Metamaterial head coil for Ultra High Field MRI

Project Information

M-ONE

Grant agreement ID: 952106

DOI

10.3030/952106

Project closed

EC signature date 10 June 2020

Start date 1 October 2020

End date 30 September 2022

Funded under

• EXCELLENT SCIENCE - Future and Emerging Technologies (FET)

Total cost

€ 1 997 511,25

EU contribution

€ 1 997 510,75

Coordinated by

MULTIWAVE TECHNOLOGIES AG
Switzerland

Periodic Reporting for period 2 - M-ONE (Metamaterial head coil for Ultra High Field MRI)

Reporting period: 2021-10-01 to 2022-09-30

Summary of the context and overall objectives of the project

Ultra-High Field MRI allows a better understanding of brain mechanism and a better diagnostic of brain disease. Nevertheless, radio frequency field inhomogeneities appears strongly in the brain at 7T on transmit magnetic field B1+ images, leading to dark areas on brain images, in the temporal lobes and the cerebellum, making diagnosis either impossible or non-conclusive in these regions of interest. M-One Project consortium works all together to develop the MRI metamaterial coil to homogenize the transmit magnetic field B1+ for brain imaging at 7T in order to have a better quality of the image.
From 2017 to 2021, thanks to the M-CUBE project (MetaMaterial antenna for ultra-high field MRI - grant n°736937), two technologies based on metamaterials have been developed to homogenize the brain images: the hybridized meta-atom (HMA) and the connected birdcage. During the M-ONE project, these two initial metamaterial solutions have been improved and optimized for 7T head MRI, while multi-channel receive array coils were developed to improve SNR in brain imaging. We have compared our results to the current state-of-the-art coil for 7T head MRI, the 1Tx/32Rx Nova Medical coil, made in the USA. This coil is the most popular head coil that has obtained CE marking and FDA approval for 7T MRI . Nevertheless, this coil does not solve the aforementioned issue of inhomogeneities in the transmit B1+ field. Our overall objective is to produce a head coil that can compete with the NOVA one.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

A new numerical method, named FE-BI, has been developed and demonstrated. FE-BI is the combination of Finite Element and Boundary Integral methods that allows to separate the numerical problem and only solves the electromagnetic fields in regions that have been changed with respect to a reference field used as prior information and calculated once per bio-model. With this method, magnetic and Electric field distribution can be obtained in order to quantify transmit performance on relevant metrics such as B1+ and SAR efficiencies.
By the end of RP1, the connected birdcage for 3T was tested and the design of the 7T prototype was being finalized. The 7T connected birdcage was built during RP2 and bench tests are in progress to allow the coil for in vitro MRI characterization. Simulations were performed to evaluate the impact of receive coils on B1+ distribution and confirmed a more homogeneous B1+ field when compared to a standard birdcage coil of similar dimensions.
The second metamaterial approach (HMA) pushed forward by WP3 led to the design and testing of R’dipoles in commercial head coils by the end of RP1. Through RP2, the R’dipole solution has been validated in vitro and in vivo in commercial head coils with and without integrated receive arrays. It was shown that a single R’dipole judiciously placed could improve homogeneity of B1+ better than the more traditional bi-lateral configuration with two resonators on each side of the head. R’dipoles were also successfully integrated into the birdcage coil with receive array developed jointly in WP3 and WP4.
8-channels and 32-channels receive array coils were fabricated, characterized and integrated in detunable birdcage coils to provide the first prototypes of metamaterial birdcage coils of the M-One project. The whole coils were designed and built by M-One partners allowing better optimization of positioning of the R’dipoles inside the coils and better precision in the first SAR simulation report for the different manufactured coils. Initial safety tests were also performed to allow in vivo testing within the extended restricted SAR mode developed by WP5.
WP5 efforts were mostly focused on ethical authorizations to prepare for the in vivo measurements. A decisive progress of the M-One project has consisted in the extension of the restricted SAR protocol. This protocol was first developed in M-Cube and initially used to characterize transmit field of MRI coil prototypes. Thanks to the work accomplished in M-ONE, it now allows to characterize SNR and receive efficiency on healthy volunteers for MRI coils at early stage of development accelerating the pace of coil and technology validation.
This new protocol was tested in vivo for the 1Tx/8Rx metamaterial coil (R’dipoles included) on a small cohort of volunteers. Results have shown systematic improvement of the B1+ homogeneity compared to the Nova coil on the same cohort. The 1Tx/32Rx metamaterial coil was validated on phantom with better transmit homogeneity and SNR level similar to NOVA. The partners collaboration and efforts have not stopped with the official end of the project on September the 30th, 2022. We are now expecting to validate in vivo the high SNR performance of the finalized prototype of 1Tx/32Rx metamaterial coils.

Main results achieved:
- FE-BI numerical method: The combination of the two simulations methods in the Finite Element – Boundary Integral method enables faster simulations of MRI coils and metamaterials with realistic bio-models of human anatomy.
- 7T Connected Birdcage: Finalized design to improve the transmit field (B1+) homogeneity. First prototype is built and bench-tests are in progress.
- R'dipole: a new generation of metamaterial pads has been designed and validated for B1+ homogeneity improvements as a metamaterial add-on to commercial 7T head coils (Invivo Corp & NOVA medical head coils). R’dipoles were also successfully integrated to two of the head coils developed within M-One (1Tx/8Rx & 1Tx/32Rx).
- 1Tx/8Rx: Fabrication of a detunable birdcage coil with an integrated 8 channels receive array coil. In vitro and in vivo tests with R’dipoles included have demonstrated a better homogeneity of the B1+ field compared to the NOVA head coil.
- 1Tx/32Rx: Fabrication of a detunable birdcage coil with an integrated 32 channels receive array coil. In vitro tests with R’dipoles included have demonstrated a better homogeneity of the B1+ field and comparable SNR values with respect to the NOVA head coil. In vivo tests are planned in November 2022.
- Restricted SAR mode extension: Quantitative evaluation of SNR and receive efficiency of prototype MRI coils is now available in the restricted SAR mode which was originally focused on B1+ characterization. This allows for full performance characterization of coil prototypes on healthy volunteers at an earlier stage of development.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

We have raised the general awareness of M-ONE results and impacts in order to position Europe at the forefront of 7T medical imaging, for improving citizen and patient quality of life, while reinforcing European competitiveness and economic growth. The PEDR (Plan for Exploiting and Disseminating Results) has enhanced the achievement of M-ONE’s impacts.
M-ONE has contributed to attract private investment. To ensure a larger uptake of project results, the coordinator will make use of other European instruments, such as the EIC accelerator which aims at fostering innovative technologies until TRL9. The combination of private and public investments will position Multiwave and Europe at the forefront of 7T MRI technologies.

Economic impacts:
- R'dipole: M-ONE has broaden its target market to all MRI scanners with a passive solution that can be added to standard commercial birdcage coils.
- Metamaterial Birdcage / 32-channel Rx-array: M-ONE birdcage aims to compete with the Nova Medical coil by reaching coparable SNR, while homogeneizing the B1+.

M-ONE poster