A Preliminary Study for Reference RF Coil at 11.7 T MRI: Based on Electromagnetic Field Simulation of Hybrid-BC RF Coil According to Diameter and Length at 3.0, 7.0 and 11.7 T.

Jeung-Hoon Seo,Jun-Young Chung

doi:10.3390/s22041512

Abstract

Magnetic resonance imaging (MRI) systems must undergo quantitative evaluation through daily and periodic performance assessments. In general, the reference or standard radiofrequency (RF) coils for these performance assessments of 1.5 to 7.0 T MRI systems have been low-pass-type birdcage (LP-BC) RF coils. However, LP-BC RF coils are inappropriate for use as reference RF coils because of their relatively lower magnetic field (B1-field) sensitivity than other types of BC RF coils, especially in ultrahigh-field (UHF) MRI systems above 3.0 T. Herein, we propose a hybrid-type BC (Hybrid-BC) RF coil as a reference RF coil with improved B1-field sensitivity in UHF MRI system and applied it to an 11.7 T MRI system. An electromagnetic field (EM-field) analysis on the Hybrid-BC RF coil was performed to provide the proper dimensions for its use as a reference RF coil. Commercial finite difference time-domain program was used in EM-field simulation, and home-made analysis programs were used in analysis. The optimal specifications of the proposed Hybrid-BC RF coils for them to qualify as reference RF coils are proposed based on their B1+-field sensitivity under unnormalized conditions, as well as by considering their B1+-field uniformity and RF safety under normalized conditions.

Highlights

In magnetic resonance imaging (MRI) devices below 7.0 T, birdcage (BC) radiofrequency (RF) coils are widely used for the production of a circularly polarized mode in quadrature current driving [1,2]
To suggest an optimal BC coil for each magnetic field strength, we have comprehensively investigated the use of a Hybrid-BC RF coil as a reference RF coil by utilizing a cylindrical phantom model and human body model under various B0 -field strengths and by considering signal sensitivity, field uniformity, and specific absorption rate (SAR) analysis
In the EM-field simulation results using the water phantom, the unnormalized |B1 + |field sensitivity at 127.74 MHz was verified by an increase in parallel to the length increases, and the diameter of the Hybrid-BC coil is fixed at 300 mm (Figure 2a)

Summary

Introduction

In magnetic resonance imaging (MRI) devices below 7.0 T, birdcage (BC) radiofrequency (RF) coils are widely used for the production of a circularly polarized mode in quadrature current driving [1,2]. Because the BC coil configuration provides superior magnetic flux density field (B1 -field) sensitivity and uniformity, this BC geometry has been widely applied to MRI fields requiring uniform RF transmission field (B1 + -field) and RF reception field (B1 − -field) instead of other RF coil geometries [3]. For these advantages, BC coils are usually used as reference RF coils when performing quality assurance testing in monthly system checks as well as in image quality checks, especially when used to validate quantitative performance. LP-BC RF coils provide excellent B1 -field sensitivity in low-field MRI systems below 3.0 T, and their

Methods

Results

Conclusion