High-Impedance Nonlinear Metasurface Arrays with Self-Decoupling for Modular and Wearable Magnetic Resonance Imaging.

Magnetic resonance imaging (MRI) signal acquisition relies heavily on radio frequency (RF) coils, which play a critical role in obtaining high-quality images. However, traditional RF coils are often rigid and bulky and require complex decoupling mechanisms, limiting their adaptability and effectiveness for anatomically curved or dynamic regions. In this study, we present a novel high-impedance nonlinear metasurface (HINM) coil based on a "building bricks" concept to overcome these limitations. The HINM coil features a lightweight, flexible, wireless, and compact design that enables direct attachment to various anatomical regions, providing localized signal enhancement without the need for intricate adjustments for decoupling. This innovative approach utilized a flexible coaxial cable with a shielded design, ensuring stable frequency characteristics under bending, stretching, and dynamic conditions. Furthermore, the HINM coil with passive detuning did not alter the RF transmit field distribution while improving the signal-to-noise ratio (SNR) up to 87% in the surface region, as demonstrated by the phantom studies. In the knee and hand imaging, the SNR in the joint and finger areas was also doubled when using the HINM arrays. Enhanced image quality was achieved, and more subtle blood vessels were revealed in the hand vascular imaging with the use of the HINM arrays in combination with the commercial RF coils. Additionally, the HINM arrays were applied for the knee and hand imaging at 0.5 T, which achieved up to 74% SNR improvement, demonstrating its effectiveness for both low-field and ultrahigh-field MRI. By offering a versatile and adaptable solution, the HINM coil demonstrates its potential to transform MRI coil designs, particularly for imaging anatomically complex and dynamic environments.