483 research outputs found
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
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
A Residual Fully Convolutional Network (Res-FCN) for Electromagnetic Inversion of High Contrast Scatterers at an Arbitrary Frequency Within a Wide Frequency Band
Many successful machine learning methods have been developed for
electromagnetic inverse scattering problems. However, so far, their inversion
has been performed only at the specifically trained frequencies. To make the
machine-learning-based inversion method more generalizable for realistic
engineering applications, this work proposes a residual fully convolutional
network (Res-FCN) to perform EM inversion of high contrast scatterers at an
arbitrary frequency within a wide frequency band. The proposed Res-FCN combines
the advantages of the Res-Net and the fully convolutional network (FCN).
Res-FCN consists of an encoder and a decoder: the encoder is employed to
extract high-dimensional features from the measured scattered field through the
residual frameworks, while the decoder is employed to map from the
high-dimensional features extracted by the encoder to the electrical parameter
distribution in the inversion region by the up-sample layer and the residual
frameworks. Four numerical examples verify that the proposed Res-FCN can
achieve good performance in the 2-D EM inversion problem for high contrast
scatterers with anti-noise ability at an arbitrary frequency point within a
wide frequency band
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