Sparsity-regularized image reconstruction of decomposed K-edge data in spectral CT
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The development of spectral computed tomography (CT) using binned photon-counting detectors has garnered great interest in recent years and has enabled selective imaging of K-edge materials. A practical challenge in CT image reconstruction of K-edge materials is the mitigation of image artifacts that arise from reduced-view and/or noisy decomposed sinogram data. In this note, we describe and investigate sparsity-regularized penalized weighted least squares-based image reconstruction algorithms for reconstructing K-edge images from few-view decomposed K-edge sinogram data. To exploit the inherent sparseness of typical K-edge images, we investigate use of a total variation (TV) penalty and a weighted sum of a TV penalty and an ℓ1-norm with a wavelet sparsifying transform. Computer-simulation and experimental phantom studies are conducted to quantitatively demonstrate the effectiveness of the proposed reconstruction algorithms.Carbon-beam therapy has been successfully carried out at HIMAC, Japan. This treatment offers two advantages over conventional radiation therapy: better dose concentration due to the Bragg peak and higher RBE. In treatment planning at HIMAC, the dose distribution is calculated based on dose measurements in water. We previously made three types of phantoms by using CT images: a liver-cancer phantom and two lung-cancer phantoms (one with bone and one without it). This study evaluates carbon-beam attenuation in inhomogeneous layered phantoms and compares their results with beam attenuation in a water phantom. The phantoms consist of plates of tissue-equivalent materials for the x-rays; these plates are stacked along the beam direction. The beam attenuation in the lung-cancer phantom (with bone) is about 23%, similar to the result in the water phantom, attenuation in the lung-cancer phantom (without bone) is about 25%, which is higher than the result in the water phantom by 2%. Finally, the beam attenuation in the liver-cancer phantom is about 33%, which is lower than the result in the water phantom by 3%. Our evaluation of the carbon-beam attenuation using inhomogeneous layered phantoms is successful and comparison with the results in a water phantom is possible.
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Image noise
Radon transform
Reconstruction algorithm
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In the image inpainting task, the ability to repair both high-frequency and low-frequency information in the missing regions has a substantial influence on the quality of the restored image. However, existing inpainting methods usually fail to consider both high-frequency and low-frequency information simultaneously. To solve this problem, this paper proposes edge information and mask shrinking based image inpainting approach, which consists of two models. The first model is an edge generation model used to generate complete edge information from the damaged image, and the second model is an image completion model used to fix the missing regions with the generated edge information and the valid contents of the damaged image. The mask shrinking strategy is employed in the image completion model to track the areas to be repaired. The proposed approach is evaluated qualitatively and quantitatively on the dataset Places2. The result shows our approach outperforms state-of-the-art methods.
Inpainting
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Thermal Mapping using MRI is a non-invasive method for probing the body and has both diagnostic and interventional applications. If conducted on more accessible low field strength systems, these can improve the accessibility of the method for wider use. In order to validate and compare thermal mapping, a temperature control phantom was developed with tools for heating the phantom and externally tracking the temperature of the phantom. A heating study was performed with the phantom at two temperatures, and the thermometry methods showed good connection to the change in temperature in the phantom.
Tracking (education)
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Objective To develop a new water phantom specialized for absorbed dose measurement in total body irradiation(TBI) treatment.The width and height of water phantom have been fixed at 300 mm while the length can be adjust between 50 mm and 400 mm to meet the demands of different patients' physical sizes.Methods Cubical box was made by splicing 10 mm thick plexiglass sheet.A sleeve-like piston with suitable size and motion function was installed on one side wall of cubical box and then a tabular plexiglass piston was fixed inside the sleeve.Thus,the length of the water phantom could be controlled to meet our need by pulling and pushing the piston.Results In order to determine the accuracy of the water phantom,our water phantom was compared with the international standard water phantom.The absorbed doses at different water depths for these two water phantoms were detected by 6MV and 15MV X-ray,respectively.The results were used for comparison and statistical analysis which indicated that there were no statistical differences between two water phantoms.Conclusion The water phantom can fully meet the needs of clinical absorbed dose measurement in total body irradiation treatment.
Piston (optics)
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The design rationale and motivation for a new phantom for 3D ultrasound calibration are presented. The phantom design is intended to present an alternative to complex 3D ultrasound calibration phantoms that require difficult or high precision fabrication. Registration precision of the calibration at a mean depth of 22.3 mm was found to be 1.26 mm. At the same mean depth, lengths of 10 mm and 20 mm were registered with mean absolute errors of 0.67 mm and 0.65 mm respectively. The volume of an egg phantom was scanned using a non-parallel image acquisition and was determined to within 1.7%. The calibration phantom is shown to require reduced complexity of fabrication yet produce comparable performance to existing calibration phantom designs.
3D ultrasound
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今回試作したphantomは低コントラストスト分解能が、わずかな線量の変化で描出像の変化となるように試行錯誤の結果ある程度目的に近ずいたと考える。また、同時に収集したステップのコントラスト値やDSAインデックスで評価可能な事より、このphantomは描出像の僅かな変化を把握出来ると考えられる。以上から、試作phantomはDSA値のコントラス値DSAインデックスを求めることにより日常保守管理の低コントスト分解能用phantomとして有用と考える。今後は、描出される分解能ディスクの大きさ、形状の検討をさらに進めてゆきたい。
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In the image inpainting task, the ability to repair both high-frequency and low-frequency information in the missing regions has a substantial influence on the quality of the restored image. However, existing inpainting methods usually fail to consider both high-frequency and low-frequency information simultaneously. To solve this problem, this paper proposes edge information and mask shrinking based image inpainting approach, which consists of two models. The first model is an edge generation model used to generate complete edge information from the damaged image, and the second model is an image completion model used to fix the missing regions with the generated edge information and the valid contents of the damaged image. The mask shrinking strategy is employed in the image completion model to track the areas to be repaired. The proposed approach is evaluated qualitatively and quantitatively on the dataset Places2. The result shows our approach outperforms state-of-the-art methods.
Inpainting
Filling-in
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Diffuse optical imaging
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Digital radiography
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