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A novel traceable point-like 68Ge/68Ga source was developed for calibration of positron emission tomography (PET) scanners. The source was equipped with a spherically symmetric acrylic positron absorber. The physical characteristics of photons emitted from the point-like source were evaluated by Monte Carlo simulation, considering possible geometrical uncertainties. The calibration factor of a clinical PET/CT scanner was evaluated using four manufactured point-like sources as a practical application of the point-like source. The results were consistent with that determined by the conventional cross-calibration method. The traceable point-like 68Ge/68Ga source is expected to be a simple and practical tool for determining the calibration factor and evaluating the physical characteristics of PET scanners.

X-ray and gamma-ray photons are widely used for imaging but require a mathematical reconstruction step, known as tomography, to produce cross-sectional images from the measured data. Theoretically, the back-to-back annihilation photons produced by positron–electron annihilation can be directly localized in three-dimensional space using time-of-flight information without tomographic reconstruction; however, this has not yet been demonstrated due to the insufficient timing performance of available radiation detectors. Here we develop techniques based on detecting prompt Cherenkov photons, which, when combined with a convolutional neural network for timing estimation, resulted in an average timing precision of 32 ps, corresponding to a spatial precision of 4.8 mm. We show this is sufficient to produce cross-sectional images of a positron-emitting radionuclide directly from the detected coincident annihilation photons, without using any tomographic reconstruction algorithm. The reconstruction-free imaging demonstrated here directly localizes positron emission and frees the design of an imaging system from the geometric and sampling constraints that are normally present for tomographic reconstruction. Positron emission imaging without tomographic reconstruction is demonstrated. A Cherenkov radiation detector detects gamma rays produced by positron–electron annihilation. The position of a positron source is determined with a precision of 4.8 mm.

Coincidence time resolution (CTR) of 10 ps is an ultimate goal toward reconstruction-less positron emission tomography (PET). One of the ways to enhance the timing performance of the PET detector is to make use of Cherenkov photons which is promptly emitted on the order of picosecond. A Cherenkov detector composed of a Cherenkov radiator and a fast photo-detector, such as a microchannel plate photomultiplier tube (MCP-PMT) can reach the CTR better than 100 ps full width at half maximum (FWHM). Previously, we have developed the Cherenkov detector where the Cherenkov radiator is integrated with the MCP-PMT to enhance the timing performance, and the CTR of 41.9 ps FWHM was obtained. In this study, we performed two types of experiments; (1) increasing statistics roughly ten times larger than the previous study to precisely determine the timing performance of the detector, (2) stepping a 22Na point source and validating transitions of timing histograms according to the source positions. As a result, the CTR of 41.7 ps FWHM was obtained. Moreover, the CTR between the radiator and the MCP direct interaction was also investigated and approximately 55 ps FWHM was obtained. The transitions of the timing histograms according to the source positions were successfully observed. Finally, we show physical components affecting the CTR and potential capability toward the ultimate goal of 10 ps CTR is discussed.

With the upgradation of detector components, such as scintillators and photodetectors , the PET-image signal-to-noise ratio of time-of-flight positron emission tomography (TOF-PET) systems has been improved, compared to those of ordinary nonTOF-PET systems. A TOF-PET with an ultrahigh time resolution, for example a coincidence time resolution (CTR) better than few tens of picoseconds, can not only improve the image quality, but also remove the image reconstruction process, significantly impacting medical imaging. Therefore, it is crucial to develop a high-time resolution PET detector. We focus on the prompt emission of Cherenkov radiation , owing to the instantaneousness of which, a high time resolution can be expected. One of the candidates for the Cherenkov radiator is lead fluoride (PbF 2 ) due it has excellent properties, including transparency toward the ultraviolet region, high refractive index (n = 1.82), and high density (7.77 g/cm 3). Moreover, it does not contain radioisotopes, unlike lutetium-based scintillators, which are commonly used in the currently available TOF-PET detectors. In this work, we experimentally investigate the timing performance of PbF2-based Cherenkov detectors, breaking down the timing performance into physical components. 3 × 3 × 5 mm3 and 9.6 × 9 . 6 × 5 mm3 PbF2 crystals are used as Cherenkov radiators; both are attached to a microchannel plate photomultiplier tube (MCP-PMT) because the single channel MCP-PMT is one of the best photodetectors in terms of the SPTR, which is 25 ps full width at half maximum (FWHM). All the surfaces, except the end surface where the MCP-PMT is connected, are wrapped in black tape to suppress the reflections of the Cherenkov photons in the crystal. The CTR is measured by placing a detector pair face-to-face, using an 22 Na point source, and an oscilloscope at 20 GS/s with a set bandwidth of 4.2 GHz. A CTR of 46.9 ps FWHM, corresponding to a position resolution of 7.0 mm, is obtained, consistent with our simulation results.

In order to achieve the ultimate goal of reducing coincidence time resolution (CTR) to 10 ps, thus enabling reconstruction-less positron emission tomography, a Cherenkov-radiator-integrated microchannel plate photomultiplier tube (CRI) reaching CTR of sub-50 ps full width at half maximum (FWHM) has been developed. However, a histogram of time differences between a pair of the CRIs shows undesirable side peaks, which are caused by gamma rays directly interacting with the micro channel plates (MCPs). Such direct interaction events are detrimental to the timing performance of the CRI. In this paper, we demonstrate an analytical method of deconvolving MCP direct interaction events from the timing histogram. Considering the information of the main and the two side peaks, the timing uncertainty caused by the MCP direct interaction events is deconvolved and the CTR of the CRI is analytically investigated. Consequently, the CTR is improved from 41.7 to 40.5 ps FWHM by the deconvolution. It means that a mixture of the Cherenkov radiator events and the MCP direct interaction events contribute to the CTR by a factor of 10 ps. The timing performance of the MCP direct interaction events are also evaluated. The CTR between the two MCPs is found to be 66.2 ps FWHM. This indicates that a photocathode-free radiation detector with high timing performance is possible. Elimination of the photocathode from the detector would make detector construction easier and more robust.

Aim Cardiopulmonary resuscitation is vital for survival after cardiac arrest, and chest compressions are an important aspect of this. When performing chest compression in a hospital setting, the rescuer often has to kneel on the bed to overcome inconvenient differences in height between the rescuer and the bed. However, as yet no study has evaluated the quality of chest compressions in this position. The aim of this study was to examine the impact on the quality of chest compressions while kneeling on the bed. Methods Fifteen female students performed 2‐min chest compressions on a manikin placed on the floor and a bed. Measurement parameters included compression depth, heart rate, integrated electromyogram, and a visual analog scale. The parameters were measured every 30 s and were statistically compared between the conditions. Results Compression depth at 30, 60, 90, and 120 s differed significantly between the conditions. Heart rate values at 150 and 210 s of recovery significantly differed between the conditions. Integrated electromyogram values for the trapezius, rectus femoris, and biceps femoris differed between the floor and bed conditions during 2‐min chest compressions, whereas the external oblique muscle significantly differed at 60 and 120 s. Visual analog scales for fatigue, effectiveness, and stability significantly differed between the conditions. Conclusion Kneeling on the bed does not enable grounding of the toe, causing the upper body to be unstable and limiting generation of the power required for chest compression. Our results suggest that rotation every minute is necessary to maintain effective cardiopulmonary resuscitation while kneeling on the bed.

Purpose Cherenkov radiation has recently received attention due to its prompt emission phenomenon, which has the potential to improve the timing performance of radiation detectors dedicated to positron emission tomography (PET). In this study, a Cherenkov-based three-dimensional (3D) position-sensitive radiation detector was proposed, which is composed of a monolithic lead fluoride (PbF2 ) crystal and a photodetector array of which the signals can be readout independently. Methods Monte Carlo simulations were performed to estimate the performance of the proposed detector. The position- and time resolution were evaluated under various practical conditions. The radiator size and various properties of the photodetector, e.g., readout pitch and single photon timing resolution (SPTR), were parameterized. The single photon time response of the photodetector was assumed to be a single Gaussian for the simplification. The photo detection efficiency of the photodetector was ideally 100% for all wavelengths. Compton scattering was included in simulations, but partly analyzed. To estimate the position at which a γ-ray interacted in the Cherenkov radiator, the center-of-gravity (COG) method was employed. In addition, to estimate the depth-of-interaction (DOI) principal component analysis (PCA), which is a multivariate analysis method and has been used to identify the patterns in data, was employed. The time-space distribution of Cherenkov photons was quantified to perform PCA. To evaluate coincidence time resolution (CTR), the time difference of two independent γ-ray events was calculated. The detection time was defined as the first photon time after the SPTR of the photodetector was taken into account. Results The position resolution on the photodetector plane could be estimated with high accuracy, by using a small number of Cherenkov photons. Moreover, PCA showed an ability to estimate the DOI. The position resolution heavily depends on the pitch of the photodetector array and the radiator thickness. If the readout pitch were ideally 0 and practically 3 mm, a full-width at half-maximum (FWHM) of 0.348 and 1.92 mm was achievable with a 10-mm-thick PbF2 crystal, respectively. Furthermore, first-order correlation could be observed between the primary principal component and the true DOI. To obtain a coincidence timing resolution better than 100-ps FWHM with a 20-mm-thick PbF2 crystal, a photodetector with SPTR of better than σ = 30 ps was necessary. Conclusions From these results, the improvement of SPTR allows us to achieve CTR better than 100-ps FWHM, even in the case where a 20-mm-thick radiator is used. Our proposed detector has the potential to estimate the 3D interaction position of γ-rays in the radiator, using only time and space information of Cherenkov photons.

Background To investigate the potential prognostic value of image analysis of pelvic bone metastasis in newly diagnosed prostate cancer patients.Methods Data from 69 patients with both bone scintigraphy and pelvic CT images were selected for this analysis. Open source software (3D Slicer version 4.8.1.) was used for image analysis. Metastatic pelvic bone lesions were manually contoured, and radiomic features were extracted. As risk factors for overall survival (OS) and cause-specific survival (CSS), 105 radiomic features and clinical risk factors including age, initial prostate-specific antigen, Gleason score, TNM stage, lactate dehydrogenase (LDH), hemoglobin (Hb), alkaline phosphatase, extent of disease, visceral metastases, castration-resistant prostate cancer (CRPC), and number of systemic agents including abiraterone, enzalutamide, docetaxel and cabazitaxel which CRPC patients received were assessed by uni- and multivariate analyses.Results Median follow-up was 41 months (range, 0-157 months). Three- and 5-year overall survival rates were 66.6% and 37.9%, respectively. Three- and 5-year cause-specific survival rates were 69.4% and 43.5%, respectively. After multivariate analysis, LDH, Hb, and “maximum 2D diameter” defined as maximum tumor size in the axial plane were detected as risk factors for OS. Gleason sum, LDH, and maximum 2D diameter were detected as risk factors for CSS.Conclusion Maximum 2D diameter of pelvic bone metastasis was detected as a significant prognostic factor for metastatic prostate cancer patients.

Achieving direct imaging of the annihilation position of a positron on an event-by-event basis using an ultrafast detector would have a great impact on the field of nuclear medicine. Cherenkov emission is the most attractive physical phenomenon for realizing such an ultrafast timing performance. Moreover, a microchannel-plate photomultiplier tube (MCP-PMT) is one of the most promising photodetectors for fully exploiting the fast timing properties of Cherenkov emission owing to its excellent single photon time resolution of 25 ps full width at half maximum (FWHM). However, as the MCP structure generally contains a lead compound, the gamma rays frequently and directly interact with the MCP, resulting in the degradation of its timing performance and generation of undesirable side peaks in its coincidence timing histogram. To overcome this problem, we have developed a new MCP-PMT based on an MCP consisting of borosilicate glass, thus drastically reducing the probability of the photoelectric effect occurring in the MCP. To evaluate its insensitivity to gamma rays and its timing performance, a coincidence experiment was performed and showed that the probability of direct interactions was reduced by a factor of 3.4. Moreover, a coincidence time resolution of 35.4 ± 0.4 ps FWHM, which is equivalent to a position resolution of 5.31 mm, was obtained without any pulse height/area cut, improving to 28.7 ± 3.0 ps when selecting on the highest amplitude events by careful optimization of the voltage divider circuit of the new MCP-PMT. The timing performance of this new MCP-PMT presents an important step toward making direct imaging possible.

To apply deep learning to estimate the three-dimensional interaction position of a Cherenkov detector, an experimental measurement of the true depth of interaction is needed. This requires significant time and effort. Therefore, in this study, we propose a direct annihilation position classification method based on deep learning using paired Cherenkov detectors. The proposed method does not explicitly estimate the interaction position or time-of-flight information and instead directly estimates the annihilation position from the raw data of photon information measured by paired Cherenkov detectors. We validated the feasibility of the proposed method using Monte Carlo simulation data of point sources. A total of 125 point sources were arranged three-dimensionally with 5 mm intervals, and two Cherenkov detectors were placed face-to-face, 50 mm apart. The Cherenkov detector consisted of a monolithic PbF2 crystal with a size of 40 &times, 40 &times, 10 mm3 and a photodetector with a single photon time resolution (SPTR) of 0 to 100 picosecond (ps) and readout pitch of 0 to 10 mm. The proposed method obtained a classification accuracy of 80% and spatial resolution with a root mean square error of less than 1.5 mm when the SPTR was 10 ps and the readout pitch was 3 mm.

Radiation detectors dedicated to time-of-flight positron emission tomography (PET) have been developed, and coincidence time resolution (CTR) of sub-100 ps full width at half maximum (FWHM) has been achieved by carefully optimizing scintillators and photodetectors. Achieving a CTR of 30 ps FWHM by using a pair of annihilation γ-rays would allow us to directly localize the annihilation point within an accuracy of 4.5 mm. Such direct localization can potentially eliminate the requirement of image reconstruction processes in clinical PET systems, which would have a huge impact on clinical protocols and molecular imaging. To obtain such a high CTR, researchers have investigated the use of prompt emissions such as Cherenkov radiation and hot-intra band luminescence. Although it is still challenging to achieve a CTR of 30 ps FWHM even with a Cherenkov-based detector, the experimentally measured CTR is approaching the goal. In this work, we developed a Cherenkov-radiator-integrated micro-channel plate photomultiplier tube (CRI-MCP-PMT), where there are no optical boundaries between the radiator and photocathode, and its timing performance was investigated. By removing the optical boundaries, reflections are eliminated and transmission to the photocathode is improved, resulting in high timing capability. As a result, a CTR of 30.1 ± 2.4 ps FWHM, which is equivalent to a position resolution of 4.5 ± 0.3 mm along a line of response (LOR), was obtained by using a pair of CRI-MCP-PMTs.

To improve the reliability and convenience of the calibration procedure of positron emission tomography (PET) scanners, we have been developing a novel calibration path based on traceable point-like sources. When using (22)Na sources, special care should be taken to avoid the effects of 1.275-MeV γ rays accompanying β (+) decays. The purpose of this study is to validate this new calibration scheme with traceable point-like (22)Na sources on various types of PET scanners.Traceable point-like (22)Na sources with a spherical absorber design that assures uniform angular distribution of the emitted annihilation photons were used. The tested PET scanners included a clinical whole-body PET scanner, four types of clinical PET/CT scanners from different manufacturers, and a small-animal PET scanner. The region of interest (ROI) diameter dependence of ROI values was represented with a fitting function, which was assumed to consist of a recovery part due to spatial resolution and a quadratic background part originating from the scattered γ rays.The observed ROI radius dependence was well represented with the assumed fitting function (R (2)0.994). The calibration factors determined using the point-like sources were consistent with those by the standard cross-calibration method within an uncertainty of ±4 %, which was reasonable considering the uncertainty in the standard cross-calibration method.This novel calibration scheme based on the use of traceable (22)Na point-like sources was successfully validated for six types of commercial PET scanners.

Purpose: The purpose of this study is to propose a microfocus x-ray imaging technique for observing the internal structure of small radioactive sources and evaluating geometrical errors quantitatively, and to apply this technique to traceable pointlike22 Na sources, which were designed for positron emission tomography calibration, for the purpose of quality control of the pointlike sources. Methods: A microfocus x-ray imaging system with a focus size of 0.001 mm was used to obtain projection x-ray images and x-ray CT images of five pointlike source samples, which were manufactured during 2009–2012. The obtained projection and tomographic images were used to observe the internal structure and evaluate geometrical errors quantitatively. Monte Carlo simulation was used to evaluate the effect of possible geometrical errors on the intensity and uniformity of 0.511 MeV annihilation photon pairs emitted from the sources. Results: Geometrical errors were evaluated with sufficient precision using projection x-ray images. CT images were used for observing the internal structure intuitively. As a result, four of the five examined samples were within the tolerance to maintain the total uncertainty below ±0.5%, given the source radioactivity; however, one sample was found to be defective. Conclusions: This quality control procedure is crucial and offers an important basis for using the pointlike22 Na source as a basic calibration tool. The microfocus x-ray imaging approach is a promising technique for visual and quantitative evaluation of the internal geometry of small radioactive sources.

Purpose: In the conventional techniques for determining the calibration factors of positron emission tomography (PET) scanners, cylindrical water and resin phantoms with radioisotope 18F or 68Ge/68Ga are used. In these methods, however, the results depend on attenuation and scatter correction. The purpose of this study is to develop a point-like 68Ge/68Ga radioactive source that can be used to determine the calibration factors of PET scanners without the uncertainty of attenuation and scatter correction. Methods: A spherical absorber design was employed to realize a symmetric angular distribution of emitted annihilation photons. A Geant4-based Monte Carlo simulation code was used to compare physics characteristics of point-like sources with various absorber materials. On the basis of this simulation, a point-like 68Ge/68Ga source with a spherical aluminum absorber was manufactured. Its radioactivity was calibrated at an accredited national calibration facility. A calibration factor of a clinical PET scanner was then obtained with a point-like source and compared with that obtained by a standard cross-calibration method. Results: The emission probability of 0.511 MeV annihilation photon pairs per positron decay was typically 0.6-0.8. The fraction of background photon pairs was 6-8% in the energy region of 0.4-0.6 MeV. Considering these two figures, lower density materials such as aluminum and pol(ymethyl methacrylate) (PMMA) were preferable. For the aluminum absorber, a diameter of 8 mm was suitable to prevent positrons from escaping. The calibration factor obtained with the point-like source agreed with that obtained by the standard method within 2-3%. Conclusion: A point-like 68Ge/68Ga radioactive source was successfully designed, manufactured, and used for determining a calibration factor of a PET scanner. It can be considered a practical tool for calibrating and evaluating the quantitative aspects of PET scanners.

Electronic portal imaging device (EPID) is a popular tool for a verification of the patient setup for radiation therapy. Recently, it is grabbing attention as a tool for in vivo dosimetry. It detects therapeutic photons which penetrated the patient body to acquire an image. Conversion to absorbed dose is required from the digital pixel value. However, the response of the EPID is susceptible to the energy spectrum changes through the body [1] , [2] . The purpose of this study was to perform the energy response correction of the EPID image using Monte Carlo simulation (MC) to improve the accuracy of the EPID dosimetry. Geant4.9.6 patch04 was used for the MC with a combination of a HTCondor 7.6 parallel computing software. The MC simulated the 6 and 10 MV photon beams from Trilogy (Varian Medical Systems) linear accelerator. The EPID response to the energy spectrum was evaluated. CT DICOM data set of a chest phantom was imported to the MC, and the simulated EPID images were acquired after irradiating 6 and 10 MV photon beams. The measurement was performed with the same setup as the MC and obtained the EPID images. The energy response was corrected to obtain the absorbed dose and compared with that measured with 2D array detector (PTW) as a reference. EPID was more sensitive to the photons penetrated the mediastinum than those penetrated the lung due to the contamination of the scattered photons with the energy of

Purpose: Point-like 22Na radioactive sources have been widely used for checking radiation detectors that measure annihilation photons and for evaluating PET scanners. We developed new types of 22Na point-like radioactive sources that are expected to be more symmetric than conventional source types in the angular distribution of the emitted photons. The purpose of this study is to use Monte Carlo simulation to investigate the basic characteristics of the photons emitted from the new type 22Na point-like radioactive sources. Methods: Two new types of 22Na point-like sources, a cylinder type and a sphere type, were considered in comparison with two conventional source types, a disk type and a cube type. The angular distribution and energy spectra of the emitted 0.511 MeV annihilation photons and 1.275 MeV gamma rays were calculated using a Monte Carlo code based on Geant4. Results: The angular distribution of the emitted photons was more symmetric in the new type point-like sources than in the conventional types. The asymmetry of the angular distribution of the unscattered 0.511 MeV annihilation photon pairs counted in coincidence was 0.1 ±0.1% and 1.6±0.1% in the sphere and cylinder types, compared with 4.1±0.1% and 22.6±0.1% for the cube and disk types. The scatter components around the 0.511 MeV photopeaks in the new source types were typically less than 2/3 and 1/2 of those in the disk and cube types, respectively. Conclusion: The new point-like 22Na sources offer a more symmetric angular distribution of the emitted photons with fewer scatter components. They are useful for applications where the symmetry of the emitted photons is crucial.

症例は38歳，男性．既往歴として生後まもなくHirschsprung病にて二期的手術を受けていた．小学生時には右停留精巣にて右精巣摘除術を受けたと説明されていた．入院約1カ月前より下腹部痛を自覚．近医を受診し，下腹部腫瘤を指摘され当院消化器科紹介受診した．精査にてβ-HCG高値，3D-CT-angiograpyで腫瘍の栄養血管が右精巣動脈である可能性が示唆され，腹部右精巣腫瘍も疑われたが，病歴より否定的と判断．オリジン不明の腹腔内腫瘍摘出目的に当科入院した．術中所見では腫瘍は後腹膜に覆われた巨大な精巣様の形態であり，肉眼的に精索，精巣上体，精巣導帯などが確認された．腫瘍摘出術を施行した．病理検査結果は単一型のセミノーマであった．術後12カ月目の現在，明らかな再発を認めていない．成人の腹部セミノーマ国内報告例は本症例を加えて10症例と少なく，停留精巣術後の報告は本症例のみであった．文献的考察を加え報告する．

症例は20歳の男性で，小児期から腹部てんかんの診断で経過観察されていたが，2009年4月右上腹部痛を主訴に当院紹介となった．腹部造影CTで上腸間膜動脈の周囲を腸管が取り巻くwhirl-like patternを認め，CT-colonographyでは上行結腸の左方変位が認められた．上部消化管造影検査で十二指腸空腸移行部の位置異常を認め，腸回転異常症に伴う中腸軸捻転症と診断された．同時に下腹部に造影効果のない多房性の嚢胞性病変を認め，MRIでも嚢胞内に結節性病変を認めないことから，腸間膜嚢腫と診断した．腸管血流障害の可能性が低いことから，待機的に腹腔鏡下に空腸部分切除，Ladd手術および虫垂切除を施行した．病理組織検査で嚢胞性病変が空腸筋層まで連続し，腸間膜リンパ管腫と診断された．中腸軸捻転，腸間膜嚢腫に対する腹腔鏡下手術は，腸管の血流障害がない症例に対して安全で有効な手技と考えられる．

Thus far, cylindrical phantoms with (18)F or (68)Ge/(68)Ga have been used in the standard techniques for determining the cross-calibration factors (CCFs) of PET scanners. This paper describes a new practical method that uses a point-like (22)Na radioactive source for determining CCFs.A point-like (22)Na radioactive source (about 700 kBq) was equipped with a spherical aluminium absorber capsule to ensure the symmetry of the emitted photons. During measurements, the source was moved in the axial direction to cover the whole axial field of view (FOV) of a clinical PET scanner, SET-2400 W. The region-of-interest (ROI) values obtained in reconstructed images without scatter and attenuation corrections were used to calculate the CCFs of the PET scanner.The CCFs obtained by the proposed method agreed with those obtained by the standard cross-calibration (CC) method within a precision of 1.5% (σ). The temporal variations in the CCFs by the standard CC method were reproduced by the proposed method with a precision better than 1%.The CC method with a moving (22)Na point-like radioactive source is practically useful for determining the CCFs of PET scanners and monitoring their variations.

Radioactive sources for evaluating sensitivity and uncertainty in the radioactivity measurements performed using PET scanners must be equipped with absorber materials that ensure the annihilation of positrons. Attenuation and scattering owing to the absorber materials produce uncertainty in the performance evaluation. The aim of this study is to propose a point-like radioactive source with multiple absorber capsules, for which evaluation can be independent of scatter and attenuation owing to the source absorbers. The point-like source consists of a small spherical radioactive part and a set of successively sized cylindrical aluminum absorber capsules. Data were collected for different total absorber thicknesses. By an extrapolation technique, the effects of the source absorbers were eliminated. Sensitivity and uncertainty in the radioactivity measurements of PET scanners were evaluated with this technique. Sensitivity and uncertainty of radioactivity measurement to the point-like radioactive source were evaluated successfully with this method. The proposed point-like radioactive source is useful for evaluating performance characteristics of PET scanners in a way that is independent of the effects of the source absorbers.

症例は74歳，女性．入院14日前より腹痛を自覚した．近医を受診したが改善せず，発熱，臍下部の腫瘤も伴うようになり当院紹介入院した．入院時，体温38.1℃，臍下に発赤，圧痛を伴う腫瘤を認めた．腹部CTで横行結腸に接して腹腔内より腹壁に至る膿瘍を認めた．絶飲食とし抗生剤を投与したが，腹部CTで腹壁膿瘍の増大を認め，局所麻酔下に腹壁膿瘍のドレナージを施行した．経口摂取を開始後，腸閉塞症を併発しイレウス管を留置した．イレウス管を用いた注腸造影にて横行結腸に不整な狭窄を認め，腹壁膿瘍を合併した横行結腸癌および腸閉塞症と診断した．33病日，大網合併横行結腸部分切除術，D2郭清を施行した．病理検査結果は横行結腸癌，2型，tub1，SE，N0，StageII．術後補助化学療法を開始し，76病日に退院した．術後1年6カ月目の現在，再発を認めていない．本症例を含む腹壁膿瘍を合併した横行結腸癌本邦報告22例に検討を加えた．

Physics-related subjects are important in the educational fields of radiological physics and technology. However, conventional teaching tools, for example texts, equations, and two-dimensional figures, are not very effective in attracting the interest of students. Therefore, we have created several multimedia educational materials covering radiological physics and technology. Each educational presentation includes several segments of high-quality computer-graphic animations designed to attract students' interest. We used personal computers (PCs) and commercial software to create and compile these. Undergraduate and graduate students and teachers and related professionals contributed to the design and creation of the educational materials as part of student research. The educational materials can be displayed on a PC monitor and manipulated with popular free software. Opinion surveys conducted in undergraduate courses at Kitasato University support the effectiveness of our educational tools in helping students gain a better understanding of the subjects offered and in raising their interest.

In a conventional PET scanner, coincidence events are limited by the energy window for detection of photoelectric events. In contrast, Compton scatter events occur both in a patient and in detector crystals. Scatter events within the patient cause scatter coincidences, but scatter events within crystals have useful information for an activity distribution. The PET scanner with an extended energy window has higher sensitivity but higher scatter fraction than the PET scanner with a default energy window. In this work, we develop a scatter reduction method using a depth-of-interaction (DOI) detector. The DOI detector can make an upper layer act as an absorber of patient scatter, thus shielding a lower layer. Therefore, Compton scatter events with an interaction at the lower layer mainly have more crystal scatter events than patient scatter events. Our method proposes a different energy window for each layer. The energy window of the upper layer is limited to the region of photopeak events, the same as done for the conventional PET scanner. The energy window of the lower layer is extended to the region of crystal scatter events and photopeak events. We tested our proposed technique for a whole-body PET scanner using GATE simulations. Simulation results show the DOI-PET scanner can provide more true events while keeping a low scatter fraction using our scatter reduction method. We conclude this method is promising for obtaining high image quality using DOI information and energy information.

We are developing a high-performance brain PET scanner, jPET-D4, which provides 4-layer depth-of-interaction (DOI) information. The scanner is designed to achieve not only high spatial resolution but also high scanner sensitivity with the DOI information obtained from multi-layered thin crystals. The scanner has 5 rings of 24 detector blocks each, and each block consists of 1024 GSO crystals of 2.9 mm/spl times/2.9 mm/spl times/7.5 mm, which are arranged in 4 layers of 16/spl times/16 arrays. At this stage, a pair of detector blocks and a coincidence circuit have been assembled into an experimental prototype gantry. In this paper, as a preliminary experiment, we investigated the performance of the jPET-D4's spatial resolution using the prototype system. First, spatial resolution was measured from a filtered backprojection reconstructed image. To avoid systematic error and reduce computational cost in image reconstruction, we applied the DOI compression (DOIC) method followed by maximum likelihood expectation maximization that we had previously proposed. Trade-off characteristics between background noise and resolution were investigated because improved spatial resolution is possible only when enhanced noise is avoided. Experimental results showed that the jPET-D4 achieves better than 3 mm spatial resolution over the field-of-view.

This paper describes a depth-of-interaction recognition method that can be applied to radiation detectors for positron emission tomography (PET). The proposed method uses optical filters to differentiate wavelength distribution of scintillation photons depending on crystal depth positions. Then the crystal of interaction can be identified with a multi-anode photo-detector whose sensitive surface is partly covered with optical filters. A validation experiment was performed with a position sensitive photomultiplier. As a result, it was proved that the crystal depth of interaction was clearly identified for photo-absorption events.

A high-performance positron emission tomography (PET) scanner, which measures depth-of-interaction (DOI) information, is under development at the National Institute of Radiological Sciences in Japan. Image reconstruction methods with accurate modeling of the system response functions have been successfully used to improve PET image quality. It is, however, difficult to apply these methods to the DOI-PET scanner because the dimension of DOI-PET data increases in proportion to the square of the number of DOI layers. In this paper, we propose a compressed imaging system model for DOI-PET image reconstruction, in order to reduce computational cost while keeping image quality. The basic idea of the proposed method is that the DOI-PET imaging system is highly redundant. First, DOI-PET data is transformed into compact data so that data bins with highly correlating sensitivity functions are combined. Then image reconstruction methods based on accurate system modeling, such as the maximum likelihood expectation maximization (ML-EM), are applied. The proposed method was applied to simulated data for the DOI-PET scanner operated in 2-D mode. Then the tradeoff between the background noise and the spatial resolution was investigated. Numerical simulation results show that the proposed method followed by ML-EM reduces computational cost effectively while keeping the advantages of the accurate system modeling and DOI information.

Organ movements that occur naturally as a result of vital functions such as respiration and heartbeat cause deterioration of image quality in nuclear medicine imaging. Among these movements, respiration has a large effect, but there has been no practical method of correcting for this. In the present study, we examined a method of correction that uses ultrasound images to correct baseline shifts caused by respiration in cardiac nuclear medicine examinations. To evaluate the validity of this method, simulation studies were conducted with an X-ray TV machine instead of a nuclear medicine scanner. The X-ray TV images and ultrasound images were recorded as digital movies and processed with public domain software (Scion Image). Organ movements were detected in the ultrasound images of the subcostal four-chamber view mode using slit regions of interest and were measured on a two-dimensional image coordinate. Then translational shifts were applied to the X-ray TV images to correct these movements by using macro-functions of the software. As a result, respiratory movements of about 20.1 mm were successfully reduced to less than 2.6 mm. We conclude that this correction technique is potentially useful in nuclear medicine cardiology.

We report the usefulness of coarse septa in positron emission tomography (PET) by Monte Carlo simulation. Coarse septa result in higher sensitivity than found with the two-dimensional mode with conventional full septa and lower scatter fraction than the three-dimensional mode without septa. We propose a new scatter correction method using coarse septa, where scatter components are estimated from coincidence data for those line-of-responses that are intercepted by the coarse septa. This scatter correction potentially has the ability to cope with scatter from radioactivity outside the field of view. In addition, we show the feasibility of a lead tungstate PET scanner with coarse septa.

Electric energy consumption for cooling (Wc) and the coefficient of performance for cooling (C) were investigated in a closed-type transplant production system (CTPS). C is defined as the ratio of heat energy absorbed by the evaporator of the air conditioner to Wc. A Basic Module Room with thermally insulated walls (5.8 m (W), 2.7 m (L), 5.4 m (H)) in the Research Unit for Closed Plant Production Systems at Chiba University was considered as a model CTPS. Home-use air conditioners, fluorescent lamps, fans and humidifier were installed in the CTPS. One hundred fifty-one data sets were collected for the analysis during the period from 1 May 2000 to 30 April 2001 when air temperatures inside the CTPS (Tin) during photo-and dark period were 29-31°C and 27-29°C, respectively. The chemical energy assimilated by the transplants was considered to be negligible. In the preliminary study, the number of air exchanges of the system was found to be 0h-1 Heat energy transmission through the walls was estimated as the product of heat transmission coefficient (ceiling and side walls : 0.3 W m-2 k-1 floor : 0.2 W m-2 K-1) and the air temperature difference between inside and outside the CTPS. Subsequently, C was estimated by dividing the heat energy generated inside the CTPS (Q) by Wc. Wc increased with increasing air temperature outside the CTPS (Tout) and with increasing Q. Most (72-86%) of the electric energy was consumed by lamps. The rest was consumed by air conditioners (7-17%) and other equipments (5-15%). The average value of C was 7.6 under this experiment condition. The estimated values of C were 1.1-2.6 times greater in this experiment condition than the catalog value measured in the standard condition (Tin : 27°C, Tout : 35°C), because Tout was lower than Tin. C increased with decreasing Tout and with increasing Q. These results show that C of a recent model of home-use air conditioner is relatively high, and its application is beneficial for reducing Wc in the CTPS.

Objective To study the effects of trabeculectomy and needling revision of poorly functioning blebs on the optic nerve head (ONH) circulation in patients with primary open-angle glaucoma (POAG). Design Prospective, nonrandomized, self-controlled trial. Participants Nineteen POAG patients (age range, 52 ± 12 years; mean ± standard deviation) undergoing trabeculectomy and six POAG patients (age range, 62 ± 14 years) undergoing needling revision of the bleb. Methods Using the laser speckle method, the normalized blur (NB) value, a quantitative index of blood velocity, was determined every 0.125 seconds and averaged more than three cardiac pulses in the optic nerve head (NB ONH ). Main outcome measures The NB ONH and intraocular pressure (IOP) in both eyes, and blood pressure (BP) and pulse rate (PR) were measured before and 2 days and 1, 4, and 8 weeks after trabeculectomy, and also before and 10 and 40 min after needling procedures. Results Intraocular pressure in the operated eye was significantly decreased after trabeculectomy or needling procedures, and the ocular perfusion pressure was significantly increased by a maximum of 38%. The IOP in the unoperated eye, BP, and PR did not significantly change. The NB ONH did not significantly change in either the operated or unoperated eye. Conclusions Trabeculectomy and needling procedures induced little change in the ONH circulation.

This paper presents a PET scanner capable of acquiring projection data in three-dimensional (3D) and two-dimensional (2D) modes simultaneously. The scanner has rotating partial slice-septa, and coincidence events are stored as 2D data or as 3D data depending on whether the lines of response are collimated by the septa or not. 68Ge/Ga rod sources can be set on the rotating septa, and a transmission scan for attenuation correction is performed in the 2D mode. The scanner allows simultaneous 3D-emission/2D-transmission scanning or post-injection transmission scanning with little cross-talk. A blank scan for detector normalization is also performed with the rotating rod sources in the 2D mode, from which we can derive the normalizing factors in both modes. The 3D/2D difference method is available for scatter correction, even in a dynamic study where the source distribution is changing. A 'summation method' is proposed as a new image reconstruction algorithm, in which the high- and low-frequency components of images are reconstructed from the 3D and 2D data respectively. In this method, most of the scatter contribution in the 3D data is removed by high-pass filtering, not by subtracting estimated scatter distribution, and hence the method is expected to be robust for scatter from outside the axial field of view. Computer simulations revealed that the rotating partial septa offer a single-scatter to true ratio similar to that of the conventional full septa if the depth of the partial septa is properly lengthened, with a small increase in multiple scattering.

The effect of external end-shields in screening radiation from outside the Field of View (FOV) was studied by phantom measurements and confirmed by Monte Carlo simulation of the ECAT EXACT HR+. Accidental coincidence rates were measured with a standard calibration cylinder placed outside the FOV with and without one of several external end shields. These measurements were in excellent agreement with the Monte-Carlo simulation, which included details, such as the count rate as a function of the ring number.

Conventionally, positron emission tomograph (PET) scanners use scintillators which have a high effective atomic number. Recently, novel scintillators like LaBr 3 have been developed which have excellent timing and energy resolutions. LaBr 3 has a high performance for PET scanner use, but its effective atomic number is lower than that of lutetium oxyorthosilicate (LSO). As an alternative, we have developed a scatter reduction method using depth-of-interaction (DOI) information and energy information to increase the sensitivity. The sensitivity of the PET scanner with LaBr 3 can be improved using the DOI-dependent extended-energy window (DEEW) method. In this work, our method is applied to the whole-body LSO/LaBr 3 PET scanner using the GATE simulation toolkit. Simulation results show the number of true coincidences can be increased while minimizing the scatter and random coincidences by using the DEEW method. Noise equivalent count rate (NECR) can be improved by 20–70% for the whole-body DOI-PET scanner. Sensitivity of the PET scanner with a scintillator of low-effective atomic number can be improved by the DEEW method.

The performance of ECAT EXACT HR/sup +/ (Siemens/CTI) was analyzed with reference to the following adjustable data-acquisition parameters in the operation software: maximum ring difference, span, angular compression and overlap. The standard protocol by the National Electrical Manufacturers Association (NEMA) was followed with minor modification. Scanner performance such as sensitivity and resolution was shown to be dependent on the parameters in a variety of manners in the three-dimensional mode. The advantages and disadvantages of altering the data-acquisition parameters were discussed. It was concluded that the data-acquisition parameters should be carefully selected for a specific clinical situation in order to maximize the efficiency of PET measurement.

Purpose: We have been developing a practical and reliable calibration scheme based on the use of traceable pointlike sources. In using 22Na sources, special care should be taken to avoid the effects of 1.275-MeV γ rays accompanying β+ decays. The purpose of this study is to validate this calibration method with traceable point-like 22Na sources on various types of PET scanners. Method: The traceable point-like 22Na sources with a spherical absorber design used in this study were of the same type as those used in a previous study. The tested PET scanners included one clinical whole-body PET scanner, four types of clinical PET/CT scanners from different manufacturers, and one small-animal PET scanner. The ROI (region of interest) diameter dependence of ROI values were represented with a fitting function, which was assumed to consist of a recovery part due to spatial resolution and a quadratic background part originating from the scattered γ rays. Results: The calibration factors determined using the point-like source were consistent with those by the standard cross-calibration method within ±4%, which was comparable to the uncertainty of the standard cross-calibration method. Conclusion: The novel calibration scheme based on the use of traceable 22Na point-like sources was validated for six types of commercial PET scanners.

We have been developing reliable and convenient calibration methods based on the use of point-like radioactive sources. In the present study, we used a newly developed traceable point-like Ge68/Ga68 radioactive source for determining calibration factors of a PET scanner. The point-like Ge68/Ga68 radioactive source consists of a spherical aluminum absorber with an outer diameter of 8 mm and a small radioactive bead in it. The physical characteristics of the source were evaluated with a Monte Carlo simulation code based on Geant4. The source radioactivity was calibrated at an accredited calibration facility. The point-like source was placed in the field-of-view of a clinical PET scanner, SET-2400W (Shimadzu Co.). The calibration factors determined with the point-like source were consistent with those determined by a conventional standard calibration method within a reasonable uncertainty. In conclusion, the proposed method with newly developed traceable point-like sources is useful for calibrating PET scanners.

We have devised a standardization method for a sealed point source that can be applied to nuclides such as 22Na that emit a positron and at least one gamma ray. This method is based on coincidence counting of annihilation radiation and gamma rays using a scintillation detector array. In the present study, we performed Monte Carlo simulations to examine this method for various measurement conditions. EGS5 Monte Carlo simulation results confirm that this method is effective for measurements of a 22Na sealed point source using BGO scintillation detector arrays

Objective: In order to improve the convenience and reliability of the calibration procedure with respect to the quantitative aspects of PET scanners, we have been developing new methods that rely on the use of point-like radioactive sources. The aim of this study is to report the results of the application of the proposed method for obtaining the cross-calibration factors (CCFs) of a clinical PET scanner for the first time. Methods: A 22Na point-like source was moved in the axial direction to cover the axial field-of-view (FOV) of a commercial PET scanner, SET-2400W (Shimadzu). From reconstructed images, saturated regions-of-interest (ROI) values were used to calculate the CCFs that were defined slice by slice. Results: It was possible to obtain CCFs that were practically equivalent to those obtained by the standard method with cylindrical water phantoms. The variations in the CCFs obtained over about a half-year were well reproduced by the proposed method. Conclusion: The proposed calibration method, which is based on the use of a point-like radioactive source, is useful for determining CCFs and their variations for a clinical PET scanner.

In order to calibrate PET devices by a sealed point source, we contrived an absolute activity measurement method for the sealed point source using scintillation detector arrays. This new method was verified by EGS5 Monte Carlo simulation.

Background: In order to evaluate the uncertainty in the radioactivity measurements performed using PET scanners and to determine the calibration factors of these scanners, it is essential that the radioactive sources are equipped with absorber materials that ensure the annihilation of positrons. Therefore, the evaluation and calibration depend on scatter and attenuation corrections in conventional techniques based on phantoms. Although an extrapolation method that involves the use of multiple absorber sleeves for a line radioactive source is effective in eliminating the dependence, the long line shape limits its application range. Objective: The objective of this study is to propose a point-like radioactive source with multiple absorber capsules, which can be used to evaluate the uncertainty in the radioactivity measurements performed using a PET scanner and to determine a calibration factor in a way that is independent of scatter and attenuation corrections. Methods: The proposed radioactive source consists of a small spherical radioactive part and a set of successively sized aluminum absorber capsules. Extrapolation over the total absorber thickness made it possible to estimate the results that were approximately free from scatter and absorption caused by the absorber materials. As an example application, the proposed method was used to a research PET scanner. In addition, the basic characteristic of the point-like radioactive source was investigated using a Monte Carlo simulation code. Results and Conclusion: Performance characteristics and a calibration factor of the PET scanner were successfully evaluated and determined. Therefore, the proposed method is useful for this purpose. Further studies are expected to improve the design of the radioactive source and enhance the practicability and traceability of our proposed method.

Purpose To study the 3-year effect of oral nilvadipine, a calcium antagonist, on visual field performance and ocular circulation in open-angle glaucoma (OAG) with low-normal intraocular pressure (IOP). Design A randomized, placebo-controlled, double-masked, single-center trial. Participants Patients with OAG who were younger than 65 years and had untreated IOP consistently of 16 mmHg or less. Intervention Oral nilvadipine (2 mg twice daily) or placebo was assigned randomly to patients fulfilling the criteria by the minimization method of balancing the groups according to age, refraction, and the mean deviation (MD) value (Humphrey Perimeter 30-2 SITA Standard Program; Humphrey Instruments, Inc., San Leandro, CA) of the eye with less negative MD. No topical ocular hypotensive drugs were prescribed. Visual field testing was performed every 3 months; fundus examination and IOP, blood pressure, and pulse rate measurements were carried out every month; and quantitative indexes of circulation in the optic disc rim (NB ONH ) and choroid in the foveal area (NB fovea ) were determined using the laser speckle method at 0, 3, 6, 12, 18, 24, 30, and 36 months. Main Outcome Measures The time courses of MD, NB ONH , and NB fovea in the eye with less negative MD. Results Thirty-three patients were enrolled; 17 were assigned to nilvadipine and 16 were assigned to placebo; 13 in each group completed the study. No significant intergroup difference was seen in age, refraction, or baseline values of any of the parameters. During the 3-year period, the IOP averaged 12.6 mmHg in the nilvadipine group and 12.8 mmHg in the placebo group ( P >0.1), and no significant change from baseline or intergroup difference was seen in blood pressure or pulse rate. The estimated slope of change in the MD was less negative in the nilvadipine than in the placebo group (−0.01 vs. −0.27 decibels/year; P = 0.040). The NB ONH and NB fovea values remained increased compared with baseline for the study period by approximately 30% to 40% only in the nilvadipine group, and the intergroup difference was significant ( P = 0.003 for NB ONH and P = 0.007 for NB fovea ). Conclusions Nilvadipine (2 mg twice daily) slightly slowed the visual field progression and maintained the optic disc rim, and the posterior choroidal circulation increased over 3 years in patients with OAG with low-normal IOP. Financial Disclosure(s) The authors have no proprietary or commercial interest in any materials discussed in this article.