A compact circuit-based metasurface for enhancing magnetic resonance imaging

Herein, we propose a compact 0.36 T MRI-enhancing circuit-based metasurface working at its third order mode. Different from most MRI-enhancing metasurface designs which exploit the fundamental mode with the highest enhancement, our choice is a trade-off between the enhancement and homogeneity. The metasurface is organized with capacitively-loaded metal wires where the capacitors decrease the electric length of the wires thus enabling a deep subwavelength scale. The working frequency of metasurface is tuned to the Larmor frequency, contributing to the redistribution of transmitted field. Full-wave simulations based on CST Microwave Studio compare the magnetic field in a mimicked MRI environment with and without the metasurface. The utilization of metasurface leads to a field enhancement ratio of 9.36-fold over a 28 x 28 cm(2) area at 2 cm height while exceeding unity till almost 12 cm. Meanwhile, the variation of the quasi-homogenous magnetic field is less than 1/3 over a relatively large area. The impact of metasurface is further demonstrated by simulations with a head bio-model to evaluate the transmitted field strength and electromagnetic energy absorption. A preliminary measuring experiment is also conducted to validate the special mode pattern. The proposed metasurface effectively enhances the transmitted efficiency thus can be employed in clinical MRI to enhance imaging quality or reduce the input power. Moreover, this design paradigm is compatible with other enhancing approaches due to the nonmagnetic inclusions and frequency-dependent response and can be adapted for higher-field MRI systems by adjusting the length of metal wires and the value of loaded capacitors.