Resonant Mode Reduction in Radiofrequency Volume Coils for Ultrahigh Field Magnetic Resonance Imaging

Abstract

In a multimodal volume coil, only one mode can generate homogeneous Radiofrequency (RF) field for Magnetic Resonance Imaging. The existence of other modes may increase the volume coil design difficulties and potentially decreases coil performance. In this study, we introduce common-mode resonator technique to high and ultrahigh field volume coil designs to reduce the resonant mode while maintain the homogeneity of the RF field. To investigate the design method, the common-mode resonator was realized by using a microstrip line which was split along the central to become a pair of parallel transmission lines within which common-mode currents exist. Eight common-mode resonators were placed equidistantly along the circumference of a low loss dielectric cylinder to form a volume coil. Theoretical analysis and comparison between the 16-strut common-mode volume coil and a conventional 16-strut volume coil in terms of RF field homogeneity and efficiency was performed using Finite-Difference Time-Domain (FDTD) method at 298.2 MHz. MR imaging experiments were performed by using a prototype of the common-mode volume coil on a whole body 7 Tesla scanner. FDTD simulation results showed the reduced number of resonant modes of the common-mode volume coil over the conventional volume coil, while the RF field homogeneity of the two type volume coils was kept at the same level. MR imaging of a water phantom and a kiwi fruit showing the feasibility of the proposed method for simplifying the volume coil design is also presented.

Flexible transceiver array for ultrahigh field human MR imaging

“…In this work, the primary (first) and secondary (second) harmonics of microstrip transmission lines (24,(26)(27)(28) were chosen to build the coil elements. Two types of microstrip resonators named primary (or first) harmonic elements and second harmonic elements were utilized for coil array design.…”

Loss Path Influence on the MRI Radio Frequency Pulse Sequence: A Theoretical Evidence

“…This challenge has been reduced by introducing TEM resonators to control the distribution of the magnetic field [10]. It also assists meta/nano materials to focus on the RF magnetic field [11]. While solving the uniform distribution of the electromagnetic field, there exists the basic challenge of signal attenuation which leads to Loss Path Concept (LPC).…”

A dual-tuned quadrature volume coil with mixed λ/2 and λ/4 microstrip resonators for multinuclear MRSI at 7 T

“…This technique has been successfully applied to designs of surface coils [23,24], volume coils [25–28], and coil array [23,29–35] for high and ultrahigh field MR applications in humans. Because of the high frequency property of the microstrip resonator and the behavior of resonator length dependence of the frequency, the microstrip coil design shows challenges in reducing the resonant frequency for heteronuclear MR studies especially for the small animal applications where the coil size is much smaller than that used in humans.…”