Tailored RF magnetic field distribution along the bore of a 7-Tesla traveling-wave magnetic resonance imaging system

This paper provides a highly efficient method for tailoring the RF magnetic field (B₁) distribution along the cylindrical bore of a high-field (7T) magnetic resonance imaging (MRI) scanner operating in the advanced traveling-wave scheme. Here the B₁ wave field propagates as a circularly polarized TE₁₁ waveguide mode and is excited, molded and dumped by a lengthwise equidistant array of thin quadrature-fed (metamaterial) ring antennas where each of them perfectly conforms to the inner surface of the cylindrical MRI bore. All individual antenna excitations associated to the desired longitudinal field profile are retrieved from an inverse problem that is efficiently solved in a (weighted) least-squares sense. The electromagnetic modeling is carried out with our equivalent-circuit (EC) FDTD simulation platform openEMS, and a convincing showcase involving a narrow illumination window for larynx diagnostics is presented.