximum noise equivalent count rate (NECR) of geometry A, B and C at the same condition were also 1250kcps, 920 kcps and 1060kcps, respectively. The decrease of the maximum NECR was caused by dead-time effect. By using an appropriate anode segmentation of the FP-PS-PMT, the maximum NECR was improved by factors of 1.7 for all geometries. Simulation results show that small bore PET geometry improves scanner sensitivity while it affects count rate performance, and parallel readout with appropriate anode segmentation improves count rate performance drastically., World Congress on Medical Physics and Biomedical Engineering 2006

Depth-of-interaction (DOI) detectors, which can improve resolution uniformity in the field-of-view (FOV), enable high sensitivity PET scanners with small bore detector rings. We are developing a small bore PET scanner dedicated for small animals or mammography. We have proposed a DOI detector which consists of a four-layer array of 32x32 LYSO crystals (1.44mmx1.44mmx4.5mm). In this work, we simulated following three geometries based on this detector blocks using GATE, and compared imaging performance: (A) six detector blocks arranged in a hexagonal shape (85.2mm diameter FOV), (B) four detector blocks arranged in a tetragonal shape (49.2mm diameter FOV), and (C) in overlapped tetragonal shape (38.1mm diameter FOV). In order to deal with irregular detector sampling, list-mode maximum likelihood expectation maximization image reconstruction with accurate system modeling was applied. At this stage, effects of positron range, attenuation and Compton scattering were not included, and implementation was restricted to 2D in this simulation. The spatial resolution of geometry (B) and geometry (C) were approximately 1.35mm and that of geometry (A) was 1.25mm. The resolution non-uniformity of geometry (A) and geometry (C) improved 17% comparing to geometry (B). These results show that the hexagonal geometry has better resolution performance than the tetragonal geometry, and the uniformity of spatial resolution can be improved by overlapping detector blocks and filling gap. We should note that the resolution performance of overlapped tetragonal geometry almost equals hexagonal geometry in spite of fewer total number of crystals (hexagon geometry has 49152 crystals, while overlapped tetragonal geometry has 32768 crystals)., World Congress on Medical Physics and Biomedical Engineering 2006

We are developing a high-performance brain PET scanner, jPET-D4. This scanner is designed to achieve not only high spatial resolution but also high sensitivity using four-layered depth-of-interaction (DOI) detectors with GSO scintillators. DOI information can minimize the effect of the crystal penetration of obliquely incident gamma rays. The scanner has five block detector rings with the ring diameter of 390 mm and each block detector ring consists of 24 DOI detectors. The size of a crystal element is 2.9 x 2.9 x 7.5 mm3 and total length of crystal block is 30 mm. Axial length is 260 mm with five DOI detectors. The jPET-D4 has a smaller ring diameter and larger crystal length compared to other brain PET scanners for high sensitivity. Parallel disk system allows data acquisition with a maximum storage rate of 80 MB/sec for list mode data. The noise equivalent counts rate (NECR) performance has been evaluated based on the NU 2-1994 protocol. The count rate capability is measured for a 20 cm diameter and 20 cm cylinder phantom using several coincidence time windows and energy windows. Default energy window was 400-600 keV from the system energy resolution of 16 %. A coincidence time window can be changed electrically from 6 to 30 ns with 4 ns steps. At 15 kBq/ml the random rate equals the true and scatter rate with about 1 Mcps. Maximum NECR is 154 kcps at 11 kBq/ml with 10 ns coincidence time window. This evaluation measurement promises the jPET-D4 has excellent performance. We will continue to evaluate count rate performance of the jPET-D4 based on the NU 2-2001 protocol., 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

In a conventional PET detector, detected events are projected to 2D position histogram with Anger calculation for a crystal identification. However, the measured histogram is affected by inter-crystal scatterings (ICS) which occur in a whole detector. Peaks with projected each crystal in the histogram are blurred, and it causes ICS's mispositioning. A depth of interaction (DOI) detector has been developed for the small animal PET scanner: jPET-RD. This DOI detector uses 32 x 32 crystals with four layers and a 256-channel multi-anode flat panel photomultiplier tube (FP-PMT) was developed by Hamamatsu Photonics K.K. Each crystal element is 1.45 x 1.45 x 4.5 mm3. The FP-PMT has a large detective area (49 x 49 mm2) and small anode pitch (3.04 mm). Therefore, the FP-PMT can extensively trace the behavior of incident gamma rays in the crystals including ICS. We therefore propose a novel method for ICS estimation using a statistical pattern recognition based on the support vector machine (SVM). In this study, we applied the SVM for discriminating photoelectric events from ICS events generated from multiple-anode outputs. The SVM was trained by uniform irradiation events generated from a detector simulator using Monte Carlo calculation. Initial result of ICS identification is about 78 % for non-training data. This method can archive a true subtraction of ICS from measured events, and it is also useful for random correction in PET., 1st European Conference on Molecular Imaging Technology

2004 IEEE Nuclear Science Symposium Medical Imaging Conference

51th Society of Nuclear Medicine Annual Meeting

Medical Imaging Conference