Capacitively-loaded metasurfaces and their application in magnetic resonance imaging

Glybovski, Stanislav; Shchelokova, Alena; Kozachenko, A. V.; Slobozhanyuk, Alexey P.; Melchakova, Irina V.; Belov, Pavel A.; Sokolov, A. V.; Efimtsev, A. Yu.; Fokin, V. A.

doi:10.1109/radio.2015.7323400

Cited by 11 publications

(8 citation statements)

References 7 publications

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“…To do so, the wires used need to be either of a resonant length 10 or miniaturized by high-permittivity loading, 11 or by capacitive interconnections. 12 These studies demonstrate the possibility of using such metasurface structures to achieve a dual-frequency coil for proton and fluorine imaging, 13 and a coil for whole-body imaging with higher SNR than a volume coil. 14 It has been shown that the optimal impedance matching of such metasurface-based coils is obtained with a nonresonant feed loop when one of the metasurface resonances coincides with the targeted Larmor frequency.…”

Section: Introductionmentioning

confidence: 80%

Wireless coils based on resonant and nonresonant coupled‐wire structure for small animal multinuclear imaging

et al. 2019

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Earlier work on RF metasurfaces for preclinical MRI has targeted applications such as whole‐body imaging and dual‐frequency coils. In these studies, a nonresonant loop was used to induce currents into a metasurface that was operated as a passive inductively powered resonator. However, as we show in this study, the strategy of using a resonant metasurface reduces the impact of the loop on the global performance of the assembled coil. To mitigate this deficiency, we developed a new approach that relies on the combination of a commercial surface coil and a coupled‐wire structure operated away from its resonance. This strategy enables the extension of the sensitive volume of the surface coil while maintaining its local high sensitivity without any hardware modification. A wireless coil based on a two parallel coupled‐wire structure was designed and electromagnetic field simulations were carried out with different levels of matching and coupling between both components of the coil. For experimental characterization, a prototype was built and tested at two frequencies, 300 MHz for 1H and 282.6 MHz for 19F at 7 T. Phantom and in vivo MRI experiments were conducted in different configurations to study signal and noise figures of the structure. The results showed that the proposed strategy improves the overall sensitive volume while simultaneously maintaining a high signal‐to‐noise ratio (SNR). Metasurfaces based on coupled wires are therefore shown here as promising and versatile elements in the MRI RF chain, as they allow customized adjustment of the sensitive volume as a function of SNR yield. In addition, they can be easily adapted to different Larmor frequencies without loss of performance.

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Section: Introductionmentioning

confidence: 80%

Wireless coils based on resonant and nonresonant coupled‐wire structure for small animal multinuclear imaging

et al. 2019

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“…1(d), the top and the bottom ones, were both placed on coaxial cylindrical surfaces with a constant angular periodicity α = 10 • to repeat the shape of a human arm. To make the structure resonant at 81 and 200.1 MHz the tips of all wires on one side of the structure were connected by structural capacities [21]. On the other side of the structure the wires were connected by sliding short-circuiting contacts as shown in Fig.…”

Section: Rf-coil Design and Characterizationmentioning

confidence: 99%

Radio Frequency Coil for Dual-Nuclei MR Muscle Energetics Investigation Based on Two Capacitively Coupled Periodic Wire Arrays

Hurshkainen¹,

Dubois²,

Nikulin³

et al. 2020

Antennas Wirel. Propag. Lett.

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In this paper, we describe a dedicated radiofrequency coil for magnetic resonance imaging and spectroscopy (MRSI) at 4.7 T optimized for investigation of muscle energetics in a human forearm. The coil operating at the Larmor frequencies of protons 1 H (200.1 MHz) and phosphorous 31 P (81 MHz) is based on two cylindrical periodic structures made of thin metal wires with tips interconnected through structural capacities of printed overlapping patches and sliding electric contacts. By independently exciting two orthogonal eigenmodes of the structure, the coil can be tuned and matched at both frequencies without lumped capacitors and cover the target region of interest for the forearm flexor muscles.

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“…This effect locally increased the transmit efficiency and signal-to-noise ratio (SNR) of the BC. The water-filled wire MS was followed by several modifications proposed for the same type of resonant focusing operation, [25][26][27][28][29][30][31][32] and some alternative MS-based coupled resonators were proposed (eg, Refs. 33,34).…”

Section: Introductionmentioning

confidence: 99%

Improving homogeneity in abdominal imaging at 3 T with light, flexible, and compact metasurface

Vorobyev

Shchelokova

Efimtsev

et al. 2021

Magnetic Resonance in Med

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Purpose: Radiofrequency field inhomogeneity is a significant issue in imaging large fields of view in high-and ultrahigh-field MRI. Passive shimming with coupled coils or dielectric pads is the most common approach at 3 T. We introduce and test light and compact metasurface, providing the same homogeneity improvement in clinical abdominal imaging at 3 T as a conventional dielectric pad. Methods: The metasurface comprising a periodic structure of copper strips and parallel-plate capacitive elements printed on a flexible polyimide substrate supports propagation of slow electromagnetic waves similar to a high-permittivity slab. We compare the metasurface operating inside a transmit body birdcage coil to the stateof-the-art pad by numerical simulations and in vivo study on healthy volunteers. Results: Numerical simulations with different body models show that the local minimum of B + 1 causing a dark void in the abdominal domain is removed by the metasurface with comparable resulting homogeneity as for the pad with decreasing maximum and whole-body SAR values. In vivo results confirm similar homogeneity improvement and demonstrate the stability to body mass index. Conclusion:The light, flexible, and inexpensive metasurface can replace a relatively heavy and expensive pad based on the aqueous suspension of barium titanate in abdominal imaging at 3 T.

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Capacitively-loaded metasurfaces and their application in magnetic resonance imaging

Cited by 11 publications

References 7 publications

Wireless coils based on resonant and nonresonant coupled‐wire structure for small animal multinuclear imaging

Wireless coils based on resonant and nonresonant coupled‐wire structure for small animal multinuclear imaging

Radio Frequency Coil for Dual-Nuclei MR Muscle Energetics Investigation Based on Two Capacitively Coupled Periodic Wire Arrays

Improving homogeneity in abdominal imaging at 3 T with light, flexible, and compact metasurface

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