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SWS04: Radiofrequency coils for Magnetic Resonance Imaging

Thursday - 1:30-4:20pm

Redha Abdeddaim, Université d’Aix-Marseille (AMU): Institut Fresnel UMR 7249

Stanislav Glybovski, ITMO University, Department of Nanophotonics and Metamaterials

Context

Nowadays the technology of Magnetic Resonance Imaging (MRI) is rapidly developing thanks to great advances in powerful superconductive magnets and efficient transceivers. However, these two development trends face serious limitations, especially in clinical applications, due to increasing power deposition, higher biological influence of static fields, higher risks as well as dramatic raise of costs. In this situation a very attractive, but still not very elaborated solution is development of novel radiofrequency (RF) coils, which are usually UHF near-field antennas working under conditions of a shielded bore of MRI scanners in the vicinity of a subject (e.g. a human body). Novel RF coils providing better control over near fields, as compared to conventional loop coils, would noticeably increase SNR, resolution and quality of images. On this step a fruitful collaboration between antenna engineers and specialists on MRI is required. Namely, recent advances and application experience on antennas could be involved in RF coils to further improve MRI technology.

Workshop structure

The Workshop is planned to be a half day event containing 8 slots for 20min invited talks. The talks will cover the following topics:

  • Novel designs of RF coils for Ultra-High-Field MRI
  • RF coils based on metamaterials and periodic structures
  • Structures for manipulation with RF fields in MRI scanners

Speakers

List of confirmed invited speakers and their talks:

      1. Dr. Alexandre Vignaud, Researcher and clinical 7T MRI manager, CEA NeuroSpin, France
        “Ultra-High Field MRI radiofrequency inhomogeneity mitigation”.
      2. Dr. Nico van den Berg, 7 Tesla Group Head, University Medical Center Utrecht, Netherlands“An RF engineering vs EM metamaterials perspective on the RF field challenges of MRI”
      3. Prof. Andrew Webb, director, Gorter Center, University Medical Center Leiden, Netherlands
        “Integrating novel materials into magnetic resonance resonators and detectors”.
        Conventional magnetic resonance transmitters and detectors are based on copper conducting elements arranged in either cylindrical or planar geometries. These circuits are impedance matched using a large number of variable and fixed capacitors to resonate at the relevant Larmor frequency. In this presentation new designs using high permittivity ceramics and metamaterial-like structures are described and evaluated, particularly with respect to high frequency operation.
      4. Dr. Stefan Enoch, CNRS Senior Researcher, Institut fresnel, France
        “Ultra-High Field MRI: how to homogenize RF fields with metamaterials“
      5. Dr. Pavel Belov, Chief research fellow, Head of laboratory, ITMO University, Russia
        “MRI sensitivity enhancement with hybrid and tunable metasurfaces”
        Magnetic resonance imaging (MRI), one of the most important clinical modalities for detection of various diseases in humans.  MR image quality and spatial resolution are ultimately limited by the signal-to-noise ratio obtainable in a relevant clinical scanning timeframe. Recently a new conceptual idea has been suggested to substantially increase signal-to-noise ratio of commercial MRI with the aid of metasurfaces made by resonant metallic inclusions. However, the previous designs required a significant minimum thickness and fine tuning of the spectral response was also very impractical. Therefore, in this contribution we suggest and demonstrate experimentally a novel type of metasurface capable of dramatic enhancing the MR image quality. We employ a hybrid metasurface and, by changing the effective permittivity of the structure, we observe a substantial spectral shift of the metasurface eigenmodes and dynamically adjust their properties in experiment. Finally, we present in vivo results from a metasurface based device employed to enhance sensitivity of human knee imaging at 1.5 T.
      6. Dr. David Bendahan, Researcher, Center for Magnetic Resonance in Biology and Medicine, France
        “MRI and MRS investigation of exercising muscle”.
      7. Dr. Nikolai Avdievich, Senior Research Scientist, High-Field MR Center, Max Planck Institute for Biological Cybernetics, Tübingen, Germany, Institute of Physics, Ernst-Moritz-Arndt University Greifswald, Greifswald, Germany

        “Optimization of the Transmit and Receive Performance of the Transceiver Head Phased Array for Human Brain Imaging at Ultra-High Fields”.
        Commonly, for optimal MRI performance at low (<3T) magnetic fields, a local receive-only (Rx) RF phased array is used in combination with an integrated transmit-only (Tx) body RF volume coil. This technique is difficult to apply at ultra-high (>7T) magnetic fields (UHF) because large body coils are very inefficient at UHF, and cannot satisfy requirements in RF magnetic field, B1, anymore. To improve Tx-efficiency, B1/√P, and achieve a good Rx-performance, a local Transmit-Only volume coil (or Tx-array) in combination with a smaller tight-fit Receive-Only array, a ToRo coil, is used instead. Since most of the commercial UHF scanners provide only 8 kW of RF power, half of which is lost on a way to the coil, ToRo design still does not deliver sufficient B1. Tight-fit transceiver (TxRx) phased arrays improve Tx-efficiency in comparison to Tx-only arrays, which are larger to fit Rx-only arrays inside. However, the number of elements in a TxRx-array is restricted by the number of available RF Tx-channels (commonly <16) and difficulties associated with decoupling during transmission. In this work, we optimized the decoupling and developed new methods to increase the number of Rx-elements without compromising the Tx-performance. Thus, both the Tx- and Rx-performance of the TxRx-array can be optimized at same time.

The Workshop is supported by “M-CUBE” research project (mcube-project.eu).

This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 736937

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