Journal of X-Ray Science and Technology - Volume 22, issue 2

Authors: Chen, Xiaodong | Li, Junwei | Zhang, Zhaoxia | Wang, Yi | Jia, Zhongwei | Pu, Kui | Yu, Daoyin

Article Type: Research Article

Abstract: BACKGROUND: Coronary stenosis is the main cause of the coronary heart disease (CHD). However, coronary arteriography (CAG), which is considered as the 'gold standard' of determining the location and severity of CHD, hardly acquires a satisfactory image for some lesions by traditional viewing angles. OBJECTIVE: We proposed a new approach to calculate the optimal viewing angles of CAG system to observe vessel segment of interest. METHODS: Firstly, the 4-D coronary arteries are segmented to obtain …a dynamic vessel model. Then, a "rendering" method in computer graphics is used to calculate the optimal viewing angles of the vessel segment in the entire cardiac cycle. At last, an intersection of these angles can be regarded as the optimal ones in the whole cardiac cycle. RESULTS: Within the constraint of 2% foreshortening, the single phase data show 1% foreshortening without overlapping at the optimal angles proposed by our method, compared with 1.8% foreshortening at working angles set by clinical experts. And the multi-phase experiments also have good results. CONCLUSIONS: The new approach can provide doctors optimal viewing angles of interested vessel segment in the whole cardiac cycle. Show more

Keywords: 4-D cardiac CT, coronary angiography (CAG), 3-D coronary segmentation, optimal viewing angles

DOI: 10.3233/XST-140415

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 137-145, 2014

Authors: Li, Liang | Chen, Zhiqiang | Wang, Ge | Chu, Jiyang | Gao, Hao

Article Type: Research Article

Abstract: Different from the single-energy CT (SECT), multi-energy CT (MECT) acquires projection data at different energy spectra, which makes that the MECT has more sparsity among the data of separate energy and over energy. In order to maximize utilization of all these sparse characteristics, this paper proposed a new tensor PRISM model to consistently treat a priori knowledge of the low rank, intensity and sparsity with the higher-dimensional tensor technique. The priori knowledge of low rank corresponds …to the stationary background and similarity over the energy, and the intensity and sparsity represents the rest of image features at single energy. Then, the regularization and convex minimization problem was solved by tensor unfolding and an extended tensor-based split-Bregman algorithm. Different from the previous PRISM algorithm, the new algorithm mixed and treated different constraints consistently. Numerical experiments have shown that our tensor PRISM approach performs much better than the popular l_{1} regularization algorithm in terms of image quality for MECT. Show more

Keywords: Multi-energy CT (MECT), image reconstruction, tensor, unfolding, tensor PRISM

DOI: 10.3233/XST-140416

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 147-163, 2014

Authors: Qiang, Yong-Gang | Liao, Yong-Hua | Zhang, Xiu-Ping | Li, Jian | Huang, Zheng

Article Type: Research Article

Abstract: OBJECTIVES: To study the effect of γ irradiation on β-adrenergic receptors of the lung. MATERIALS AND METHODS: Healthy Sprague-Dawley rats were used as an animal model. Cell membrane proteins of lung tissue were harvested after the whole lung received 20 Gy of ^{60} Co γ irradiation. ^{125} I-labeled iodopindolol (^{125} I-IPIN) was used as a ligand of β-adrenergic receptors. The numbers of the β-adrenergic receptors were determined by radioligand-receptor binding assay (RBA). Data were compared …with irreversible blockage using antagonist bromoacetylalprenololmenthan (BAAM). RESULTS: The post-radiation RBA assay showed that the number of β-adrenergic receptors in lung tissue decreased at a steady rate. It decreased to 48% of the normal level at the 15th day after irradiation. At 40 days after radiation the level of β-adrenergic receptors started to increase at a steady rate and reached to the normal level around 70 days after radiation. There were significant differences in receptor synthesis, degradation and regeneration rates between irradiation group and BAMM group. CONCLUSIONS: The whole lung irradiation could severely affect the levels of β-adrenergic receptors. The potential clinical implications of radiation-induced changes of β-adrenergic receptors warrant further investigation. Show more

Keywords: β-adrenergic receptor, lung, ^{60}Co γ radiation

DOI: 10.3233/XST-140417

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 165-173, 2014

Authors: Karimi, Seemeen | Jiang, Xiaoqian | Cosman, Pamela | Martz, Harry

Article Type: Research Article

Abstract: BACKGROUND: Imaging systems used in aviation security include segmentation algorithms in an automatic threat recognition pipeline. The segmentation algorithms evolve in response to emerging threats and changing performance requirements. Analysis of segmentation algorithms' behavior, including the nature of errors and feature recovery, facilitates their development. However, evaluation methods from the literature provide limited characterization of the segmentation algorithms. OBJECTIVE: To develop segmentation evaluation methods that measure systematic errors such as …oversegmentation and undersegmentation, outliers, and overall errors. The methods must measure feature recovery and allow us to prioritize segments. METHODS: We developed two complementary evaluation methods using statistical techniques and information theory. We also created a semi-automatic method to define ground truth from 3D images. We applied our methods to evaluate five segmentation algorithms developed for CT luggage screening. We validated our methods with synthetic problems and an observer evaluation. RESULTS: Both methods selected the same best segmentation algorithm. Human evaluation confirmed the findings. The measurement of systematic errors and prioritization helped in understanding the behavior of each segmentation algorithm. CONCLUSIONS: Our evaluation methods allow us to measure and explain the accuracy of segmentation algorithms. Show more

Keywords: Segmentation evaluation, computed tomography, luggage screening, feature recovery

DOI: 10.3233/XST-140418

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 175-195, 2014

Authors: Arroyo, Fangjun | Arroyo, Edward | Li, Xiezhang | Zhu, Jiehua

Article Type: Research Article

Abstract: The block cyclic projection method in the compressed sensing framework (BCPCS) was introduced for image reconstruction in computed tomography and its convergence had been proven in the case of unity relaxation (λ=1). In this paper, we prove its convergence with underrelaxation parameters λ∈(0,1). As a result, the convergence of compressed sensing based block component averaging algorithm (BCAVCS) and block diagonally-relaxed orthogonal projection algorithm (BDROPCS) with underrelaxation parameters under a certain condition are …derived. Experiments are given to illustrate the convergence behavior of these algorithms with selected parameters. Show more

Keywords: Compressed sensing, image reconstruction, total variation minimization, amalgamated projection method, block iterative algorithm

DOI: 10.3233/XST-140419

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 197-211, 2014

Authors: Chen, Fong-Lin | Horng, Tzyy-Leng | Shih, Tzu-Ching

Article Type: Research Article

Abstract: This study presents a computational fluid dynamics (CFD) model to simulate the three-dimensional airflow in the trachea before and after the vascular ring surgery (VRS). The simulation was based on CT-scan images of the patients with the vascular ring diseases. The surface geometry of the tracheal airway was reconstructed using triangular mesh by the Amira software package. The unstructured tetrahedral volume meshes were generated by the ANSYS ICEM CFD software package. The airflow in the tracheal …airway was solved by the ESI CFD-ACE+ software package. Numerical simulation shows that the pressure drops across the tracheal stenosis before and after the surgery were 0.1789 and 0.0967 Pa, respectively, with the inspiratory inlet velocity 0.1 m/s. Meanwhile, the improvement percentage by the surgery was 45.95%. In the expiratory phase, by contrast, the improvement percentage was 40.65%. When the inspiratory velocity reached 1 m/s, the pressure drop became 4.988~Pa and the improvement percentage was 43.32%. Simulation results further show that after treatment the pressure drop in the tracheal airway was significantly decreased, especially for low inspiratory and expiratory velocities. The CFD method can be applied to quantify the airway pressure alteration and to evaluate the treatment outcome of the vascular ring surgery under different respiratory velocities. Show more

Keywords: Complete vascular ring (CVR), vascular ring surgery (VRS), pressure drop, computational fluid dynamics (CFD), tracheal airway resistance

DOI: 10.3233/XST-140420

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 213-225, 2014

Authors: Zhu, Lei | Niu, Tianye | Petrongolo, Michael

Article Type: Research Article

Abstract: BACKGROUND: Iterative reconstruction via total variation (TV) minimization has demonstrated great successes in accurate CT imaging from under-sampled projections. When projections are further reduced, over-smoothing artifacts appear in the current reconstruction especially around the structure boundaries. OBJECTIVE: We propose a practical algorithm to improve TV-minimization based CT reconstruction on very few projection data. METHOD: Based on the theory of compressed sensing, the L-0 norm approach is more desirable to further reduce the projection views. …To overcome the computational difficulty of the non-convex optimization of the L-0 norm, we implement an adaptive weighting scheme to approximate the solution via a series of TV minimizations for practical use in CT reconstruction. The weight on TV is initialized as uniform ones, and is automatically changed based on the gradient of the reconstructed image from the previous iteration. The iteration stops when a small difference between the weighted TV values is observed on two consecutive reconstructed images. RESULTS: We evaluate the proposed algorithm on both a digital phantom and a physical phantom. Using 20 equiangular projections, our method reduces reconstruction errors in the conventional TV minimization by a factor of more than 5, with improved spatial resolution. CONCLUSIONS: By adaptively reweighting TV in iterative CT reconstruction, we successfully further reduce the projection number for the same or better image quality. Show more

Keywords: Iterative reconstruction, CT, total variation, compressed sensing

DOI: 10.3233/XST-140421

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 227-240, 2014

Authors: Liu, Bin | Han, Yan | Pan, Jinxiao | Chen, Ping

Article Type: Research Article

Abstract: For complicated structural components characterized by wide X-ray attenuation ranges, the conventional fixed-energy imaging mode cannot obtain all structural information using a single tube voltage. This limitation results in information shortage, because the effective thickness of components along the orientation of the X-ray penetration exceeds the limit of the dynamic range of the X-ray imaging system. To solve this problem, multi-energy image sequence fusion technology has been advanced. In this new method, the tube voltage is …adjusted several times by matching the voltage and the effective thickness to obtain all the effective local information on an object. Then, the subset sequences in the multi-energy image sequence are extracted based on the recursive template, and that are fused to reconstruct the full projection information based on linear weighting. An accompanying experiment demonstrates that the new technology can extend the dynamic range of X-ray imaging and provide a complete representation of the internal structure of complicated structural components. Show more

Keywords: X-ray imaging, dynamic range, complicated structural component, multi-energy fusion, effective thickness, linear weighting

DOI: 10.3233/XST-140422

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 241-251, 2014

Authors: Mory, Cyril | Auvray, Vincent | Zhang, Bo | Grass, Michael | Schäfer, Dirk | Rit, Simon | Peyrin, Françoise | Douek, Philippe | Boussel, Loïc

Article Type: Research Article

Abstract: BACKGROUND: 4D cardiac computed tomography aims at reconstructing the beating heart from a series of 2D projections and the simultaneously acquired electrocardiogram. Each cardiac phase is reconstructed by exploiting the subset of projections acquired during this particular cardiac phase only. In these conditions, the Feldkamp, Davis and Kress method (FDK) generates large streak artifacts in the reconstructed volumes, hampering the medical interpretation. These artifacts can be substantially reduced by deconvolution methods. …OBJECTIVE: The aim of this paper is to compare two 4D cardiac CT reconstruction methods based on deconvolution, and to evaluate their practical benefits on two applications: cardiac micro CT and human cardiac C-arm CT. METHODS: The first evaluated method builds upon inverse filtering. It has been proposed recently and demonstrated on 4D cardiac micro CT. The second one is an iterative deconvolution method, and turns out equivalent to an ECG-gated Iterative Filtered Back Projection (ECG-gated IFBP). RESULTS: Results are presented on simulated data in 2D parallel beam, 2D fan beam and 3D cone beam geometries. CONCLUSIONS: Both methods are efficient on the cardiac micro CT simulations, but insufficient to handle 4D human cardiac C-Arm CT simulations. Overall, ECG-gated IFPB largely outperforms the inverse filtering method. Show more

Keywords: C-Arm, computed tomography, cardiac, electrocardiogram, 4D, deconvolution, iterative FBP, inverse filtering, micro CT

DOI: 10.3233/XST-140423

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 253-270, 2014

Authors: Zhang, Hao | Li, Lihong | Zhu, Hongbin | Han, Hao | Song, Bowen | Liang, Zhengrong

Article Type: Research Article

Abstract: Orally administered tagging agents are usually used in CT colonography (CTC) to differentiate residual bowel content from native colonic structures. However, the high-density contrast agents tend to introduce pseudo-enhancement (PE) effect on neighboring soft tissues and elevate their observed CT attenuation value toward that of the tagged materials (TMs), which may result in an excessive electronic colon cleansing (ECC) since the pseudo-enhanced soft tissues are incorrectly identified as TMs. To address this …issue, we integrated a 3D scale-based PE correction into our previous ECC pipeline based on the maximum a posteriori expectation-maximization partial volume (PV) segmentation. The newly proposed ECC scheme takes into account both the PE and PV effects that commonly appear in CTC images. We evaluated the new scheme on 40 patient CTC scans, both qualitatively through display of segmentation results, and quantitatively through radiologists' blind scoring (human observer) and computer-aided detection (CAD) of colon polyps (computer observer). Performance of the presented algorithm has shown consistent improvements over our previous ECC pipeline, especially for the detection of small polyps submerged in the contrast agents. The CAD results of polyp detection showed that 4 more submerged polyps were detected for our new ECC scheme over the previous one. Show more

Keywords: CT colonography, electronic colon cleansing, pseudo-enhancement correction, partial volume image segmentation, computer-aided detection

DOI: 10.3233/XST-140424

Citation: Journal of X-Ray Science and Technology, vol. 22, no. 2, pp. 271-283, 2014