Impact of MRI Field Strengths on Metasurface Enhancement

Metasurfaces have proved valuable in magnetic resonance imaging (MRI) applications through modifying the field profiles of radiofrequency coils to enhance imaging. Using metasurfaces to enhance a conventional coil, such as the table-integrated spine coil, allows imaging with practically no cables inside the bore. This work investigated the fundamental relationship between an MRI system's field strength and the enhancement effect of a metasurface. We simulated and manufactured grid metasurfaces for field strengths of 0.55 Tesla (0.55 T), 1.5 T and 3 T and evaluated them experimentally. We found increased enhancements of the signal-to-noise ratio (SNR) with lower field strengths. At 0.55 T, the enhancement in the vicinity of the metasurface (10.9-fold) was measured 3.8 times higher than at 3 T. Moreover, the SNR decreased less with field strength next to the metasurface compared to the spine coil. Our results indicate the capability of metasurfaces in low field MRI systems and can stimulate further research. This could benefit future applications in MRI-guided interventions through simplified handling, as well as countries currently underserved with MRIs due to low manufacturing costs.