Journal of X-Ray Science and Technology - Volume 18, issue 3

Authors: Lee, Byeonghun | Lee, Ho | Shin, Yeong Gil

Article Type: Research Article

Abstract: This paper presents a fast hybrid CPU- and GPU-based CT reconstruction algorithm to reduce the amount of back-projection operation using air skipping involving polygon clipping. The algorithm easily and rapidly selects air areas that have significantly higher contrast in each projection image by applying K-means clustering method on CPU, and then generates boundary tables for verifying valid region using segmented air areas. Based on these boundary tables of each projection image, clipped polygon that indicates active …region when back-projection operation is performed on GPU is determined on each volume slice. This polygon clipping process makes it possible to use smaller number of voxels to be back-projected, which leads to a faster GPU-based reconstruction method. This approach has been applied to a clinical data set and Shepp-Logan phantom data sets having various ratio of air region for quantitative and qualitative comparison and analysis of our and conventional GPU-based reconstruction methods. The algorithm has been proved to reduce computational time to half without losing any diagnostic information, compared to conventional GPU-based approaches. Show more

Keywords: Cone-beam CT, GPU, FDK reconstruction, back-projection, air skipping, polygon clipping

DOI: 10.3233/XST-2010-0256

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 3, pp. 221-234, 2010

Authors: Gloria, Cruz | Li, Qin | Xu, Liping | Zhang, Wanshi

Article Type: Research Article

Abstract: Taking advantage of Diffusion Weighted Imaging (DWI) to characterize the random movement of water molecules in biological tissue, this article intends to review the Intravoxel Incoherent Motion (IVIM) theory as a valuable method to find the differentiation between malignant and benign tumor based on the microcirculation of blood in the capillaries. IVIM is measured by means of a parameter called apparent diffusion coefficient (ADC). Through the application of IVIM to the imaging processing software, it will …be possible to set up an expert system with screening, discrimination, staging and therapeutic evaluation function of tumor. Show more

Keywords: Diffusion weighted imaging, intravoxel incoherent motion, apparent diffusion coefficient, diffusion, perfusion, tumor

DOI: 10.3233/XST-2010-0257

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 3, pp. 235-249, 2010

Authors: Tang, Xiangyang | Narayanan, Suresh | Hsieh, Jiang | Pack, Jed D. | Mcolash, Scott M. | Sainath, Paavana | Nilsen, Roy A. | Taha, Basel

Article Type: Research Article

Abstract: The spatial resolution of diagnostic Computed Tomography (CT) has increased substantially, and 3D isotropic sub-millimeter spatial resolution in both axial and helical scan modes is routinely available in the clinic. However, driven by advanced clinical applications, the pursuit for higher spatial resolution and free of aliasing artifacts in diagnostic CT has never stopped. A method to accommodate focal spot wobbling at an arbitrary number of projection views per gantry rotation in CT is presented and evaluated …here. The method employs a beta-correction scheme in the row-wise fan-to-parallel rebinning to transform the native cone beam geometry into the cone-parallel geometry under which existing 3D weighted cone beam filtered backprojection algorithms can be utilized for image reconstruction. The experimental evaluation shows that the row-wise fan-to-parallel rebinning with the beta-correction can increase the quantitative in-plane spatial resolution (Modulation Transfer Function) substantially, while the visual spatial resolution can be enhanced significantly. Consequently, the architectural designers of CT scanners are no longer constrained to choosing the number of projection views per rotation determined by gantry geometry. Instead, they can choose the number of projection views per rotation to optimize the trade-offs between in-plane spatial resolution and noise characteristics. Therefore, the presented method is of practical relevance in the architectural design of state-of-the-art diagnostic CT. Show more

Keywords: Cone-beam volume CT, CT reconstruction, 3D reconstruction, Reconstruction algorithms, focal spot wobbling

DOI: 10.3233/XST-2010-0258

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 3, pp. 251-265, 2010

Authors: Zeng, Li | Liu, Baodong | Liu, Linghui | Xiang, Caibing

Article Type: Research Article

Abstract: The exterior computed tomography (CT) problem is one kind of truncation problem. It is very ill-posed, so that accurate reconstruction of the attenuation function is hardly possible from real data. Based on projection onto convex sets (POCS) algorithm, total variation minimization (TVM) methods, and C-V model, we develop and investigate a new iterative reconstruction algorithm, which is referred to as subregion-averaged-TVM-POCS (SA-TVM-POCS). Numerical simulations are presented to illustrate the efficiency of the …algorithm. The results of this paper can be easily applied to other x-ray CT reconstruction problems. Show more

Keywords: CT, Image reconstruction, Exterior problem, POCS, TVM, C-V model

DOI: 10.3233/XST-2010-0259

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 3, pp. 267-277, 2010

Authors: Gong, Shaorun | Gao, Feng | Zhou, Zhongxing

Article Type: Research Article

Abstract: To investigate the degrading effects of the physical parameters on the in-line X-ray phase-contrast imaging (XPCi), a simulation tool based on the Fresnel/Kirchhoff diffraction integral was firstly developed with comprehensively considering effects of the source-to-sample (S-S) and sample-to-detector (S-D) distances, the practical characteristics of a polychromatic and finite size source, the point spread function (PSF) of the fluorescent screen and the spatial resolution of the detector on the theoretical phase-contrast pattern. By …a comparison between the simulative profile and the experimental one under the commonly-used parameters, an acceptable consistency has been demonstrated in despite of the deviation between the theoretically-predicted contrast (0.188) and the original experimental one (0.12). From the simulations, it is apparently observed that the fine interference pattern has been severely degraded by the finite spatial resolution, and will inevitably be further deteriorated by the system noise in practice. Since the image quality of the X-ray phase-contrast imaging is strongly dependent on the physical parameters of the system, a model-based deblurring procedure to upgrade the image visibility is preferably desired. As a simple restoration way, a Wiener filter was then introduced to offer an optimal tradeoff between the contrast preservation and the noise suppression. Finally, to minimize the deviation resulting from the finite spatial resolution, one-dimensional interpolation was performed by positioning the set square at a tiny angle to the vertical direction. The result after the Wiener-filtering-based deblurring has shown a considerably improved profile visibility: the processed experimental contrast (0.156) increased by 30% as compared to the original one (0.12) in company with the increase in the signal-to-noise ratio (SNR) by 0.9dB. With the trend of the post-filtered experimental contrast to the theoretical one, it could be motivated that higher visibility would be achieved with the introduction of more precise blurring mask and noise spectrum estimation. Show more

DOI: 10.3233/XST-2010-0260

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 3, pp. 279-292, 2010

Authors: Guo, Wen-Jing | Chen, Tong-Sheng | Wang, Xiao-Ping | Chen, Rong

Article Type: Research Article

Abstract: Taxol (Paclitaxel) is an important natural product for the treatment of solid tumors such as ovarian, breast, non-small-cell lung tumors, and some head and neck carcinomas. Different concentrations of taxol trigger distinct effects on cell death forms. In present study, cell counting kit (CCK-8) assay, confocal fluorescence microscopy imaging, flow cytometry (FCM) and western blotting (WB) analysis were used to analyze the characteristics of cell death induced by low (35 nM) and high (70 μM) concentration …of taxol respectively in human lung adenocarcinoma (ASTC-a-1) cells. Our results showed that low concentration of taxol induced cell death dominantly in apoptotic fashion associated with nuclear fragmentation, protein synthesis, phosphatidylserine (PS) externalization, G2/M cell cycle arrest, Bax translocation into mitochondria and caspase-3 activation, whereas high concentration of this drug induced significant cytoplasm vacuolization, mitochondria swelling and paraptosis-like cell death form without protein synthesis that is necessary for paraptosis. Although the mechanism of high concentration of taxol-induced paraptosis-like cell death has not been clear, this finding might have a potential implication for cancer therapy, especially for apoptosis-resistant cancer. Show more

Keywords: Taxol, caspase-3, apoptosis, paraptosis, protein synthesis

DOI: 10.3233/XST-2010-0261

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 3, pp. 293-308, 2010

Authors: Johnson, Daniel A. | Ahmad, Salahuddin

Article Type: Research Article

Abstract: The objective of this work has been to develop and implement an empirical calculation method for the determination of clinical electron output factors. Electron beams with various energies, field sizes, and source to surface distances using cutouts of varying radii were used to measure dose output at the depth of maximum dose in water. A 30 cm × 30 cm × 17.8 cm water equivalent phantom with a 0.125 cc cylindrical ion-chamber (PTW Model 31010) was …used. The calculation model predicted the output factor as a product of the cone factor, radius dependent cutout factor, the effective source to surface distance factor and the area dependent aspect ratio factor. A comparative analysis of clinical cutout output factors, determined through both empirical calculation and direct measurement was performed to evaluate the clinical viability of the calculation method before its implementation in our clinic. A total of 643 output factors for 294 different cutout shapes were determined through both traditional measurement and predictive calculation. Predictive calculation differed from definitive measurement by at most 3.5% for all cases, a majority of cases falling within 1%. The method developed successfully predicts electron output factors on the basis of cutout geometry with accuracy better than 96% for all cases and better then 98% for most cases. This ability holds true for all practical SSD, electron energy, cone, and irregular shape combinations. The method has been clinically implemented and in use at our center since 2007. Show more

Keywords: Electron output factor, radiation therapy, cancer treatment

DOI: 10.3233/XST-2010-0262

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 3, pp. 309-318, 2010

Authors: Ali, Imad | Matthiesen, Chance | Algan, Ozer | Thompson, Spencer | Bogardus, Carl | Herman, Terence | Ahmad, Salahuddin

Article Type: Research Article

Abstract: Purpose: To investigate the increase in surface dose under immobilization thermoplastic masks by measurements and calculation in the build-up region using Gafchromic films and Monte Carlo simulation. Materials and methods: Surface doses were measured underneath three thermoplastic masks in open fields using 6 and 18 MV photon beams. These masks are used to immobilize patients for head and neck (H&N), pelvis and thoracic treatment. Gafchromic EBT films were placed on the top of the flat …surface of a phantom partially underneath the mask and exposed in open 10 × 10 cm^2 photon fields. The depth doses were calculated using BEAMnrc Monte Carlo code for water-equivalent film detectors with different layers of thickness ranging from 50 μm to 2.5 mm and compared with film measurements. Results: Surface dose increased by a factor of 3 to 4 underneath the mask relative to the open areas and 6 MV beam delivers more skin dose than 18 MV. H&N mask increased surface dose by a factor of 3 using 18 MV and a factor of 4 using 6 MV. In addition, increase in surface dose depended on the type of the mask, the size of openings, and the amount of stretching performed during the mask preparation. The measured depth doses were compared with BEAMnrc Monte Carlo calculation for water-equivalent detectors using different sizes. The calculated depth dose depended significantly on the thickness of film detector and varies by more than 15% using layer thickness of 2.5 mm compared to 50 μm. Surface doses measured by Gafchromic EBT films agreed within 3% with the Monte Carlo calculations using a small detector layer of 50 μm. Conclusion: Thermoplastic masks used for patient immobilization can significantly increase skin doses by up to a factor of 4 more than that without the mask using 6 MV beams. The skin reactions resulting from thermoplastic masks should be monitored and corrective measures should be taken during treatment such as partially removing the mask over skin areas with complications and optimizing the skin dose in IMRT planning. Gafchromic EBT films provide accurate skin dosimetry which agrees within 3% with Monte Carlo calculations. Gafchromic EBT film makes an excellent tool for measuring depth doses in the buildup region and these data can be applied for treatment planning calculations and IMRT optimization. Show more

Keywords: Skin dose, toxicity, thermoplastic immobilization mask, Gafchromic EBT film, IMRT, Monte Carlo simulation

DOI: 10.3233/XST-2010-0263

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 3, pp. 319-326, 2010

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

Article Type: Research Article

Abstract: Synchrotron-based scattered radiation form low-contrast phantom materials prepared from polyethylene, polystyrene, nylon, and Plexiglas is used as test objects in X-ray CT was examined with 8, 10 and 12 keV X-rays. These phantom materials of medical interest will contains varying proportions of low atomic number elements. The assessment will allowed us to estimate the fluorescence to total scattered radiation. Detected the fluorescence spectra and the associated scattered radiation from calcium hydroxyapatite phantom with …8, 10 and 12 keV synchrotron X-rays. Samples with Bonefil (60% and 70% of calcium hydroxyapatite) and Bone cream (35 ∼ 45% of calcium hydroxyapatite), were used. Utilized the X-ray micro-spectroscopy beamline facility, X27A, available at NSLS, BNL, USA. The primary beam with a spot size of the order of ∼ 10 μm, has been used for focusing. With this spatial resolution and high flux throuput, the synchrotron-based scattered radiation from the phantom materials were measured using a liquid-nitrogen-cooled 13-element energy-dispersive high-purity germanium detector. Show more

DOI: 10.3233/XST-2010-0255

Citation: Journal of X-Ray Science and Technology, vol. 18, no. 3, pp. 327-337, 2010