Enhancement of transmit and receive efficiencies with hybridized meta-atom in 7T head coil

Abstract : Background B1 homogeneity in 7T MRI remains an important challenge in order to fully benefit from the signal enhancement due to the stronger magnetization available in ultra-high field scanners. High-dielectric constant pads have been proposed and optimized for passive shimming purposes [1-3]. Common formulations of dielectric pads for 7T applications are based on BaTiO 3 mixed with water. They present some drawbacks such as performance decay over time and toxicity. While previous studies tackled directly the formulation problem introducing new dielectric materials and solvent [4], we adopted a new approach based on metamaterials [5]. We demonstrated that the hybridization of four parallel metallic wires arranged on a square unit cell provides the ability to control radiofrequency field inside a 7T head birdcage. In the present work, we show that these hybridized meta-atom (HMA) can be used to improve MRI acquisition in the presence of a head receive array routinely used for in vivo MRI protocol.