Impact of wire metasurface eigenmode on the sensitivity enhancement of MRI system

Abstract

The sensitivity of magnetic resonance imaging (MRI) is dictated by the signal-to-noise ratio. It was recently noted that the signal-to-noise ratio could be substantially increased via excitation of certain metasurface eigenmodes. Here, we provide a detailed discussion of the wire metasurface eigenmode impact on the sensitivity of MRI. We experimentally show that due to the spatial redistribution of the electromagnetic near field, mediated by the metasurface eigenmode, the received signal from the studied object becomes essentially dependent on its position on the metasurface. Moreover, we analyzed how the metasurface performance significantly depends on the dimensions of an examined object. Our work provides metasurface design guidelines for substantial enhancement of MRI sensitivity.

Adaptive Cylindrical Wireless Metasurfaces in Clinical Magnetic Resonance Imaging

“…Some studies have investigated the application of metasurfaces in MRI systems. [11][12][13][14][15][16][17][18][19][20][21][22][23] They can be divided into two types in terms of their configurations. The first involves planar metasurfaces, such as Swiss-roll arrays, [11] split-ring arrays with negative magnetic permeability, [12,13] and metallic wire arrays.…”

“…The first involves planar metasurfaces, such as Swiss-roll arrays, [11] split-ring arrays with negative magnetic permeability, [12,13] and metallic wire arrays. [14][15][16][17][18][19][20] However, these configurations perform poorly in terms of the magnetic field uniformity, especially in the direction perpendicular to the metasurfaces. The inhomogeneous distribution of the radio frequency (RF) magnetic field changes the image contrast, reduces image uniformity, increases artifacts, and even results in incorrect diagnoses.…”

Improving Magnetic Resonance Imaging with Smart and Thin Metasurfaces

“…It was shown previously that MTMs can be used to significantly improve the SNR without the need of stronger background fields. [21][22][23][24][25][26][27][28] However, passive structures as those presented in the available literature will of course influence both, the transmit (Tx) as well as the receive (Rx) field. The influence during Tx corresponds to a local increase of power transmitted, posing a potential threat of tissue heating and high SAR values.…”

A Magnetic Resonance Imaging Surface Coil Transceiver Employing a Metasurface for 1.5T Applications

“…In this paper we demonstrate, using theoretical design, numerical simulations, vector network analyzer (VNA) measurements, and MRI measurement in phantoms, that the RF magnetic flux density (B 1 ) and SNR can be increased when a capacitive impedance surface (CIS) is placed between a RF loop transceiver coil and a homogeneous phantom for 1 H MRI on a 1.5T system. Here, we demonstrate a non-resonant metasurface as compared to structures that employ resonance through the use of lumped components or other means [10], [17], [20]- [22]. Another key novel aspect of the approach is the demonstration of significant B 1 field spatial modulation and SNR improvement away from the center of the RF coil which would enhance MRI acquisition capability in certain anatomical surface receive applications.…”