Leaky-Wave Coil Element With Improved Tx-Efficiency for 7T MRI Using a Non-Uniform Current Design

Imaging of the human body at ultra-high fields (static magnetic field$B_{0}\geq 7$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 excitation in the reactive near-field region, in the sense that they are resonant devices that produce a field pattern with a fixed relative phase distribution between the currents in different parts of the structure along the commensurable conductor elements. 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$B_{1}^{+ }$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$B_{1}^{+ }$in the desired region compared to e.g., a fractionated dipole.