Impact of Unit Cell Density on Grid and Stripe Metasurfaces for MRI Receive Enhancement

Metasurfaces enable magnetic resonance imaging (MRI) without cables inside the bore by locally improving the sensitivity of scanner-integrated receive coils. This study systematically evaluates a novel grid design to provide signal enhancement for patient imaging. The potential of the proposed metasurface grid design was analyzed regarding its unit cell density and compared with stripe type metasurfaces. The effects were examined in-depth by numerical simulation, workbench measurements, and MRI experiments at 3 Tesla. Differences in the signal-to-noise ratio (SNR) using either the integrated body or spine coils were evaluated, as well as the influence of the metasurface orientation. The grid design provided a favorable eigenmode usable for MR imaging, where it has shown significantly less dependence on orientation, compared to stripe metasurfaces. With the densest grid, more than 26% higher SNR than its most spaced design was achieved. Combining the metasurface for imaging with the spine coil proved to be superior to the body coil. Applying the metasurface for knee imaging, the SNR was locally enhanced by more than 10-fold compared to the scan with only the spine coil. The high-density grid metasurfaces provided benefits compared to the multitude of designs evaluated. This work provides a comprehensive foundation for future developments of metasurfaces for MRI, whose advantages may be exploited e.g. in the domain of interventional radiology.