Aperture-patch sandwich metasurface for magnetic field enhancement in 1.5 T MRI.

Magnetic resonance imaging (MRI) is an increasingly popular non-invasive technique for clinical diagnosis. Signal-to-noise ratio (SNR) is a crucial performance metric of MRI, improvement of which can be exchanged for increased image resolution or decreased scan time. Besides the progress in various hardware and software techniques for improving SNR in MRI scanners, use of metasurfaces as accessories has recently shown potential towards enhancing SNR by boosting local magnetic field in the scanned volume. Magnetic field enhancement over a larger depth from the skin is essential for imaging of deeper tissues, which can be facilitated by a specifically designed metasurface. Here we present such a metasurface with complementary-type resonant structures on the two sides of a high-permittivity dielectric, which substantially increases magnetic flux density on the skin (forty-five fold) that decays down to unity at a depth of 95 mm from the skin. This results in boosting of SNR up to forty-fold on the skin in 1.5 T MRI, while keeping tissue heating below the safety limit. An original analytical approach is formulated to readily estimate the SNR enhancement factor of this metasurface. Using the designed metasurface as an accessory for MRI scanners could help making MRI scans more efficient and affordable.