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. 2024 Dec 23:7:0560.
doi: 10.34133/research.0560. eCollection 2024.

Conformal Metamaterials with Active Tunability and Self-Adaptivity for Magnetic Resonance Imaging

Ke Wu  1   2 , Xia Zhu  1   2 , Xiaoguang Zhao  2   3 , Stephan W Anderson  2   3 , Xin Zhang  1   2
Affiliations

Conformal Metamaterials with Active Tunability and Self-Adaptivity for Magnetic Resonance Imaging

Ke Wu et al. Research (Wash D C). .

Abstract

Metamaterials hold great potential to enhance the imaging performance of magnetic resonance imaging (MRI) as auxiliary devices, due to their unique ability to confine and enhance electromagnetic fields. Despite their promise, the current implementation of metamaterials faces obstacles for practical clinical adoption due to several notable limitations, including their bulky and rigid structures, deviations from optimal resonance frequency, and inevitable interference with the radiofrequency (RF) transmission field in MRI. Herein, we address these restrictions by introducing a flexible and smart metamaterial that enhances sensitivity by conforming to patient anatomies while ensuring comfort during MRI procedures. The proposed metamaterial selectively amplifies the magnetic field during the RF reception phase by passively sensing the excitation signal strength, remaining "off" during the RF transmission phase. Additionally, the metamaterial can be readily tuned to achieve a precise frequency match with the MRI system through a controlling circuit. The metamaterial presented here paves the way for the widespread utilization of metamaterials in clinical MRI, thereby translating this promising technology to the MRI bedside.

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Conflict of interest statement

Competing interests: The authors have filed 2 patent applications on the work described herein. The first application No.:16/002,458 (Status: Active) and 16/443,126 (Status: Active). Applicant: Trustees of Boston University. Inventors: Xin Zhang, Stephan Anderson, Guangwu Duan, and Xiaoguang Zhao. The second application No.: 17/065,812 (Status: Active) and 17/545,538 (Status: Pending). Applicant: Trustees of Boston University. Inventors: Xin Zhang, Stephan Anderson, Xiaoguang Zhao, and Guangwu Duan.

Figures

Fig. 1.
Fig. 1.
Concept and characterizations of the metamaterial. (A) Image of the metamaterial in a flexible state. (B) Photograph of a human wearing the proposed metamaterial. Scale bar, 20 cm. (C) Schematic diagram of the equivalent circuit of the unit cell in the metamaterial. (D) Theoretical frequency responses of the unit cell. (E and F) Experimentally measured reflection spectra as a function of excitation power strength when the metamaterial is configured in planar (E) and semi-cylindrical shapes (F). (G and H) Experimentally measured reflection spectra of the metamaterial as a function of the biasing voltage when metamaterial is configured in planar (G) and semi-cylindrical shapes (H).
Fig. 2.
Fig. 2.
Magnetic field mapping in the vicinity of the metamaterial. (A) Diagram of the field mapping setup. (B and C) Experimentally measured magnetic field strength distributed along the planar metamaterial cross-section (depicted as the blue plane in the inset) at different excitation strengths, e.g., s+ = −10 dBm (B) and s+ = 10 dBm (C). (D) Spectra of the magnetic field distribution at points A1, B1, and C1, as shown in (B). (E and F) Magnetic field strength distributed along the semi-cylindrical metamaterial cross-section (depicted as the blue plane in the inset) at different excitation strengths, e.g., s+ = −10 dBm (E) and s+ = 10 dBm (F). (G) Spectra of the magnetic field distribution at points A2, B2, and C2, as shown in (E).
Fig. 3.
Fig. 3.
MRI validations for metamaterial when combined with the BC. (A) Experimental setups for metamaterial in planar and semi-cylindrical configurations. (B) SNR images on sagittal and axial planes captured by the BC only. (C) SNR images captured by the BC enhanced by the planar metamaterial. (D) SNR images captured by the BC enhanced by the semi-cylindrical metamaterial. (E) Comparison of the SNR enhancement ratio along the blue dashed lines in (C) and (D). (F) SNR performance as a function of frequency. (G) Variations of the SNR as a function of FA. Scale bars, 5 cm (B to D).
Fig. 4.
Fig. 4.
MRI scans of ex vivo porcine leg by the BC through different imaging sequences. (A) SNR images captured with and without the presence of metamaterial. (B) Quantitative assessment of the SNR performance of specific tissues.
Fig. 5.
Fig. 5.
MRI validations for the surface coil enhanced by the metamaterial. (A) Experimental setups. Inset: Configuration of surface coil integrated with the metamaterial. (B) SNR images captured by the BC only. (C) SNR images captured by the surface coil only. (D) SNR image captured by the surface coil combined with the metamaterial. (E) SNR enhancement ratio along blue dashed lines in (C) and (D). Scale bars, 5 cm (B to D).
Fig. 6.
Fig. 6.
Comparisons between images captured by the Flex coil in the absence and presence of the metamaterial.
See this image and copyright information in PMC

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