Leaky-wave Coil Element with Improved Tx-efficiency for 7 T MRI Using a Non-Uniform Current Design

TL;DR

This paper introduces a non-resonant leaky-wave coil element for 7 T MRI that employs a non-uniform current design to enhance transmit efficiency and improve B1+ field strength in the target region.

Contribution

It proposes a novel leaky-wave antenna-based coil with optimized current distribution to surpass traditional resonant elements in transmit efficiency at ultra-high magnetic fields.

Findings

Stronger B1+ field in the region of interest compared to traditional dipoles.

Non-resonant leaky-wave approach effectively controls current phase.

Enhanced transmit efficiency at 7 Tesla MRI.

Abstract

Imaging of the human body at ultra-high fields (static magnetic field B0>7 Tesla) is challenging due to the radio-frequency field inhomogeneities in the human body tissues caused by the short wavelength. These effects could be partially mitigated using an array of antennas and by parallel transmission allowing for control of the radio-frequency field distribution in the region of interest. All commonly-used radio-frequency arrays for ultra-high field MRI consist of resonant elements: dipoles, TEM-resonators, loops and individual slots. All these elements rely on standing wave excitation, in the sense that they are resonant devices that produce a field pattern with a constant phase distribution along the commensurable conductor elements. However, it was shown previously, that a non-uniform phase of surface current is required to reach the ultimate intrinsic signal-to-noise ratio or a maximized signal in the desired region of interest. In our work we propose to use a previously demonstrated non-resonant leaky-wave approach to control the phase of currents in radio-frequency coil conductors to increase the B1+ field in the center or in the region of interest. Using this approach, we developed a radio-frequency coil based on a leaky-wave antenna approach with optimized surface current distribution resulting in stronger B1+ in the desired region compared to e.g. a fractionated dipole.