Numerical methods and software tools for simulation, design, and resonant mode analysis of radio frequency birdcage coils used in MRI

Abstract

Design of magnetic resonance imaging (MRI) radiofrequency (RF) coils using lumped circuit modeling based techniques begins to fail at high frequencies, and therefore more accurate models based on the electromagnetic field calculations must be used. Field calculations are also necessary to understand the interactions between the RF field and the subject inside the coil. Furthermore, observing the resonance behavior of the coil and the fields at the resonance frequencies have importance for design and analysis. In this study, finite element method (FEM) based methods have been proposed for accurate time-harmonic electromagnetic simulations, estimation of the tuning capacitors on the rungs or end rings, and the resonant mode analysis of the birdcage coils. Capacitance estimation was achieved by maximizing the magnitude of the port impedance at the desired frequency while simultaneously minimizing the variance of RF magnetic field in the region of interest. In order for the proposed methods to be conveniently applicable, two software tools, resonant mode and frequency domain analyzer (RM-FDA) and Optimum Capacitance Finder (OptiCF), were developed. Simulation results for the validation and verification of the software tools are provided for different cases including human head simulations. Additionally, two handmade birdcage coils (low-pass and high-pass) were built and resonance mode measurements were made. Results of the software tools are compared with the measurement results as well as with the results of the lumped circuit modeling based method. It has been shown that the proposed software tools can be used for accurate simulation and design of birdcage coils.

Use of dielectric padding to eliminate low convective field artifact in cr‐MREPT conductivity images

“…The coil was 24 cm in height, 14.5 cm in radius, and had 16 rungs. The coil was excited in the quadrature volume transmit mode where 2 ports that were spatially 90° apart were driven by voltage sources (100 V rms) with 90° phase offset with respect to each other . Electromagnetic study was performed at 127.7 MHz, the nominal frequency of a 3T MR system.…”

“…In some studies, the anomalies were removed and a homogeneous phantom with = 80 and = 0.5 S/m was obtained. Figure D displays a 3D head model, the conductivity properties of which are shown in Figure F. Mesh was arranged similar to the cylindrical phantom (Figure E), and the data were taken from the z = 0 slice.…”

A Boundary-Value-Free Reconstruction Method for Magnetic Resonance Electrical Properties Tomography Based on the Neumann-Type Integral Formula over a Circular Region

“…1, a 16-leg high-pass shielded birdcage coil with a diameter of 240 mm and height of 270 mm was constructed and a cylindrical phantom with a diameter of 144 mm and height of 270 mm was loaded into the birdcage coil. The optimal capacitance value of the birdcage coil was determined according to the method proposed by Gurler et al [34]. The magnetic field at 123.2 MHz (corresponding to 2.89 T MRI system) was excited in a quadrature excitation mode in which the coil was driven by two ports 90…”

Gradient‐based electrical conductivity imaging using MR phase

“…In the simulations, quadrature RF birdcage coil was modeled and loaded with the simple phantom model or the human head model shown in Figures 1a and 1b (43). The simulations were made at 128 MHz (3 T) with a voxel size of 2 Â 2 Â 2mm 3 .…”