Engineering Design of phased array EPI using TDM

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HTS coil design using artificial neural network and fuzzy interference system

The design of High Temperature Superconducting (HTS) RF coil highly relies on the computer simulation because HTS materials are very expensive and the coil fabrication requires high accuracy. Normally, the simulation for the HTS coil design is time consuming and not straightforward. In this paper, two novel approaches for HTS coil design, the electromagnetically (EM) trained artificial neural networks (EM-ANN) and the electromagnetically trained fuzzy inference systems (EM-FIS) are presented. These two models can simplify the normal simulation and speed up by millions of times. Therefore, the difficult tuning procedure of HTS coil can be easily simulated before its fabrication.published_or_final_versio

Relationship among SAR, RF frequency and tissue

SAR is one of the most important parameters and as a guideline for MRI safety. The relationships among SAR, different tissues and different resonant frequencies have not been discussed quantitatively. In this abstract, we present some comparisons and results about this important issue.published_or_final_versio

Optimization of a multi-channel transmit, Quadrature Receive Birdcage Coil

A multi-channel transmit, quadrature receive birdcage coil are optimized by using singular value decomposition (SVD) method. Compared with conventional transceiver quadrature birdcage, this coil has dramatically improved B1 + filed homogeneity and relative SNR, with slight penalty of increased average SAR.published_or_final_versio

Algebraic Rreconstruction for Parallel Imaging with Radial Trajectory

A novel algebraic reconstruction method for parallel imaging with radial trajectory is proposed. Taking advantage of projection-slice theorem, the reconstruction can be performed by first carrying out a 1-D FFT and then iteratively solving a system of linear equations. Since the data in non-Cartesian coordinate are directly used, the bulk work of gridding is not required. The feasibility of this method was demonstrated by simulation.published_or_final_versio

Single Cable Transmission for Multi-Channel MRI using Frequency Division Multiplexing

Parallel imaging and RF array coils require a great quantity of MRI channels, which can produce ghosting and interference to decrease imaging SNR. In this work, we make use of a frequency division multiplexing (FDM) technique to combine several channel signals and transmit them in single cable. At present the PCB board is prototyped and tested with the signal generator. We propose to build the completed circuit with coil array on board to recover the multichannel FID signals.published_or_final_versio

A shielding-based decoupling technique for coil array design

A new decoupling technique which takes advantage of shielding for coil array design is proposed. A ground plane is used to reduce mutual inductance by reducing the effective coupling loop area of circuits; in addition, a "screen track" is placed between adjacent coils to minimize magnetic interferences. This technique requires no modification of circuit and doesnít cause loss of flexibility of coil geometry. Simulation and experiments show that a ground plane beneath surface coils can reduce mutual coupling by 10-20dB, and a "screen track" can further provide a 2-8dB more isolation.published_or_final_versio

Array with multiple loops for vertical field system

For vertical field MRI applications, the structure of the loop array is quite different from those in a horizontal-magnetic-field system. The conventional decoupling techniques are hard to be extended to vertical MRI system. Therefore, the loops for vertical MRI system are quite difficult to decouple. So far the coil array with up to two loop coils have been investigated on open low-field MRI, the array with more than three loop coils is sparsely reported. In this study, we present a decoupling technique using inductors for vertical-field loop coils. A four-channel array consisted of 3 loops and a saddle coil has been built for human knee at 0.5T vertical MRI system.published_or_final_versio

Comparison of RF Penetration and G-factor of Different Coil Arrays for Parallel Imaging

Geometry factor and RF penetration of different kinds of coil arrays for parallel imaging were evaluated by simulations using MATLAB and XFDTD software. The results show that the coil arrays with loop structure are superior to the planar strip arrays in terms of g-map and RF penetration. The overlapped loop array has better RF penetration, while the non-overlapped one has a lower noise level in parallel imaging.published_or_final_versio

Comparison of Optical Modulation Methods for RF Coil Interlinks

Optical modulation method is one of the key factors in the optical link design for MRI RF coil interlinks. In this work, link performances of direct modulation by laser diode and external modulation by Mach Zehnder Interferometer are compared in the aspects of power gain, modulation bandwidth, noise figure and dynamic range. An external optical link can achieve better performance by the use of a low noise and high power laser. However, a direct optical link shows advantages in link structure, compact size and low cost. It is more feasible in engineering for large coil array interlinks.published_or_final_versio