Journal of X-Ray Science and Technology - Volume 22, issue 1

Authors: Miao, Chuang | Liu, Baodong | Xu, Qiong | Yu, Hengyong

Article Type: Research Article

Abstract: Fast and accurate image reconstruction is the ultimate goal of iterative methods for limited-angle, few-view, interior problems, etc. Recently, a finite-detector-based projection model was proposed for iterative CT reconstructions, which was called area integral model (AIM) and has shown a high spatial resolution but with a high computational complexity. On the other hand, the distance-driven model (DDM) is the state-of-the-art technology to model forward projection and backprojection, which has shown a low …computational complexity but relative low spatial resolution than AIM-based method. Inspired by the DDM, here we propose an improved distance-driven model (IDDM), which has a similar computational complexity with the DDM-based method and comparative spatial resolution with the AIM-based method. In an ordered-subset simultaneous algebraic reconstruction technique (OS-SART) framework, the AIM, IDDM and DDM are implemented and evaluated using a sinogram from a phantom experiment on a Discovery CT750 HD scanner. The results show that the computational cost of DDM- and IDDM-based methods is similar, which is 6 to 13~times faster than the AIM-based method assuming the same number of iterations. The spatial resolution of AIM- and IDDM-based method is comparable, which is better than DDM-based method in terms of full-width-of-half-maximum (FWHM). Show more

Keywords: Computed tomography (CT), image reconstruction, area integral model, distance-driven model, OS-SART

DOI: 10.3233/XST-130405

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 1-18, 2014

Authors: Zhang, Feng | Yan, Bin | Li, Lei | Xi, Xiaoqi | Jiang, Hua

Article Type: Research Article

Abstract: In helical cone-beam industrial computed tomography (ICT), the reconstructed images may be interfered by geometry artifacts due to the presence of mechanical misalignments. To obtain artifact-free reconstruction images, a practical geometric calibration method for helical scan is investigated based on Noo's analytic geometric calibration method for circular scan. The presented method is implemented by first dividing the whole ascending path of helical scan into several pieces, then acquiring the projections of a …dedicated calibration phantom in circular scan at each section point, of which geometry parameters are calculated using Noo's analytic method. At last, the geometry parameters of each projection in a piece can be calculated by those of the two end points of the piece. We performed numerical simulations and real data experiments to study the performance of the presented method. The experimental results indicated that the method can obtain high-precision geometry parameters of helical scan and give satisfactory reconstruction images. Show more

Keywords: Cone-beam CT, helical scan, geometric calibration, image reconstruction

DOI: 10.3233/XST-130406

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 19-35, 2014

Authors: Wang, Xianchao | Tang, Ziyue | Yan, Bin | Li, Lei | Bao, Shanglian

Article Type: Research Article

Abstract: In various applications of computed tomography (CT), it is common that the reconstructed object is over the field of view (FOV) or we may intend to sue a FOV which only covers the region of interest (ROI) for the sake of reducing radiation dose. These kinds of imaging situations often lead to interior reconstruction problems which are difficult cases in the reconstruction field of CT, due to the truncated projection data at every view angle. In …this paper, an interior reconstruction method is developed based on a rotation-translation (RT) scanning model. The method is implemented by first scanning the reconstructed region, and then scanning a small region outside the support of the reconstructed object after translating the rotation centre. The differentiated backprojection (DBP) images of the reconstruction region and the small region outside the object can be respectively obtained from the two-time scanning data without data rebinning process. At last, the projection onto convex sets (POCS) algorithm is applied to reconstruct the interior region. Numerical simulations are conducted to validate the proposed reconstruction method. Show more

Keywords: CT, interior reconstruction, truncation, POCS algorithm

DOI: 10.3233/XST-130407

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 37-45, 2014

Authors: Brabant, L. | Dierick, M. | Pauwels, E. | Boone, M.N. | Van Hoorebeke, L.

Article Type: Research Article

Abstract: A novel reconstruction method is presented to improve the image quality of three dimensional (3D) datasets for samples consisting of only one material and surrounding air, obtained with high resolution X-ray Computed Tomography (μCT). It combines discrete tomography with iterative reconstruction algorithms, it is applicable for routine μCT applications and is referred to as the Experimental Discrete Algebraic Reconstruction Technique (EDART). A fast and intuitive method to estimate the attenuation coefficient and …segmentation threshold, in case these are unknown, is included. Experimental results illustrate that EDART allows the improvement of the reconstruction quality as compared to standard iterative reconstruction when few projections are available, without significantly increasing the reconstruction time. Show more

Keywords: Discrete tomography, high resolution CT, iterative reconstruction

DOI: 10.3233/XST-130408

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 47-61, 2014

Authors: Kim, Jae G. | Park, So E. | Lee, Soo Y.

Article Type: Research Article

Abstract: In tissue elasticity imaging, measuring the strain tensor components is necessary to solve the inverse problem. However, it is impractical to measure all the tensor components in ultrasound or MRI elastography because of their anisotropic spatial resolution. The objective of this study is to compute 3D strain tensor maps from the 3D CT images of a tissue-mimicking phantom. We took 3D micro-CT images of the phantom twice with applying two different mechanical compressions to it. Applying …the 3D image correlation technique to the CT images under different compression, we computed 3D displacement vectors and strain tensors at every pixel. To evaluate the accuracy of the strain tensor maps, we made a 3D FEM model of the phantom, and we computed strain tensor maps through FEM simulation. Experimentally obtained strain tensor maps showed similar patterns to the FEM-simulated ones in visual inspection. The correlation between the strain tensor maps obtained from the experiment and the FEM simulation ranges from 0.03 to 0.93. Even though the strain tensor maps suffer from high level noise, we expect the x-ray strain tensor imaging may find some biomedical applications such as malignant tissue characterization and stress analysis inside the tissues. Show more

Keywords: Displacement vector, strain tensor, x-ray elastography, tissue elasticity, 3D CT

DOI: 10.3233/XST-130409

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 63-75, 2014

Authors: Dabravolski, Andrei | Batenburg, Kees Joost | Sijbers, Jan

Article Type: Research Article

Abstract: BACKGROUND: In computed tomography (CT), the source-detector system commonly rotates around the object in a circular trajectory. Such a trajectory does not allow to exploit a detector fully when scanning elongated objects. OBJECTIVE: Increase the spatial resolution of the reconstructed image by optimal zooming during scanning. METHODS: A new approach is proposed, in which the full width of the detector is exploited for every projection angle. This approach is based on the …use of prior information about the object's convex hull to move the source as close as possible to the object, while avoiding truncation of the projections. RESULTS: Experiments show that the proposed approach can significantly improve reconstruction quality, producing reconstructions with smaller errors and revealing more details in the object. CONCLUSIONS: The proposed approach can lead to more accurate reconstructions and increased spatial resolution in the object compared to the conventional circular trajectory. Show more

Keywords: Acquisition geometry, adaptive zooming, computed tomography, prior information

DOI: 10.3233/XST-130410

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 77-89, 2014

Authors: Nakashima, Yoshito | Nakano, Tsukasa

Article Type: Research Article

Abstract: Iodine is commonly used as a contrast agent in nonmedical science and engineering, for example, to visualize Darcy flow in porous geological media using X-ray computed tomography (CT). Undesirable beam hardening artifacts occur when a polychromatic X-ray source is used, which makes the quantitative analysis of CT images difficult. To optimize the chemistry of a contrast agent in terms of the beam hardening reduction, we performed computer simulations and generated synthetic CT images of a homogeneous …cylindrical sand-pack (diameter, 28 or 56 mm; porosity, 39 vol.% saturated with aqueous suspensions of heavy elements assuming the use of a polychromatic medical CT scanner. The degree of cupping derived from the beam hardening was assessed using the reconstructed CT images to find the chemistry of the suspension that induced the least cupping. The results showed that (i) the degree of cupping depended on the position of the K absorption edge of the heavy element relative to peak of the polychromatic incident X-ray spectrum, (ii) _{53} I was not an ideal contrast agent because it causes marked cupping, and (iii) a single element much heavier than _{53} I (_{64} Gd to _{79} Au) reduced the cupping artifact significantly, and a four-heavy-element mixture of elements from _{64} Gd to _{79} Au reduced the artifact most significantly. Show more

Keywords: Beam hardening, contrast agent, cupping, K absorption edge, lanthanoid, X-ray CT

DOI: 10.3233/XST-130411

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 91-103, 2014

Authors: Lu, Faming | Xia, Yuanqin | Zhang, Sheng | Chen, Deying | Zhao, Yang | Liu, Bin

Article Type: Research Article

Abstract: We experimentally study the harmonics from a Xe-He gas mixture using tight-focusing femtosecond laser pulses. The spectrum in the mixed gases exhibits an extended cutoff region from the harmonic H21 to H27. The potential explanation is that the harmonics photons from Xe contribute the electrons of He atoms to transmit into the excited-state. Therefore, the harmonics are emitted from He atoms easily. Furthermore, we show that there are the suppressed harmonics H15 and H17 in the …mixed gases. The underlying mechanism is the destructive interference between harmonics generated from different atoms. Our results indicate that HHG from Xe-He gas mixture is an efficient method of obtaining the coherent soft X-ray source. Show more

Keywords: Femtosecond laser pulses, soft X-ray, high harmonic generation, gas mixture

DOI: 10.3233/XST-130412

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 105-111, 2014

Authors: Chighvinadze, Tamar | Pistorius, Stephen

Article Type: Research Article

Abstract: The reconstructed electron density image quality is sensitive to the detector size and energy resolution, which contribute to the blurring and noise in the image. This work evaluates optimal values of the detector parameters for a realistic system through analytical simulations of the transverse slice of the dedicated breast CT system geometry. This study introduces a spectroscopic x-ray tomography technique which uses multiple projections to reconstruct electron density images by backprojecting scattered photons over isogonic …curves. The reconstruction can be obtained using a single projection yet its quality degrades as the acquisition conditions i.e. detector size and energy resolution deviate from the ideal. The reconstruction quality becomes inconsistent throughout the image due to the data under sampling caused by the finite resolution of the detector. The extension to the multi-projection mode effectively fills-in the missing data space and improves the ability to reconstruct an object. This work demonstrates the possibility to obtain images in the presence of noise. Show more

Keywords: Compton scatter tomography, detector size, detector energy resolution

DOI: 10.3233/XST-130413

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 113-128, 2014

Authors: Lin, Yang-Hsien | Huang, Yung-Hui | Lin, Kang-Ping | Liu, Juhn-Cherng | Huang, Tzung-Chi

Article Type: Research Article

Abstract: Ventricular hemodynamics plays an important role in assessing cardiac function in clinical practice. The aim of this study was to determine the ventricular hemodynamics based on contrast movement in the left ventricle (LV) between the phases in a cardiac cycle recorded using an electrocardiography (ECG) with cardiac computed tomography (CT) and optical flow method. Cardiac CT data were acquired at 120 kV and 280 mA with a 350 ms gantry rotation, which covered one cardiac cycle, …on the 640-slice CT scanner with ECG for a selected patient without heart disease. Ventricular hemodynamics (mm/phase) were calculated using the optical flow method based on contrast changes with ECG phases in anterior-posterior, lateral and superior-inferior directions. Local hemodynamic information of the LV with color coating was presented. The visualization of the functional information made the hemodynamic observation easy. Show more

Keywords: Left ventricle, hemodynamics, computed tomography

DOI: 10.3233/XST-130414

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 1, pp. 129-136, 2014