A Simple Analytical Solution for the Designing of the Birdcage RF Coil Used in NMR Imaging Applications

Abstract

A novel analytical solution for the designing of the birdcage RF coil has been demonstrated in this paper. A new concept of dominant resonance path has been introduced in this paper which is used to identify the specific closed current loop in the birdcage RF coil which is responsible for the dominant resonance frequency mode. This concept is used to determine the precise numerical values of the lumped capacitance deployed in the legs and/or end-rings of the birdcage RF coil for its proper operation at the desired resonance frequency. The analytical solution presented in this paper has been established by performing the two-port network based equivalent circuit modeling of the birdcage RF coil. The proposed analytical solution uses T-matrix theory and develops a relationship between the input impedance of the birdcage coil and the impedances of its leg and end-ring segments. The proposed analytical solution provides the information about the resonance frequency spectrum of the birdcage RF coil and solves the issue of its interfacing with external circuits without affecting its resonance characteristics. Based upon the proposed analysis and designing strategy presented in this paper, the low pass, high pass and band pass configurations of the birdcage RF coil were successfully implemented with FPCB (Flexible Printed Circuit board) technique for small volume NMR imaging applications at 1.5 T and 3.0 T MRI system. The results obtained for the implemented birdcage coils using the proposed analysis and designing technique are in closed agreement with already established methods.

Electromagnetic simulation of RF burn injuries occurring at skin-skin and skin-bore wall contact points in an MRI scanner with a birdcage coil

“…Additionally, this study focused on performing simulations for MRI systems with a birdcage transmission coil. Thus, because the electromagnetic properties vary according to the transmission coil design [41][42][43], the values of SAR and patient position dependence would be different for a different design. In this study, we employed the octagonal design of the end-ring of the birdcage transmission coil in order to shorten the simulation time greatly [37].…”

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

“…The current intensity and phase of the RF can be defined at each current drive point replacing the capacitor, and the EM-field can be obtained at a specific resonance frequency. This simulation was performed under the assumption that the current was ideally drive by the micro-stripe line of the BC RF coil [5,9,19,28,32,36,44]. The results of the FDTD complex data matrix were computed using MATLAB (version 2020a, Mathworks, Inc., Natick, MA, USA) for the positioning of the B 1 -, B 1 + -, and B 1 − -components within their phase map and for the comparison of the electric field (E-field) and SAR components under various B 0 -field strengths.…”

“…A D/L-ratio of 1.0 provides high B 1 -field uniformity, whereas the D/L-ratio must be set to 0.7 to ensure maximum sensitivity at the middle plane [15]. However, the B 1 -field inhomogeneity effect usually appears as a bright region in the middle of the image when the B 0 -field strength is set at over 3.0 T. Despite these disadvantages, studies on Hybrid-BC RF coils operating at 3.0 T and above have been steadily conducted to address several changes in B 1 + -field sensitivity in the traverse plane as well as in the peak uniformity in different locations along the traverse plane [19,20]. The Hybrid-BC RF coil provides low sensitivity to loading (electromagnetic balance) with lossy dielectric loads, and when combined with carefully selected leg capacitor and ring capacitor ratios, it can reduce frequency sensitivity to loading by canceling the leg and ring effects [17,21].…”

A Comparative Study of Birdcage RF Coil Configurations for Ultra-High Field Magnetic Resonance Imaging

“…We have previously described a set of electromagnetic field (EM-field) simulations that combine various methods to improve B + 1 -field efficiency and B − 1 -field sensitivity and have proposed the use of an optimal combination of a band-pass type bird cage coil (BP-BC RF coil) with a multi-channel wireless RF element (MCWE) [43]. A BP-BC RF coil was the optimal choice because it provided the greatest uniformity and signal sensitivity among the three types of BC RF coils (Low-pass, High-pass, and Band-pass) tested in UHF MRI [44][45][46]. Although the role of MCWE in improving B 1 -field sensitivity has been evaluated in previous studies, no studies have compared MCWE with optimized combinations of RF coils and additional methods of simultaneously improving B + 1 -field efficiency and B − 1 -field sensitivity.…”