'Accurate and fast longitudinal RF magnetic field profiling for 7T traveling-wave MRI systems,'

In their pioneering publication [1] Brunner et al. have proposed propagating traveling waves as a very efficient mean to provide uniform, circularly polarized, Radio frequency (RF) B1 fields along the bore of a high-field (7T) MRI scanner while relying on the bore’s fundamental circular waveguide mode (TE11). Most of the current traveling-wave excitation schemes rely on closed-end antenna systems, which pose a serious challenge to the patient’s comfort. As a workaround to this drawback and in support of either selectivity or uniformity in the longitudinal magnetic field profile we are investigating a fully adaptive RF antenna system that perfectly conforms to the bore surface [2-4]. Fig. 1 depicts the MetaBore [5], which labels our «open» excitation architecture consisting of multiple composite right-/left-handed (CRLH) metamaterial ring antennas, each supporting a full-wave resonance (at 298 MHz) with an azimuthal current density profile that perfectly mimics the surface current distribution of the TE11 mode with respect to the given specific bore diameter. In our present research we are now looking for most efficient (potentially real-time) solutions to then inverse problem, encompassing all quadrature current amplitudes and phases of the periodically arranged ring antennas, in order to get correspondingly tailored field profiles along the bore. Besides our extensive numerical studies we have set up an experimental system for validation purposes that is designed for an easy insertion into the scanner for first proofs of concept.