Journal of X-Ray Science and Technology - Volume 20, issue 3

Authors: Li, Linsheng | Zeng, Li | Qiu, Changjun | Liu, Linghui

Article Type: Research Article

Abstract: Intensity inhomogeneity may cause considerable difficulties in segmentation of CT image. In order to overcome the difficulties caused by intensity inhomogeneity, the region-scalable fitting (RSF) model was put forward. RSF model draws upon intensity information in local regions with a controllable scale. But only using intensity information may lead to slow convergence rate and poor denoise ability. Combining the method of robust statistics, RSF model is improved in this paper. In the improved model, the …intensity in RSF model is replaced with local robust statistics which is the weighted combination of inter-quartile range, mean absolute deviation and intensity median in local region. Inter-quartile range and mean absolute deviation in local region are introduced to sharpen object boundaries, and intensity median in local region is introduced to reduce image noise. The contrast experiments between RSF model and the improved model are provided, which demonstrate the fast convergence rate and robustness to noise of the improved model. Show more

Keywords: Image segmentation, intensity inhomogeneity, computer tomography (CT), robust statistics, region-scalable fitting (RSF)

DOI: 10.3233/XST-2012-0334

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 255-267, 2012

Authors: Eom, Sangheum | Shin, Hyoungsup | Kang, Jungwon | Lee, Hakjae | Lee, Kisung

Article Type: Research Article

Abstract: In this study we have investigated a 2-dimensional gas type detector based on plasma display technology as a candidate for the flat-panel radiation detector. By using the Garfield code, the dependence of X-ray absorption and multiplication on gas composition, cell gap and electric field were examined. Considering the simulation results, three prototype detectors were designed and fabricated. The performance of these detectors was evaluated by measuring the collected charge density, dark current density and sensitivity. The …collected charge had the highest value at a condition when Xe 100% and 2.8 mm gap was 108.8 nC/cm^{2} at 1000 V. The dark current of the same detector was varied from 0.0095 to 0.10 nA/cm^{2} and about a fourth of the dark current density of a-Se based detector was at the bias range of 100–1000 V. The sensitivity of Xe 100% and 2.8 mm detector was 0.20 nC/mR·cm^{2} at 0.36 V/um. It is about a tenth lower than that of a-Se based detector at 10 V/um. Show more

Keywords: Radiation detectors, gas-filled detectors, sensors, X-ray

DOI: 10.3233/XST-2012-0335

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 269-276, 2012

Authors: Lu, Yang | Yang, Zhenyu | Zhao, Jun | Wang, Ge

Article Type: Research Article

Abstract: In this paper, we study how to reconstruct multiple objects tomographically from their overlapped x-ray projections. We propose a new rotation-translation scanning mode for a fixed source-detector geometry, in which the objects are individually translated periodically while they are rotated during the data acquisition. The reconstruction scheme performs SART reconstruction and TV minimization alternatingly. The scanning parameters are evaluated in a series of numerical experiments. Promising results are obtained in the cases …of two and four objects respectively. The major advantage of our approach is that the scanning time can be reduced by about 46% (for two objects) and 67% (for four objects) respectively, improving the imaging facility throughput significantly. Show more

Keywords: Computed tomography (CT), total variation (TV) minimization, image reconstruction, multiple objects

DOI: 10.3233/XST-2012-0337

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 277-289, 2012

Authors: Rao, Donepudi V. | Cesareo, Roberto | Brunetti, Antonio | Akatsuka, Tako | Yuasa, Tetsuya | Takeda, Tohoru | Gigante, Giovanni E.

Article Type: Research Article

Abstract: Synchrotron-based micro-CT was utilized to image the embedded biological soft-tissue of a small animal shell. Micro-CT images of the biological soft-tissue were acquired using 20, 25, and 27 keV synchrotron X-rays with contrast agents, such as water, physiological saline and iodine. Visualized the complex features of the animal at the above energies with water, physiological saline and iodine. The choice of the optimum energy was chosen based on the contrast mechanisms to know more about soft-matter …and the associated internal complex biological features of the small animal shell. This way, the images at 27 keV (optimum energy) was reasonably acceptable for better visualization of the interior micro-architecture, such as soft-anatomy, physiology and internal organs of the animal with better visibility. The introduction of water, physiological, or iodine as contrast agents is shown to enhance minute image features in synchrotron-based tomographic imaging. Show more

Keywords: Synchrotron, soft tissue, contrast agents, biological features, optimum energy, snail

DOI: 10.3233/XST-2012-0338

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 291-299, 2012

Authors: Xue, Hui | Zhang, Li | Chen, Zhiqiang | Li, Liang

Article Type: Research Article

Abstract: With its capability of material discrimination, dual energy computed tomography (DECT) is widely used in security inspection for the purpose of detecting contraband. DECT provides effective atomic number image and electron density image in addition to traditional attenuation images. In dual energy liquid inspection system, the presence of metallic containers will cause partial volume effect (PVE) that leads to severe deviation in effective atomic number image. Usually, the deviation is too large for a reliable material …discrimination and may cause false results. In this paper, a projection splitting method is proposed to combat the PVE. This method is based on the assumption that a prior projection of the empty container is available and photoelectric and Compton coefficient integrals can be calculated via dual energy decomposition. Each integral is split into two parts by subtracting the integral of the empty container from the total integral. The subtraction removes the integral part contributed by the container, thus discarding the error source created by PVE that appears on the boundary of the sinogram. Images are reconstructed in which only the interior liquid area remains. Experiments are performed in a real liquid inspection system to demonstrate the effectiveness of this method. Accuracy of the reconstructed effective atomic number is greatly improved with this method, which helps a lot in determining the type of the object. Show more

Keywords: DECT, partial volume effect, liquid inspection, effective atomic number

DOI: 10.3233/XST-2012-0339

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 301-316, 2012

Authors: Lau, Andy | Chen, Yong | Ahmad, Salahuddin

Article Type: Research Article

Abstract: A Monte Carlo application is developed to investigate the yields of positron-emitting nuclei (PEN) used for proton and carbon ion range verification techniques using the GEANT4 Toolkit. A base physics list was constructed and used to simulate incident proton and carbon ions onto a PMMA or water phantom using pencil like beams. In each simulation the total yields of PEN are counted and both the PEN and their associated positron depth-distributions were recorded and compared to …the incident radiation's Bragg Peak. Alterations to the physics lists are then performed to investigate the PEN yields dependence on the choice of physics list. In our study, we conclude that the yields of PEN can be estimated using the physics list presented here for range verification of incident proton and carbon ions. Show more

Keywords: Positron emitting nuclei, radiation therapy, Geant4 simulation

DOI: 10.3233/XST-2012-0340

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 317-329, 2012

Authors: Li, Zhihong | Li, Dongfeng | Wu, Zhonghua | Wu, Ziyu | Liu, Jun

Article Type: Research Article

Abstract: Using the three slit collimation system with a divergent beam simplifies the design of a small angle X-ray scattering (SAXS) cameras and improves both flux and stability. To achieve the required low angle and a high spatial resolution, the collimation system must be optimized in the design and operation phases. Simulation of a slit divergent camera yields optimal distance between the beam defining slits and optimal distance between sample and detector at which the maximum SAXS …resolution is achieved with a minimal parasitic scattering for any length of the SAXS camera. The narrower the beam defining slits and the longer the total camera length, the smaller the minimum resolvable angle and the higher the attainable resolution. Show more

Keywords: SAXS resolution, three slits collimation system, divergent beam

DOI: 10.3233/XST-2012-0341

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 331-338, 2012

Authors: Chen, Tai-Been | Chen, Jyh-Cheng | Lu, Henry Horng-Shing

Article Type: Research Article

Abstract: Segmentation of positron emission tomography (PET) is typically achieved using the K-Means method or other approaches. In preclinical and clinical applications, the K-Means method needs a prior estimation of parameters such as the number of clusters and appropriate initialized values. This work segments microPET images using a hybrid method combining the Gaussian mixture model (GMM) with kernel density estimation. Segmentation is crucial to registration of disordered 2-deoxy-2-fluoro-D-glucose (FDG) accumulation locations with functional …diagnosis and to estimate standardized uptake values (SUVs) of region of interests (ROIs) in PET images. Therefore, simulation studies are conducted to apply spherical targets to evaluate segmentation accuracy based on Tanimoto's definition of similarity. The proposed method generates a higher degree of similarity than the K-Means method. The PET images of a rat brain are used to compare the segmented shape and area of the cerebral cortex by the K-Means method and the proposed method by volume rendering. The proposed method provides clearer and more detailed activity structures of an FDG accumulation location in the cerebral cortex than those by the K-Means method. Show more

Keywords: PET, FDG, cerebral cortex, K-Means, Gaussian mixture model, kernel density estimation

DOI: 10.3233/XST-2012-0342

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 339-349, 2012

Authors: Zou, Jing | Gui, Jianbao | Rong, Junyan | Hu, Zhanli | Zhang, Qiyang | Xia, Dan

Article Type: Research Article

Abstract: A mathematical derivation was conducted to illustrate that exact 3D image reconstruction could be achieved for z-homogeneous phantoms from data acquired with 2D general trajectories using the back projection filtration (BPF) algorithm. The conclusion was verified by computer simulation and experimental result with a circular scanning trajectory. Furthermore, the effect of the non-uniform degree along z-axis of the phantoms on the accuracy of the 3D reconstruction by BPF algorithm was investigated by numerical …simulation with a gradual-phantom and a disk-phantom. The preliminary result showed that the performance of BPF algorithm improved with the z-axis homogeneity of the scanned object. Show more

Keywords: Cone-beam computed tomography, 2D general trajectory, BPF algorithm, z-homogeneous phantom

DOI: 10.3233/XST-2012-0343

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 351-362, 2012

Authors: Wu, Shengnan | Xing, Da

Article Type: Research Article

Abstract: Photofrin-mediated photodynamic therapy (PF-PDT) can induce cell apoptosis via the mitochondria/caspase-3 pathway. Here, we further investigate the mechanism involved in the mitochondrial apoptotic process induced by PF-PDT. A high-level intracellular reactive oxygen species (ROS) generation in mitochondria, mitochondrial swelling, and dissipation of mitochondrial transmembrane potential were observed immediately after irradiation, indicating that mitochondria were the major ROS generation sites and also the first oxidative damage sites after PF-PDT treatment. For mitochondrial permeability …detection, the decrease of calcein fluorescence emission intensity and release of cytochrome c were observed immediately after PF-PDT treatment, indicating the occurrence of mitochondrial inner membrane permeabilization (MIMP) and the mitochondrial outer membrane permeabilization (MOMP). However, cytochrome c release was not prevented by cyclosporine (CsA), a specific inhibitor of mitochondrial permeability transition (MPT). Taken together, these results demonstrated that PF-PDT caused simultaneous onset of MIMP and MOMP immediately after the treatment, and MOMP was independent of the MPT. Besides, inducible mitochondrial ROS generation played key roles in PF-PDT-induced cell apoptosis. This study will be benefit for understanding the mechanism involved in the initial mitochondrial oxidative damage by PF-PDT. Show more

Keywords: Photofrin, photodynamic therapy, mitochondria, reactive oxygen species

DOI: 10.3233/XST-2012-0344

Citation: Journal of X-Ray Science and Technology, vol. 20, no. 3, pp. 363-372, 2012