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Purpose: Imaging of the secondary electron bremsstrahlung (SEB) x rays emitted during particle‐ion irradiation is a promising method for beam range estimation. However, the SEB x‐ray images are not directly correlated to the dose images. In addition, limited spatial resolution of the x‐ray camera and low‐count situation may impede correctly estimating the beam range and width in SEB x‐ray images. To overcome these limitations of the SEB x‐ray images measured by the x‐ray camera, a deep learning (DL) approach was proposed in this work to predict the dose images for estimating the range and width of the carbon ion beam on the measured SEB x‐ray images. Methods: To prepare enough data for the DL training efficiently, 10,000 simulated SEB x‐ray and dose image pairs were generated by our in‐house developed model function for different carbon ion beam energies and doses. The proposed DL neural network consists of two U‐nets for SEB x ray to dose image conversion and super resolution. After the network being trained with these simulated x‐ray and dose image pairs, the dose images were predicted from simulated and measured SEB x‐ray testing images for performance evaluation. Results: For the 500 simulated testing images, the average mean squared error (MSE) was 2.5 × 10−5 and average structural similarity index (SSIM) was 0.997 while the error of both beam range and width was within 1 mm FWHM. For the three measured SEB x‐ray images, the MSE was no worse than 5.5 × 10−3 and SSIM was no worse than 0.980 while the error of the beam range and width was 2 mm and 5 mm FWHM, respectively. Conclusions: We have demonstrated the advantages of predicting dose images from not only simulated data but also measured data using our deep learning approach. [ABSTRACT FROM AUTHOR]

Low-energy x-ray imaging of secondary electron bremsstrahlung x-rays emitted during carbon-ion irradiation is a promising method for range estimation and could be used for imaging with almost clinical dose levels of carbon ion. However, the number of counts in images with clinical dose levels is relatively small, making it difficult to obtain precise range estimations. Since improving the sensitivity of the x-ray camera may solve this issue, we developed two new types of x-ray cameras. One uses a 1 mm thick, 40 mm × 40 mm cerium-doped yttrium aluminum perovskite (YA1O3: YAP(Ce)) scintillator plate combined with a 2 inch square flat panel photomultiplier tube (FP-PMT) contained in a 2 cm thick tungsten shield with a pinhole collimator positioned 50 mm from the scintillator; the other uses a 0.5 mm thick, 20 mm × 20 mm YAP(Ce) scintillator plate combined with a 1 inch square position sensitive photomultiplier tube (PSPMT) contained in the same tungsten shield with a pinhole collimator, but with the scintillator positioned closer (30 mm) to the pinhole collimator to obtain a similar field of view. For both cameras, we used a wider angle (∼55°) pinhole collimator to measure the phantom closer to improve sensitivity. Although the 40 mm × 40 mm YAP(Ce) camera had high system spatial resolution, the background count fractions were high and produced a high count area at the center of the images due to the pulse pileup of the signals. With the 20 mm × 20 mm YAP(Ce) camera, we obtained x-ray images with low background counts without a high count area at the image center. By smoothing the measured images, we were able to estimate the ranges even for clinical dose levels. We therefore confirmed that one of our newly developed YAP(Ce) cameras had high sensitivity and is promising for the imaging of secondary electron bremsstrahlung x-rays during irradiation of carbon ions in clinical conditions. [ABSTRACT FROM AUTHOR]

Abstract In nuclear-medical imaging, most clinically applied gamma rays have energies less than or equal to 511 keV. There is growing interest in the applications of radioisotopes emitting higher-energy gamma rays for pretherapeutic and therapeutic imaging. Compton cameras have the capability of imaging gamma rays with a wide range of energies. Since sensitivity of Compton cameras decrease with increase in gamma-ray energy, high sensitivity is required to image such radioisotopes. In this study, we developed a cost-effective Compton camera using high-sensitive inorganic scintillators and a commercially available data acquisition system for a positron emission tomography camera. An imaging experiment of a 54Mn point source was performed to demonstrate the imaging capability for the camera, and the source was successfully imaged. [ABSTRACT FROM AUTHOR]

Astatine-211 is a promising radionuclide for targeted radiotherapy. It is required to image the distribution of targeted radiotherapeutic agents in a patient's body for optimization of treatment strategies. We proposed to image 211 At with high-energy photons to overcome some problems in conventional planar or single-photon emission computed tomography imaging. We performed an imaging experiment of a point-like 211 At source using a Compton camera, and demonstrated the capability of imaging 211 At with the high-energy photons for the first time. [ABSTRACT FROM AUTHOR]

A feasibility study on an imaging technique of a therapeutic proton-beam trajectory using a gamma camera by measuring secondary electron bremsstrahlung (SEB) was performed by means of Monte Carlo simulations and a beam-irradiation experiment. From the simulation and experimental results, it was found that a significant amount of SEB yield exists between the beam-injection surface and the range position along the beam axis and the beam trajectory is clearly imaged by the SEB yield. It is concluded that the SEB imaging is a promising technique for monitoring of therapeutic proton-beam trajectories. [ABSTRACT FROM AUTHOR]

We studied feasibility of detection of a gap which is located across a beam track by measuring low-energy (63-68 keV) photons generated by beam irradiation. An experiment was performed with the Heavy Ion Medical Accelerator in Chiba (HIMAC). A 12C beam having 290 MeV/u was injected on a target consisting of two acrylic blocks. These two blocks were placed with a 10 mm gap along the beam axis. A detection system consisting of a semiconductor detector, a lead collimator having a slit, and borated polyethylene blocks was placed on a movable stage to detect low-energy photons emitted perpendicularly to the beam axis. The position of the detection system was moved at 2 mm intervals along the beam axis. It was found that the yield of 63-68 keV photons was clearly correlated with the position of the detection system. The position at which the yield curve had the lowest value agreed with the gap position. We also confirmed that the experimental result was well reproduced by a Monte Carlo simulation that includes generation of secondary electron bremsstrahlung. [ABSTRACT FROM AUTHOR]

We describe a new method for estimating the beam range in heavy-ion radiation therapy by measuring the ion beam bremsstrahlung. We experimentally confirm that the secondary electron bremsstrahlung process provides the dominant bremsstrahlung contribution. A Monte Carlo simulation shows that the number of background photons from annihilation gamma rays is about 1% of the bremsstrahlung strength in the low-energy region used in our estimation (63-68 keV). Agreement between the experimental results and the theoretical prediction for the characteristic shape of the bremsstrahlung spectrum validates the effectiveness of our new method in estimating the ion beam range. [ABSTRACT FROM AUTHOR]

Abstract: Recently, the demand for the low kerf-loss slice of the silicon wafer for photovoltaic cells is increasing from the point of view of saving raw materials. In this work, we studied the silicon-slicing technique using plasma-etching processing, which is thought to be promising to reduce the kerf loss. Finally, the slice conditions were optimized and slice speed and kerf loss were improved to about 1μm/s and 150μm, respectively. [Copyright &y& Elsevier]

Monitoring methods of therapeutic beams based on the measurement of secondary particles have been proposed and studied worldwide. Since secondary particles are influenced by substances in the human body before they reach detectors, estimation methods of the water-equivalent thickness of the tracks of the secondary particles are required for attenuation correction. In this work, we studied a novel estimation method of the water-equivalent thickness based on the observation of energy distribution of secondary electron bremsstrahlung (SEB) emitted from the trajectories of the therapeutic beams by Monte Carlo simulations. A 12C-ion beam with an energy of 290 MeV/u was injected into a water phantom. The phantom was surrounded by a collimator having a CdTe detector behind the collimator. A distribution of energy deposition due to SEB emission was recorded during beam injection. The simulation was iterated by varying the radius of the phantom. The simulation results were plotted as an R 1 vs. R 2 scatter plot, where R 1 was defined as the ratio of the yield having a deposition energy between 30 and 40 keV to that between 20 and 30 keV, and R 2 was defined as the ratio of the yield having a deposition energy between 60 and 70 keV to that between 20 and 30 keV. We found that clusters are formed at different positions on the scatter plot by different radii of the phantom and that the water-equivalent thickness of the secondary particle tracks could be estimated using the R 1 vs. R 2 plot. • First simulation study on estimation of water-equivalent thicknesses of secondary-particle tracks produced by a therapeutic carbon beam in a water phantom based on observation of secondary electron bremsstrahlung (SEB). • The water-equivalent thicknesses can be estimated using the low energy region (approximately 20 to 30 keV) of the energy distribution of the SEB. • The high energy region (approximately 60 to 70 keV) of the energy distribution slightly depends on depth of the SEB production in the water phantom. [ABSTRACT FROM AUTHOR]

Abstract: We are constructing a three-dimensional imaging system for medical and biological applications. The system will allow simultaneous imaging at high spatial and energy resolutions across a wide energy range, from several tens of keV to a few MeV. The system relies on a Si/CdTe semiconductor Compton camera, incorporating state-of-the-art space-observation technology developed by ISAS/JAXA. The Si/CdTe Compton camera was developed for use at moderate temperatures. Moreover, the solid, thin scattering layer allows the target to be placed close to the camera, a good angular resolution corresponds directly to a good spatial resolution. These aspects allow the construction of a compact medical system. In this work, we have developed a prototype head module for a multi-head system. The performance of the prototype was evaluated with a sealed Ba-133 radiation source. The experiments confirmed that the imaging results were consistent with source positioning. The experimental results were also compared with those of a Monte Carlo simulation. [Copyright &y& Elsevier]

Summary: Rice (Oryza sativa) plants have porous or hollow organs consisting of aerenchyma, which is presumed to function as a low‐resistance diffusion pathway for air to travel from the foliage above the water to submerged organs. However, gas movement in rice plants has yet to be visualized in real time.In this study involving partially submerged rice plants, the leaves emerging from the water were fed nitrogen‐13‐labeled nitrogen ([13N]N2) tracer gas, and the gas movement downward along the leaf blade, leaf sheath, and internode over time was monitored.The [13N]N2 gas arrived at the bottom of the plant within 10 min, which was 20 min earlier than carbon‐11 photoassimilates. The [13N]N2 gas movement was presumably mediated by diffusion along the aerenchyma network from the leaf blade to the root via nodes functioning as junctions, which were detected by X‐ray computed tomography.These findings imply the diffusion of gas along the aerenchyma, which does not consume energy, has enabled plants to adapt to aquatic environments. Additionally, there were no major differences in [13N]N2 gas movement between paddy rice and deepwater rice plants, indicative of a common aeration mechanism in the two varieties, despite the difference in their response to flooding. [ABSTRACT FROM AUTHOR]

Abstract: We have developed a new Compton camera based on silicon (Si) and cadmium telluride (CdTe) semiconductor double-sided strip detectors (DSDs). The camera consists of a Si-DSD and four layers of CdTe-DSDs all of which have common electrode configuration segmented into 128 strips on each side with pitches of . In order to realize high angular resolution and to reduce size of the detector system, a stack of DSDs with short stack pitches of 4mm is utilized to make the camera. Taking advantage of the excellent energy and position resolutions of the semiconductor devices, the camera achieves high angular resolutions of 4.5° at 356keV and 3.5° at 662keV. To obtain such high resolutions together with an acceptable detection efficiency, we demonstrate data reduction methods including energy calibration using Compton scattering continuum and depth sensing in the CdTe-DSD. We also discuss imaging capability of the camera and show simultaneous multi-energy imaging. [Copyright &y& Elsevier]

Visualizing the dynamics of cesium (Cs) is desirable to understand the impact of radiocesium when accidentally ingested or inhaled by humans. However, visualization of radiocesium in vivo is currently limited to plants. Herein, we describe a method for the production and purification of 127Cs and its use in visualizing Cs dynamics in a living animal. The positron-emitting nuclide 127Cs was produced using the 127I (α, 4n) 127Cs reaction, which was induced by irradiation of sodium iodide with a 4He2+ beam from a cyclotron. We excluded sodium ions by using a material that specifically adsorbs Cs as a purification column and successfully eluted 127Cs by flowing a solution of ammonium sulfate into the column. We injected the purified 127Cs tracer solution into living rats and the dynamics of Cs were visualized using positron emission tomography; the distributional images showed the same tendency as the results of previous studies using disruptive methods. Thus, this method is useful for the non-invasive investigation of radiocesium in a living animal. [ABSTRACT FROM AUTHOR]

Compton cameras can simultaneously detect multi-isotopes; however, when simultaneous imaging is performed, crosstalk artifacts appear on the images obtained using a low-energy window. In conventional single-photon emission computed tomography, a dual energy window (DEW) subtraction method is used to reduce crosstalk. This study aimed to evaluate the effectiveness of employing the DEW technique to reduce crosstalk artifacts in Compton images obtained using low-energy windows. To this end, in this study, we compared reconstructed images obtained using either a photo-peak window or a scatter window by performing image subtraction based on the differences between the two images. Simulation calculations were performed to obtain the list data for the Compton camera using a 171 and a 511 keV point source. In the images reconstructed using these data, crosstalk artifacts were clearly observed in the images obtained using a 171 keV photo-peak energy window. In the images obtained using a scatter window (176–186 keV), only crosstalk artifacts were visible. The DEW method could eliminate the influence of high-energy sources on the images obtained with a photo-peak window, thereby improving quantitative capability. This was also observed when the DEW method was used on experimentally obtained images. [ABSTRACT FROM AUTHOR]

Research on the distribution and dynamics of photoassimilates in plants, especially those in fruits, is important for increasing food production. Positron emission tomography (PET) and carbon-11 (11C) can be used for obtaining 3-D images of photoassimilates. For plant experiments, however, it is important to adjust the system to the plant's growth environment. A small OpenPET prototype can visualize an open space between two detector rings, and thus facilitate adjustment of the environment around a target plant during fruit PET imaging. In this work, we improve the OpenPET for plant studies and discuss its applications in the analysis of the dynamics and distributions of photoassimilates in plants with fruits. 11C-labeled photoassimilate translocation into the fruit of a strawberry plant is imaged using 11C-labeled CO 2 and the OpenPET. The OpenPET has been found to be promising for researching the physiological functions of the photoassimilates in plants with fruits. [ABSTRACT FROM AUTHOR]