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Structural changes of the raffinose crystal on dehydration from the pentahydrate to the tetrahydrate were investigated by single-crystal time-of-flight neutron diffraction. It was revealed that during the dehydration, rearrangement occurs in the hydrogen bonds related to the lost water molecule, while the symmetry of the crystal structure is retained. The hydrogen-bonding status of raffinose pentahydrate and tetrahydrate were discussed comprehensively according to Jeffrey's hydrogen-bonding classification. It was shown that the water molecules are hydrogen bonded to the surrounding molecules by moderate O—H...O hydrogen bonds and weak C—H...O hydrogen bonds, and the number of these two types of hydrogen bonds determines the water molecules that are removed by dehydration. The lattice constant c showed a significant decrease on dehydration and further dehydration leads to loss of crystallinity of the raffinose crystals.

Marker-less head motion correction methods have been well-studied; however, no reports discussing potential issues in positional calibration between a PET system and an external sensor remain limited. In this study, we develop a method for positional calibration between the PET system and an external range sensor to achieve practical head motion correction. The basic concept of the developed method involves using the subject's face model as a marker not only for head motion detection but also for the system positional calibration. The face model of the subject, which can be obtained easily using the range sensor, can also be calculated from a computed tomography (CT) image of the same subject. The CT image, which is acquired separately for attenuation correction in PET, has the same coordinates as the PET image because of the appropriate matching algorithm between CT and PET images. The proposed method was implemented in the helmet-type PET and the motion correction accuracy was assessed quantitatively using a mannequin head. The phantom experiments demonstrated the performance of the developed motion correction method; high-resolution images with no trace of the applied motion were obtained as if no motion was provided. Statistical analysis supported the visual assessment results in terms of the spatial resolution, contrast recovery; uniformity, and the results implied that motion with correction slightly improved image quality compared with the motionless case. The tolerance of the developed method against potential tracking errors had a minimum 10% difference in the amplitude of the rotation angle.

Objective The clinical significance of decreased physiological lung uptake of 123I-metaiodobenzylguanidine (MIBG) has not been well investigated. This study aimed to elucidate the association between a decrease in lung MIBG uptake with antidepressant intake and the myocardial MIBG uptake in patients who were clinically diagnosed with Lewy body disease (LBD) and patients who were diagnosed as not having LBD. Methods We retrospectively reviewed the heart and lung uptakes on 167 consecutive MIBG scans, antidepressant status, and clinical diagnosis of LBD. The images were visually classified into two groups: decreased lung uptake and preserved lung uptake. A semi-quantitative analysis was performed using the heart-to-mediastinum ratio (H/M), lung-to-mediastinum ratio (L/M), and myocardial washout rate (WR). Results All 17 patients with decreased lung uptake were on treated with antidepressants, while none of the 150 patients with preserved lung uptake were treated with any antidepressants. Of the 17 patients with decreased lung uptake, 6 patients were clinically diagnosed as LBD and other 11 were clinically diagnosed as non-LBD. There was not significant difference in early H/M, delayed H/M, and myocardial WR between the 11 non-LBD patients with decreased lung uptake and 83 non-LBD patients with preserved lung uptake (2.87 ± 0.69 vs. 2.89 ± 0.44, 3.09 ± 0.48 vs. 2.98 ± 0.59, and 21.8 ± 11.3% vs. 21.1 ± 12.5%, respectively). Moreover, in LBD patients, there were no significant differences in those values between six patients with decreased lung uptake and 67 patients with preserved lung uptake (1.68 ± 0.32 vs. 1.73 ± 0.42, 1.34 ± 0.21 vs. 1.54 ± 0.57, 46.2 ± 22.8% vs. 42.8 ± 21.3%, respectively). Conclusions Antidepressants probably blocked MIBG uptake in the lungs, and a decreased lung uptake was not significantly associated with heart uptake. A remarkable decrease in lung uptake can be a signal to check a patient’s medication status.

2021年8月25日に行われた新春座談会

Purpose To reduce postoperative complications, intraoperative lymph node (LN) diagnosis with 18F-fluoro-2-deoxy-D-glucose (FDG) is expected to optimize the extent of LN dissection, leading to less invasive surgery. However, such a diagnostic device has not yet been realized. We proposed the concept of coincidence detection wherein a pair of scintillation crystals formed the head of the forceps. To estimate the clinical impact of this detector, we determined the cut-off value using FDG as a marker for intraoperative LN diagnosis in patients with esophageal cancer, the specifications needed for the detector, and its feasibility using numerical simulation. Methods We investigated the dataset including pathological diagnosis and radioactivity of 1073 LNs resected from 20 patients who underwent FDG-positron emission tomography followed by surgery for esophageal cancer on the same day. The specifications for the detector were determined assuming that it should measure 100 counts (less than 10% statistical error) or more within the intraoperative measurement time of 30 s. The detector sensitivity was estimated using GEANT4 simulation and the expected diagnostic ability was calculated. Results The cut-off value was 620 Bq for intraoperative LN diagnosis. The simulation study showed that the detector had a radiation detection sensitivity of 0.96%, which was better than the estimated specification needed for the detector. Among the 1035 non-metastatic LNs, 815 were below the cut-off value. Conclusion The forceps-type coincidence detector can provide sufficient sensitivity for intraoperative LN diagnosis. Approximately 80% of the prophylactic LN dissections in esophageal cancer can be avoided using this detector.

Purpose To reduce postoperative complications, intraoperative lymph node (LN) diagnosis with 18F-fluoro-2-deoxy-D-glucose (FDG) is expected to optimize the extent of LN dissection, leading to less invasive surgery. However, such a diagnostic device has not yet been realized. We proposed the concept of coincidence detection wherein a pair of scintillation crystals formed the head of the forceps. To estimate the clinical impact of this detector, we determined the cut-off value using FDG as a marker for intraoperative LN diagnosis in patients with esophageal cancer, the specifications needed for the detector, and its feasibility using numerical simulation. Methods We investigated the dataset including pathological diagnosis and radioactivity of 1073 LNs resected from 20 patients who underwent FDG-positron emission tomography followed by surgery for esophageal cancer on the same day. The specifications for the detector were determined assuming that it should measure 100 counts (less than 10% statistical error) or more within the intraoperative measurement time of 30 s. The detector sensitivity was estimated using GEANT4 simulation and the expected diagnostic ability was calculated. Results The cut-off value was 620 Bq for intraoperative LN diagnosis. The simulation study showed that the detector had a radiation detection sensitivity of 0.96%, which was better than the estimated specification needed for the detector. Among the 1035 non-metastatic LNs, 815 were below the cut-off value. Conclusion The forceps-type coincidence detector can provide sufficient sensitivity for intraoperative LN diagnosis. Approximately 80% of the prophylactic LN dissections in esophageal cancer can be avoided using this detector.

THz electron spin resonance (ESR) measurements of the spinel compound GeCo2O4, which consists of the Co2+ pyrochlore structure, were performed. The temperature dependence measurements revealed new antiferromagnetic phases, AF1 and AF2, below TN. Moreover, a wide magnetic field range of ESR study using a single crystal at 1.8 K also revealed various field-induced phases due to the competition between the spin–lattice coupling and the spin frustration. Critical field resonances were observed at 5.0 T, 8.6 T, and 11.0 T for B//[111] and 5.1 T, 7.7 T, 11.2 T, and 13.0 T for B//[110] at 1.8 K. Although it became difficult to observe ESR above 86 K, the g-values of Co2+ ions were estimated to be g[111] = 3.34 and g[110] = 3.27 for [111] and [110], respectively, from the observed ESR mode above the saturation field at 1.8 K. Detailed frequency-field diagrams of the ESR modes at 1.8 K suggested the existence of spin–lattice coupling energy of 250 GHz (= 1.03 meV = 12 K) at the critical field resonances. The spin gap mode in the frequency-field diagram at 1.8 K showed excitation energies of E[111] = 1004 GHz (= 4.15 meV = 48 K) and E[110] = 1044 GHz (= 4.32 meV = 50 K) for [111] and [110], respectively. These results will be discussed in connection with the di-tetramer model suggested previously.

Positron emission tomography (PET) is useful to detect malignant tumors by imaging glucose or amino acid metabolism. Whole-body PET with the detector arrangement in a large diameter is currently used for brain imaging, however, the detector arrangement in small diameter is better for brain imaging. Stereotactic radiosurgery (SRS) treats brain tumor with maintaining cognitive function. Therefore, it needs more dedicated PET to identify small lesions and their localization. Then, we developed the world's first brain-dedicated PET with detectors arranged in a hemisphere of 28 cm diameter, attaining 2.2 mm in spatial resolution. This development was performed with ATOX CO., LTD and the brain-dedicated PET has been commercialized as VrainTM. Ten normal volunteers (22 - 45 age male) underwent 18FDG-PET using a whole-body PET (Discovery MI, GE) and the brain-PET for 10-min each, which were started 30-min and 45-min after FDG injection, respectively. A phantom with 10-22 diameter hot spheres and background (radioactivity ratio, 4:1) was also acquired by both PET systems, then estimated the radioactivity ratio in case of 2-mm diameter hot sphere. As a results, the inferior colliculus, substantia nigra, red nucleus, and brain stem raphe nucleus were identified with the brain-PET. The inferior colliculus was identified with the whole-body PET, but other nuclei were not. Based on phantom study, it was estimated that radioactivity in a 2-mm diameter sphere was measured with 1.4 - 2.9 times higher contrast than whole-body PET. The substantia nigra and the red nucleus has 5.0-6.0mm in short diameter on MRI T2WI axial image. The raphe nucleus extends laterally to 2.5mm on postmortem brain specimens. We concluded that our brain-dedicated PET can identify approximately 2.5mm diameter tumor clearly and will be particularly useful in SRS.

[Objectives] A PET system can be more efficient in terms of size and cost when it is designed as an organ-dedicated or application-specific system. Considering the potential need for brain PET, we proposed the concept of a hemispherical detector arrangement, which enables higher sensitivity with fewer number of detectors than a conventional cylindrical geometry has. A laboratory benchtop prototype has been evolved into a complete brain PET system, which has been commercialized in Japan under the product name of VrainTM. In this work, we characterize the system and carry out its first human imaging tests. [Methods] The VrainTM has 54 detectors. A hemispherical part is formed by 45 detectors and the other 9 detectors are located at the backside of the neck. Each detector is a one-to-one combination of lutetium-based scintillators (crystal element size: 4.1×4.1×10 mm3) and silicon photomultipliers (SiPMs) (active area size: 4×4 mm2). The inner diameter of the bottom detector ring is 279 mm. The crystal thickness is optimized by simulation to reduce the parallax error and to improve the TOF performance. The energy window is also optimized to 450–590 keV to get better image quality. We evaluated the physical performance of the VrainTM according to the NEMA NU 2-2018 standards. Some measurements were added and others were modified to suit the hemispherical detector arrangement. Finally, we carried out the first healthy volunteer imaging. 18F-FDG of 3.7 MBq/kg was intravenously injected to a male subject (42 years old). The PET measurement duration was 10 min starting at 45 min after injection. PET images were reconstructed using the OSEM with 4 iterations and 8 subsets. A Gaussian filter of 4 mm FWHM was applied to PET images. CT images, which were obtained by another PET/CT scanner, were used for attenuation and scatter corrections. [Results] The 2.2 mm rods of a small rod phantom were resolved. The TOF resolution at the peak noise-equivalent count ratio (NECR) (9.8 kBq/mL) was 256 ps and the TOF gain in sensitivity was calculated as 5.2 (20 cm diameter / 3.8 cm localization accuracy). The effective sensitivity was 21.8 kcps/MBq and the effective peak NECR was 129 kcps at 9.8 kBq/mL. The sensitivity was higher at the upper position in the axial direction. For the brain-sized image quality phantom evaluation, the percent contrast of the 10 mm sphere was 48% with the percent background variability of 8.6%. For the human FDG PET imaging, the whole brain was successfully imaged without any artifacts. Gray and white matters were clearly visualized with a high contrast. [Conclusion] The helmet-type brain PET system VrainTM showed 2.2 mm spatial resolution, 256 ps TOF resolution, and excellent image quality. The brain FDG PET images of the healthy volunteer were high contrast and low noise. Further studies are warranted to assess the potential clinical impact of PET imaging with the VrainTM., SNMMI 2022 Annual Meeting

Objective. For PET imaging systems, a smaller detector ring enables less intrinsic spatial resolution loss due to the photon non-collinearity effect as well as better balance between production cost and sensitivity, and a hemispherical detector arrangement is more appropriate for brain imaging than a conventional cylindrical arrangement. Therefore, we have developed a brain-dedicated PET system with a hemispherical detector arrangement, which has been commercialized in Japan under the product name of VRAINTM. In this study, we evaluated imaging performance of VRAIN. Approach. The VRAIN used 54 detectors to form the main hemispherical unit and an additional half-ring behind the neck. Each detector was composed of a 12 × 12 array of lutetium fine silicate crystals (4.1 × 4.1 × 10 mm3) and a 12 × 12 array of silicon photomultipliers (4 × 4 mm2 active area) with the one-to-one coupling. We evaluated the physical performance of VRAIN according to the NEMA NU 2–2018 standards. Some measurements were modified so as to fit the hemispherical geometry. In addition, we performed 18F-FDG imaging in a healthy volunteer. Main results. In the phantom study, the VRAIN showed high resolution for separating 2.2 mm rods, 229 ps TOF resolution and 19% scatter fraction. With the TOF gain for a 20 cm diameter object (an assumed head diameter), the peak noise-equivalent count rate was 144 kcps at 9.8 kBq ml−1 and the sensitivity was 25 kcps MBq−1. Overall, the VRAIN provided excellent image quality in phantom and human studies. In the human FDG images, small brain nuclei and gray matter structures were clearly visualized with high contrast and low noise. Significance. We demonstrated the excellent imaging performance of VRAIN, which supported the advantages of the hemispherical detector arrangement.

PETを用いた小動物イメージングは創薬や病態解明研究に活用されている。一方で、全ての研究者にPETが十分に行き届いているとは言い難い。例えば、特定エリアでの管理が必要な遺伝子操作マウスのPET撮像、粒子線照射直後のラットのPET撮像、マウスやラットの全身薬物動態の観察、微小腫瘍内の不均一薬剤集積の可視化、限られたスペースへの小動物用PET装置の導入、といった様々なアンメットニーズが存在する。このような多様な研究ニーズに応えるべく、サブミリ分解能を有する多目的用途のポータブル小型PET装置を開発した。 独自に開発した22 mm角のcrosshair light-sharing (CLS) 検出器（1.45×1.45×15 mm3のGFAGシンチレータ14×14アレイと3×3 mm2の半導体光センサSiPM 8×8アレイを接合）を使用した。相互作用を起こした深さによって光の分配パターンに差がでるように反射材が組んであり、深さ方向の検出位置（DOI）を5 mm単位で識別できる。128個の検出器を用いて体軸方向視野207 mmの8リング装置を製作し、CLS-PETと名付けた（下図a）。ガントリやデータ収集機器は台車上に配置し、1人で移動できるポータブル仕様とした（重量約100 kg）。撮像場所を選ばないよう、100V電源1つで動作する仕様とした。空間分解能評価として、22Na密封ロッドファントム（1 MBq）の30分撮像を行った。小動物全身撮像の実証として、健常ラットに18F-NaF（37 MBq）を投与し、60分後より60分撮像を行った。ファントムでは0.75 mmロッドが識別でき、サブミリ分解能を達成した（下図b）。ラットNaF PETでは、骨構造が明瞭に描出された全身画像を得た（下図c）。 サブミリ分解能を有する多目的ポータブル装置CLS-PETを開発した。PET室に縛られないポータブル装置のため様々なニーズに対応でき、新しいPET応用研究を開拓できる可能性がある。, 第16回日本分子イメージング学会総会・学術集会参加発表

[Purpose] We developed the world’s first helmet-type time-of-flight (TOF) PET, which had a hemispherical detector arrangement. The developed system is characterized as its high-performance and compactness as well as an unusual seat-type design which enables keeping the subject’s eye view wide. Here, we report the basic performance characteristics and the first FDG imaging results of healthy volunteers. [Methods] The helmet-type PET consisted of 54 detectors. The 45 detectors were arranged to form a hemisphere and the other 9 detectors were placed to form a half-ring behind the neck. The detector was composed of 12×12 lutetium fine silicate (LFS) scintillators (4×4×10 mm3) connected to a 12×12 silicon photomultiplier (SiPM) array with one-to-one coupling. The energy window was 450–590 keV and the coincidence time window was 3.6 ns. Image reconstruction was performed using 3D-OSEM with 4 iterations and 8 subsets. The performance was characterized based on the NEMA NU2 standards. The coincidence timing resolution was measured using a 22Na point source. 18F-FDG PET and MRI were performed for 11 normal control subjects. The PET data were measured for 10 minutes starting at 45 minutes after injection of 285±23 MBq. [Results] The coincidence timing resolution was 235 ps. With the sensitivity gain of 5.7 (= 20-cm-diameter object / 3.5 cm TOF localization), the effective sensitivity was 24 cps/kBq and the effective noise-equivalent count ratio was 120 kcps@9 kBq/mL. The spatial resolution of the FBP image was 2.9 mm at the central position (1 cm offset) of the field-of-view. For the human FDG PET images, the gray matter was clearly visualized with a high contrast to the white matter. Small brain nuclei such as the substantia nigra, the red nucleus, and the superior colliculus were able to be identified. [Conclusion] We have successfully demonstrated first human imaging on the helmet-type PET., 第78回日本放射線技術学会総会学術大会

Objective Head motions during brain PET scan cause degradation of brain images, but head fixation or external-maker attachment become burdensome on patients. Therefore, we have developed a motion correction method that uses a 3D face-shape model generated by a range-sensing camera (Kinect) and by CT images. We have successfully corrected the PET images of a moving mannequin-head phantom containing radioactivity. Here, we conducted a volunteer study to verify the effectiveness of our method for clinical data. Methods Eight healthy men volunteers aged 22–45 years underwent a 10-min head-fixed PET scan as a standard of truth in this study, which was started 45 min after 18F-fluorodeoxyglucose (285 ± 23 MBq) injection, and followed by a 15-min head-moving PET scan with the developed Kinect based motion-tracking system. First, selecting a motion-less period of the head-moving PET scan provided a reference PET image. Second, CT images separately obtained on the same day were registered to the reference PET image, and create a 3D face-shape model, then, to which Kinect-based 3D face-shape model matched. This matching parameter was used for spatial calibration between the Kinect and the PET system. This calibration parameter and the motion-tracking of the 3D face shape by Kinect comprised our motion correction method. The head-moving PET with motion correction was compared with the head-fixed PET images visually and by standard uptake value ratios (SUVRs) in the seven volume-of-interest regions. To confirm the spatial calibration accuracy, a test–retest experiment was performed by repeating the head-moving PET with motion correction twice where the volunteer’s pose and the sensor’s position were different. Results No difference was identified visually and statistically in SUVRs between the head-moving PET images with motion correction and the head-fixed PET images. One of the small nuclei, the inferior colliculus, was identified in the head-fixed PET images and in the head-moving PET images with motion correction, but not in those without motion correction. In the test–retest experiment, the SUVRs were well correlated (determinant coefficient, r2 = 0.995). Conclusion Our motion correction method provided good accuracy for the volunteer data which suggested it is useable in clinical settings.

肺移植後早期のFDG-PETから慢性拒絶の兆候をいち早く掴むことを課題として，肺移植モデルラットを対象にFDG-PET画像と炎症の病理診断結果を関連付ける研究を行った．今回，ImageNetで学習済みのVGG16を使用し，肺移植後３週目のFDG-PET画像から６週目の病理診断結果を予測したところ，最も精度の高かったエポックで感度96%，特異度91％と高い精度で予測することができたので報告する．さらに入力画像の特徴量を削減することで予測精度への影響を分析し，病理予測には左肺下部の情報が重要である可能性が示された．

Purpose Esophagectomy with extended lymph node (LN) dissection is a standard treatment for resectable esophageal cancer to prevent recurrence, but severe, potentially life-threatening postoperative complications are still important issues. Accurate diagnosis of LN metastases would enable the decision to dissect or leave the LNs in regions with high risk of complications. Advancements in intraoperative gamma probe and radioactivity detectors have made intraoperative navigation surgery possible using a radiotracer as a marker. F-FDG is one such candidate markers, and the diagnostic power of FDG through counting the radioactivity close to each LN should be elucidated. Materials and methods In 20 patients, 1073 LNs including 38 metastatic LNs were prospectively investigated. Preoperative FDG PET was performed on the same day before esophagectomy and visually surveyed in each LN station to identify abnormal uptake. The FDG radioactivity of each individual dissected LN was measured by a well-type counter, and the pathological diagnosis was compared with LN radioactivity on a one-by-one basis and with the preoperative FDG PET findings for each LN station. Results Lymph node station-based analysis showed a sensitivity and specificity of 28.6% and 96.7%, respectively. One-by-one LN-based analysis using a cutoff value obtained from the receiver operating characteristic curve showed a sensitivity and specificity of 94.7% and 78.7%, respectively, demonstrating higher accuracy compared with the use of LN weight or the shortest diameter. Conclusions The FDG uptake by each LN is a potentially useful marker for navigation surgery in esophageal cancer and has higher accuracy than LN weight or diameter.

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.

The clinical significance of decreased physiological lung uptake ofWe retrospectively reviewed the heart and lung uptakes on 167 consecutive MIBG scans, antidepressant status, and clinical diagnosis of LBD. The images were visually classified into two groups: decreased lung uptake and preserved lung uptake. A semi-quantitative analysis was performed using the heart-to-mediastinum ratio (H/M), lung-to-mediastinum ratio (L/M), and myocardial washout rate (WR).All 17 patients with decreased lung uptake were on treated with antidepressants, while none of the 150 patients with preserved lung uptake were treated with any antidepressants. Of the 17 patients with decreased lung uptake, 6 patients were clinically diagnosed as LBD and other 11 were clinically diagnosed as non-LBD. There was not significant difference in early H/M, delayed H/M, and myocardial WR between the 11 non-LBD patients with decreased lung uptake and 83 non-LBD patients with preserved lung uptake (2.87 ± 0.69 vs. 2.89 ± 0.44, 3.09 ± 0.48 vs. 2.98 ± 0.59, and 21.8 ± 11.3% vs. 21.1 ± 12.5%, respectively). Moreover, in LBD patients, there were no significant differences in those values between six patients with decreased lung uptake and 67 patients with preserved lung uptake (1.68 ± 0.32 vs. 1.73 ± 0.42, 1.34 ± 0.21 vs. 1.54 ± 0.57, 46.2 ± 22.8% vs. 42.8 ± 21.3%, respectively).Antidepressants probably blocked MIBG uptake in the lungs, and a decreased lung uptake was not significantly associated with heart uptake. A remarkable decrease in lung uptake can be a signal to check a patient's medication status.

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

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

Positron emission tomography (PET) is a powerful molecular imaging technique that can provide functional information of living objects. However, the spatial resolution of PET imaging has been limited to around 1 mm which makes it difficult to visualize mouse brain functions in detail. Here we report an ultrahigh resolution small animal PET scanner we developed that can provide a resolution approaching 0.6 mm to visualize the mouse brain functions with unprecedented detail.

Positron-emission tomography (PET) and single-photon-emission computed tomography (SPECT) are well-established nuclear-medicine imaging methods used in modern medical diagnoses. Combining PET with 18F-fluorodeoxyglucose (FDG) and SPECT with an 111In-labelled ligand provides clinicians with information about the aggressiveness and specific types of tumors. However, it is difficult to integrate a SPECT system with a PET system because SPECT requires a collimator. Herein, we describe a novel method that provides simultaneous imaging with PET and SPECT nuclides by combining PET imaging and Compton imaging. The latter is an imaging method that utilizes Compton scattering to visualize gamma rays over a wide range of energies without requiring a collimator. Using Compton imaging with SPECT nuclides, instead of the conventional SPECT imaging method, enables PET imaging and Compton imaging to be performed with one system. In this research, we have demonstrated simultaneous in vivo imaging of a tumor-bearing mouse injected with 18F-FDG and an 111In-antibody by using a prototype Compton-PET hybrid camera. We have succeeded in visualizing accumulations of 18F-FDG and 111In-antibody by performing PET imaging and Compton imaging simultaneously. As simultaneous imaging utilizes the same coordinate axes, it is expected to improve the accuracy of diagnoses.

Standardized uptake values (SUVs) derived fromLTx was performed on 4 groups of rats: isograft, allograft-cyclosporineIn total, 837 radiomic features were extracted from each PET image. The SUVSUV

123I-metaiodobenzylguanidine scintigraphy is used to differentiate Lewy body disease from other neurodegenerative disorders. We identified 2 cases with remarkably changed pulmonary uptake between 2 metaiodobenzylguanidine scintigraphies; pulmonary uptake was reduced when patients were taking selective serotonin reuptake inhibitor/serotonin noradrenaline reuptake inhibitor and preserved during the medication-naive or withdrawal state, suggesting that pulmonary uptake involves not only the noradrenaline transporter, but also the serotonin transporter. Pulmonary accumulation may affect the heart-to-mediastinum ratio as the region of interest on the planner image is usually placed on the heart and includes part of the lung. Therefore, we should pay attention to the medication state of patients with decreased pulmonary uptake.

Positronium (Ps) is generated before electron–positron annihilation in positron emission tomography (PET). As the Ps lifetime reflects the surrounding electron density, we aimed at its use for an innovative PET imaging. Here, as our first step, we demonstrated two-dimensional Ps lifetime imaging of certified reference materials using a pair of time-of-flight PET detectors. The imaged and calculated Ps lifetimes were very close to those of the reference materials, but the error values were larger than those of the reference materials. The results suggested that the accuracy of PET imaging with the ortho-positronium lifetime could be verified by those materials.

[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

[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

This study aimed to assess efficacy and limitations of regional cerebral blood flow imaging using single-photon emission computed tomography (rCBF-SPECT) in the diagnosis of Alzheimer’s disease (AD) with amyloid-positron emission tomography (amyloid-PET). Thirteen patients, who underwent both rCBF-SPECT and amyloid-PET after clinical diagnosis of AD or mild cognitive impairment, were retrospectively identified. The rCBF-SPECTs were classified into 4 grades, from typical AD pattern to no AD pattern of hypoperfusion; amyloid-beta (Aβ) positivity was assessed by amyloid-PET. Four patients were categorized into a typical AD pattern on rCBF-SPECT, and all were Aβ+. The other 9 patients did not exhibit a typical AD pattern; however, 4 were Aβ+. The Mini-Mental State Examination score and Clinical Dementia Rating scale were not significantly different between Aβ+ and Aβ– patients. A typical AD pattern on rCBF-SPECT can reflect Aβ+; however, if not, rCBF-SPECT has a limitation to predict amyloid pathology.

Purpose of the report This study aimed to determine the most effective metabolic index of FDG-PET and MET-PET to differentiate high- and low-grade gliomas, and then to characterize tumor metabolism according to the 2016 WHO classification. We also developed a new calculation method of potential infiltrative tumor volume to overcome the current limitations of tumor evaluation according to metabolic index, which focuses solely on tumor core area. Materials and methods Patients who underwent both FDG-PET and MET-PET, as well as surgical treatment, were retrospectively identified. All tumors were diagnosed histologically and included 44 high-grade and 19 low-grade gliomas. Metabolic indices of tumor-to-normal (T/N) ratio and maximum value within the tumor itself were compared between high- and low-grade tumors. A calculation method for potential infiltrative tumor volume was developed and compared between these 2 grades. Results T/N, calculated as tumor value divided by normal cortex value, was the most effective (area under the curve, 0.800 for FDG-PET; area under the curve, 0.773 for MET-PET) for differentiating high- and low-grade gliomas. Potential infiltrative volume effectively distinguished between high- and low-grade glioma (43.8 ± 30.2 mL vs 14.0 ± 12.6 mL; P = 0.005 [t test]). A combination of T/N, with a cutoff value of 0.9 or higher on FDG-PET and/or 3.0 or higher on MET-PET, and potential infiltrative volume, with a cutoff value of 20.0 mL or higher, provided a diagnostic accuracy of 89% in distinguishing high- from low-grade gliomas. Conclusions Evaluation of potential infiltrative volume surrounding the tumor core area, in addition to the T/N ratio of the tumor core, may help distinguish between high- and low-grade gliomas.

Objective. The biological washout of positron emitters should be modeled and corrected in order to achieve quantitative dose range verification in charged particle therapy based on positron emission tomography (PET). This biological washout effect is affected by physiological environmental conditions such as blood perfusion and metabolism, but the correlation to tumour pathology has not been studied yet. Approach. The aim of this study was to investigate the dependence of the biological washout rate on tumour vascular status in rat irradiation. Two types of tumour vascularity conditions, perfused and hypoxic, were modelled with nude rats. The rats were irradiated by a radioactive 15O ion beam and time activity curves were acquired by dynamic in-beam PET measurement. Tumour tissue sections were obtained to observe the histology as well. The biological washout rate was derived using a single-compartment model with two decay components (medium decay, k 2m and slow decay, k 2s ). Main results. All k 2m values in the vascular perfused tumour tissue were higher than the values of the normal tissue. All k 2m values in the hypoxic tumour tissue were much lower than the values of the vascular perfused tumour tissue and slightly lower than the values of the normal tissue. Significance. The dependency of the biological washout on the tumour vasculature conditions was experimentally shown.