A Self-Matched Leaky-Wave Antenna for Ultrahigh-Field MRI with Low SAR

Solomakha, G., Svejda, J.T., van Leeuwen, C. et al. A Self-Matched Leaky-Wave Antenna for Ultrahigh-Field MRI with Low SAR, Nature Communications 12, 455 (2021).

https://doi.org/10.1038/s41467-020-20708-w

Abstract :

The technology of magnetic resonance imaging is developing towards higher magnetic fieldsto improve resolution and contrast. However, whole-body imaging at 7 T or even higher fieldsremains challenging due to wave interference, tissue inhomogneities and high RF power depo-sition. Nowadays, proper RF excitation of a human body in prostate and cardiac MRI is onlypossible to achieve by using phased arrays of antennas attached to the body (so-called surfacecoils). Due to safety concerns, the design of such coils aims to minimize the local specific absorp-tion rate (SAR) keeping the highest possible RF signal in the region of interest. All previouslydemonstrated approaches were based on resonant structures such as e. g. dipoles, capacitively-loaded loops, TEM-line sections. In this study, we show that there is a better compromisebetween the transmit signalB+1and the local SAR using non-resonant surface coils due toweaker RF near fields in the close proximity of their conductors. With this aim, we propose andexperimentally demonstrate a first leaky-wave surface coil implemented as a periodically-slottedmicrostrip transmission line. Due to its non-resonant radiation, the proposed coil induces onlyslightly over half the peak local SAR compared to a state-of-the-art dipole coil, but has thesame transmit efficiency in prostate imaging at 7 T. Unlike other coils, the leaky-wave coilintrinsically matches its input impedance to the averaged wave impedance of body tissues ina broad frequency range, which makes it very attractive for future clinical applications of 7 TMRI.

Keywords : Leaky-wave antennas, MRI, RF-coil, ultrahigh fields, 7 Tesla, SAR, impedance matching

Partners : ITMO University, University of Duisburg-Essen and CENIDE, UMC Utrecht, Technical University of Eindhoven