Improving B1+ homogeneity in abdominal imaging at 3 T with light, flexible, and compact metasurface. Issue 1 (27th July 2021)

• Record Type: Journal Article
• Authors: Vorobyev, Vsevolod; Shchelokova, Alena; Efimtcev, Alexander; Baena, Juan D.; Abdeddaim, Redha; Belov, Pavel; Melchakova, Irina; Glybovski, Stanislav
• Is Part Of: Magnetic resonance in medicine. Volume 87:Issue 1(2022)
• Page Start: 496
• Page End: 508
• Publication Date: 2021-07-27
• Subjects: 3 T -- abdominal imaging -- B1 inhomogeneity -- dielectric pad -- image shading -- metasurface -- passive shimming; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.28946
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: 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. Methods: 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. Results: Numerical simulations with different body models show that the local minimum of B 1 + 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. Conclusion: 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.