Flexible and compact hybrid metasurfaces for enhanced ultra high field in vivo magnetic resonance imaging

Schmidt, Rita; Slobozhanyuk, Alexey P.; Belov, Pavel A.; Webb, Andrew

doi:10.1038/s41598-017-01932-9

Cited by 99 publications

(60 citation statements)

References 43 publications

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“…14 Furthermore, the improvement of an RF field distribution may be achieved not only by applying particular WLCs but also by inserting high permittivity dielectric materials into the area close to a surface of an ROI [18][19][20][21][22] or metal-dielectric structures. 23 The improved devices based on this novel idea -high-dielectric resonators 20,24,25 used either as pads or quadrature RF coils-have shown a significant increase of RF magnetic field and consequently SNR.…”

Section: Introductionmentioning

confidence: 99%

Volumetric wireless coil based on periodically coupled split‐loop resonators for clinical wrist imaging

Shchelokova

Berg

Dobrykh

et al. 2018

Magnetic Resonance in Med

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Section: Introductionmentioning

confidence: 99%

Volumetric wireless coil based on periodically coupled split‐loop resonators for clinical wrist imaging

Shchelokova

Berg

Dobrykh

et al. 2018

Magnetic Resonance in Med

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“…The SNR in the region of interest (ROI) was evaluated as the ratio between the signal and the standard deviation of the noise image. [28,29,37] The larger peak SNR enhancement in the case of the NLMM is partially attributed to the additional magnetic field enhancement resulting from the VLSRR component, which is absent in the LMM. In the presence of the NLMM, the SNR was markedly increased particularly in proximity to the NLMM, and decayed gradually along the vertical axis, as shown in Figure 3b.…”

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confidence: 99%

Intelligent Metamaterials Based on Nonlinearity for Magnetic Resonance Imaging

Zhao

Duan

et al. 2019

Advanced Materials

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the optical regime. [10,11] The capacity of metamaterials for electric field confinement has enabled the realization of a range of physical phenomena in metamaterials, such as electron emission [12] and phase transition in quantum materials. [13] In turn, the electric field enhancement resulting from the near-field confinement leads to nonlinear responses in metamaterials that have been harnessed to enable high harmonic generation, [14] saturable absorption, [15] phase-conjugation, [16] and optical electrifying effects, [17] among other features.In addition to confining the electric field, metamaterials are capable of interacting with and efficiently tailoring the magnetic field. The ability of metamaterials to manipulate the magnetic field has enabled their applications to inductive wireless power transfer, [18] enhancement of the magneto-optic effect, [19] high-quality sensing, [20,21] plasmonic perfect absorption, [22] and magnetic field confinement, [23,24] among others. Another important application of the capacity for magnetic field manipulation is magnetic resonance imaging (MRI), which is the focus herein. For example, negative permeability metamaterials have been employed as waveguides [25] and lenses [26] to image deep tissues using 1.5 Tesla (T) MRI systems and a cylindrical meta-atom has been developed to mitigate the field inhomogeneity in 7 T MRI systems based on the Kerker effect. [27] Recently, judiciously designed metamaterials, consisting of wire [28] or helical resonator arrays, [29] have been utilized to enhance the signal-to-noise ratio (SNR) of the MRI by amplifying the radio-frequency (RF) magnetic field strength due to their capacity for magnetic field enhancement. However, an ongoing limitation of currently available linear metamaterials (LMMs) for enhancing SNR in MRI systems reported to date is their linear nature, resulting in an amplification of the magnetic field during both RF transmission and reception phases in MRI, as shown in Figure 1a. The adoption of an LMM in MRI therefore requires modification of the RF excitation pulses during the transmission phase, [28,29] resulting in undue complications, suboptimal performance, potential safety concerns, and a substantial impediment to clinical adoption.Nonlinear metamaterials (NLMMs) yield an opportunity to construct intelligent and self-adaptive metamaterials in order to selectively enhance the magnetic field during MRI. By leveraging the voltage-dependent capacitance of a varactor diode induced by a reverse-biased p-n junction, [30,31] we developed an NLMM operating at RF frequencies. As opposed

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“…However, it may offer in-time and at-site detection and diagnosis of acute medical situations, for example, time-sensitive posttraumatic brain haemorrhage, for patient management. For compensating a low SNR, advanced physical concepts, such as metasurface, could be a good remedy to apply to redistribute the B1-field of receive coils, in ways to increase the coil sensitivity and to increase the penetration depth [70,71]. Besides, to increase the SNR, staying away from pulsed excitations, approaches of using continuous waves to simultaneously transmit and receive RF signals can be helpful [79,80].…”

Section: Discussionmentioning

confidence: 99%

Portable Low-Cost MRI System Based on Permanent Magnets/Magnet Arrays

Huang

Ren

Obruchkov

et al. 2019

Investig Magn Reson Imaging

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Portable low-cost magnetic resonance imaging (MRI) systems have the potential to enable "point-of-care" and timely MRI diagnosis, and to make this imaging modality available to routine scans and to people in underdeveloped countries and areas. With simplicity, no maintenance, no power consumption, and low cost, permanent magnets/magnet arrays/magnet assemblies are attractive to be used as a source of static magnetic field to realize the portability and to lower the cost for an MRI scanner. However, when taking the canonical Fourier imaging approach and using linear gradient fields, homogeneous fields are required in a scanner, resulting in the facts that either a bulky magnet/magnet array is needed, or the imaging volume is too small to image an organ if the magnet/magnet array is scaled down to a portable size. Recently, with the progress on image reconstruction based on nonlinear gradient field, static field patterns without spatial linearity can be used as spatial encoding magnetic fields (SEMs) to encode MRI signals for imaging. As a result, the requirements for the homogeneity of the static field can be relaxed, which allows permanent magnets/magnet arrays with reduced sizes, reduced weight to image a bigger volume covering organs such as a head. It offers opportunities of constructing a truly portable lowcost MRI scanner. For this exciting potential application, permanent magnets/magnet arrays have attracted increased attention recently. A magnet/magnet array is strongly associated with the imaging volume of an MRI scanner, image reconstruction methods, and RF excitation and RF coils, etc. through field patterns and field homogeneity. This paper offers a review of permanent magnets and magnet arrays of different kinds, especially those that can be used for spatial encoding towards the development of a portable and low-cost MRI system. It is aimed to familiarize the readers with relevant knowledge, literature, and the latest updates of the development on permanent magnets and magnet arrays for MRI. Perspectives on and challenges of using a permanent magnet/magnet array to supply a patterned static magnetic field, which does not have spatial linearity nor high field homogeneity, for image reconstruction in a portable setup are discussed.

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Flexible and compact hybrid metasurfaces for enhanced ultra high field in vivo magnetic resonance imaging

Cited by 99 publications

References 43 publications

Volumetric wireless coil based on periodically coupled split‐loop resonators for clinical wrist imaging

Volumetric wireless coil based on periodically coupled split‐loop resonators for clinical wrist imaging

Intelligent Metamaterials Based on Nonlinearity for Magnetic Resonance Imaging

Portable Low-Cost MRI System Based on Permanent Magnets/Magnet Arrays

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