Improving B 1 + homogeneity in abdominal imaging at 3 T with light, flexible, and compact metasurface

• Published in: Magnetic resonance in medicine Vol. 87; no. 1; pp. 496 - 508
• Main Authors: Vorobyev, Vsevolod, Shchelokova, Alena, Efimtcev, Alexander, Baena, Juan D, Abdeddaim, Redha, Belov, Pavel, Melchakova, Irina, Glybovski, Stanislav
• Format: Journal Article
• Language: English
• Published: United States 01-01-2022
• Subjects: Abdomen - diagnostic imaging; Computer Simulation; Humans; Magnetic Resonance Imaging; Phantoms, Imaging; Radio Waves; image shading; abdominal imaging; dielectric pad; 3 T; passive shimming; inhomogeneity; metasurface
• ISSN: 1522-2594
• DOI: 10.1002/mrm.28946

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
causing a dark void in the abdominal domain is removed by the metasurface with comparable resulting homogeneity as for the pad with decreasing maximum and whole-body SAR values. In vivo results confirm similar homogeneity improvement and demonstrate the stability to body mass index.
The light, flexible, and inexpensive metasurface can replace a relatively heavy and expensive pad based on the aqueous suspension of barium titanate in abdominal imaging at 3 T.