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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 ([13 N]N2 ) tracer gas, and the gas movement downward along the leaf blade, leaf sheath, and internode over time was monitored. The [13 N]N2 gas arrived at the bottom of the plant within 10 min, which was 20 min earlier than carbon-11 photoassimilates. The [13 N]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 [13 N]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.
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Oryza , Oxígeno , Presión Parcial , Hojas de la Planta , Raíces de Plantas , AguaRESUMEN
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.
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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.
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Terapia de Protones , Protones , Rayos X , Electrones , Terapia de Protones/métodos , Tomografía Computarizada por Rayos X , Fotones/uso terapéutico , Rayos gamma , Fantasmas de Imagen , Método de MontecarloRESUMEN
PURPOSE: To develop a silicon (Si) and cadmium telluride (CdTe) imaging Compton camera for biomedical application on the basis of technologies used for astrophysical observation and to test its capacity to perform three-dimensional (3D) imaging. MATERIALS AND METHODS: All animal experiments were performed according to the Animal Care and Experimentation Committee (Gunma University, Maebashi, Japan). Flourine 18 fluorodeoxyglucose (FDG), iodine 131 ((131)I) methylnorcholestenol, and gallium 67 ((67)Ga) citrate, separately compacted into micro tubes, were inserted subcutaneously into a Wistar rat, and the distribution of the radioisotope compounds was determined with 3D imaging by using the Compton camera after the rat was sacrificed (ex vivo model). In a separate experiment, indium 111((111)In) chloride and (131)I-methylnorcholestenol were injected into a rat intravenously, and copper 64 ((64)Cu) chloride was administered into the stomach orally just before imaging. The isotope distributions were determined with 3D imaging after sacrifice by means of the list-mode-expectation-maximizing-maximum-likelihood method. RESULTS: The Si/CdTe Compton camera demonstrated its 3D multinuclear imaging capability by separating out the distributions of FDG, (131)I-methylnorcholestenol, and (67)Ga-citrate clearly in a test-tube-implanted ex vivo model. In the more physiologic model with tail vein injection prior to sacrifice, the distributions of (131)I-methylnorcholestenol and (64)Cu-chloride were demonstrated with 3D imaging, and the difference in distribution of the two isotopes was successfully imaged although the accumulation on the image of (111)In-chloride was difficult to visualize because of blurring at the low-energy region. CONCLUSION: The Si/CdTe Compton camera clearly resolved the distribution of multiple isotopes in 3D imaging and simultaneously in the ex vivo model.
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Compuestos de Cadmio/química , Cámaras gamma , Silicio/química , Telurio/química , Animales , Citratos/química , Cobre/química , Diseño de Equipo , Fluorodesoxiglucosa F18/química , Galio/química , Radioisótopos de Galio/química , Imagenología Tridimensional , Indio/química , Radioisótopos de Yodo/química , Mascotas , Radiofármacos/química , Ratas , Ratas Wistar , Tomografía Computarizada de Emisión de Fotón ÚnicoRESUMEN
Prompt secondary electron bremsstrahlung X-ray (prompt X-ray) imaging using a low-energy X-ray camera is a promising method for observing a beam shape from outside the subject. However, such imaging has so far been conducted only for pencil beams without a multi-leaf collimator (MLC). The use of spread-out Bragg peak (SOBP) with an MLC may increase the scattered prompt gamma photons and decrease the contrast of the images of prompt X-rays. Consequently, we performed prompt X-ray imaging of SOBP beams formed with an MLC. This imaging was carried out in list mode during irradiation of SOBP beams to a water phantom. An X-ray camera with a 1.5-mm diameter as well as 4-mm-diameter pinhole collimators was used for the imaging. List mode data were sorted to obtain the SOBP beam images as well as energy spectra and time count rate curves. Due to the high background counts from the scattered prompt gamma photons penetrating the tungsten shield of the X-ray camera, the SOBP beam shapes were difficult to observe with a 1.5-mm-diameter pinhole collimator. With the 4-mm-diameter pinhole collimators, images of SOBP beam shapes at clinical dose levels could be obtained with the X-ray camera. The use of a 4-mm-diameter pinhole collimator attached to the X-ray camera is effective for prompt X-ray imaging with high sensitivity and low background counts. This approach makes it possible to image SOBP beams with an MLC when the counts are low and the background levels are high.
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Carbono , Rayos X , Radiografía , Fantasmas de Imagen , IonesRESUMEN
Prompt x-ray imaging is a promising method for observing the beam shape from outside a subject. However, its distribution is different from dose distribution, and thus a comparison with the dose is required. Meanwhile, luminescence imaging of water is a possible method for imaging the dose distribution. Consequently, we performed simultaneous imaging of luminescence and prompt x-rays during irradiation by proton beams to compare the distributions between these two different imaging methods. Optical imaging of water was conducted with spot-scanning proton beams at clinical dose level during irradiation to a fluorescein (FS) water phantom set in a black box. Prompt x-ray imaging was also conducted simultaneously from outside the black box using a developed x-ray camera during proton beam irradiation to the phantom. We measured images of the luminescence of FS water and prompt x-rays for various types of proton beams, including pencil beams, spread-out Bragg peak (SOBP) beams, and clinically used therapy beams. After the imaging, ranges were estimated from FS water and prompt x-rays and compared with those calculated with a treatment planning system (TPS). We could measure the prompt x-ray and FS water images simultaneously for all types of proton beams. The ranges estimated from the FS water and those calculated with the TPS closely matched, within a difference of several mm. Similar range difference was found between the results estimated from prompt x-ray images and those calculated with the TPS. We confirmed that the simultaneous imaging of luminescence and prompt x-rays were possible during irradiation with spot-scanning proton beams at a clinical dose level. This method can be applied to range estimation as well as comparison with the dose for prompt x-ray imaging or other imaging methods used in therapy with various types of proton beams at a clinical dose level.
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Luminiscencia , Protones , Rayos X , Radiografía , Fluoresceína , AguaRESUMEN
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.
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Terapia de Protones , Protones , Rayos X , Electrones , Cámaras gamma , Terapia de Protones/métodos , Fantasmas de Imagen , Rayos gamma , Imagen Multimodal , Método de MontecarloRESUMEN
PURPOSE: Proton-induced secondary-electron-bremsstrahlung (SEB) imaging is a promising method for estimating the ranges of particle beam. However, SEB images do not directly represent dose distributions of particle beams. In addition, the ranges estimated from measured images were deviated because of limited spatial resolutions of the developed x-ray camera as well as statistical noise in the images. To solve these problems, we proposed a method for predicting high-resolution dose images from SEB images with various count level using a deep learning (DL) approach for range and width verification. METHODS: In this study, we adopted the double U-Net model, which is a previously proposed deep convolutional network model. The first U-Net model in the double U-Net model was used to denoise the SEB images with various count level. The first U-Net model for denoising was trained on 8000 pairs of SEB images with various count level and noise-free images which were created by a sophisticated in-house developed model function. The second U-Net model for dose prediction was trained using 8000 pairs of denoised SEB images from the first U-Net model and high-resolution dose images generated by Monte Carlo simulation. RESULTS: For both simulation and measurement data, the trained DL model could successfully predict high-resolution dose images which showed a clear Bragg peak and no statistical noise. The difference of the range and width was less than 2.1 mm, even from the SEB images measured with a decrease in the number of irradiated protons to less than 11% of 3.2 × 1011 protons. CONCLUSIONS: High-resolution dose images from measured and simulated SEB images were successfully predicted by using the trained DL model for protons. Our proposed DL model was feasible to predict dose images accurately even with smaller number of irradiated protons.
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Aprendizaje Profundo , Terapia de Protones , Electrones , Método de Montecarlo , ProtonesRESUMEN
Rice is susceptible to abiotic stresses such as drought stress. To enhance drought resistance, elucidating the mechanisms by which rice plants adapt to intermittent drought stress that may occur in the field is an important requirement. Roots are directly exposed to changes in the soil water condition, and their responses to these environmental changes are driven by photosynthates. To visualize the distribution of photosynthates in the root system of rice plants under drought stress and recovery from drought stress, we combined X-ray computed tomography (CT) with open type positron emission tomography (OpenPET) and positron-emitting tracer imaging system (PETIS) with 11C tracer. The short half-life of 11C (20.39 min) allowed us to perform multiple experiments using the same plant, and thus photosynthate translocation was visualized as the same plant was subjected to drought stress and then re-irrigation for recovery. The results revealed that when soil is drier, 11C-photosynthates mainly translocated to the seminal roots, likely to promote elongation of the root with the aim of accessing water stored in the lower soil layers. The photosynthates translocation to seminal roots immediately stopped after rewatering then increased significantly in crown roots. We suggest that when rice plant experiencing drought is re-irrigated from the bottom of pot, the destination of 11C-photosynthates translocation immediately switches from seminal root to crown roots. We reveal that rice roots are responsive to changes in soil water conditions and that rice plants differentially adapts the dynamics of photosynthates translocation to crown roots and seminal roots depending on soil conditions.
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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 (â¼55°) 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.
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Compuestos de Calcio/química , Cerio/química , Electrones , Radioterapia de Iones Pesados , Óxidos/química , Radiografía/instrumentación , Relación Señal-Ruido , Titanio/química , Itrio/química , Humanos , Fantasmas de Imagen , Conteo por Cintilación , Rayos XRESUMEN
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.
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Aprendizaje Profundo , Electrones , Carbono , Flujo de Trabajo , Rayos XRESUMEN
The Compton camera can simultaneously acquire images of multiple isotopes injected in a body; therefore, it has the potential to introduce a new subfield in the field of biomedical imaging applications. The objective of this study is to assess the ability of a prototype semiconductor-based silicon/cadmium telluride (Si/CdTe) Compton camera to simultaneously image the distributions of technetium (99mTc)-dimercaptosuccinic acid (DMSA) (141 keV emission) and 18F-fluorodeoxyglucose (FDG) (511 keV emission) injected into a human volunteer. 99mTc-DMSA and 18F-FDG were injected intravenously into a 25-year-old male volunteer. The distributions of 99mTc-DMSA and 18F-FDG were simultaneously made visible by setting a specified energy window for each radioisotope. The images of these radiopharmaceuticals acquired using the prototype Compton camera were superimposed onto computed tomography images for reference. The reconstructed image showed that 99mTc-DMSA had accumulated in both kidneys, which is consistent with the well-known diagnostic distribution determined by clinical imaging via single-photon emission computed tomography. In the 18F-FDG image, there is broad distribution around the liver and kidneys, which was expected based on routine clinical positron emission tomography imaging. The current study demonstrated for the first time that the Si/CdTe Compton camera was capable of simultaneously imaging the distributions of two radiopharmaceuticals, 99mTc-DMSA and 18F-FDG, in a human body. These results suggest that the Si/CdTe Compton camera has the potential to become a novel modality for nuclear medical diagnoses enabling multi-probe simultaneous tracking.
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Fluorodesoxiglucosa F18 , Cámaras gamma , Tomografía Computarizada por Tomografía de Emisión de Positrones/métodos , Radiofármacos , Ácido Dimercaptosuccínico de Tecnecio Tc 99m , Adulto , Compuestos de Cadmio , Humanos , Procesamiento de Imagen Asistido por Computador/métodos , Riñón/diagnóstico por imagen , Hígado/diagnóstico por imagen , Masculino , Tomografía Computarizada por Tomografía de Emisión de Positrones/instrumentación , Silicio , TelurioRESUMEN
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.
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Radioisótopos de Cesio/análisis , Radioisótopos de Cesio/farmacocinética , Electrones , Tomografía de Emisión de Positrones/métodos , Monitoreo de Radiación/métodos , Imagen de Cuerpo Entero/métodos , Animales , Radioisótopos de Cesio/aislamiento & purificación , Masculino , Ratas , Ratas Wistar , Distribución TisularRESUMEN
Low-energy x-ray imaging of the secondary electron bremsstrahlung (SEB) x-ray emitted during carbon-ion irradiation is a promising method for range estimation. However, it remains unclear whether the method can be used for imaging with the clinical dose levels of carbon-ion and whether the bremsstrahlung x-ray can be detected from the deeper part of the body. To clarify these points, we developed a new high resolution low-energy x-ray camera and conducted imaging of the SEB x-ray during the irradiation of carbon-ions of different energies and intensities. Imaging was also tried with an x-ray camera using a human-head-sized, 17 cm diameter cylindrical phantom. To develop a high resolution imaging detector for a low-energy x-ray, we used a 20 × 20 × 0.5 mm thick cerium-doped yttrium aluminum perovskite, YA1O3 (YAP(Ce)) scintillator plate, which was optically coupled to a 25 mm square high quantum efficiency (HQE) type position sensitive photomultiplier tube (PSPMT). The imaging detector was encased in a 2 cm thick tungsten container and a pinhole collimator was attached to its camera head. After evaluating the camera's performance, SEB x-ray imaging was tried during irradiation of the carbon-ion and compared the results with a Monte Carlo simulation. We imaged the beam tracks by the SEB x-ray in real-time during irradiation of the carbon-ion and imaging and range estimation were possible even with near clinical dose level of 7.5 × 108 particles of carbon-ion. Clear images of a SEB x-ray were also obtained for a 17 cm diameter cylindrical phantom. The measured images were good agreement with the Monte Carlo simulation. We confirmed that our developed YAP(Ce) camera is promising for imaging SEB x-rays during irradiation of carbon-ions even near clinical conditions.
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Electrones , Radioterapia de Iones Pesados , Radiografía/instrumentación , Itrio/química , Humanos , Método de Montecarlo , Fantasmas de ImagenRESUMEN
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 211At 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 211At source using a Compton camera, and demonstrated the capability of imaging 211At with the high-energy photons for the first time.
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Astato/uso terapéutico , Cintigrafía/instrumentación , Radioterapia/instrumentación , Partículas alfa/uso terapéutico , Simulación por Computador , Humanos , Método de Montecarlo , Neoplasias/diagnóstico por imagen , Neoplasias/radioterapia , Fotones , Cintigrafía/estadística & datos numéricos , Radiofármacos/uso terapéutico , Radioterapia/estadística & datos numéricosRESUMEN
Although the luminescence images of water during proton-beam irradiation using a cooled charge-coupled device camera showed almost the same ranges of proton beams as those measured by an ionization chamber, the depth profiles showed lower Bragg peak intensities than those measured by an ionization chamber. In addition, a broad optical baseline signal was observed in depths that exceed the depth of the Bragg peak. We hypothesize that this broad baseline signal originates from the interaction of proton-induced prompt gamma photons with water. These prompt gamma photons interact with water to form high-energy Compton electrons, which may cause luminescence or Cherenkov emission from depths exceeding the location of the Bragg peak. To clarify this idea, we measured the luminescence images of water during the irradiations of protons in water with minimized parallax errors, and also simulated the produced light by the interactions of prompt gamma photons with water. We corrected the measured depth profiles of the luminescence images by subtracting the simulated distributions of the produced light by the interactions of prompt gamma photons in water. Corrections were also conducted using the estimated depth profiles of the light of the prompt gamma photons, as obtained from the off-beam areas of the luminescence images of water. With these corrections, we successfully obtained depth profiles that have almost identical distributions as the simulated dose distributions for protons. The percentage relative height of the Bragg peak with corrections to that of the simulation data increased to 94% from 80% without correction. Also, the percentage relative offset heights of the deeper part of the Bragg peak with corrections decreased to 0.2%-0.4% from 4% without correction. These results indicate that the luminescence imaging of water has potential for the dose distribution measurements for proton therapy dosimetry.
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Rayos gamma , Luz , Fantasmas de Imagen , Fotones , Terapia de Protones/métodos , Radiometría/instrumentación , Agua/química , Humanos , Luminiscencia , Mediciones Luminiscentes , Dosis de Radiación , Radiometría/métodosRESUMEN
INTRODUCTION: We have been developing a medical imaging technique using a Compton camera, which is expected to reconstruct three-dimensional images. If the number of views is not sufficient, star-shaped artifacts (streak artifacts) could arise in cross-sectional images. Therefore, we estimated the point spread function (PSF) of cross-sectional Compton images and the effect of the number of views by Monte Carlo simulations and experimental studies. MATERIALS AND METHODS: A cross-sectional Compton image was reconstructed using a dataset comprising 719 view directions and PSF was analyzed using a radial distribution. The peak height, full width at half maximum (FWHM), background (BG), and residual sum of squares (RSS) were calculated from the obtained PSF. In addition, RSSs were plotted against the number of views to estimate the required number to suppress star-shaped artifacts. RESULTS: There was no correlation found between the number of views and both FWHM (16â¯mm) and peak/BG ratio (â¼1â¯×â¯104). RSSs were reduced with the number of views and approached the minimum asymptotically. Correlation was observed between the required number of views and the number of Compton events used for image reconstruction. CONCLUSION: We determined the PSF of cross-sectional Compton images and the effect of the number of views on the images. The required number of views to suppress the star-shaped artifact is related to the square root of the number of Compton events used to reconstruct the image. From this study, we concluded that 21 or more views are required for clinical purposes.
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Imagenología Tridimensional/métodos , Cintigrafía/métodos , Simulación por Computador , Diseño de Equipo , Radioisótopos de Flúor , Cámaras gamma , Rayos gamma , Humanos , Método de MontecarloRESUMEN
A feasibility study on the imaging of monochromatic carbon-ion beams for carbon-ion therapy was performed. The evaluation was based on Monte Carlo simulations and beam-irradiation experiments, using a pinhole x-ray camera, which measured secondary electron bremsstrahlung (SEB). The simulation results indicated that the trajectories of the carbon-ion beams with injection energies of 278, 249 and 218 MeV/u in a water phantom, were clearly imaged by measuring the SEB with energies from 30 to 60 keV, using a pinhole camera. The Bragg-peak positions for these three injection energies were located at the positions where the ratios of the counts of SEB acquisitions to the maximum counts were approximately 0.23, 0.26 and 0.29, respectively. Moreover, we experimentally demonstrated that it was possible to identify the Bragg-peak positons, at the positions where the ratios coincided with the simulation results. However, the estimated Bragg-peak positions for the injection energies of 278 and 249 MeV/u were slightly deeper than the expected positions. In conclusion, for both the simulations and experiments, we found that the 25 mm shifts in the Bragg-peak positions can be observed by this method.
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Electrones , Radioterapia de Iones Pesados/métodos , Humanos , Método de Montecarlo , Fantasmas de Imagen , Rayos XRESUMEN
We have been developing a medical imaging technique using a Compton camera. This study evaluates the feasibility of clear imaging with 99mTc and 18F simultaneously, and demonstrates in vivo imaging with 99mTc and/or 18F. We used a Compton camera with silicon and cadmium telluride (Si/CdTe) semiconductors. We estimated the imaging performance of the Compton camera for 141 keV and 511 keV gamma rays from 99mTc and 22Na, respectively. Next, we simultaneously imaged 99mTc and 18F point sources to evaluate the cross-talk artifacts produced by a higher energy gamma-ray background. Then, in the in vivo experiments, three rats were injected with 99mTc-dimercaptosuccinic acid and/or 18F-fluorodeoxyglucose and imaged. The Compton images were compared with PET images. The rats were euthanized, and the activities in their organs were measured using a well counter. The energy resolution and spatial resolution were measured for the sources. No apparent cross-talk artifacts were observed in the practical-activity ratio (99mTc:18F = 1:16). We succeeded in imaging the distributions of 99mTc and 18F simultaneously, and the results were consistent with the PET images and well counter measurements. Our Si/CdTe Compton camera can thus work as a multi-tracer imager, covering various SPECT and PET probes, with less cross-talk artifacts in comparison to the conventional Anger cameras using a collimator. Our findings suggest the possibility of human trials.
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Fluorodesoxiglucosa F18/metabolismo , Cámaras gamma , Procesamiento de Imagen Asistido por Computador/métodos , Tomografía Computarizada de Emisión de Fotón Único/métodos , Imagen de Cuerpo Entero/métodos , Radioisótopos de Itrio , Animales , Masculino , Ratas , Ratas WistarRESUMEN
Imaging of secondary electron bremsstrahlung x-ray emitted during proton irradiation is a possible method for measurement of the proton beam distribution in phantom. However, it is not clear that the method is used for range estimation of protons. For this purpose, we developed a low-energy x-ray camera and conducted imaging of the bremsstrahlung x-ray produced during irradiation of proton beams. We used a 20 mm × 20 mm × 1 mm finely grooved GAGG scintillator that was optically coupled to a one-inch square high quantum efficiency (HQE)-type position-sensitive photomultiplier tube to form an imaging detector. The imaging detector was encased in a 2 cm-thick tungsten container, and a pinhole collimator was attached to its camera head. After performance of the camera was evaluated, secondary electron bremsstrahlung x-ray imaging was conducted during irradiation of the proton beams for three different proton energies, and the results were compared with Monte Carlo simulation as well as calculated value. The system spatial resolution and sensitivity of the developed x-ray camera with 1.5 mm-diameter pinhole collimator were estimated to be 32 mm FWHM and 5.2 × 10-7 for ~35 keV x-ray photons at 100 cm from the collimator surface, respectively. We could image the proton beam tracks by measuring the secondary electron bremsstrahlung x-ray during irradiation of the proton beams, and the ranges for different proton energies could be estimated from the images. The measured ranges from the images were well matched with the Monte Carlo simulation, and slightly smaller than the calculated values. We confirmed that the imaging of the secondary electron bremsstrahlung x-ray emitted during proton irradiation with the developed x-ray camera has the potential to be a new tool for proton range estimations.