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Pancreatic cancer (PC) has a poor prognosis owing to difficulties in the diagnosis of resectable PC at early stages. Several clinical studies have indicated that the detection and surgery of small resectable PC (64Cu-labeled anti-epidermal growth factor receptor antibody cetuximab was intraperitoneally administered into mice. It clearly identified PC tumors ≥3 mm. In contrast, neither OpenPET with intravenous-administered 64Cu-cetuximab nor intraperitoneal/intravenous-administered 18F-FDG (a traditional PET probe) could detect PC in this model. Immuno-OpenPET-guided surgery accurately resected small PC in mice and achieved significantly prolonged survival. This technology could provide a novel diagnostic and therapeutic strategy for small resectable PC to improve patient survival.

High-performance computing (HPC) cluster systems sometimes adopt a two-layered file system composed of local and global file systems to achieve both capacity and performance in storage. In such a cluster system, the input data of an application needs to be staged from the global storage into the local storage, and the output data needs to be staged from the local storage out to the global storage. This staging operation must be efficiently and quickly performed to gain higher job throughput because an inefficient staging operation prevents waiting job requests from being executed. In particular, in the case of the cluster system with the oversubscribed interconnect shared by the storage and the computing nodes, the inter-node communication and this staging operation traffic collides, which may degrade the job throughput. In this research, we focus on the traffic collision of the inter-node communication and the staging traffic to improve job throughput, targeting the cluster system with the oversubscribed interconnect where these two types of traffic flow. In other words, whether the dynamic control of the traffic flow derived from the staging operation leads to the improvement in the job throughput or not is investigated. For the investigation, we present a traffic collision avoidance method to dynamically configure a set of data paths for each type of the traffic only while the staging operation is conducted. The evaluation in this article shows that the proposed method avoids a traffic collision and accelerates the staging operation by 22.0% on our cluster system. Also, this evaluation indicates the overhead of the application incurred by the proposed method is negligible. Furthermore, 8.7% of the job execution time is reduced by the proposed method.

Noninvasive quantification of myocardial blood flow with PET is a vital tool for detecting and monitoring of coronary artery disease. However, current standard cylindrical PET scanners are not optimized for cardiac imaging because they are designed mainly for whole-body imaging. In this study, we proposed two compact geometries, the elliptical geometry and the D-shape geometry, for cardiac-dedicated PET systems. We then evaluated their performance compared with a whole-body-size cylindrical geometry by using the Geant4 Monte Carlo simulation toolkit. In the simulation, an elliptical water phantom was scanned for 10-sec, and we calculated the sensitivity and the noise-equivalent count rate (NECR). Subsequently, a digital chest phantom was scanned for 30-sec and the coincidence data were reconstructed by in-house image reconstruction software. We evaluated the image noise in the liver region and the contrast recoveries in the heart region. Even with the limited number of detectors, the proposed compact geometries showed higher sensitivity than the whole-body geometry. The D-shape geometry achieved 47% higher NECR and 44% lower image noise compared with the whole-body cylindrical geometry. However, the contrasts in the hot area obtained by the proposed compact geometries were not as good as that obtained by the whole-body cylindrical geometry. There was no considerable difference in image quality between the elliptical geometry and the D-shape geometry. In conclusion, the compact geometries we have proposed are promising designs for a high-sensitivity and low-cost cardiac-dedicated PET system. A further study using a defect phantom model is required to evaluate the contrast of cold areas.

Silicon photomultiplier (SiPM) based scintillation detectors are widely used for positron emission tomography (PET), but their application to Compton cameras should be further explored. Whole gamma imaging (WGI) is a combination of PET and a Compton camera realized by inserting a scatter detector ring into a PET ring. In a previous study, we developed a WGI prototype in which the scatter detector consists of Gd3Al2Ga3O12:Ce (GAGG) scintillators coupled with SiPM for a proof-of-concept. However, its Compton imaging performance was not as good as its PET imaging performance. In this paper, we developed a two-layer staggered GAGG scatter detector which was optimized for WGI. GAGG crystals 1.45×1.45×4.5 mm3 in size were arranged into a 13×13 array for the 1st layer and a 14×14 array for the 2nd layer with a staggered arrangement. The two-layer crystal block was optically coupled to an 8×8 SiPM array (3 mm pixel). Using radioactive sources with different energies, we investigated the energy resolution performance experimentally. Almost all crystals were clearly separated in the flood histogram at multiple energies. The developed detector showed energy resolutions of 7.7% to 8.5% at 511 keV, which was better than that of the detector of the current WGI prototype. The next generation WGI system was modeled in simulations using the obtained energy resolution data. The simulation results showed that the WGI with the developed detector had 1.2 times better sensitivity and better angular resolution in the peripheral region than the current WGI prototype.

我々が開発を進めているWGI(Whole Gamma Imaging)は、散乱検出器リングを吸収検出器リングへ挿入することでPETとコンプトンイメージングを融合した構造となっており、様々なガンマ線の利用を目指している。また、これまでに開発したWGI試作機は、コンプトンイメージング装置としては世界初のフルリング型ジオメトリを実現したものであった。ここで、コンプトン画像再構成の条件に着目すると、理論的にはフルリング型である必要性はなく、検出器を削減できれば設計の柔軟性向上や、コスト削減が期待できる。しかしながら、実際には散乱角度の検出限界やブロック型検出器の配置方法などの影響で、再構成条件は保証されていない。そこで、本研究では、WGI試作機の89Zr円柱ファントム測定データに対し、後処理によって検出器を制限し、909keVのコンプトン画像のアーチファクトを評価することで3次元画像再構成に必要なジオメトリ条件の検討を行った。その結果、散乱検出器、吸収検出器共に、測定対象上のすべての領域を180°以上囲うことが必要であると示唆された。, 第61回日本核医学会学術総会

膵がんは生存率が低く、有効な診断・治療法の開発が望まれる。我々はこれまでに、1 cm未満の早期膵がん同所移植モデルにおいて、64Cu標識抗EGFR抗体（セツキシマブ）腹腔投与を用いた高分解能開放型PET（OpenPET）ガイド手術により、早期膵がんを的確に検出し切除できることを報告してきた。本発表では、より浸潤の進んだ>1cmの膵がん同所移植モデルを作成しOpenPETガイド手術を実施し、術中残存膵がん切除における本法の有用性を検討した。【方法・結果】ヒト膵がんxPA-1-RFP細胞液をマウス膵臓に移植しモデルを作成した。64Cu-セツキシマブ（7.4 MBq）を腹腔投与し24h後リアルタイムOpenPETガイド手術を行った。本法より肉眼では検出できない約3mmの膵臓内微小残存膵がんを術中で明瞭に検出し摘出できた。また、OpenPETガイド手術は従来の肉眼による手術に比べ、生存を有意に延長した。【結論】本法は、腫瘍の術中残存を防ぎ、膵がんの生存率改善に寄与すると期待される。, 第61回日本核医学会学術総会

Purpose Early management is crucial for acute intestinal blood flow disorders; however, no published study has identified criteria for the time limit for blood flow resumption. This study specifically examines the time factors for avoiding intestinal resection. Methods The subjects of this retrospective cohort study were 125 consecutive patients who underwent emergency surgery for a confirmed diagnosis of intestinal strangulation (n = 86), incarceration (n = 27), or volvulus (n = 12), between January 2015 and March 2021. Intestinal resection was performed when intestinal irreversible changes had occurred even after ischemia was relieved surgically. We analyzed the relationship between the time from computed tomography (CT) imaging to the start of surgery (C-S time) and intestinal resection using the Kaplan–Meier method and calculated the estimated intestinal rescue rate. Patient background factors affecting intestinal resection were also examined. Results The time limit for achieving 80% intestinal rescue rate was 200 min in C-S time, and when this exceeded 300 min, the intestinal rescue rate dropped to less than 50%. Multivariate analysis identified the APACHE II score as a significant influencing factor. Conclusion A rapid transition from early diagnosis to early surgery is critical for patients with acute abdomen originating from intestinal blood flow disorders. The times from presentation at the hospital to surgery should be reduced further, especially for severe cases.

Breast-dedicated PET systems are categorized into two geometries: a ring-shaped detector arrangement and a dual flat-panel (FP) detector arrangement. Although there are some advantages in the FP arrangement, PET images are blurred due to the limited angular coverage. To compensate for this issue, we have proposed a dual round-edge (RE) detector arrangement, in which detectors at both edge positions are tilted toward the center of the field-of-view. In this study, for a proof-of-concept of the RE arrangement, we developed the first bench-top prototype. Our original crosshair light-sharing (CLS) depth-of-interaction (DOI) detector was used; it consisted of a 14×14 array of 1.45×1.45×15 mm3 GFAG scintillator crystals coupled with an 8×8 array of silicon photomultipliers each with a photosensitive area of 3.0×3.0 mm2. The data acquisition system was the TOFPET2 ASIC (PETsys Electronics). We examined the conventional FP arrangement and the proposed RE arrangement using 32 CLS detectors. A 22Na point source and a multi-rod phantom (rod diameters: 1.6, 2.2, 3.0, 4.0, 5.0 and 6.0 mm) were used for spatial resolution measurements. The RE arrangement showed better spatial resolution compared with the FP arrangement (64% improvement in the vertical direction). For the multi-rod phantom, in the coronal plane (parallel to the detector surface), the 1.6 mm rods were clearly resolved in both arrangements. However, in the axial plane (perpendicular to the detector surface), the RE arrangement resolved the 2.2 mm rods that had not been resolved by the FP arrangement. We demonstrated that the proposed RE detector arrangement showed better spatial resolution than the conventional FP arrangement., 2021 IEEE NSS/MIC

Once a high-resolution PET detector with both depth-of-interaction and time-of-flight capabilities is established, it will be applied to various-type PET systems using a software-based coincidence method. Toward this goal, we have developed a crosshair light-sharing (CLS) detector. In this work, as the first development of a practical system based on the CLS detector, we realized a high-resolution portable small animal PET with a long axial field-of-view (FOV) of 20 cm. The system was composed of 128 CLS detectors. All devices were mounted on a pushcart, and the system was operated on a 100V power supply. The axial FOV was 207 mm, which covered the total-body of a rat. A 22Na ultra-micro hot phantom was used for spatial resolution measurement, and the NEMA NU4 image quality phantom was used for image quality test. The developed CLS-PET system successfully resolved 0.75 mm rods. Subsequently, normal mouse and rat imaging with 18F-NaF and 18F-FDG were demonstrated. For the NaF-PET, mouse and rat total-body images were obtained, and detailed bone structures were clearly imaged. For the mouse FDG-PET, cardiac FDG uptakes were clearly visualized by the CLS-PET system. In conclusion, the CLS-PET system achieved, 2021 IEEE NSS/MIC

We developed a whole gamma imaging (WGI) prototype composed of a scatterer ring insert and an absorber ring. It was the world’s first realization of a full-ring Compton camera geometry. In this study, we focused on the data sufficiency condition (DSC) for Compton image reconstruction. Contrary to PET which requires a full-ring geometry to satisfy the DSC, Compton imaging does not require a full ring theoretically. Reducing the detector-ring coverages can improve flexibility of the geometry design and reduce manufacturing costs although sensitivity is decreased. However, the DSC for reconstruction is not guaranteed in a practical situation due to actual absorber ring arrangement and detection limits in scattering angle. In this study, we experimentally assessed the DSC for the angular coverages. We evaluated image artifacts on reconstructed Compton images because, in general, images distort and exhibit artifacts when the DSC is not satisfied, degrading quantitative accuracy. We measured a cylindrical phantom filled with 89Zr solution of 10.2 MBq by the WGI prototype for 60 min and extracted 909-keV Compton events. We selected events related to the detector blocks marked as available to change detector angular coverages defined for the phantom bottom point. First, we changed the number of detectors in the scatterer ring, keeping the full-ring absorber. Next, we changed the absorber ring angular coverage by changing the number of detectors, keeping the scatterer ring at the number where the angular coverage just exceeded 180°. As a result, when the angular coverage of the scatterer detector was less than 180°, reconstructed images exhibited artifacts. The absorber ring detector with less than 180° coverage showed artifacts when used with the scatterer detector with more than 180° coverage. We concluded that angular coverages of more than 180° for both the scatterer and absorber detectors against any region on a subject are the DSC for Compton image reconstruction., IEEE NSS MIC 2021

昨年の発表では，我々が開発を進めているWGI(Whole Gamma Imaging) の小動物実証機におけるコンプトンイメージングによって，高精細なマウス画像が得られたことを報告した．高精細な画像が得られた要因の一つとして，WGI がフルリング型であることが考えられるが，実際にどの程度寄与しているのか明らかにはなっていない．そこで，本研究では，画像再構成に利用する測定データを限定し，フルリングの場合と比較することで，物体を囲むリングの範囲の変化が再構成画像へ与える影響を検討した．円筒型ファントムの測定データを用い，再構成画像を視覚的に評価した結果，散乱検出器に囲まれる範囲が180°未満の領域が物体にある場合，画像にアーチファクトが生じたが，物体全域が180°以上囲まれている場合には，フルリングと同様にアーチファクトのない画像が得られた．よって，WGI コンプトン画像再構成の完全性条件として，対象視野全域を180°以上囲む必要があることが示唆された．, 第40回日本医用画像工学会大会

Coincidence timing resolution (CTR) is an important parameter in clinical positron emission tomography (PET) scanners to increase the signal-to-noise ratio of PET images by using time-of-flight (TOF) information. Lutetium (Lu) based scintillators are often used for TOF-PET systems. However, the self-radiation of Lu-based scintillators may influence the image quality for ultra-low activity PET imaging. Recently, a gadolinium fine aluminum gallate (Ce:GFAG) scintillation crystal that features a fast decay time (∼55 ns) and no self-radiation was developed. The present study aimed at optimizing the GFAG crystal surface treatment to enhance both CTR and energy resolution (ER). The TOF-PET detector consisted of a GFAG crystal (3.0 × 3.0 × 20 mm3) and a SiPM with an effective area of 3.0 × 3.0 mm2. The timing and energy signals were extracted using a high-frequency SiPM readout circuit and then were digitized using a CAMAC DAQ system. The CTR and ER were evaluated with nine different crystal surface treatments such as partial saw-cut and chemical polishing and the 1-side saw-cut was the best choice among the treatments. The respective CTR and ER of 202 ± 2 ps and 9.5 ± 0.1% were obtained with the 1-side saw-cut; the other 5-side mechanically polished GFAG crystals had respective values which were 18 ps (9.0%) and 1.3% better than those of the all-side mechanically polished GFAG crystal. The chemically polished GFAG crystals also offered enhanced CTR and ER of about 17 ps (8.2%) and 2.1%, respectively, over the mechanically polished GFAG crystals.

[Objectives] 18F-FDG PET is useful for diagnosis of breast cancer. Compared to whole-body imaging, local breast imaging with a dedicated PET system can more clearly visualize the extent of the primary breast tumor and axillary lymph nodes metastasis. Breast-dedicated PET systems are categorized into two geometries: a ring-shaped detector arrangement and a dual flat-panel detector arrangement. Although the flat-panel system allows imaging axillary lymph nodes from a similar view as X-ray mammography, PET images are blurred (i.e. spatial resolution is degraded) in the direction perpendicular to the detectors due to the limited angular coverage. To compensate for this issue, we proposed a dual round-edge detector arrangement, in which the detector blocks at both edge positions were tilted toward the center of the field-of-view (FOV). The proposed detector arrangement is expected to reduce image blurring and improve spatial resolution while keeping the advantages of the dual panel arrangement. For a proof of concept, we developed a small prototype and evaluated the spatial resolution. [Methods] We used the crosshair light-sharing (CLS) detectors which had depth-of-interaction (DOI) and time-of-flight (TOF) measurement capabilities*. A 14×14 array of 1.45×1.45×15 mm3 GFAG scintillator was coupled with an 8×8 array of silicon photomultipliers (SiPMs) each with a photosensitive area of 3.0×3.0 mm2. DOI was digitalized into three bins. The data acquisition system was the TOFPET2 ASIC (PETsys Electronics), which was designed to digitize energy and time signals from photo sensors. The small prototype was composed of 32 detector blocks. We examined the conventional flat-panel arrangement and our proposed round-edge arrangement. A 22Na Derenzo-like multi-rod phantom (rod diameters: 1.6, 2.2, 3.0, 4.0, 5.0 and 6.0 mm) was used for spatial resolution measurement. The phantom was measured (90 min) in the two directions (coronal and axial planes) at the center of the FOV. [Results] In the coronal plane, the 1.6 mm rods were clearly resolved in both arrangements. In the axial plane, the round-edge arrangement significantly improved the spatial resolution compared with the flat-panel arrangement. While the conventional flat-panel arrangement could not resolve the 3.0 mm rods, the proposed round-edge arrangement resolved the 2.2 mm rods. [Conclusion] The proposed dual round-edge detector arrangement showed better spatial resolution than the conventional flat-panel arrangement while keeping the geometrical advantage for the breast PET imaging. (*Yoshida, et al. A crosshair light sharing PET detector with DOI and TOF capabilities using four-to-one coupling and single-ended readout. IEEE TRPMS 2020.), SNMMI 2021 Annual Meeting

The quality and uniformity of positron emission tomography (PET) images can be improved significantly using a PET scanner, which has both time-of-flight (TOF) and depth-of-interaction (DOI) capabilities. We have already developed a DOI dual-end detector using segmented crystal bars by applying a subsurface laser engraving (SSLE) technique, and the DOI was determined by the ratio of the detected light between two readouts using the Anger calculation. In this study, we investigated the influence of the number of DOI segments on the performance of DOI identification and the coincidence timing performance of the detector. The detector consisted of a single lutetium fine silicate (LFS) crystal bar (3 × 3 × 20 mm3) with various numbers of DOI segments that were made by applying the SSLE technique and Hamamatsu silicon photomultiplier (SiPM) modules. The maximum number of DOI segments was six, and the SiPM module included one hundred forty-four 4 mm × 4 mm SiPM readouts. The coincidence resolving time (CRT) of each DOI segment was obtained from the side irradiation of the dual-end detector. All DOI segments of the detector with 2, 3, 4, 5 or 6 DOI segments were clearly identified, and average energy resolutions of 9.8 ± 0.5% and 12.5 ± 1.4% were obtained at the 511 keV photo peak for the detectors with 2 DOI and 6 DOI segments, respectively. The minimum and maximum estimated CRT of 180 ± 6 ps and 236 ± 6 ps were obtained for the detectors with 2 DOI and 6 DOI segments, respectively. Insignificant differences were observed between the CRT values of different segments of one detector. Greater CRT values were obtained for detectors with larger DOIs. The results of this study prove that there is a high potential for segmented crystal bars using the SSLE technique as a good candidate for PET scanners with TOF and DOI capabilities, which can significantly improve the quality of PET images.

Previously, we had developed a four-layered depth-of-interaction (DOI) PET detector based on the light sharing method. Reflectors , which were inserted in every two lines of crystal segments and shifted differently for each layer, projected 3D crystal positions onto a 2D position histogram without any overlapping after applying the Anger-type calculation. The best crystal separation we ever obtained was for the four-layered 32 × 32 array of LYSO crystals sized at 1.45 × 1.45 × 5 mm3. However, assembling small crystals tended to cost a lot, and fine tuning of the front-end circuit was required to get fine crystal identification. In this paper, therefore, we proposed a more practical four-layered DOI detector. Its key concept was that the crystals in the top layer, which have the highest detection efficiency, are the biggest contributors to the PET spatial resolution. We applied two new ideas: (1) using quarter size crystals only for the first (top) layer and (2) inserting a thin light guide between the first and the second layers of the crystal array. In the developed prototype detector, we used 24 × 24 LYSO crystals of quarter size (1.4 × 1.4 × 5.0 mm3) in the first layer and the other layers were 12 × 12 arrays of crystals of 2.8 × 2.8 × 5.0 mm3. For better crystal identification of small crystals in the first layer, we optimized the optical condition between crystals by using an optical adhesive and air. Also, the thin light guide of 0.5 mm thickness was inserted between the first and the second layers for improvement of crystal identification of the first layer. With the appropriate insertion of the light guide, all crystals of the first layer were identified as well as the crystals in the other layers. Our developed four-layered DOI detector showed good potential for high spatial resolution without a large increase in the number of crystals.

This work presents a simulation study evaluating relative biological effectiveness at 10% survival fraction (RBE10) of several different positron-emitting radionuclides in heavy ion treatment systems, and comparing these to the RBE10s of their non-radioactive counterparts. RBE10 is evaluated as a function of depth for three positron-emitting radioactive ion beams (10C, 11C and 15O) and two stable ion beams (12C and 16O) using the modified microdosimetric kinetic model (MKM) in a heterogeneous skull phantom subject to a rectangular 50 mm × 50 mm × 60 mm spread out Bragg peak. We demonstrate that the RBE10 of the positron-emitting radioactive beams is almost identical to the corresponding stable isotopes. The potential improvement in PET quality assurance image quality which is obtained when using radioactive beams is evaluated by comparing the signal to background ratios of positron annihilations at different intra- and post-irradiation time points. Finally, the incidental dose to the patient resulting from the use of radioactive beams is also quantified and shown to be negligible.

[Purpose] Breast-dedicated PET systems are categorized into two types: a ring-shaped detector arrangement and a dual (top and bottom) flat-panel detector arrangement. Although the flat-panel system allows imaging axillary lymph nodes from the same view as X-ray mammography, PET images are blurred (i.e. spatial resolution is degraded) along the direction connecting the detectors (defined as Z direction) due to the limited angular coverage. To compensate for this issue, we proposed a third type, a dual round-edge detector arrangement. The “round-edge” is a geometry in which the detector blocks at both edge positions were tilted toward the center of the field-of-view (FOV). For proof of concept, we developed a small prototype and evaluated the spatial resolution. [Methods] The prototype was composed of 32 detector blocks (Top and bottom pairs of 2 rows × 8 columns). A 14×14 array of 1.45×1.45×15 mm3 GFAG scintillator was coupled with an 8×8 array of silicon photomultiplier (SiPM) with a photosensitive area of 3.0×3.0 mm2. A 22Na Derenzo-like multi-rod phantom (rod diameters: 1.6, 2.2, 3.0, 4.0, 5.0 and 6.0 mm) was used for spatial resolution measurement. The phantom was measured in the two directions (XY plane and XZ plane) at the center of the FOV. The flat-panel arrangement was also examined for comparison. [Results] In the XY plane, the 1.6 mm rods were clearly resolved in both arrangements. In the XZ plane, the round-edge arrangement significantly improved the spatial resolution compared with the flat-panel arrangement. While the flat-panel arrangement could not resolve the 3.0 mm rods, the round-edge arrangement clearly resolved the 2.2 mm rods. [Conclusion] We have demonstrated the dual round-edge detector arrangement can provide a better spatial resolution than the conventional flat-panel arrangement., 第121回日本医学物理学会学術大会

[Purpose] Compton imaging has been expected to be realized as collimator-less SPECT, but it has not yet been put to practical use in the field of nuclear medicine. Last year, in contrast, we had succeeded in obtaining 909-keV Compton images with a quality approaching that of PET in a mouse experiment using the whole gamma imaging (WGI) prototype. In this study, therefore, we aimed at experimentally identify the factors behind this success. [Method] The WGI prototype was composed of an absorber ring with 4-layer DOI detectors of 2.8×2.8×7.5 mm3 GSO crystals and a scatterer ring with non-DOI detectors of 0.9×0.9×6.0 mm3 GAGG crystals. We measured a cylindrical phantom with a 38 mm diameter filled with a 89Zr solution of 10.2 MBq by the WGI prototype for 60 min. We also measured a mouse placed at a close position to the upper side of the scatterer ring for 60 min, 22 hours after injection of 9.8 MBq 89Zr oxalate. To compare with the full-ring geometry, we simulated partial scatterer ring geometries with various angular coverage by limiting the number of the scatterer detectors used in the ring direction. Image artifacts in reconstructed images were visually evaluated. [Results] Strong streaking artifacts appeared in the direction from the scatterer detector toward the subjects when only one detector was used in the scatterer ring. The more the scatterer detectors covered, the better the streaking artifacts mitigated. We found that, when the cylindrical phantom was covered by more than 180° with the scatterer detectors, the streaking artifact was suppressed, and the shape of the cylinder was reproduced equivalently to the full-ring geometry. In the mouse imaging case, we also found that the streaking artifacts were suppressed when the subjects were covered more than 180° by the scatterer detectors. [Conclusion] We experimentally showed that it is necessary to cover the field-of-view with more than 180° with the scatterer detector to achieve accurate 3D Compton images., 第121回日本医学物理学会学術大会

我々は，PETとコンプトンイメージングの同時測定を可能とするWGIの開発を進めている．そして，2種類の異なる測定イベントを組み合わせることが可能なハイブリッド画像再構成手法を開発した．本手法を応用し，PETでは測定できないシングルガンマ線を組み合わせることによる高画質化，及び，開放部を設けた部分リング型装置を構成した際にPETのみでは避けられないアーチファクトの低減が可能であることを示した．, 医用画像研究会（MI） JAMITフロンティア2021

This work presents an iterative method for the estimation of the absolute dose distribution in patients undergoing carbon ion therapy, via analysis of the distribution of positron annihilations resulting from the decay of positron-emitting fragments created in the target volume. The proposed method relies on the decomposition of the total positron-annihilation distributions into profiles of the three principal positron-emitting fragment species - 11C, 10C and 15O. A library of basis functions is constructed by simulating a range of monoenergetic 12C ion irradiations of a homogeneous polymethyl methacrylate phantom and measuring the resulting one-dimensional positron-emitting fragment profiles and dose distributions. To estimate the dose delivered during an arbitrary polyenergetic irradiation, a linear combination of factors from the fragment profile library is iteratively fitted to the decomposed positron annihilation profile acquired during the irradiation, and the resulting weights combined with the corresponding monoenergetic dose profiles to estimate the total dose distribution. A total variation regularisation term is incorporated into the fitting process to suppress high-frequency noise. The method was evaluated with 14 different polyenergetic 12C dose profiles in a polymethyl methacrylate target: one which produces a flat biological dose, 10 with randomised energy weighting factors, and three with distinct dose maxima or minima within the spread-out Bragg peak region. The proposed method is able to calculate the dose profile with mean relative errors of 0.8%, 1.0% and 1.6% from the 11C, 10C, 15O fragment profiles, respectively, and estimate the position of the distal edge of the SOBP to within an average of 0.7 mm, 1.9 mm and 1.2 mm of its true location.

The goal of whole gamma imaging (WGI) is to utilize all detectable gamma rays from radioactive decays for imaging. By inserting a scatterer ring into a PET ring, the WGI detects not only 511 keV annihilation photons of positron emitters but also single gamma rays with various energies as Compton events. The Compton events include one photon of a pair of the annihilation photons in that the other photon is not detected, as well as a single gamma-ray photon emitted from a non-pure positron emitter. To realize the WGI concept, it is necessary to develop an image reconstruction method combining the two different types of events. In this study, therefore, we developed a hybrid image reconstruction algorithm which utilized PET and Compton events efficiently in each iteration based on the list-mode ordered subset expectation maximization framework. For each sub-iteration of the proposed algorithm, a weighted sum of update images individually calculated for PET and Compton events was used as an update image. To demonstrate the effectiveness, we used our WGI prototype to measure a contrast phantom filled with a 89Zr solution of 9.4 MBq having a hot to background ratio of 4:1. We extracted 511 keV PET events and 909 keV Compton events by setting different energy windows in software-based coincidence detection. Reconstructed images obtained using both PET and Compton events were compared with those using PET events only and those using Compton events only. The contrast recovery against background variability for each iteration was used as a figure of merit. The results showed the image reconstructed using both PET and Compton events had better image contrast compared with other images.

Compton imaging or Compton camera imaging has been studied well, but its advantages in nuclear medicine and molecular imaging have not been demonstrated yet. Therefore, the aim of this work was to compare Compton imaging with positron emission tomography (PET) by using the same imaging platform of whole gamma imaging (WGI). WGI is a concept that combines PET with Compton imaging by inserting a scatterer ring into a PET ring. This concept utilizes diverse types of gamma rays for 3D tomographic imaging. In this paper, we remodeled our previous WGI prototype for small animal imaging, and we developed an image reconstruction method based on a list-mode ordered subset expectation maximization algorithm incorporating detector response function modeling, random correction and normalization (sensitivity correction) for either PET and Compton imaging. To the best of our knowledge, this is the world’s first realization of a full-ring Compton imaging system. We selected 89Zr as an imaging target because a 89Zr nuclide emits a 909 keV single-gamma ray as well as a positron, and we can directly compare Compton imaging of 909 keV photons with PET, a well-established modality. We measured a cylindrical phantom and a small rod phantom filled with 89Zr solutions of 10.3 MBq and 10.2 MBq activity, respectively, for 1 h each. The uniform radioactivity distribution of the cylindrical phantom was reconstructed with normalization in both PET and Compton imaging. Coefficients of variation for region-of-interest values were 4.2% for Compton imaging and 3.3% for PET; the difference might be explained by the difference in the detected count number. The small rod phantom experiment showed that the WGI Compton imaging had spatial resolution better than 3.0 mm at the peripheral region although the center region had lower resolution. PET resolved 2.2 mm rods clearly at any location. We measured a mouse for 1 h, 1 d after injection of 9.8 MBq 89Zr oxalate. The 89Zr assimilated in the mouse bony structures was clearly depicted, and Compton imaging results agreed well with PET images, especially for the region inside the scatterer ring. In conclusion, we demonstrated the performance of WGI using the developed Compton image reconstruction method. We realized Compton imaging with a quality approaching that of PET, which is supporting a future expectation that Compton imaging outperforms PET.

A female septuagenarian had poorly controlled diabetes mellitus for more than 20 years. She had persistent pyuria, but did not seek further examination. In 2019, she was transported to our hospital by ambulance for sudden abdominal pain. Physical examination showed a sign of panperitonitis with sepsis. Computed tomography showed ascites and intraperitoneal free air. In addition, there was also a defect in the bladder wall, suggesting bladder rupture. Blood tests showed a marked increase in serum creatinine in addition to increased inflammatory reactants. Because perforation of gastrointestinal tract could not be excluded, an emergency laparotomy was performed. An intraperitoneal perforation of the posterior wall of the bladder was revealed, though there was no intestinal damage. The bladder wall was repaired and cystostomy was performed followed by irrigation and drainage of the abdominal cavity. After the operation, her abdominal symptom resolved and her general status improved. We speculated that voiding disturbance due to neurogenic bladder associated with diabetes mellitus and chronic infection caused the spontaneous bladder rupture. Most cases of spontaneous bladder rupture are associated with a history of pelvic surgery or irradiation, which suggests that this case is extremely rare. In patients with repeated urinary tract infection and underlying disease affecting bladder function, evaluation and appropriate management of bladder dysfunction should be performed ; otherwise, spontaneous bladder rupture may occur.

We investigated the adsorption of lipoteichoic acid (LTA) on titanium surfaces by using the quartz crystal microbalance (QCM) method, and confirmed the influence of mucin (MUC) pre-adsorption on LTA adsorption. Two injection methods were evaluated. Namely, Method A: single-step injection of LTA solution to the Ti sensor, and Method B: MUC solution was injected to the Ti sensor followed by LTA injection on the MUC pre-adsorbed surface. QCM measurement revealed that the adsorbed amount of LTA by Method A was low and constant regardless of the increase in LTA concentration. In contrast, the adsorption amount of LTA in Method B increased according with increasing concentration of LTA and was significantly higher than that of Method A. The hydrophobic surface after MUC pre-adsorption was presumed to contribute to the enhancement of LTA adsorption. Our results revealed that MUC pre-adsorption to Ti is necessary for LTA adsorption in living tissue.

In this paper, to further understand the bending failure mechanism of a bridge footing subjected to lateral seismic loading, the effect of pile arrangement on the bending performance of a footing is mainly investigated by parametric analysis. The pile location can considerably affect the bending failure pattern of the footing by constraining the extent of yielding of footing top bars. The piles placed at the center of the sides parallel to the loading direction can constrain the extent of yielding of the top bars in the loading direction. Similarly, the piles at the center of the sides perpendicular to the loading direction can constrain the extent of yielding of the top bars in the other direction. The center pile can constrain the extent of yielding of the top bars in two directions. Additionally, based on the analytical results of the parametric analysis, the application condition of the current beam theory-based design method expected to accurately evaluate the footing bending capacity is discussed from the aspect of pile spacing.

Datacenter networks are constructed of high speed networks, such as 40Gbps Ethernet, and quite severe communication quality, low latency and high throughput, is required from applications. RDMA (Remote Direct Memory Access) is now a hot topic in datacenter networking because it can operate high speed data transmission without TCP/IP protocol overhead. DCQCN (Datacenter Quantized Congestion Notification) has been proposed as congestion control for RDMA over Ethernet. In this paper, we reveal with our preliminary evaluation for DCQCN that 1) byte counter behavior causes fairness issues, 2) parameter setting of small timer for time counter and large byte counter makes time counter a dominant factor in rate increase algorithm, and 3) time counter behavior which is independent of transmission rate resolves fairness issues. And we also show that DCQCN has a technical problem of delaying transition timing to Hyper-Active Increase phase due to large byte counter setting, which causes slow convergence to the desirable transmission rate. We propose a new setting for byte counter in DCQCN so that its interval of counter increment is independent of transmission rate. This algorithm, named Adaptive Byte Counter DCQCN (ABCDCQCN), enables shorter interval of byte counter increment and can resolve both fairness issue and fast convergence of transmission rate.

Brain PET, which has led research in molecular imaging and diagnosis of brain cancer, epilepsy and neurodegenerative disorders, is being spotlighted again to promote earlier diagnosis of dementia with the advent of amyloid and tau tracers. To meet this demand, in this paper, we developed a brain-dedicated PET imaging device with a hemispherical detector arrangement, which provides comparable sensitivity with fewer detectors than conventional cylindrical geometries. The introduction of the time-of-flight (TOF) measurement capability was a key point for the development to get a gain in the image signal-to-noise ratio. Currently, whole-body PET scanners with around 200-400 ps coincidence resolving time (CRT) are commercially available. In order to obtain the same TOF gain which can be obtained with 400 ps CRT for a 30 cm diameter object, 267 ps CRT will be required for a 20 cm diameter object such as the human head. In this work, therefore, we aimed at developing a TOF brain-dedicated PET prototype with the hemisphere detector arrangement and the CRT faster than 267 ps. The detector was composed of a 12 × 12 lutetium fine silicate (LFS) array coupled with a 12 × 12 multi-pixel photon counter (MPPC) array. Each LFS crystal with a size of 4.14 × 4.14 × 10 mm3 was individually coupled to a separate MPPC. Singles list-mode data from each detector were stored, and coincidences were identified using a coincidence-detection software algorithm. The CRT of 245 ps was finally achieved as the system average after a fine timing correction. For image reconstruction, we implemented the list-mode TOF-OSEM. For a small rod phantom, rods of 3 mm diameter were clearly separated. Also, images of the 3D Hoffman brain phantom, which demonstrated clear contrast between gray and white matter, supported the effect of TOF information.

In heavy-ion therapy, the stopping position of primary ions in tumours needs to be monitored for effective treatment and to prevent overdose exposure to normal tissues. Positron-emitting ion beams, such as

Finding the valuable data among huge amount of data is too laborious due to the human limitation on perception capability. Reversely, pushed data about a service must miss the point without understanding user's demand. So, our base idea is to collect profiles of users and providers, and to match the user's demand with the providers' service. In this paper, we propose a communication framework for agents to find friend-agents and to share events in place of the client. Concretely we propose two-stage protocols, that is, profile sharing and event sharing. Thereby, only significant events can be shared in real time since friend-agents already have logical linkage. We verify that the latency to convey the valuable event to the receiver can be reduced. Finally, we discuss the structure of the profile data, and shows that required load for word matching can be saved by the hierarchical structure.

Persistent memory (PM) is an emerging memory device that has a larger capacity and lower cost per gigabyte than conventional DRAM. Intel has released a first PM product called Optane™ DC Persistent Memory, but its performance is several times lower than that of DRAM. Therefore, it will be used in combination with DRAM to configure hybrid memory systems that can obtain both the high performance of DRAM and large capacity of PM.In this paper, we evaluate and analyze the performance interference between various types of processes that are concurrently executed on a real server platform having a hybrid memory system. Through the evaluation with a synthetic benchmark, we show that the interference on the hybrid memory system is significantly different from that on a conventional DRAM-only memory system.

Recently, silicon photomultipliers (SiPMs) have become established as photo-sensors for PET scanners. Commercially available SiPM arrays are typically about 3–4 cm in size. In order to develop larger detectors with an Anger calculation, multiple SiPM arrays need to be combined. This configuration requires the use of a light guide and has inactive areas between SiPM arrays. If not addressed, crystal identification degrades not only for peripheral crystals but also for crystals to bridge the gap between the SiPM arrays. On the other hand, we have developed the crosshair light-sharing (CLS) PET detector, which is based on a single-ended readout scheme with roughly quadrisected crystals comparable in size to a SiPM, with depth-of-interaction (DOI) capability. The CLS PET detector based on the local centroid calculation was expected to mitigate the edge effect similar to what the one-to-one coupling detector is able to do. In this work, we developed the axially long CLS PET detector with two multipixel photon counter (MPPC) arrays. The proposed long CLS PET detector consisted of 30 × 14 gadolinium fine aluminum garnet (GFAG) arrays coupled to two 8 × 8 MPPC arrays without the light guide. From 511-keV uniform irradiation, responses of all crystal elements could be separated clearly on a 2D position histogram after applying the Anger calculation. Pulse heights of additional crystals to bridge the gap were 18% lower than those of crystals at the center of the MPPC array, but similar to that of the peripheral crystals based on non-uniformity of the MPPC array. On the other hand, energy resolutions of additional crystals to bridge the gap were almost the same to those of other crystals. The long CLS PET detector promises improvement of the packing fraction while keeping performance.

The depth-of-interaction detector which can identify gamma-ray detection position along the depth direction is essential for a PET scanner to reduce parallax error. The X’tal cube we have developed is composed of a scintillation crystal block segmented into cubes. Six arrays of multipixel photon counters (MPPCs) cover six surfaces of the crystal block. We developed the new X’tal cube consisting of 0.77 mm cubic segments. A (13.1 mm)3 LYSO crystal block had 3-D segmentation in a ${17 \times 17 \times 17}$ array fabricated by the laser engraving technique. $ {4 \times 4}$ MPPC arrays with a size of (13 mm)2 were used. Active area of each MPPC was (3.0 mm)2. To evaluate segment identification performance, we irradiated with gamma-rays from a 22Na source and obtained a 3-D position histogram made by the 3-D Anger-type calculation with all MPPC signals. The histogram showed 17 segments in a row can be identified clearly. Further, to measure its intrinsic spatial resolution with incident angles of 0° and 45°, gamma-rays in a fan-beam were irradiated and scanned onto the X’tal cube. Spatial resolutions of 0.74 ± 0.10 mm and 0.89 ± 0.10 mm were obtained by both scan experiments, respectively.

Peritoneal dissemination is a common cause of death from gastrointestinal cancers and is difficult to treat using current therapeutic options, particularly late-phase disease. Here, we investigated the feasibility of integrated therapy using 64Cu-intraperitoneal radioimmunotherapy (ipRIT), alone or in combination with positron emission tomography (PET)-guided surgery using a theranostic agent (64Cu-labeled anti-epidermal growth factor receptor antibody cetuximab) to treat early- and late-phase peritoneal dissemination in mouse models. In this study, we utilized the OpenPET system, which has open space for conducting surgery while monitoring objects at high resolution in real time, as a novel approach to make PET-guided surgery feasible. 64Cu-ipRIT with cetuximab inhibited tumor growth and prolonged survival with little toxicity in mice with early-phase peritoneal dissemination of small lesions. For late-phase peritoneal dissemination, a combination of 64Cu-ipRIT for down-staging and subsequent OpenPET-guided surgery for resecting large tumor masses effectively prolonged survival. OpenPET clearly detected tumors (≥3 mm in size) behind other organs in the peritoneal cavity and was useful for confirming the presence or absence of residual tumors during an operation. These findings suggest that integrated 64Cu therapy can serve as a novel treatment strategy for peritoneal dissemination.

We have been working on the development of a PET insert for existing magnetic resonance imaging (MRI) systems for simultaneous PET/MR imaging, which integrates radiofrequency (RF)-shielded PET detector modules with an RF head coil. In order to avoid interferences between the PET detector circuits and the different MRI-generated electromagnetic fields, PET detector circuits were installed inside eight Cu-shielded fiber-reinforced plastic boxes, and these eight shielded PET modules were integrated in between the eight elements of a 270-mm-diameter and 280-mm-axial-length cylindrical birdcage RF coil, which was designed to be used with a 3-T clinical MRI system. The diameter of the PET scintillators with a 12-mm axial field-of-view became 255mm, which was very close to the imaging region. In this study, we have investigated the effects of this PET/RF-coil integrated system on the performance of MRI, which include the evaluation of static field (Bo) inhomogeneity, RF field (B1) distribution, local specific absorption rate (SAR) distribution, average SAR, and signal-to-noise ratio (SNR). For the central 170-mm-diameter and 80-mm-axial-length of a homogenous cylindrical phantom (with the total diameter of 200mm and axial-length of 100mm), an increase of about a maximum of 3μT in the Bo inhomogeneity was found, both in the central and 40-mm off-centered transverse planes, and a 5 percentage point increase of B1 field inhomogeneity was observed in the central transverse plane (from 84% without PET to 79% with PET), while B1 homogeneity along the coronal plane was almost unchanged (77%) following the integration of PET with the RF head coil. The average SAR and maximum local SAR were increased by 1.21 and 1.62 times, respectively. However, the SNR study for both spin-echo and gradient-echo sequences showed a reduction of about 70% and 60%, respectively, because of the shielded PET modules. The overall results prove the feasibility of this integrated PET/RF-coil system for using with the existing MRI system.

We have developed a four-layer depth of interaction (DOI) detector with single-side photon readout, in which segmented crystals with the patterned reflector insertion are separately identified by the Anger-type calculation. Optical conditions between segmented crystals, where there is no reflector, affect crystal identification ability. Our objective of this work was to improve crystal identification performance of the four-layer DOI detector that uses crystals segmented with a recently developed laser processing technique to include laser processed boundaries (LPBs). The detector consisted of 2 × 2 × 4 mm 3 LYSO crystals and a 4 × 4 array multianode photomultiplier tube (PMT) with 4.5 mm anode pitch. The 2D position map of the detector was calculated by the Anger calculation method. At first, influence of optical condition on crystal identification was evaluated for a one-layer detector consisting of a 2 × 2 crystal array with three different optical conditions between the crystals: crystals stuck together using room temperature vulcanized (RTV) rubber, crystals with air coupling and segmented crystals with LPBs. The crystal array with LPBs gave the shortest distance between crystal responses in the 2D position map compared with the crystal array coupled with RTV rubber or air due to the great amount of cross-talk between segmented crystals with LPBs. These results were used to find optical conditions offering the optimum distance between crystal responses in the 2D position map for the four-layer DOI detector. Crystal identification performance for the four-layer DOI detector consisting of an 8 × 8 array of crystals segmented with LPBs was examined and it was not acceptable for the crystals in the first layer. The crystal identification was improved for the first layer by changing the optical conditions between all 2 × 2 crystal arrays of the first layer to RTV coupling. More improvement was observed by combining different optical conditions between all crystals of the first layer and some crystals of the second and the third layers of the segmented array.