In our work, we present a novel concept for the ultra-high-field (UHF) human magnetic resonance imaging (MRI) based on a coaxial cavity is described. Physical dimensions make the proposed conducting structure resonant at the required frequency and tuning lumped elements are no longer needed. Based on this concept a two-channel slotted coaxial cavity radio frequency (RF) applicator was designed for human head MRI at 9.4 Tesla. Numerical modeling was used to optimize the design. RF safety was assessed with two representative human body models. MR experiments on a 9.4T scanner included gradient-echo magnetic-resonance images and mapping of the circularly polarized RF magnetic field of a human head phantom. The simulations and the phantom MR-experiments showed an agreement both qualitatively and quantitatively. The two-channel, coaxial RF applicator was compared to the existing multi-channel arrays at 9.4T in terms of a transmit efficiency and homogeneity. The design is relatively simple, robust and requires only a few additional reactive elements for matching while it’s transmit efficiency is only 20 % and homogeneity 4 % lower than the ones of a similar-sized 8-channel head array.
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