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phase-sensitive fat suppression steady-state free procession sequence with phase correction

Chinese Physics B 2008年第1期17卷 328-334页

作者：俎中良周堃张仕刚高篙包尚联 Beijing City Key Laboratory of Medical Physics and Engineering Peking University Siemens Mindit MRI Center Medical Physics Department Health Science Center of Peking University

Robust and fast fat suppression is a challenge in balanced steady-state free precession （SSFP） magnetic resonance imaging. Although single-acquisition phase-sensitive SSFP can provide fat-suppressed images in short scan time, phase errors, especially spatially-dependent phase shift, caused by a variety of factors may result in misplacement of fat and water voxels. In this paper, a novel phase correction algorithm was used to calibrate those phase errors during image reconstruction. This algorithm corrects phase by region growing, employing both the magnitude and the phase information of image pixels. Phantom and in vivo imagings were performed to validate the technique. As a result, excellent fat-suppressed images were acquired by using single-acquisition phase-sensitive SSFP with phase correction.

关键词： steady-state free precession fat suppression phase-sensitive phase correction

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Amplitude spectrum compensation and phase spectrum correction of seismic data based on the generalized S transform

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Applied Geophysics 2014年第4期11卷 468-478,510,511页

作者：周怀来王峻王明春沈铭成张听锟梁平成都理工大学地球探测与信息技术教育部重点实验室成都610059 成都理工大学油气藏地质及开发工程国家重点实验室成都610059 成都理工大学地球物理学院成都610059 成都理工大学沉积研究院成都610059 中海石油(中国)有限公司天津分公司渤海油田勘探开发研究院天津300452 成都理工大学能源学院成都610059

We propose a method for the compensation and phase correction of the amplitude spectrum based on the generalized S transform. The compensation of the amplitude spectrum within a reliable frequency range of the seismic record is performed in the S domain to restore the amplitude spectrum of reflection. We use spectral simulation methods to fit the time-dependent amplitude spectrum and compensate for the amplitude attenuation owing to absorption. We use phase scanning to select the time-, space-, and frequencydependent phases correction based on the parsimony criterion and eliminate the residual phase effect of the wavelet in the S domain. The method does not directly calculate the Q value; thus, it can be applied to the case of variable Q. The comparison of the theory model and field data verify that the proposed method can recover the amplitude spectrum of the strata reflectivity, while eliminating the effect of the residual phase of the wavelet. Thus, the wavelet approaches the zero-phase wavelet and, the seismic resolution is improved.

关键词： generalized S transform amplitude spectra phase spectra seismic resolution phase correction

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Structure-preserving properties of Strmer-Verlet scheme for mathematical pendulum

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Applied Mathematics and Mechanics(English Edition) 2017年第9期38卷 1225-1232页

作者： Weipeng HU Mingzhe SONG Zichen DENG School of Mechanics Civil Engineering and ArchitectureNorthwestern Polytechnical UniversityXi'an 710072China State Key Laboratory of Structural Analysis of Industrial Equipment Dalian University of TechnologyDalian 116023Liaoning ProvinceChina

The structure-preserving property, in both the time domain and the frequency domain, is an important index for evaluating validity of a numerical method. Even in the known structure-preserving methods such as the symplectic method, the inherent conser- vation law in the frequency domain is hardly conserved. By considering a mathematical pendulum model, a Stormer-Verlet scheme is first constructed in a Hamiltonian frame- work. The conservation law of the StSrmer-Verlet scheme is derived, including the total energy expressed in the time domain and periodicity in the frequency domain. To track the structure-preserving properties of the Stormer-Verlet scheme associated with the con- servation law, the motion of the mathematical pendulum is simulated with different time step lengths. The numerical results illustrate that the StSrmer-Verlet scheme can preserve the total energy of the model but cannot preserve periodicity at all. A phase correction is performed for the StSrmer-Verlet scheme. The results imply that the phase correction can improve the conservative property of periodicity of the Stormer-Verlet scheme.

关键词： Strmer-Verlet scheme symplectic mathematical pendulum structure-preserving Hamiltonian system phase correction

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