arXiv subjects

Anna A. Hurshkainen

Publications and source records attributed to Anna A. Hurshkainen.

5 recordsLinked to original sources

arXiv2026

A Concept of LNA with Low Input Impedance Using Common Base BJT for Low-Field MRI

Purpose: In magnetic resonance imaging (MRI), preamplifier decoupling is used to improve the signal-to-noise ratio of a multichannel receive coil array. In low-field and ultra-low-field MRI, low-noise amplifier (LNA) solutions with low input impedance (LII) are poorly represented and consist mostly of field-effect transistors. We propose a low-cost LNA based on a common-base circuit with bipolar transistors to achieve LII (<5 Ohm), a low noise figure (<1.3 dB), and high gain (>30 dB). Methods: The proposed LNA circuits were simulated, fabricated, and tested at frequencies of 3 MHz and 21.2 MHz. The decoupling capabilities of the proposed LNA were experimentally evaluated, and MR imaging was performed in a 0.5T MRI scanner alongside a comparative study with a commercial LNA. At 3 MHz, the LNA was evaluated by analyzing free induction decay signals. Results: Proposed LNA solutions demonstrate a low noise figure below 1.3 dB with an input impedance of 3 Ohm. It was also shown that the presented LNA circuit enables high SNR values in MR imaging. The developed amplifiers demonstrate superior performance compared to available commercial options within the selected HF band. Conclusion: Due to the availability and cost-effectiveness of the selected transistors, the proposed LNA circuit is highly suitable for low-field MRI applications.

physics.app-ph↗

arXiv2024

A wireless bilateral transceiver coil based on volume decoupled resonators for a clinical MR mammography

Wireless radio frequency coils provide a promising solution for clinical MR applications due to several benefits, such as cable-free connection and compatibility with MR platforms of different vendors. Namely, for the purpose of clinical high-field human breast imaging several wireless transceiver coils are known to the date, those operational principle is based on inductive coupling with a body coil. These coils are commonly consist of a several volume resonators to perform bilateral breast imaging. Due to the electrically close location of volume resonators, strong inductive coupling is observed, resulting in the occurrence of hybrid modes. In principle, MR imaging using one of the hybrid modes is possible provided by the homogeneity of a B+ distribution. However, the question of influence of volume resonators coupling on wireless coil transmit efficiency and receive sensitivity was not previously studied. By this work, we performed study to understand this issue. The first wireless coil with decoupled resonators is developed, evaluated numerically and experimentally including in vivo study on healthy volunteers. According to the obtained results, transmit efficiency and receive sensitivity of a pair of decoupled Helmholtz resonators is at least 24% higher than for a pair of coupled resonators.

physics.med-ph↗

arXiv2020

A Parametric Study of Radiative Dipole Body Array Coil for 7 Tesla MRI

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 in phased arrays, particularly for body imaging targets. This study reveals the effects of dipole positioning in the array (elevation of dipoles above the subject and inter-dipole spacing) on their mutual coupling, $B_1^{+}$ per $P_{acc}$ and $B_1^{+}$ per maximum local SAR efficiencies as well as the RF-shimming capability. The numerical and experimental results are obtained and compared for a homogeneous phantom as well as for a real human models confirmed by in-vivo experiments.

physics.med-ph↗

arXiv2018

Experimental observation of hybrid TE-TM polarized surface waves supported by hyperbolic metasurface

Hyperbolic metasurfaces have gained significant attention due to their extraordinary electromagnetic properties to control propagating plane waves, but the excitation and propagation of the surface plasmon-polaritons at hyperbolic metasurfaces, called hyperbolic plasmons, have been experimentally observed just recently. However, the advantages of the hyperbolic plasmons, such as hybrid TE-TM polarization discussed below, are not yet fully revealed and analyzed. In this paper we focus on the numerical and experimental characterization of surface waves in the frequency range from 2 to 8 GHz supported by a hyperbolic metasurface composed of anisotropic metallic Jerusalem crosses printed on a thin dielectric substrate. We show different shapes of equal frequency contours, which correspond to a plethora of excitation and propagation regimes of surface waves. The principal novelty of this work consists in the experimental demonstration of the surface waves with a hybrid, i.e. mixed TE-TM, polarization. Surface waves with a hybrid polarization are the promising tool in a number of applications and phenomena including polarization converters, plasmonic sensors, plasmon steering over a surface, optical forces, spin-orbit photonics, and highlight the impact for the on-chip and planar networks.

physics.app-ph↗

arXiv2016

Element Decoupling of 7T Dipole Body Arrays by EBG Metasurface Structures: Experimental Verification

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 metasurfaces provide a number of important applications in microwave antennas and antenna arrays, their features are also highly suitable for MRI applications. In this work we manufacture and experimentally study finite samples based on mushroom-type EBG metasurfaces and employ them for suppression of inter-element coupling in dipole transmit coil arrays for body imaging at 7T. We show experimentally that employment of the samples EBG leads to reduction of coupling between adjacent closely-spaced dipole antenna elements of a 7T transmit/receive body array, which reduces scattering losses in neighboring channels and thereby improves the B1+ efficiency. The setup consists of two fractionated dipole antennas previously designed by the authors for body imaging at 7 Tesla. These are placed on top of a body-mimicking phantom and equipped with the manufactured finite-size sample of the metasurface tuned to have EBG properties at the Larmor frequency of 298 MHz. To improve the detection range of the B1+ field distribution of the top elements, four additional elements were positioned along the bottom side of the phantom. Scattering matrix measurements show that coupling between the two top elements is indeed reduced while the measurements performed on a 7T MRI machine confirm the array's B1+ efficiency improvement due to reduced scattering losses. This study provides a tool for the decoupling of dipole antennas in ultrahigh field transmit arrays, possibly resulting in denser element placement and/or larger subject-element spacing.

physics.med-ph↗