Bin Xu

An inverse methodology for high-frequency RF coil design for MRI with de-emphasized B/sub 1/ fields

An inverse methodology for the design of biologically loaded radio-frequency (RF) coils for magnetic resonance imaging applications is described. Free space time-harmonic electromagnetic Greens functions and de-emphasized B/sub 1/ target fields are used to calculate the current density on the coil cylinder. In theory, with the B/sub 1/ field de-emphasized in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the central overemphasis effect caused by field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T (170 MHz) is calculated using an inverse methodology with de-emphasized B/sub 1/ target fields. An in-house finite-difference time-domain routine is employed to evaluate B/sub 1/ field and signal intensity inside a homogenous cylindrical phantom and then a complete human head model. A comparison with a conventional RF birdcage coil is carried out and demonstrates that this method can help in decreasing the normal bright region caused by field/tissue interactions in head images at 170 MHz and higher field strengths.

Model Implementation and Case Study for the Lossy, Multilayered Spherical Head Phantom in MRI Application

To better simulate RF field behavior in the human head for MRI applications, dyadic Greens function (DGF)/method of moment (DGF/MOM) -based solutions of the electromagnetic field (EMFs) inside a head-sized, stratified sphere in different MRI coils are presented. The lossy, multilayered spherical head phantom has similar radial conductivity and permeability profiles as human head and is loaded in MRI surface and RF volume coils. B1 field pattern, SAR distribution, flip angle, signal intensity (SI), and other MRI image parameters are calculated in this study. The results reported herein show the operating characteristics of the field/tissue interactions and safety properties for human head model in different coils

A New Approach for Magnetic Resonance RF Head Coil Design

In this work, a new concept in high field RF head coil design for MRI applications is presented. An 8-element phased array head coil operating at 4T is designed based on a hybrid method combining reciprocity theorem and inverse method. Both circularly or linearly polarized head coils can be designed. A FDTD/MOM calculation method is used to model the phased array head coil and to accurately calculate the RF behavior inside a human head model. The simulation results reported herein demonstrate the feasibility and flexibility of the design concept and show that, compared to conventional methods, improved B1 field homogeneity is achievable at high field

An inverse methodology for high frequency RF head coil design with preemphasized B/sub 1/ field in MRI

An inverse methodology to assist in the design of radio-frequency (RF) head coils for high field MRI application is described in this work. Free space time-harmonic electromagnetic Greens functions and preemphasized B/sub 1/ field are used to calculate the current density on the coil cylinder. With B/sub 1/ field preemphasized and lowered in the middle of the RF transverse plane, the calculated current distribution can generate an internal magnetic field that can reduce the EM field/tissue interactions at high frequencies. The current distribution of a head coil operating at 4 T is calculated using inverse methodology with preemphasized B/sub 1/ fields. FDTD is employed to calculate B/sub 1/ field and signal intensity inside a homogenous cylindrical phantom and human head. A comparison with conventional RF birdcage coil is reported here and demonstrated that inverse-method designed coil with preemphasized B/sub 1/ field can help in decreasing the notorious bright region caused by EM field/tissue interactions in the human head images at 4 T.