Language：English   Publishing type：Research paper (scientific journal)  

Prompt gammas imaging (PGI) is a promising method for observing a beam's shape and estimating the range of the beam from outside a subject. However 2-dimensional images of prompt gammas (PGs) during irradiation of protons were still difficult to measure. To achieve PGI, we developed a new gamma camera and imaged PGs while irradiating a phantom by proton beams. We also simultaneously measured prompt X-ray (PX) images with an X-ray camera from opposed direction and compared the images. The developed gamma camera uses a 10 mm thick GAGG block optically coupled to a flat panel photomultiplier tube (FP-PMT), and it is contained in a 20 mm thick tungsten container with a pinhole collimator attached. A poly-methyl-methacrylate (PMMA) block was irradiated by proton beams with total number of the protons similar to the clinical level, and the gamma camera imaged PGs and X-ray camera imaged PXs simultaneously. For all of the tested beams, we could measure the beam shapes of the PGs and the PXs and the ranges could also be estimated from the images. For both PG and PX images, time sequential images and accumulated images could be derived. We confirmed that the PGI using our developed gamma camera, as well as PXI, is promising for beam imaging and range estimation in proton therapy.

DOI： 10.1016/j.ejmp.2024.104847

PubMed

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Objective

Dead-time loss is reported to be non-negligible for some patients with a high tumor burden in Lu-177 radionuclide therapy, even if the administered activity is 7.4 GBq. Hence, we proposed a simple method to shorten the apparent dead time and reduce dead-time loss using a thin lead sheet in previous work. The collimator surface of the gamma camera was covered with a lead sheet in our proposed method. While allowing the detection of 208-keV gamma photons of Lu-177 that penetrate the sheet, photons with energies lower than 208 keV, which cause dead-time loss, were shielded. In this study, we evaluated the usefulness of tungsten functional paper (TFP) for the proposed method using Monte Carlo simulation.

Methods

The count rates in imaging of Lu-177 administered to patients were simulated with the International Commission on Radiological Protection (ICRP) 110 phantom using the GATE Monte Carlo simulation toolkit. The simulated gamma cameras with a 0.5-mm lead sheet, 1.2-mm TFP, or no filter were positioned closely on the anterior and posterior sides of the phantom. The apparent dead times and dead-time losses at 24 h after administration were calculated for an energy window of 208 keV ± 10%. Moreover, the dead-time losses at 24–120 h were analytically assessed using activity excretion data of Lu-177-DOTATATE.

Results

The dead-time loss without a filter was 5% even 120 h after administration in patients with a high tumor burden and slow excretion, while those with a lead sheet and TFP were 0.22 and 0.58 times less than those with no filter, respectively. The count rates with the TFP were 1.3 times higher than those with the lead sheet, and the TFP could maintain primary count rates at 91–94% of those without a filter.

Conclusions

Although the apparent dead time and dead-time loss with the lead sheet were shorter and less than those with TFP, those with TFP were superior to those without a filter. The advantage of TFP over the lead sheet is that the decrease in primary count rates was less.

DOI： 10.1007/s12149-024-01987-5

Other Link： https://link.springer.com/article/10.1007/s12149-024-01987-5/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Scintillator-based X-ray imaging detectors are pivotal in numerous scientific and practical domains, including medical imaging, food and device inspection, and security monitoring. Recent advancements have spurred interest in 4D X-ray imaging using synchrotron radiation, necessitating higher temporal resolutions. Consequently, this places stringent demands on X-ray detector technology, especially when X-ray energy exceeds 20 keV. The selection of a suitable scintillator material is crucial for achieving optimal timing resolution, yet it poses a significant challenge in dynamic X-ray imaging. This study delves into the optimization of scintillator properties and their impact on spatial resolution and light output, elucidating the performance of Ce-doped Gd₃Ga₃Al₂O₁₂ (GAGG:Ce) scintillators for X-ray imaging applications. We developed a micro X-ray imaging detector using a 100 μm-thick GAGG:Ce scintillator plate and conducted X-ray imaging tests at the Aichi SR facility. The results demonstrated that the resolution, quantified as the chart slit width at a contrast transfer function (CTF) value of 10%, reached 2 ∼ 3 μm with a 4× lens, 0.52 μm± 0.03 μm with a 20× lens, and 0.42 μm± 0.01 μm with a 40× lens. Although the results of this study did not achieve a spatial resolution nearing the effective pixel size of the 40× lens, the text also elucidates the underlying reasons for this limitation. Furthermore, we compared the X-ray sensitivity of our GAGG:Ce scintillator plate with that of a commercial LuAG:Ce scintillator, revealing an approximately 1.5-fold increase in light output. As a demonstration, transmission images of dried small fish were captured using the GAGG:Ce scintillator plate and the developed X-ray imaging system. These findings highlight the potential of the X-ray imaging detector devised in this study for future generations of X-ray imaging applications.

DOI： 10.1088/1748-0221/19/10/p10030

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.nima.2024.169673

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.nima.2024.169484

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

An imaging technique utilizing a scintillator plate in conjunction with a magnifying unit and a cooled electron multiplying charge-coupled device (EM-CCD) camera shows promise for capturing high-resolution trajectory images. Nevertheless, in the 2-dimensional trajectory images, the incident directions of the alpha particles entering the scintillator plate remained unknown due to the line-shaped trajectories. To elucidate the incident directions in our trajectory images, we conducted experiments capturing trajectory images of alpha particles under off-focus conditions. To capture off-focus images of alpha particles, we systematically varied the distance between the GAGG plate and the lens during imaging using an americium-241 (Am-241) source. Through images obtained at different distances between the GAGG plate and the lens, we successfully acquired trajectory images with varying degrees of off-focus, revealing that trajectory images focused on the upper surface of the GAGG plate exhibited blurred and wider trajectories in the deeper regions, making the incident directions of the alpha particles evident. We conclude that the proposed off-focus method for trajectory imaging of alpha particles holds promise for estimating the incident directions in the trajectory images.

DOI： 10.1088/1748-0221/19/04/t04010

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

It is known that scintillators exhibit non-proportional behavior between light output and the energy of gamma photons or beta particles. However, the non-proportionality between light output in scintillators and the energy of alpha particles has not been extensively measured, likely due to the challenges associated with preparing alpha particles with varying energies. To address this issue, we propose a novel method to modulate the energy of alpha particles using an americium-241 (Am-241) source covered with different numbers of Mylar films. By irradiating various scintillators, including GAGG, GGAG, YAP(Ce), and plastic scintillator, with alpha particles of different energies, we measured and evaluated the non-proportional response of these scintillators. We then compared the measured response as a function of incident energy to a simulation, which assumes a proportional response to evaluate the non-proportionality. For all the scintillators tested, non-proportionality was observed; the light output per MeV at 1.8 MeV ranged from 0.60 to 0.81 of the values observed at 5.2 MeV. The non-proportional response was largest for plastic scintillator (0.60) and smallest for GAGG (0.81). We conclude that the proposed method could be an efficient means of measuring the non-proportionality of scintillators between light output and alpha particle energies

DOI： 10.1088/1748-0221/19/04/p04011

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ejmp.2024.103298

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Objective. Prompt gamma photon, prompt x-ray, and induced positron imaging are possible methods for observing a proton beam’s shape from outside the subject. However, since these three types of images have not been measured simultaneously nor compared using the same subject, their advantages and disadvantages remain unknown for imaging beam shapes in therapy. To clarify these points, we developed a triple-imaging-modality system to simultaneously measure prompt gamma photons, prompt x-rays, and induced positrons during proton beam irradiation to a phantom. Approach. The developed triple-imaging-modality system consists of a gamma camera, an x-ray camera, and a dual-head positron emission tomography (PET) system. During 80 MeV proton beam irradiation to a polymethyl methacrylate (PMMA) phantom, imaging of prompt gamma photons was conducted by the developed gamma camera from one side of the phantom. Imaging of prompt x-rays was conducted by the developed x-ray camera from the other side. Induced positrons were measured by the developed dual-head PET system set on the upper and lower sides of the phantom. Main results. With the proposed triple-imaging-modality system, we could simultaneously image the prompt gamma photons and prompt x-rays during proton beam irradiation. Induced positron distributions could be measured after the irradiation by the PET system and the gamma camera. Among these imaging modalities, image quality was the best for the induced positrons measured by PET. The estimated ranges were actually similar to those imaged with prompt gamma photons, prompt x-rays and induced positrons measured by PET. Significance. The developed triple-imaging-modality system made possible to simultaneously measure the three different beam images. The system will contribute to increasing the data available for imaging in therapy and will contribute to better estimating the shapes or ranges of proton beam.

DOI： 10.1088/1361-6560/ad25c6

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

An imaging method that utilizes a scintillator plate combined with a magnifying unit and a cooled electron multiplying charge-coupled device (EM-CCD) camera shows promise for obtaining high-resolution trajectory images. However, it is not yet clear whether the ranges of the trajectory images change with the energy of the alpha particles. Additionally, it remains unclear whether the intensity of the trajectory images is affected by the energy of the alpha particles. To address these questions in our trajectory imaging research, we conducted experiments to capture trajectory images of alpha particles with varying energy levels. To generate alpha particles with different energies, we modulated the energy using an americium-241 (Am-241) source covered with varying numbers of Mylar films. With this alpha source and imaging system, we successfully captured trajectory images with different alpha particle energies and were able to assess the ranges and intensities of these trajectories at various energy levels. The estimated ranges from the measured images with different alpha particle energies closely matched the results obtained through simulations. However, it's worth noting that the light output, as evaluated for the measured trajectory images, was slightly lower than the simulated results at lower energy levels probably due to the non-proportionality of the GAGG plate with respect to alpha particle energies.

DOI： 10.1088/1748-0221/19/01/p01010

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.apradiso.2023.111143

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

Objective: Precise monitoring of the position and dwell time of iridium-192 (Ir-192) during high-dose-rate (HDR) brachytherapy is crucial to avoid serious damage to normal tissues. Source imaging using a compact gamma camera is a potential approach for monitoring. However, images from the gamma camera are affected by blurring and statistical noise, which impact the accuracy of source position monitoring. This study aimed to develop a deep-learning approach for estimating ideal source images that reduce the effect of blurring and statistical noise from experimental images captured using a compact gamma camera.
Approach: A double pix2pix model was trained using the simulated gamma camera images of an Ir-192 source. The first model was responsible for denoising the Ir-192 images, whereas the second model performed super resolution. Trained models were then applied to the experimental images to estimate the ideal images. 
Main results: At a distance of 100 mm between the compact gamma camera and the Ir-192 source, the difference in full width at half maximum (FWHM) between the estimated and actual source sizes was approximately 0.5 mm for a measurement time of 1.5 s. This difference has been improved from approximately 2.7 mm without the use of DL. Even with a measurement time of 0.1 s, the ideal images could be estimated as accurately as in the 1.5 s measurements. This method consistently achieved accurate estimations of the source images at any position within the field of view; however, the difference increased with the distance between the Ir-192 source and the compact gamma camera.
Significance: The proposed method successfully provided estimated images from the experimental images within errors smaller than 0.5 mm at 100 mm. This method is promising for reducing blurring and statistical noise from the experimental images, enabling precise real-time monitoring of Ir-192 sources during HDR brachytherapy.

DOI： 10.1088/2057-1976/ad0bb2

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

It is known that a lithium-6 (⁶Li) absorbs a neutron and is divided into a triton and an alpha particle. However, the trajectories of the produced tritons have not yet been imaged in real time and high resolution. We developed an ultrahigh-resolution imaging system that can clearly observe the trajectories of neutron induced particles in real time. The developed system is based on a magnifying unit and a cooled electron multiplying charge-coupled device (EM-CCD) camera combined with a ⁶Li plate and a Ce-doped Gd₃Al₂Ga₃O₁₂(GAGG) scintillator plate. Neutrons from a californium-252 (²⁵²Cf) source were irradiated to the ⁶Li plate, which produced tritons and alpha particles. The produced tritons or alpha particles entered the GAGG plate and produced scintillation light along the trajectories. The scintillation trajectories were magnified by the unit, light intensified, and imaged by the EM-CCD camera. Using our system, we could measure the elongated trajectory images of the particles in real time. Most of these trajectories had Bragg peak like shapes in the images. The average range was 15 μm and the width was 4.6 μm FWHM. From the ranges we estimated, we found that these trajectories could be attributed to the induced tritons. Consequently, the developed real time imaging system is promising for research on the ultrahigh resolution imaging of neutron produced particles.

DOI： 10.1088/1748-0221/18/10/t10002

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

High-resolution and real-time imaging of the trajectories of alpha particles is desired in nuclear medicine and nuclear engineering. Although an imaging method using a scintillator plate combined with a magnifying unit and a cooled electron multiplying charge-coupled device (EM-CCD) camera is a possible method of obtaining high-resolution trajectory images, the spatial resolution of the system is limited to ∼2 μm. To overcome the spatial resolution limitations of this method on trajectory imaging, we used a cooled complementally metal oxide (CMOS) camera in which the sensor had a much larger number of pixels, which were also smaller. Using the CMOS camera based imaging system, we could measure the trajectories of alpha particles in real time with the spatial resolution of 0.34 μm FWHM. With smoothing of the images to reduce image noise, spatial resolution was still kept to less than 0.75 μm. We conclude that this CMOS camera-based alpha-particle trajectory-imaging system is promising for alpha-particle or other particles imaging where ultrahigh spatial resolution is required.

DOI： 10.1088/1748-0221/18/10/t10003

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.apradiso.2023.111084

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

High-resolution imaging of neutron induced particles is required in such methods as neutron radiography. However, the scintillation spots in a neutron-sensitive scintillator have not yet been imaged nor measured for size. We developed a high-resolution, real-time neutron induced particle imaging system for observing these particles' trajectories in a scintillator. The developed system is based on a magnifying unit and a cooled electron multiplying charge-coupled device (EM-CCD) camera combined with a lithium-containing silver-doped zinc sulfide (Li-ZnS(Ag)) scintillator plate. Neutrons from a californium-252 (²⁵²Cf) source were irradiated to the Li-ZnS(Ag) scintillator and imaged with the system. Using our system, we measured the scintillation spots of the neutron induced particles having different shapes in real time. In some of these measured scintillation spots, those with elliptical shapes were observed due to the trajectories of the particles in the scintillator. The spatial resolution calculated from the widths of the scintillation spots was ∼56 μm. Consequently, the developed imaging system is promising for research on neutron imaging that requires high spatial resolution.

DOI： 10.1088/1748-0221/18/06/t06009

Language：English   Publishing type：Research paper (scientific journal)  

Objective. Prompt x-ray imaging using a low-energy x-ray camera is a promising method for observing a proton beam's shape from outside the subject. Furthermore, imaging of positrons produced by nuclear reactions with protons is a possible method for observing the beam shape. However, it has not been possible to measure these two types of images with a single imaging system due to the limited imaging capability of existing systems. Imaging of both prompt x-rays and the distribution of positrons may compensate for the shortcomings of each method.Approach. We conducted imaging of the prompt x-ray using a pinhole x-ray camera during irradiation with protons in list mode. Then, after irradiation with protons, imaging of annihilation radiations from the produced positrons was conducted using the same pinhole x-ray camera in list mode. After this imaging, list-mode data were sorted to obtain prompt x-ray images and positron images.Main results. With the proposed procedure, we could measure both prompt x-ray images and induced positron images with a single irradiation by a proton beam. From the prompt x-ray images, ranges and widths of the proton beams could be estimated. The distributions of positrons were slightly wider than those of the prompt x-rays. From the time sequential positron images, we could derive the time activity curves of the produced positrons.Significance. Hybrid imaging of prompt x-rays and induced positrons using a pinhole x-ray camera was achieved. The proposed procedure would be useful for measuring prompt x-ray images during irradiation to estimate the beam structures as well as for measuring the induced positron images after irradiation to estimate the distributions and time activity curves of the induced positrons.

DOI： 10.1088/1361-6560/acd2a2

PubMed

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s13246-023-01281-0

Other Link： https://rdcu.be/ddcLy

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

High-resolution imaging of alpha particles is required in the detection of alpha radionuclides in cells or small organs for the development of radio-compounds for targeted alpha-particle therapy or other purposes. We developed an ultrahigh resolution, real time alpha-particle imaging system for observing the trajectories of alpha particles in a scintillator. The developed system is based on a magnifying unit and a cooled electron multiplying charge-coupled device (EM-CCD) camera, combined with a 100-µm-thick Ce-doped Gd₃Al₂Ga₃O₁₂ (GAGG) scintillator plate. Alpha particles from an Am-241 source were irradiated to the GAGG scintillator and imaged with the system. Using our system, we measured the trajectories of the alpha particles having different shapes in real time. In some of these measured trajectories, the line shapes of the alpha particles that flew in the GAGG scintillator were clearly observed. The lateral profiles of the alpha-particle trajectories were imaged with widths of ~ 2 µm. We conclude that the developed imaging system is promising for research on targeted alpha-particle therapy or other alpha particle detections that require high spatial resolution.

DOI： 10.1038/s41598-023-31748-9

Other Link： https://www.nature.com/articles/s41598-023-31748-9

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Purpose: Although real-time imaging of the high-activity iridium-192 (Ir-192) source position during high-dose -rate (HDR) brachytherapy using a high-energy gamma camera system is a promising approach, the energy window was not optimized for spatial resolution or scatter fraction.Methods: By using a list-mode data-acquisition system that can acquire energy information of a cerium-doped yttrium aluminum perovskite (YA1O3: YAP(Ce)) gamma camera, we tried to optimize the energy window's setting to improve the spatial resolution and reduce scatter fraction.Results: The spatial resolution was highest for the central energy of the window at-300 keV. The scatter fraction was also smallest for the central energy of the window at-300 keV, and the scatter fraction was more than 48 % smaller than that for the full energy window.Conclusions: We clarified that the spatial resolution can be improved and the scatter fraction can be reduced through optimizing the energy window of the YAP(Ce) gamma camera by setting the central energy of the window to-300 keV for HDR brachytherapy.

DOI： 10.1016/j.ejmp.2022.09.017

Web of Science

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing Ltd  

Abstract

Astatine-211 (At-211) is a promising alpha particle emitter for targeted radionuclide therapy. Since its daughter isotope (polonium-211(Po-211)) emits characteristic X-rays of about 80 keV, the distribution of At-211 in the body can be imaged by detecting the X-rays with a scintillation camera. However, the isotopes also emit high-energy gamma photons that are collimated with difficulty for a parallel-hole collimator of a clinical scintillation camera system, and thus the selection of a collimator is important. In this study, we compared the performances of low-energy high-resolution (LEHR), low-energy all-purpose (LEAP), medium-energy (ME), and high-energy (HE) parallel-hole collimators for At-211 using Monte Carlo simulation. We simulated a clinical scintillation camera system with the collimators using the Geant4 toolkit. The energy spectra, sensitivities, and spatial resolutions for the point source of At-211 were evaluated. Moreover, we simulated imaging of six sphere sources of At-211 in a 1-cm-thick cylindrical phantom filled with At-211 solution to evaluate image contrast. All of the results in this study are simulation data. The spatial resolution with LEHR was 7.6 mm full width at half maximum (FWHM) and the highest between collimators, while the sensitivity with LEAP was 85 cps/MBq and the highest. The image contrast acquired with the ME collimator was superior to those with the other collimators. We concluded that the LEHR, LEAP, and ME collimators had their advantages, so an optimum collimator should be selected depending on the purpose of imaging of At-211, although there was no advantage in using the HE collimator for the imaging of At-211.

DOI： 10.1088/1748-0221/17/10/T10007

Web of Science

Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/17/10/T10007/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Purpose Measurement of the dwell time and moving speed of a high-activity iridium-192 (Ir-192) source used for high-dose-rate (HDR) brachytherapy is important for estimating the precise dose delivery to a tumor. For this purpose, we used a cerium-doped yttrium aluminum perovskite (YA1O(3):YAP(Ce)) gamma camera system, combined with a list-mode data acquisition system that can acquire short-time sequential images, and measured the dwell times and moving speeds of the Ir-192 source. Methods Gamma photon imaging was conducted using the gamma camera in list mode for the Ir-192 source of HDR brachytherapy with fixed dwell times and positions. The acquired list-mode images were sorted to millisecond-order interval time sequential images to evaluate the dwell time at each position. Time count rate curves were derived to calculate the dwell time at each source position and moving speed of the source. Results We could measure the millisecond-order time sequential images for the Ir-192 source. The measured times for the preset dwell times of 2 s and 10 s were 1.98 to 2.00 s full width at half maximum (FWHM) and 10.0 s FWHM, respectively. The dwell times at the first dwell position were larger than those at other positions. We also measured the moving speeds of the source after the dwells while moving back to the afterloader and found the speed increased with the distance from the edge of the field of view to the last dwell position. Conclusion We conclude that millisecond-order time sequential imaging of the Ir-192 source is possible by using a gamma camera and is useful for evaluating the dwell times and moving speeds of the Ir-192 source.

DOI： 10.1002/mp.15957

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

In high-dose-rate (HDR) brachytherapy, verification of an Ir-192 source's position during treatment is required. One of the methods for this used a high-energy pinhole gamma camera to image the position of the source, but the absolute position of the source cannot be measured. To confirm the absolute position, it will be useful to acquire the transmission image of a subject in addition to the gamma photon image at the same time without using an additional X-ray system. To measure the transmission images, we tried to use the high-energy gamma photons emitted from the Ir-192 source used for the therapy. We developed a high-energy gamma photon imaging system composed of 1-mm-thick Pr doped Gd₂O₂S (GOS), a surface mirror, and a cooled charge-coupled device (CCD) camera. The developed imaging system achieved transmission imaging of high-energy gamma photons by transporting the Ir-192 source in front of the imaging system. The spatial resolution of the imaging system was better than 2.4 mm FWHM with and without a 10-cm-thick acrylic block set between the imaging system and the source. Moderate spatial resolution and contrast images of phantoms were obtained with the system. For the dynamic imaging mode, continuous images of the phantoms were measured with 1-sec intervals. There was no observable difference in the transmission images by the movement of the Ir-192 source. Transmission imaging of subjects using an Ir-192 source for HDR brachytherapy could be achieved using our developed imaging system. The system offers a new method to measure the real-time transmission images of the subject during HDR brachytherapy.

DOI： 10.1088/1748-0221/17/06/t06009

Other Link： https://iopscience.iop.org/article/10.1088/1748-0221/17/06/T06009/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa {UK} Limited  

Imaging of 14C outside of the subject is considered to be difficult because it is a radionuclide that emits only low-energy beta particles. However, we found that bremsstrahlung X-rays form 14C could be imaged from outside of subjects and is thus applicable to in vivo small animal imaging. We developed a high-resolution low-energy X-ray imaging system using a (Gd, La)2Si2O7:Ce(La-GPS) plate combined with a flat panel photomultiplier tube (FP-PMT) for in vivo imaging of a mouse to detect the X-rays from a 14C solution administered. Without using a parallel hole collimator, accumulated 14C in the mouse’s abdomen was imaged in 1 min and dynamic in vivo imaging was possible although the spatial resolution was moderate. With a parallel hole collimator, 14C in the abdomen was obtained with a higher spatial resolution with a 60-min acquisition time. We conclude that in vivo imaging of 14C is possible by using the developed high-resolution La-GPS imaging system and may be promising for molecular imaging research.

DOI： 10.1080/00223131.2022.2050319

Web of Science

Scopus

Authorship：Lead author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

DOI： 10.1109/nss/mic44867.2021.9875591

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

DOI： 10.1016/j.apradiso.2021.109861

Web of Science

Scopus

PubMed

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.1088/1748-0221/16/08/t08005

Web of Science

Scopus

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

Since Ce-doped YAlO3 (YAP(Ce)) scintillators have small non-proportionality, it is useful to develop a radiation imaging detector for low-energy gamma photons or X-rays. However, the YAP(Ce) performance with different Ce concentrations remains unclear. Consequently, we measured the basic performance of YAP(Ce) plates with different Ce concentrations. We used three types of YAP(Ce) scintillator plates with different Ce concentrations: 0.05% Ce, 1% Ce, and 2% Ce. The YAP(Ce) plates were 10 mm × 10 mm x 0.5 mm. We measured and compared the energy spectra, the decay times, the α-γ ratio, and the non-proportionality. We also evaluated the relation between these performances and the Ce concentrations. The light output of a YAP(Ce) showed positive correlation with the Ce concentrations, and the decay time of the YAP(Ce) showed a negative correlation with them. The energy resolution slightly improved for a YAP(Ce) with higher Ce concentrations. We found the α-γ ratio were slightly larger for higher Ce concentrations. The YAP(Ce) plate with a 2% Ce had the highest light output and the best energy resolution as well as the shortest decay time. Based on these results, the YAP(Ce) plate with a concentration of 2% Ce is a better selection for the development of radiation detectors or radiation imaging detectors for low-energy gamma photons or X-rays as well as alpha particles.

DOI： 10.1016/j.apradiso.2020.109483

Scopus

PubMed

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

Purpose: Astatine-211 (At-211) is a promising alpha emitter for radionuclide therapy. High-resolution in vivo imaging of At-211 in small animals is needed for the development of At-211 radiopharmaceuticals. For this purpose, we developed a low-energy x-ray camera using a thin YAlO3:Ce (YAP(Ce)) plate to image the low-energy x rays (73–87 keV) from the daughter radionuclide of At-211 (Po-211). Method: We optically coupled a 38 × 38 × 1-mm YAP (Ce) plate to a position-sensitive photomultiplier (PSPMT) to develop an imaging detector. A pinhole or a parallel hole collimator was attached to the imaging detector, and the performance was measured for 60-keV gamma photons. With the developed x-ray camera, we carried out imaging of a mouse that had been administered At-211-NaAt. Results: The intrinsic spatial resolution of the YAP (Ce) x-ray camera was approximately 1.2 mm FWHM, and the energy resolution was 22% FWHM. With a 5-mm-thick parallel hole collimator, the spatial resolution was 3.8 mm FWHM with a sensitivity of 8 × 10−4 at 10 mm, which is a typical distance from the surface of the collimator to a subject in mouse imaging. Using a 1-mm diameter pinhole collimator, the spatial resolution was 1.8 mm FWHM with a sensitivity of 3.5 × 10−4 at 10 mm from the collimator. In the mouse images measured by the developed x-ray camera, we could clearly observe that the At-211 accumulated in the thyroid gland and the stomach of the mouse. Conclusion: We concluded that the YAP (Ce) x-ray camera is useful for in vivo imaging of At-211.

DOI： 10.1002/mp.14455

Web of Science

Scopus

PubMed

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

DOI： 10.1016/j.apradiso.2020.109136

Web of Science

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

Tritium (H-3) is a pure beta-emitting radionuclide and beta particles have extremely low energy (maximum energy: 18.6 keV). Thus the in-vivo imaging of H-3 is thought to be impossible. However, beta particles emit bremsstrahlung X-rays in subjects that may be imaged from outside of the subjects. We tried to image the bremsstrahlung X-rays from H-3 water using a newly developed radiation imaging system. The developed imaging system used a pixelated Ce-doped (Gd, La)2Si2O7 (LaGPS) scintillator plate optically coupled to a flat-panel position-sensitive photomultiplier tube (FP-PMT). Using the imaging system, we conducted bremsstrahlung X-ray imaging from H-3 water in a plastic bag with 37-MBq radioactivity. We obtained tungsten slit mask images with a spatial resolution of ∼3 mm full width at half maximum (FWHM). The energy spectrum of the bremsstrahlung X-rays from the H-3 water showed a broad distribution with an average energy of ∼10 keV. The measured sensitivities of the LaGPS imaging system for bremsstrahlung X-rays from H-3 water in a plastic bag were 1.8 × 10-7. We conclude that the imaging of bremsstrahlung X-rays from H-3 water was really possible and it has a potential to be a new method for the in-vivo H-3 imaging of small animals, plants, or materials.

DOI： 10.1088/1748-0221/15/04/p04006

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.1088/1748-0221/14/10/p10013

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers ({IEEE})  

DOI： 10.1109/trpms.2018.2876410

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.1088/2057-1976/ab12bd

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.nima.2017.10.052

Web of Science

Scopus

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

DOI： 10.1088/2057-1976/aa635e

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

Although Lu-based scintillators, including Ce-doped Lu1.8Y0.2SiO5 (LYSO) scintillators, are often used for positron emission tomography (PET) detectors, they are not commonly used in gamma cameras for single-photon emission computed tomography (SPECT) because background counts due to contamination of the natural radioisotope in Lu are detected. However, several studies report that deterioration in image contrast due to background counts of the natural radioisotope is not critical and thus LYSO is promising for use in SPECT detectors. Meanwhile, a new scintillator, the Ce-doped Gd3Al2Ga3O12 (GAGG) with a high light yield and no natural radioisotope, has been developed and is also thought to be a promising scintillator. Thus, we compared the performance of LYSO with that of GAGG to determine which is more appropriate for a silicon photomultiplier (Si-PM)-based high-resolution small field-of-view (FOV) gamma camera for SPECT. We used finely pixelated LYSO and GAGG plates that were optically coupled to Si-PM arrays to form gamma cameras and measured the basic performance for 122-keV gamma photons. The energy resolutions of the LYSO- and GAGG-based Si-PM gamma cameras were 30% and 23% full width at half maximum (FWHM), respectively. The intrinsic spatial resolution of the GAGG (∼0.5mm FWHM) based gamma camera was better than that of the LYSO (∼0.6mm FWHM). The background counts of the LYSO-based gamma camera were 28 times larger than that of the GAGG. Based on these results, we conclude that GAGG is more appropriate than LYSO for the development of a Si-PM based gamma camera for high resolution SPECT.

DOI： 10.1016/j.nima.2017.08.013

Web of Science

Scopus

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.nima.2016.09.014

Web of Science

Scopus

Event date： 2022.4

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2022.4

Language：Japanese   Presentation type：Oral presentation (general)  

Event date： 2021.10

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Event date： 2018.11

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Event date： 2018.11

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Event date： 2018.11

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Event date： 2017.10

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Event date： 2017.10

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Event date： 2017.7

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Event date： 2017.4

Language：Japanese   Presentation type：Oral presentation (general)