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

An optimized four-chanel microstrip array at 7T

The microstrip transmission-line (MTL) transmit/receive loop array has been recently developed for MR applications at ultrahigh fields (>4T). In this study, the geometry of transmission-line array, including the substrate thickness and gap between coil elements was investigated by simulation and the capacitive decoupling method was analyzed. Finally an optimized four-channel microstrip loop array was built for 7T.published_or_final_versio

Minimizing power of RF pulse by genetic algorithm

In excitation phase of MRI, there is only a very small portion of the RF pulse energy used for rotating the net magnetization, most of them are deposited into the imaging object as heat. So, reducing the RF pulse power can effectively decrease the heat deposited. In this work, genetic algorithm is introduced to minimize the power of RF pulse in the pulse design procedure, while keeping the excited profile almost unchanged. Simulation result showed that the power of RF pulse can be reduced by about 17% using GA minimization, while the excitation profile homogeneity almost has no change.published_or_final_versio