Metamaterial Zeroth-Order Resonator RF Coil for Human Head: Preliminary Design for 10.5 T MRI

The objective is to develop a highly efficient RF head coil on a thin substrate for the ultra-high magnetic field MRI systems. The metamaterial zeroth-order resonator is investigated for this purpose. Simulation and experimental results are provided for an eight-channel M-ZOR-based RF coil in comparison with a standard high performance eight-channel dipole-based RF coil for the 10.5 T MRI system. Each element is 18 cm (approximately a quarter of a wavelength λ ₀ ) long, identical, evenly spaced along the circumference of the cylindrical phantom, loaded with dielectric material, and referred to as an inverted metamaterial zeroth-order resonator. The resonator elements are open circuited, matched, and tuned to 447.06 MHz with the phantom. An unloaded to loaded Q-factor ratio of 2.97 is obtained from the scattering matrix of the proposed design. The length independent nature of the proposed design and the flexibility of the lumped elements have provided an optimized element with a substrate thickness of roughly 3 mm (λ ₀ /200). With the proposed design, there is a similar RF magnetic field strength (B ₁ ⁺ ) to SAR ratio with a reduced 10 g averaged SAR of 2.892 for the same input power compared to that of a dipole coil. This could make the coil acceptable for the clinical high-quality imaging.