Improving Non-Cartesian MRI Reconstruction through Discontinuity Subtraction

Non-Cartesian sampling is widely used for fast magnetic resonance imaging (MRI). Accurate and fast image reconstruction from non-Cartesian k-space data becomes a challenge and gains a lot of attention. Images provided by conventional direct reconstruction methods usually bear ringing, streaking, and other leakage artifacts caused by discontinuous structures. In this paper, we tackle these problems by analyzing the principal point spread function (PSF) of non-Cartesian reconstruction and propose a leakage reduction reconstruction scheme based on discontinuity subtraction. Data fidelity in k-space is enforced during each iteration. Multidimensional nonuniform fast Fourier transform (NUFFT) algorithms are utilized to simulate the k-space samples as well as to reconstruct images. The proposed method is compared to the direct reconstruction method on computer-simulated phantoms and physical scans. Non-Cartesian sampling trajectories including 2D spiral, 2D and 3D radial trajectories are studied. The proposed method is found useful on reducing artifacts due to high image discontinuities. It also improves the quality of images reconstructed from undersampled data

Large-scale Electromagnetic Computation For Modeling And Applications

The papers in this special issue are devoted to the topic of large-scale electromagnetic computation methods for modeling and applicatoins. © 1963-2012 IEEE

PML and PSTD Algorithm for Arbitrary Lossy Anisotropic Media

Abstract-A general perfectly matched layer (PML) formulation is presented for lossy anisotropic media with arbitrary permittivity, permeability, and conductivity tensors. This PML is then used in a pseudospectral time-domain (PSTD) algorithm for solutions of electromagnetic fields in lossy anisotropic media. Numerical results verify the efficiency of the PML absorbing boundary condition and the PSTD algorithm

Effects of Wenxiao II Decoction on the expression of MCP-1 and VCAM-1 in atherosclerotic rabbits

AbstractObjectiveTo observe the effects of different doses of Wenxiao II Decoction on the expression of monocyte chemoattractant protein-1 (MCP-1) and vascular cell adhesion molecule-1 (VCAM-1) in an experimental model of atherosclerosis in rabbits and to explore the mechanism by which it alleviates atherosclerosis.MethodsSixty 3–4 month-old New Zealand rabbits of both sexes were randomly divided into six groups: simvastain; model; blank; and high-dose, mid-dose, and low-dose Wenxiao II Decoction groups. Except for those in the blank group, all rabbits were fed a high-cholesterol diet. Carotid atherosclerosis was established by balloon-induced injury to the endothelium of the carotid artery in conjunction with consumption of a high-cholesterol diet. After 8 weeks, all rabbits were killed to evaluate the expression of MCP-1 and VCAM-1 by immunohistochemical staining.ResultsExpressions of MCP-1 and VCAM-1 were significantly decreased in all groups except the blank group compared with the model group (P< 0.05). When compared with the simvastain group only variation of MCP-1 expression in low-dose group was not appreciable, and the differences were indistinct (P<0.05). When comparing among Wenxiao II Decoction groups, MCP-1 expression in the mid- and high-dose groups was significantly lower than that seen in the low-dose group (P< 0.01), but there were no differences among three dosage groups with respect to VCAM-1 expression (P>0.05).ConclusionThese data suggested that high, mid, and low doses of Wenxiao II Decoction can inhibit the expression of MCP-1 and VCAM-1, which may prevent the formation of or stabilize atherosclerotic plaques. There may be a direct relationship between the dosage of Wenxiao II Decoction and its therapeutic efficacy

Multimode Jahn-Teller effect in bulk systems: A case of the NV0 center in diamond

The multimode Jahn-Teller (JT) effect in a bulk system of a neutral nitrogen-vacancy ( N V 0 ) center in diamond is investigated via first-principles density-functional-theory calculations and the intrinsic distortion path (IDP) method. The adiabatic potential energy surface of the electronic ground state of the N V 0 center is calculated based on the local spin-density approximation. Our calculations confirm the presence of the dynamic Jahn-Teller effect in the ground 2 E state of the N V 0 center. Within the harmonic approximation, the IDP method provides the reactive path of JT distortion from unstable high-symmetry geometry to stable low-symmetry energy minimum geometry, and it describes the active normal modes participating in the distortion. We find that there is more than one vibrational mode contributing to the distortion, and their contributions change along the IDP. Several vibrational modes with large contributions to JT distortion, especially those modes close to 44 meV, are clearly observed as the phonon sideband in photoluminescence spectra in a series of experiments, indicating that the dynamic Jahn-Teller effect plays an important role in the optical transition of the N V 0 center