Magnetic field probe-based co-simulation method for irregular volume-type inductively coupled wireless MRI radiofrequency coils

Background

Inductively coupled wireless coils are increasingly used in MRI due to their cost-effectiveness and simplicity, eliminating the need for expensive components like preamplifiers, baluns, coil plugs, and coil ID circuits. Existing tools for predicting component values and electromagnetic (EM) fields are primarily designed for cylindrical volume coils, making them inadequate for irregular volume-type wireless coils.

Purpose

The aim of this study is to introduce and validate a novel magnetic (H-) field probe-based co-simulation method to accurately predict capacitance values and EM fields for irregular volume-type wireless coils, thereby addressing the limitations of current prediction tools.

Methods

The proposed method involves several key steps: modeling the coil in EM simulation software, replacing lumped components with 50-Ω ports, placing well-decoupled double pick-up sniffer probes within the wireless coil, conducting full-wave EM simulations, and exporting the S-parameter matrix to an RF circuit simulation tool for optimization. The RF circuit simulation optimizes component values by maximizing the average magnitude of the root square of Sxys (mean_√Sxy) of double probes and minimizing the normalized standard deviation of √Sxy (normStd_√Sxy). The optimized capacitance values are validated through re-performing EM simulations, and hardware prototypes are fabricated and tested in MRI experiments.

Results

The method was validated using bottle-shaped and dome-shaped Litzcage coils designed for 1.5 T MRI. Consistent resonant peaks and magnetic field distributions were observed across different coil designs. The optimized capacitance values obtained from circuit-level simulations were confirmed through EM simulations. Significant SNR enhancements were observed in MRI experiments, with the wireless hand and wrist/head coil showing an overall SNR enhancement of 12.8/3.4-fold in EM simulation and 13.4/3.8-fold in MRI experiments, compared to the body coil alone.

Conclusions

The H-field probe-based co-simulation method provides an efficient and accurate solution for designing and optimizing irregular wireless RF coils in MRI. By integrating EM simulation, H-field probes, and RF circuit optimization, this method reduces the need for extensive full-wave EM simulations and accurately predicts capacitance values and EM fields. The validation using irregular Litzcage coils demonstrated the method's efficacy, contributing to improved imaging quality in MRI applications. This approach offers a valuable tool for coil developers and researchers, facilitating the development of high-quality irregular wireless coils for enhanced MRI performance.