Journal of X-Ray Science and Technology - Volume 23, issue 1

Authors: Wang, Linyuan | Zhang, Hanming | Cai, Ailong | Li, Yongl | Yan, Bin | Li, Lei | Hu, Guoen

Article Type: Research Article

Abstract: Iterative image reconstruction (IIR) with sparsity-exploiting methods, such as total variation (TV) minimization, used for investigations in compressive sensing (CS) claim potentially large reductions in sampling requirements. Quantifying this claim for computed tomography (CT) is non-trivial, as both the singularity of undersampled reconstruction and the sufficient view number for sparse-view reconstruction are ill-defined. In this paper, the singular value decomposition method is used to study the condition number and singularity of the …system matrix and the regularized matrix. An estimation method of the empirical lower bound is proposed, which is helpful for estimating the number of projection views required for exact reconstruction. Simulation studies show that the singularity of the system matrices for different projection views is effectively reduced by regularization. Computing the condition number of a regularized matrix is necessary to provide a reference for evaluating the singularity and recovery potential of reconstruction algorithms using regularization. The empirical lower bound is helpful for estimating the projections view number with a sparse reconstruction algorithm. Show more

Keywords: System matrix analysis, sparse-view reconstruction, singularity, condition number, projection views number, total variation regularization

DOI: 10.3233/XST-140465

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 1-10, 2015

Authors: Dang, Jun | Luo, Ouyang | Gu, Xuejun | Wang, Jing

Article Type: Research Article

Abstract: BACKGROUND: High quality 4D-CBCT can be obtained by deforming a planning CT (pCT), where the deformation vector fields (DVF) are estimated by matching the forward projections of pCT and 4D-CBCT projections. The matching metric used in the previous study is the sum of squared intensity differences (SSID). The scatter signal level in CBCT projections is much higher than pCT, the SSID metric may not lead to optimal DVF. OBJECTIVE: To improve the DVF estimation accuracy, we develop a new …matching metric that is less sensitive to the intensity level difference caused by the scatter signal. METHODS: The negative logarithm of correlation coefficient (NLCC) is used as the matching metric. A non-linear conjugate gradient optimization algorithm is used to estimate the DVF. A 4D NCAT phantom and an anthropomorphic thoracic phantom were used to evaluate the NLCC-based algorithm. RESULTS: In the NCAT phantom study, the relative reconstruction error is reduced from 18.0% in SSID to 14.13% in NLCC. In the thoracic phantom study, the root mean square error of the tumor motion is reduced from 1.16 mm in SSID to 0.43 mm in NLCC. CONCLUSION: NLCC metric can improve the image reconstruction and motion estimation accuracy of DVF-driven image reconstruction for 4D-CBCT. Show more

Keywords: DVF estimation from projection, 4D-CBCT, DVF-driven image reconstruction

DOI: 10.3233/XST-140466

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 11-23, 2015

Authors: Lin, Yang-Hsien | Lin, Kang-Ping | Huang, Shih-Min | Lu, Hui-Ting | Lin, Tien-Hsiang | Huang}, Tzung-Chi

Article Type: Research Article

Abstract: PURPOSE: Segmentation of the left ventricle (LV) in cardiac CT (CCT) images is difficult due to the intensity heterogeneity arising from accumulation of contrast agent in papillary muscle and trabeculae carneae. In this study, we demonstrated the random walks method for LV segmentation in CCT through cardiac phases. METHODS: 63 CCT data sets from 7 patients with 9 cardiac phases were included in this study. All cardiac CT examinations were performed with GE 64-detector …CT scanner with ECG gating. In each patient, 60–80 ml iohexol was injected at a flow rate of 5 ml/sec followed by 60 ml normal saline solution. Random walks (RW) based on probability of labels was used for LV segmentation. The LV delineations generated by the experienced physician (MD), conventional image-based method (IB), and RW were compared. RESULTS: In general the contours segment the LV closely by RW and MD, but the discrepancies in papillary muscle and trabeculae carneae were observed while using the IB method. CONCLUSION: We showed the RW method potentially improved LV segmentation as compared to the volume by conventional IB method. In this study, we demonstrated the clinical feasibility of LV volume segmentation using random walks algorithm. Show more

Keywords: Left ventricle, random walks, cardiac computed tomography

DOI: 10.3233/XST-140467

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 25-31, 2015

Authors: Kwon, Ohjae | Kang, Sung-Tae | Kim, Soo-Hong | Kim, Yoon-Ho | Shin, Yeong-Gil

Article Type: Research Article

Abstract: BACKGROUND: Maximum intensity projection (MIP) is a volume rendering technique that determines the pixel intensity as the maximum of all values sampled along the viewing direction. MIP has been successfully applied to diagnose bone fractures in computed tomography (CT) and the stenosis of vascular structures in magnetic resonance angiography (MRA). However, MIP has a major drawback in that the depth and occlusion information cannot be perceived in the output images. The most universal way to alleviate …this problem is to occasionally change the viewpoint for depth perception. To support this function in real time, MIP should be performed at an interactive frame rate. OBJECTIVE: We develop an efficient rendering algorithm for MIP so that MIP is performed at an interactive frame rate without a loss of image quality. METHODS: The proposed method predicts the position of the maximum intensity for each ray using blockwise maximum bounds, after which it performs bidirectional compositing toward both ends of the ray from this predicted position. During the compositing process, block skipping is used as an acceleration method. RESULTS: The proposed method outperformed the block skipping method using the sequential compositing with a speed-up factor of 2.2 ∼ 2.8 depending on the data set without any degradation of the image quality. CONCLUSION: We proposed an efficient rendering technique for MIP. Our method was superior to the conventional block skipping method with respect to the rendering speed and degree of performance consistency. Show more

Keywords: Maximum intensity projection, acceleration techniques, prediction of the starting position, bidirectional compositing, block skipping

DOI: 10.3233/XST-140468

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 33-44, 2015

Authors: Li, Hong-Wen | Wu, Xing-Wang | Liu, Bin | Liu, Wen-Dong | Gao, Na

Article Type: Research Article

Abstract: OBJECTIVE: To quantitatively evaluate the diagnostic value of gemstone spectral CT in thyroid disease. PATIENTS and METHODS: A total of 123 patients with thyroid diseases were enrolled in the retrospective study. All the patients underwent spectral CT scan, and 39 of them underwent dual-phase enhanced scan. Iodine concentration (IC) and normalized IC (NIC) were compared between benign and malignant nodules. The optimal threshold to predict malignancy was obtained by receiver operating characteristic curve (ROC). Multivariate …ROC analysis was performed to evaluate the efficacy of combining the IC (NIC) and conventional morphological characteristics. RESULTS: Ten diffuse diseases and 113 nodular diseases were confirmed by clinical laboratory examination and histopathology. In total, 122 nodules (87 benign and 35 malignant) were detected, 41 nodules in enhanced cases. The IC and NIC_{VP} of malignant nodules were significantly lower than benign nodules in noncontrast and venous phase (VP) (P=0.000). The optimal IC and NIC_{VP} threshold was 0.68 mg/mL and 0.38, achieving 74.3% and 76.9% sensitivity, 66.7% and 80.0% specificity, respectively. For multivariate analysis, the area under ROC (AUC) was 0.88 and 0.94 in noncontrast and VP, respectively. Sensitivities of 77.1% and 84.6%, and specificities of 84.5% and 88.0% were achieved. CONCLUSION: Gemstone spectral CT can generally evaluate the abnormal iodine content in thyroid disease. Lower iodine can help differentiating malignant from benign nodules. A comprehensive analysis combining spectrum parameters and morphological characteristics is suggested in differential diagnosis. Show more

Keywords: Thyroid disease, computed tomography, gemstone spectral imaging

DOI: 10.3233/XST-140469

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 45-56, 2015

Authors: AL-Ghorabie, Fayez H.H

Article Type: Research Article

Abstract: An EGSnrc user code is developed to simulate a backscattered geometry in vivo x-ray fluorescence system for the measurement of platinum concentration in head and neck tumours. The user code is fundamentally based on a previous study which used the EGS4 Monte Carlo code. The new user code, which we have developed in this study, has new improvements which made it able to simulate the process of photon transportation through the different components of the modelled …x-ray fluorescence system. The simulation process included modelling of the photon source, collimators, phantoms and detector. Simulation results were compared and evaluated against x-ray fluorescence data obtained experimentally from an existing system developed by the Swansea In vivo Analysis and Cancer Research Group. In addition, simulation results of this study were also compared with our previous study in which the EGS4 user code was used. Comparison between results has shown that the new EGSnrc user code was able to reproduce the spectral shape obtained using the experimental x-ray fluorescence system. The area under the Compton peak differs by 2.5% between the experimental measurement and the EGSnrc simulation. Similarly, the area under the two Pt Kα peaks differs by 2.3% and 2.2%. Show more

Keywords: EGS4, EGSnrc, computer simulation, in vivo XRF

DOI: 10.3233/XST-140470

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 57-64, 2015

Authors: Lifton, Joseph J. | Malcolm, Andrew A. | McBride, John W.

Article Type: Research Article

Abstract: X-ray computed tomography (CT) is a radiographic scanning technique for visualising cross-sectional images of an object non-destructively. From these cross-sectional images it is possible to evaluate internal dimensional features of a workpiece which may otherwise be inaccessible to tactile and optical instruments. Beam hardening is a physical process that degrades the quality of CT images and has previously been suggested to influence dimensional measurements. Using a validated simulation tool, the influence of spectrum …pre-filtration and beam hardening correction are evaluated for internal and external dimensional measurements. Beam hardening is shown to influence internal and external dimensions in opposition, and to have a greater influence on outer dimensions compared to inner dimensions. The results suggest the combination of spectrum pre-filtration and a local gradient-based surface determination method are able to greatly reduce the influence of beam hardening in X-ray CT for dimensional metrology. Show more

Keywords: Computed tomography, beam hardening, dimensional metrology, X-ray spectrum estimation, ISO50, surface determination

DOI: 10.3233/XST-140471

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 65-82, 2015

Authors: Wang, Linyuan | Cai, Ailong | Zhang, Hanming | Yan, Bin | Li, Lei | Hu, Guoen | Bao, Shanglian

Article Type: Research Article

Abstract: With the development of compressive sensing theory, image reconstruction from few-view projections has been paid considerable research attention in the field of computed tomography (CT). Total variation (TV)-based CT image reconstruction has been shown experimentally to be capable of producing accurate reconstructions from sparse-view data. Motivated by the need of solving few-view reconstruction problem with large scale data, a general block distribution reconstruction algorithm based on TV minimization and the alternating direction …method (ADM) has been developed in this study. By utilizing the inexact ADM, which involves linearization and proximal point techniques, the algorithm is relatively simple and hence convenient for the derivation and distributed implementation. And because the data as well as the computation are distributed to individual nodes, an outstanding acceleration factor is achieved. Experimental results demonstrate that the proposed method can accelerate the alternating direction total variation minimization (ADTVM) algorithm with nearly no loss of accuracy, which means compared with ADTVM, the proposed algorithm has a better accuracy with same running time. Show more

Keywords: Sparse-view reconstruction, total variation minimization, inexact alternating direction method, distributed reconstruction algorithm, block-splitting distribution

DOI: 10.3233/XST-140472

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 83-99, 2015

Authors: Su, Xinhui | Zheng, Kunmu | Ma, Qilin | Huang, Jingxiong | He, Xiaojiang | Chen, Guibing | Wang, Weixing | Su, Fu | Tang, Hui | Wu, Hua | Tong, Suijun

Article Type: Miscellaneous

Abstract: OBJECTIVE: This study aimed to observe the effect of local mild hypothermia on regional cerebral blood flow (rCBF) after acute intracerebral hemorrhage (ICH) and to evaluate its relation to clinical outcome in patients with ICH. METHODS: 36 CT proven ICH patients with Glasgow coma scale (GCS) score of 5 or more were randomly assigned to 2 group: local mild hypothermia with conventional mannitol (Group A) or conventional mannitol (Group B). SPECT study was performed at …day 7 after therapy. The SPECT images were semi-quantitatively analyzed, and the radioactivity ratios of lesion to normal tissue (L/NT) were calculated. National Institutes of Health Stroke Scale (NIHSS) were used in evaluation at days 14 and 21 after therapy. RESULTS: There were significant differences in NIHSS score at days 14 and 21, and the L/NT ratios between the groups A and B (P < 0.05). Based on GCS, more patients in the group A showed favorable outcomes than patients in the group B (P < 0.05). Furthermore, the L/NT ratios significantly increased in patients with favorable outcomes compared to poor outcomes. Changes in NIHSS score at days 14 and 21 were closely negatively correlated with the L/NT ratios in the groups A and B (r= −0.58, −0.61, and −0.52, −0.75, respectively, P < 0.05). CONCLUSION: Local mild hypothermia could significantly increase rCBF and improve clinical outcome in ICH patients as evaluated by ^{99m} Tc-ECD SPECT study. Show more

Keywords: Local mild hypothermia, regional cerebral blood flow, intracerebral hemorrhage, SPECT imaging

DOI: 10.3233/XST-140473

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 101-109, 2015

Authors: Li, Zhifang | Chen, Haiyu | Li, Hui | Chen, Wei R.

Article Type: Research Article

Abstract: A method combining morphological granulometry with Mie theory to determine optical scattering in biological tissues was proposed. Otsu's method was applied to binarize phase-contrast images. Binary morphological granulometry was used to estimate size density distribution of the tissue samples based on the binary phase-contrast images. Our results showed that the optical parameters associated with light scattering in tissue could be quantitatively determined by combining size density distribution with Mie theory. It was …suggested that this unique method could be used to characterize biological tissues for disease diagnosis. Show more

Keywords: Morphological granulometry, optical scattering properties, Mie theory

DOI: 10.3233/XST-140474

Citation: Journal of X-Ray Science and Technology, vol. 23, no. 1, pp. 111-118, 2015