Journal of X-Ray Science and Technology - Volume 14, issue 2

Authors: Gu, Jianwei | Zhang, Li | Yu, Guoqiang | Xing, Yuxiang | Chen, Zhiqiang

Article Type: Research Article

Abstract: We present a sinogram inpainting approach for X-ray computed tomography (CT) with the intent of reducing metal artifacts, where "inpainting" is a synonym for "image interpolation". Metal artifacts arise in CT when rays traverse the high attenuating objects such as metal bodies and portions of projection become unavailable. In this paper, we propose a sinogram inpainting method based on Euler's elastica and curvature for metal artifacts reduction, in which the unavailable data are regarded as an …occlusion and can be inpainted inside the inpainting domain based on elastica interpolants. Numerical simulations demonstrate that, compared to conventional interpolation methods, the algorithm proposed connects the unavailable projection region more smoothly and accurately, and thus better reduces metal artifacts and more accurately reveals cross section structures, especially in the immediate neighborhood of the metallic objects. Show more

Keywords: Curvature, elastica, inpainting, metal artifacts, X-ray computed tomography (CT)

Citation: Journal of X-Ray Science and Technology, vol. 14, no. 2, pp. 73-82, 2006

Authors: Qi, Zhihua | Zhang, Li | Xing, Yuxiang | Li, Shuanglei

Article Type: Research Article

Abstract: X-ray images are often of low contrast due to the subtle distinction of attenuation coefficients and scatter effect, which makes it difficult to distinguish signals from background. This paper proposes an image enhancement algorithm using the multi-scale dyadic wavelet transform. The algorithm includes two steps: 1) In order to enhance contrast, a non-linear mapping is performed on wavelet coefficients at different scales. Inhibition factors are then applied to reduce the impact of scatter; 2) In order …to reduce the negative impact of noise amplification from the first step, wavelet coefficients are classified into two categories: irregular coefficients and edge-related and regular coefficients, and then filtered with different schemes for each category. Experimental results demonstrate that this algorithm effectively enhance the contrast of x-ray images. Examination is also done on CT reconstructions from multi-view projection data processed by the proposed method and significant improvement of image quality is observed. Our results are expected to offer great help to follow-up detection and recognition tasks. Show more

Keywords: Dyadic wavelet transform, contrast enhancement, non-linear mapping, scatter reduction, denoising, coefficient classification

Citation: Journal of X-Ray Science and Technology, vol. 14, no. 2, pp. 83-93, 2006

Authors: Zhao, Jun | Jiang, Ming | Zhuang, Tiange | Wang, Ge

Article Type: Research Article

Abstract: In this paper, we propose a helical cone-beam scanning configuration of triple symmetrically located X-ray sources, and study minimum detection windows to extend the traditional Tam-Danielsson window for exact image reconstruction. For three longitudinally displaced scanning helices of the same radius and a source location on any helix, the corresponding minimum detection window is bounded by the most adjacent turns respectively selected from the other two helices. The height of our proposed minimum detector window is …only 1/3 of that in the single helix case. Associated with proposed minimum detection windows, we define the inter-helix PI-line and establish its existence and uniqueness property: through any point inside the triple helices, there exists one and only one inter-helix PI-line for any pair of the helices. Furthermore, we prove that cone-beam projection data from such a triple-source helical scan are sufficient for exact image reconstruction. Although there are certain redundancies among those projection data, the redundant part cannot be removed by shrinking the detector window without violating the data sufficiency condition. Those results are important components for development of exact or quasi-exact image reconstruction algorithms in the case of triple-source helical cone-beam scanning in the future. Show more

Keywords: Computed tomography (CT), cone-beam, triple-sources, helical scanning, minimum detection window, inter-helix PI-line

Citation: Journal of X-Ray Science and Technology, vol. 14, no. 2, pp. 95-107, 2006

Authors: Li, Liang | Chen, Zhiqiang | Zhang, Li | Kang, Kejun

Article Type: Research Article

Abstract: In this paper, variable pitch helical cone-beam CT is studied. We prove a sufficient condition for the existence of PI-lines inside this variable pitch helix. Under this condition, we propose a new scanning configuration, called a spring scan, which can be used to scan a cylindrical object support. Based on Zou and Pan's BPF algorithm, we develop an exact BPF-type reconstruction algorithm for helical cone-beam CT in which the pitch of the helix varies with rotation …angles. The algorithm includes four steps and can be used in region-of-interest (ROI) reconstruction by the PI-line determination step without a rebinning procedure as other BPF algorithms. Moreover, the algorithm can exactly reconstruct the object image only using the projection data within the Tam-Danielsson window, while Katsevich's algorithm requires more data than it. Furthermore, we test the proposed algorithm using the 3D Shepp-Logan phantom by a spring scan. The numerical results are described to support the correctness of the algorithm. Show more

Keywords: Backprojection-filtration, cone-beam, image reconstruction, spring scan, PI-line

Citation: Journal of X-Ray Science and Technology, vol. 14, no. 2, pp. 109-118, 2006

Authors: Sidky, Emil Y. | Kao, Chien-Min | Pan, Xiaochuan

Article Type: Research Article

Abstract: In practical applications of tomographic imaging, there are often challenges for image reconstruction due to under-sampling and insufficient data. In computed tomography (CT), for example, image reconstruction from few views would enable rapid scanning with a reduced x-ray dose delivered to the patient. Limited-angle problems are also of practical significance in CT. In this work, we develop and investigate an iterative image reconstruction algorithm based on the minimization of the image total variation (TV) that …applies to divergent-beam CT. Numerical demonstrations of our TV algorithm are performed with various insufficient data problems in fan-beam CT. The TV algorithm can be generalized to cone-beam CT as well as other tomographic imaging modalities. Show more

Keywords: Computed tomography, few-view reconstruction, limited-angle reconstruction, total variation, POCS

Citation: Journal of X-Ray Science and Technology, vol. 14, no. 2, pp. 119-139, 2006

Authors: Zhang, Da | Rong, John | Chu, Robert | Chen, Wei R. | Liu, Hong

Article Type: Research Article

Abstract: In radiographic imaging, the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) are usually determined and expressed as functions of spatial frequency in the detector plane. Values thus specified would be insufficient for describing the performance of the imaging system when magnification is used to offer better spatial resolution. We are presenting a computation of DQE at the object plane as descriptor. The derivation of this quantity from measurements …at the detector and object planes is presented. With source-to-image receptor distance (SID) remains constant, changes in the DQE with magnification are shown to be determined primarily by the corresponding changing MTF. Measurements with a small animal X-ray imaging system of constant SID agreed with theoretical analysis. Show more

Keywords: Modulation transfer function, noise power spectrum, detective quantum efficiency, magnification x-ray imaging

Citation: Journal of X-Ray Science and Technology, vol. 14, no. 2, pp. 141-150, 2006