I. V. Melchakova

• PhD
• ITMO University

In this work, we propose an application of high permittivity materials (HPMs) to improve functional magnetic resonance imaging (fMRI) at 1.5 T, increasing the receive (Rx) sensitivity of a commercial multi-channel head coil. To evaluate the transmit efficiency, specific absorption rate (SAR), and the signal-to-noise ratio (SNR) changes introduced b...

The ability to control the electromagnetic near field with metasurfaces offers potential applications over the frequency range from radio frequency to optical domains. In this work, we show an essential feature of metasurfaces, subwavelength field confinement via excitation of a large number of eigenstates in a narrow frequency range, and demonstra...

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 a...

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...

The cover image is based on the Research Article Deep learning-based fully automatic segmentation of wrist cartilage in MR images by Ekaterina Brui et al., https://doi.org/10.1002/nbm.4320.

Currently, human magnetic resonance (MR) examinations are becoming highly specialized with a pre-defined and often relatively small target in the body. Conventionally, clinical MR equipment is designed to be universal that compromises its efficiency for small targets. Here, we present a concept for targeted clinical magnetic resonance imaging (MRI)...

Radio-frequency (rf) coils are used in all clinical and research magnetic-resonance-imaging (MRI) systems to excite nuclear spins and to receive signals from them. The quality of imaging depends strongly on the signal-to-noise ratio (SNR) and the transmit efficiency of the coils. The birdcage volume coils used in most MRI scanners for homogeneous i...

The study objective was to investigate the performance of a dedicated convolutional neural network (CNN) optimized for wrist cartilage segmentation from 2D MR images. CNN utilized a planar architecture and patch‐based (PB) training approach that ensured optimal performance in the presence of a limited amount of training data. The CNN was trained an...

Diffusion tensor imaging (DTI) is a magnetic resonance imaging (MRI) method for efficient nerve pathways visualization. DTI, particularly of peripheral nerves, is commonly performed in 3 T scanners. An often more accessible 1.5 T scanners are less likely to be chosen for DTI examinations due to generally lower image quality. Novel radiofrequency (R...

In the most of magnetic resonance imaging (MRI) systems, a conventional radiofrequency (RF) electric shield is typically placed around an RF volume coil to avoid the interaction with the other components of the system. Disadvantageously metal shields reduce the transmit efficiency of the RF coil as well as its receive sensitivity due to out-ofphase...

All-dielectric nanoparticles have been recently emerged as unique components for biophotonics and drug delivery due to their resonant interaction with light providing the Raman thermometry and optical field enhancement. Here we report on the light induced heating the optically resonant silicon nanoparticles (Si NPs) up to 450 K, which were used to...

In order to boost the performance of magnetic resonance imaging without increasing the static magnetic field, it is necessary to increase its intrinsic sensitivity. This allows a reduction in the scanning time, increased spatial resolution, and can enable low-field strength systems (which are much cheaper and can be used to scan patients with metal...

In this contribution, an artificial shield for an MRI birdcage coil based on a cylindrical miniaturized corrugated structure is proposed. The presence of a conventional metallic shield around the birdcage resonator leads to a destructive interference of the primary magnetic field of the coil and the reflected field inside the coil (in the region of...

In this contribution we present numerical and experimental results of a parametric quantitative study of radiative dipole antennas in a phased array configuration for efficient body magnetic resonance imaging at 7 T via parallel transmission. For magnetic resonance imaging (MRI) at ultrahigh fields (7 T and higher) dipole antennas are commonly used...

Increasing the strength of the static magnetic field is the main trend in modern magnetic resonance imaging (MRI) of humans. Performing MRI in ultrahigh fields (7 T or more) involves many effects both enhancing and diminishing the image quality, and some effects previously unobservable in weaker fields. We review the main impacts of using ultrahigh...

This work studies the guided localized electromagnetic waves propagating along finite and infinite chains of parallel thin resonant wires periodically arranged over an interface of a dielectric half-space. Both issues of guided wave propagation in an infinite chain and resonant excitation of hybridized eigenmodes of a finite chain are solved analyt...

The objective of this study is to develop, test and validate a fully automatic, deep learning-based segmentation method for the wrist joint cartilage in magnetic resonance images. The study was conducted in 8 healthy volunteers and patients with wrist joint diseases. 3D MRI datasets (20 in total) were acquired at 1.5T using a VIBE sequence. Wrist c...

A hybrid metasurface realized by a double array of brass wires inserted into two high-permittivity dielectric slabs at both sides was used to perform a magnetic resonance spectroscopy experiment at a 1.5T clinical magnetic resonance scanner. The metasurface coupled inductively to a transceive birdcage body coil located within the scanner’s bore. Th...

Increasing the static magnetic field strength into the realm of ultrahigh fields (7 T and higher) is the central trend in modern magnetic resonance (MR) imaging. The use of ultrahigh fields in MR-imaging leads to numerous effects some of them raising the image quality, some degrading, some previously undetected in lower fields. This review aims to...

Purpose To design and test an RF‐coil based on two orthogonal eigenmodes in a pair of coupled dipoles, for 7 Tesla body imaging with improved SAR, called dual‐mode dipole. Methods The proposed coil consists of two dipoles and creates two orthogonal field distributions in a sample (the even and odd modes). A coupler used to excite the modes was min...

A hybrid metasurface realized by brass wires coupled to two high-permittivity dielectric slabs at both sides was used together with a conventional birdcage body coil for transmission and reception in 1.5 T magnetic resonance spectroscopy. A feasibility of improvement of spectral quality has been shown. Up to 7.5 times increase of signal-to-noise ra...

We propose to use a resonator, consisting of mutually coupled dipoles as a radiofrequency coil with two orthogonal channels for 7 Tesla MRI in parallel trancieve configuration. In this work we show by numerical simulation that the two dipoles being driven symmetrically and anti-symmetrically produce similar field patterns to a dipole and a loop coi...

Large field of view magnetic resonance imaging is often required during small animal imaging to cover the entire body of an animal. Large field of view imaging should nevertheless be performed with sufficient signal to noise ratio and resolution. A combination of large signal to noise ratio and high resolution is usually achieved via using small lo...

The cover image, by Mikhail Zubkov et al., is based on the Research Article Small‐animal, whole‐body imaging with metamaterial‐inspired RF coil, https://doi.org/10.1002/nbm.3952.

In this work, we propose and discuss methods of tuning eigenmode resonance frequencies of wire metasurfaces. Fine tuning of metasurface properties is essential for maximizing its coupling with transmitting and receiving radiofrequency (RF) coils of a magnetic resonance imaging (MRI) system. We have studied numerically and experimentally two designs...

Metasurfaces due to their ability to individually sculpt the near-field patterns over a frequency range from radio to optical recommended themselves as good candidates for image quality enhancement that is crucially important in different areas including biology, medicine, and nanotechnologies. Particularly, one important practical application of m...

In this work we demonstrate a comparative study of the a new proposed coil based on periodic capacitively-loaded thin wires and a conventional loop coil both optimized for small-animal imaging applications at 7 Tesla. The proposed coil uses hybridized eigenmodes of the flat periodic array comprising a number of thin metal wires, excited by a small...

Particular applications in preclinical magnetic resonance imaging require the entire body of an animal to be imaged with sufficient quality. This is usually performed by combining regions scanned with small coils with high sensitivity or long scans using large coils with low sensitivity. Here, a metamaterial‐inspired design employing a parallel arr...

In this paper, we propose, design and test a new dual-nuclei RF-coil inspired by wire metamaterial structures. The coil operates as a result of resonant excitation of hybridized eigenmodes in multimode flat periodic structures comprising several coupled thin metal strips. It was shown that the field distribution of the coil (i.e. penetration depth)...

A novel tunable metasurface design based on an array of capacitively loaded improves substantially image quality of magnetic resonance imaging systems. The capacitive loads permit high miniaturization of the electrical length of the structure and adjustment of resonant frequencies of the metasurface eigenmode is realized with the aid of telescopic...

Purpose: Design and characterization of a new inductively driven wireless coil (WLC) for wrist imaging at 1.5 T with high homogeneity operating due to focusing the B1 field of a birdcage body coil. Methods: The WLC design has been proposed based on a volumetric self-resonant periodic structure of inductively coupled split-loop resonators with st...

Metasurfaces is a rapidly developing area with quite many prospective applications in light manipulation, aberration-free optical imaging, and security. One potential area where metasurface approaches may provide a valuable contribution is medical imaging. In this paper, a novel subwavelength metasurface-inspired resonator design is presented, whic...

Metasurfaces represent a new paradigm in artificial subwavelength structures due to their potential to overcome many challenges typically associated with bulk metamaterials. The ability making very thin structures and change their properties dynamically make metasurfaces an exceptional meta-optics platform for engineering advanced electromagnetic a...

Metasurfaces represent a new paradigm in artificial subwavelength structures due to their potential to overcome many challenges typically associated with bulk metamaterials. The ability making very thin structures and change their properties dynamically make metasurfaces an exceptional meta-optics platform for engineering advanced electromagnetic a...

Preclinical magnetic resonance imaging often requires the entire body of an animal to be imaged with sufficient quality. This is usually performed by combining regions scanned with small coils with high sensitivity or long scans using large coils with low sensitivity. Here, a metamaterial-inspired design employing of a parallel array of wires opera...

In this contribution we present numerical and experimental results of a parametric quantitative study of radiative dipole antennas in a phased array configuration for efficient body magnetic resonance imaging at 7T via parallel transmission. For magnetic resonance imaging (MRI) at ultrahigh fields (7T and higher) dipole antennas are commonly used i...

One of many exciting application of metasurfaces is in the magnetic resonance imaging (MRI). Here we demonstrate theoretically and experimentally how to improve substantially the MRI sensitivity by employing the concept of hybrid metasurfaces. We design a novel hybrid metasurface as an array of nonmagnetic metallic wires with high-permittivity diel...

In this work we studied electromagnetic properties of one-dimentional periodic structures composed of split-loop res-onators (SLRs) and investigated their capabilities in decoupling of two dipole antennas for full-body magnetic resonance imaging (MRI). Two different finite structures comprising a single-SLR and a double-SLR constitutive elements we...

In this contribution we propose and study numerically a new probe (radiofrequency coil) for magnetic resonance mi-croscopy in the field of 17T. The probe is based on two coupled donut resonators made of a high-permittivity and low-loss ceramics excited by a non-resonant inductively coupled loop attached to a coaxial cable. By full-wave numerical si...

In this paper we propose, design and test a new dual-nuclei RF-coil inspired by wire metamaterial structures. The coil operates due to resonant excitation of hybridized eigenmodes in multimode flat periodic structures comprising several coupled thin metal strips. It was shown that the field distribution of the coil (i.e. penetration depth) can be c...

In this contribution we propose a novel antenna design (so-called radio-frequency coil) for magnetic resonance imaging and spectroscopy (MRSI). The design is based on a duallayer periodic structure of thin metal wires inspired by wire medium resonators. Extremities of selected wires are paired by connection through a structural capacity to ensure e...

In this work we investigate capabilities of finite-size EBG metasurface for suppression of inter-element coupling between two neighboring closely-spaced dipole elements of a six-element transceive array coils for body imaging at 7 T. We confirmed the decoupling effect by measurements in a dummy bore as well as inside an MRI system. By numerical sim...

Metamaterials are able to control near electromagnetic fields what is highly desirable in Magnetic Resonance Imaging (MRI) applications. Here, we have used the features of the first eigenmode of a wire metamaterial in order to control safety level, in particularly to reduce the Specific Absorption Rate (SAR) in the region of a patient body during t...

Metasurfaces are artificial two-dimensional structures with subwavelength periodicity. A shape and a size of the unit cells are responsible for electromagnetic properties of a metasurface. Metasurfaces provide specific boundary conditions which define the reflection and transmission properties with respect to incident plane waves. In the present wo...

Metasurfaces are artificial electromagnetic boundaries or interfaces usually implemented as two-dimensional periodic structures with subwavelength periodicity and engineered properties of constituent unit cells. The electromagnetic bandgap (EBG) effect in metasurfaces prevents all surface modes from propagating in a certain frequency band. While me...

Metasurfaces provide a conceptually new and efficient way to control electromagnetic field distributions by engineering the electromagnetic response of their unit cells having subwavelength dimensions and periodicity. In this work we propose new passive resonators based on metasurfaces with strongly miniaturized unit cells due to their capacitive l...

Magnetic resonance imaging (MRI) is the cornerstone technique for diagnostic medicine, biology, and neuroscience. This imaging method is highly innovative, noninvasive and its impact continues to grow. It can be used for measuring changes in the brain after enhanced neural activity, detecting early cancerous cells in tissue, as well as for imaging...

Electromagnetic bandgap (EBG) structures belong to an important class of metamaterials that prevent wave propagation at certain frequencies. One of promising application areas of such structures is magnetic resonance imaging (MRI). Nowadays MRI technology develops towards using higher static magnetic field strengths. Particularly, development of no...

Advances in the studies of metamaterials have pushed the development of invisibility cloaks, which suppress scattering by objects within certain frequency ranges. During recent years, there has been a transition from a purely theoretical consideration of the cloaking effect to its practical implementation. This paper is an overview of the current s...

Advances in the studies of metamaterials have pushed the development of invisibility cloaks, which suppress scattering by objects within certain frequency ranges. During recent years, there has been a transition from a purely theoretical consideration of the cloaking effect to its practical implementation. This paper is an overview of the current s...

Adaptive differential evolution method has been used for optimization of all-dielectric multilayer coatings in order to reduce total scattering from spherical targets. The optimal refractive index profiles have been found for various sizes of targets and thicknesses of coatings. Few profile types that appear to be optimal for various geometrical pa...

The possibility of transfer of the spatial distribution of the near-zone RF magnetic field recorded by receiving coils during magnetic resonance imaging with the use of an endoscope designed from an extremely anisotropic metamaterial is considered. Application of such a material can lead to an increase in the image resolution and/or reduction of th...

Metamaterials have been proved very useful for their high potential in guiding and manipulating of near fields. A theoretically revealed effect of the significant enhancement of evanescent harmonics inside a wire metamaterial slab is experimentally verified in the microwave frequency range. The phenomenon originates from resonant pumping of standin...

In this paper, we report about the first experimental verification of evanescent waves enhancement inside wire metamaterial. The enhancement is originated by resonant pumping of standing waves inside the wire metamaterial. An excellent agreement between the experimental data and numerical results is found. Furthermore the applicability of this conc...

In this paper, we report about the first experimental verification of evanescent waves enhancement inside wire metamaterial. The enhancement is originated by resonant pumping of standing waves inside the wire metamaterial. An excellent agreement between the experimental data and numerical results is found. Furthermore the applicability of this conc...

A theoretically revealed effect [Belov et al., Opt. Lett. 34, 527 (2009)] of the significant enhancement of evanescent harmonics inside a wire medium slab is experimentally verified in the microwave frequency range. The phenomenon originates from resonant pumping of standing waves into which evanescent waves are converted inside the slab. We find a...

In this paper, we report about the first experimental verification of evanescent waves enhancement inside wire metamaterial. The enhancement is originated by resonant pumping of standing waves inside the wire metamaterial. An excellent agreement between the experimental data and numerical results is found. Furthermore the applicability of this conc...

The material parameters of nano-fishnet optical metamaterials are evaluated numerically through extraction from reflection and transmission coefficients of structures consisting of multiple nano-fishnet pairs. For extraction the Nicholson-Ross-Weir method was modified. Effects of convergence with increase of number layers are discussed. Bulk electr...

To more adequately extract the effective refractive index and other so-called metamaterial parameters from the reflection and transmission coefficients of a wave for multilayer grid nanostructures in the near-IR spectral range, the Nicholson-Ross-Weir method was modified. The rate of convergence of each extracted metamaterial parameter to a certain...

The work presented in this paper concerns a theoretical study on frequency selective surfaces (FSS) with application to artificial magnetic conductors or high-impedance surfaces (HIS). Current realizations of HIS are based on a planar FSS at the interface of a metal-backed dielectric slab either including vertical vias or not. A stable resonance wa...

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