  Radiofrequency field inhomogeneity is a significant issue in imaging large
fields of view in high- and ultrahigh-field MRI. Passive shimming with coupled
coils or dielectric pads is the most common approach at 3 T. We introduce and
test light and compact metasurface, providing the same homogeneity improvement
in clinical abdominal imaging at 3 T as a conventional dielectric pad. The
metasurface comprising a periodic structure of copper strips and parallel-plate
capacitive elements printed on a flexible polyimide substrate supports
propagation of slow electromagnetic waves similar to a high-permittivity slab.
We compare the metasurface operating inside a transmit body birdcage coil to
the state-of-the-art pad by numerical simulations and in vivo study on healthy
volunteers. Numerical simulations with different body models show that the
local minimum of B1+ causing a dark void in the abdominal domain is removed by
the metasurface with comparable resulting homogeneity as for the pad without
noticeable SAR change. In vivo results confirm similar homogeneity improvement
and demonstrate the stability to body mass index. The light, flexible, and
cheap metasurface can replace a relatively heavy and expensive pad based on the
aqueous suspension of barium titanate in abdominal imaging at 3 T.
