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Combination of voxel-based and projection-based methods in terms of convergence for CT reconstruction

MEDICAL PHYSICS 2016年第6期43卷 2828-2834页

作者： Chukanov, Viacheslav Bergner, Frank SPbPU St Petersburg 195251 Russia Philips GmbH Res Labs D-22335 Hamburg Germany

Purpose: Recent applications of iterative image reconstruction algorithms to multislice helical CT have shown that iterative reconstruction can significantly improve image quality and reduce artifacts. In this paper, the authors introduce a combination of two different algorithms with different convergence properties: ordered subsets separable paraboloidal surrogates (OS-SPS) and iterative coordinate descent (ICD). The first one updates image voxels simultaneously, slightly changing attenuation values iteration by iteration. The second algorithm updates image voxel by voxel, each time performing full forward and backward projections of the voxel. It has been shown that ICD converges better at high-frequency areas and requires more iterations to reconstruct low-frequency components of the image. In contrast to ICD, SPS requires multiple iterations to reconstruct high-frequency areas. In this paper, the authors introduce an algorithm which leverages the benefits of both ICD and SPS. Methods: The idea is to update the entire image with SPS, determine high-frequency components, and focus ICD computations on it using nonhomogeneous ICD update. Results: The authors have successfully implemented OS-SPS, ICD, their hybrid approach, and few variations of ICD based on spatially nonuniform updates. Conclusions: The authors have examined the convergence of different algorithms and found that proposed algorithm converges better than OS-SPS, ICD, as well as various improved variants of ICD. (C) 2016 American Association of Physicists in Medicine.

关键词： computed tomography iterative algorithm coordinate descent separable paraboloidal surrogate ordered subsets

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Minimum-norm reconstruction for sensitivity-encoded magnetic resonance spectroscopic imaging

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MAGNETIC RESONANCE IN MEDICINE 2006年第2期55卷 287-295页

作者： Sánchez-González, J Tsao, J Dydak, U Desco, M Boesiger, P Pruessmann, KP Hosp Gen Gregorio Maranon Lab Imagen Med Expt E-28007 Madrid Spain Swiss Fed Inst Technol Inst Biomed Engn Zurich Switzerland Univ Zurich Zurich Switzerland

In this work we propose minimum-norm reconstruction as a means to enhance the spatial response behavior in parallel spectroscopic MRI. By directly optimizing the shape of the spatial response function (SRF), the new method accounts for coil sensitivity variation across individual voxels and their side lobes. In this fashion, it mitigates the signal contamination and side-lobe aliasing, to which previous techniques are susceptible at low resolution. Although the computational burden is higher, minimum-norm reconstruction is shown to be feasible using an iterative algorithm. Benefits in terms of SRF shape and artifact suppression are demonstrated.

关键词： sensitivity encoding (SENSE) MR spectroscopic imaging (MRSI) minimum-norm reconstruction strong reconstruction iterative algorithm

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KACZMARZ algorithm AND FRAMES

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INTERNATIONAL JOURNAL OF WAVELETS MULTIRESOLUTION AND INFORMATION PROCESSING 2013年第5期11卷 1350036-1350036页

作者： Czaja, Wojciech Tanis, James H. Univ Maryland Dept Math College Pk MD 20742 USA Rice Univ Dept Math Houston TX 77251 USA

Sequences of unit vectors for which the Kaczmarz algorithm always converges in Hilbert space can be characterized in frame theory by tight frames with constant 1. We generalize this result to the context of frames and bases. In particular, we show that the only effective sequences which are Riesz bases are orthonormal bases. Moreover, we consider the infinite system of linear algebraic equations Ax = b and characterize the (bounded) matrices A for which the Kaczmarz algorithm always converges to a solution.

关键词： Kaczmarz algorithm frame theory iterative algorithm

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A Fast algorithm for Matching Remote Scene Images

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Geo-Spatial Information Science 2008年第3期11卷 197-200页

作者： LIU Jin YAN Li School of Geodesy and Geomatics Wuhan University 129 Luoyu Road Wuhan 430079 China State Key Laboratory of Information Engineering in Surveying Mapping and Remote Sensing Wuhan University 129 Luoyu Road Wuhan 430079 China.

An iterative algorithm to calculate mutual correlation using hierarchical key points and the search space mark principle is proposed. An effective algorithm is designed to improve the matching speed. By hi-erarchical key point algorithm and mutual correlation coefficients of the matching images, the important points can be iteratively calculated in the images hierarchically, and the correlation coefficient can be ob-tained with satisfactory precision. Massive spots in the parameter space which are impossible to match can be removed by the search space mark principle. Two approximate continuities in the correlation image matching process, the image gray level distribution continuity and the correlation coefficient value in the parameter space continuity, are considered in the method. The experiments show that the new algorithm can greatly enhance matching speed and achieve accurate matching results.

关键词： image correlation matching fast algorithm iterative algorithm

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Alternative threshold-based channel estimation and message-passing-based symbol detection in MIMO-OTFS systems using superimposed pilots

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PHYSICAL COMMUNICATION 2023年第1期59卷

作者： Ouchikh, Rabah Aissa-El-Bey, Abdeldjalil Chonavel, Thierry Djeddou, Mustapha Ecole Mil Polytech Lab Telecommun Bordj El Bahri Algeria CNRS UMR 6285 IMT Atlantique Lab STICC F-29238 Brest France

In this work, we investigate the challenging problem of channel estimation in high-mobility environ-ments for advanced mobile communication systems (5G and beyond). First, we propose an iterative algorithm for channel estimation and symbol detection in the delay-Doppler domain for multiple-input multiple-output orthogonal time-frequency space (OTFS) system. The proposed algorithm is based on a superimposed pilot pattern to improve the spectral efficiency of the system. It iterates between data-aided channel estimation and message-passing-aided data detection. The channel estimation step is based on a threshold method. This step considers interference-plus-noise caused by the data symbols and the additive noise to adapt the threshold at each iteration. The data detection step is based on an adapted version of the message-passing algorithm proposed in the literature for uncoded OTFS. Then, to improve the channel estimation efficiency, we suggest an interference cancellation scheme executed at each iteration of the proposed algorithm. Finally, we compare the computational complexity and the achieved performance in terms of normalized mean square error of channel estimation, bit error rate, and spectral efficiency against five state-of the-art methods.(c) 2023 Elsevier B.V. All rights reserved.

关键词： MIMO OTFS Channel estimation iterative algorithm Superimposed pilot

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Hybrid Model of Gravitational Fields Around Small Bodies for Efficient Trajectory Propagations

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JOURNAL OF GUIDANCE CONTROL AND DYNAMICS 2020年第2期43卷 232-249页

作者： Wei, Bingwei Shang, Haibin Qiao, Dong Beijing Inst Technol Sch Aerosp Engn Beijing 100081 Peoples R China Beijing Inst Technol Key Lab Dynam & Control Flight Vehicle Beijing 100081 Peoples R China

When modeling the gravitational fields around small bodies, the highly irregular shapes of such objects make it difficult to balance accuracy with efficiency. In this paper, a novel and general hybrid model for evaluating the gravity of a small body is proposed with the aim of reducing errors and the computational cost. The hybrid model separates dominant effects and smaller undulations. The dominant effects are represented by the gravity-best-fit ellipsoid, which is generated by solving an optimization problem in the sense of minimizing the contribution of undulations. The undulations are then approximated using the serendipity interpolation technique, which is computationally efficient. Furthermore, a discretization scheme for the region of interest is developed, and this guarantees the evaluation of gravity in the close proximity of a small body. Based on this discretization strategy, a rapid element tracking scheme is developed to improve the efficiency of trajectory propagations. The most remarkable advantage of this tracking strategy is that the runtime for identifying elements remains the same when the region of interest is arbitrarily broadened. Simulations on asteroids 1999KW4 and 1620 Geographos show that the hybrid model is highly accurate and around 196 times faster than the conventional polyhedral model.

关键词： 4179 Toutatis iterative algorithm Spherical Harmonics Frozen Orbit Random Access Memory Finite Element Program Tetrahedral Element Probability Distribution Optimization algorithm Solar System

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Analysis of laminated beams with temperature-dependent material properties subjected to thermal and mechanical loads

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COMPOSITE STRUCTURES 2019年 227卷 111304-000页

作者： Zhang, Zhong Zhou, Ding Fang, Hai Zhang, Jiandong Li, Xuehong Nanjing Tech Univ Coll Civil Engn Nanjing 211816 Jiangsu Peoples R China

This work focuses on the temperature, displacement and stress analysis of simply-supported laminated beams with temperature-dependent material properties subjected to thermal and mechanical loads. The temperature is considered to be constant along the length of the beam, however, varies along the thickness. A thin-layer model is introduced for analysis: every layer of the beam is divided into finite sublayers, each of which is approximately assumed to have uniform material properties. Based on Fourier's law, the temperature field is obtained by an iterative algorithm. Based on the thermo-elasticity theory, the two-dimensional displacement and stress solutions are obtained by using the transfer-matrix method. The comparative study shows that the results from the two-dimensional finite element method agree well with the present ones;however, the results from the classical beam theory have considerable errors, especially for thick beams. Finally a sandwich beam is taken as an example. The analysis reveals that the temperature not only produces deformations and stresses itself, but also affects the deformations and stresses induced by mechanical loads.

关键词： Laminated beam Temperature-dependent material property Thermo-elasticity theory iterative algorithm Transfer-matrix method

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Stabilization for Rectangular Descriptor Fractional Order Systems

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IEEE ACCESS 2019年 7卷 177556-177561页

作者： Liu, Huanxia Lin, Chong Chen, Bing Geng, Wentao Qingdao Univ Inst Complex Sci Qingdao 266071 Peoples R China

This paper focuses on the stabilization problem for rectangular descriptor fractional order systems (FOSs) with 0 < alpha <= 1. Firstly, a fractional order dynamic compensator is constructed to make the closed-loop systems square descriptor FOSs. Secondly, two types of input signals of the compensator are considered, which are state input signal case and output input signal case. Thirdly, a necessary and sufficient condition is proposed for the state input signal case, while a new method of controller design is given for the output input signal case in which the output matrix of the system need not to be full row rank, which reduces the conservativeness of existing methods. Finally, an efficient iterative algorithm for solving the resultant matrix inequalities is proposed, and a numerical example is offered to verify the advantage and feasibility of the results.

关键词： Rectangular descriptor FOS stabilization fractional order dynamic compensator iterative algorithm

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A fast computational algorithm for computing outer pseudo-inverses with numerical experiments

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JOURNAL OF COMPUTATIONAL AND APPLIED MATHEMATICS 2022年第0期408卷 114128-114128页

作者： Dehghan, Mehdi Shirilord, Akbar Amirkabir Univ Technol Fac Math & Comp Sci Dept Appl Math Tehran Polytech 424 Hafez Ave Tehran 15914 Iran

In many studies in applied sciences and engineering one should find outer pseudo inverse of a matrix. In this paper, we propose a new efficient algorithm for computing the outer pseudo-inverse of a matrix. We study the convergence analysis of the new algorithm. Finally, test problems and simulation results support the theoretical approach. (c) 2022 Elsevier B.V. All rights reserved.

关键词： Outer pseudo-inverses Efficiency index iterative algorithm Convergence

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Optimization-based image reconstruction with artifact reduction in C-arm CBCT

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PHYSICS IN MEDICINE AND BIOLOGY 2016年第20期61卷 7300-7333页

作者： Xia, Dan Langan, David A. Solomon, Stephen B. Zhang, Zheng Chen, Buxin Lai, Hao Sidky, Emil Y. Pan, Xiaochuan Univ Chicago Dept Radiol Chicago IL 60637 USA GE Global Res Niskayuna NY USA Mem Sloan Kettering Canc Ctr 1275 York Ave New York NY 10021 USA Univ Chicago Dept Radiat & Cellular Oncol Chicago IL 60637 USA

We investigate an optimization-based reconstruction, with an emphasis on image-artifact reduction, from data collected in C-arm cone-beam computed tomography (CBCT) employed in image-guided interventional procedures. In the study, an image to be reconstructed is formulated as a solution to a convex optimization program in which a weighted data divergence is minimized subject to a constraint on the image total variation (TV);a data-derivative fidelity is introduced in the program specifically for effectively suppressing dominant, low-frequency data artifact caused by, e.g. data truncation;and the Chambolle-Pock (CP) algorithm is tailored to reconstruct an image through solving the program. Like any other reconstructions, the optimization-based reconstruction considered depends upon numerous parameters. We elucidate the parameters, illustrate their determination, and demonstrate their impact on the reconstruction. The optimization-based reconstruction, when applied to data collected from swine and patient subjects, yields images with visibly reduced artifacts in contrast to the reference reconstruction, and it also appears to exhibit a high degree of robustness against distinctively different anatomies of imaged subjects and scanning conditions of clinical significance. Knowledge and insights gained in the study may be exploited for aiding in the design of practical reconstructions of truly clinical-application utility.

关键词： cone-beam CT C-arm optimization-based reconstruction iterative algorithm data truncation

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