A single metasurface to obtain enhanced images for various magnetic resonance nuclei and field.

Conducting magnetic resonance imaging (MRI) at field strengths greater than 7T is difficult because the shortened radiofrequency (RF) wavelengths that are inherent to higher field strength systems cause interference that result in degraded image quality. Potential remedies include using multiple coils at the time of the transmission or fixing the images afterward, but these approaches have been inadequate due to thermal hotspot formation and image correction limits respectively. Another feasible alternative is highly conductive padding. However, this approach suffers from the physical deterioration of the pad material, as well as toxicity, bulkiness, and high cost.

“Metasurfaces” are a new 2D material composed of metallic periodic unit cells. They are passive devices that can mimic homogeneous bulk dielectric materials. In contrast to dielectric pads, metasurfaces are thin, lightweight, have no shelf life, and are inexpensive to produce. This dynamically adjustable metasurface is capable of selectively enhancing MR image quality as a function of applied input voltage.

Metallic periodic structures of the metasurface carry conduction currents instead of the displacement currents carried by dielectric pads. The responses from these devices are frequency-specific; to enhance an image, the device must be tuned to the correct frequency and cannot enhance images outside of that range. Through the integration of specialized voltage controlled variable capacitors, an operator can impart dynamic surface impedance adjustments. Thus, capacitance and, consequently, phase delay can be adjusted for different readings on one metasurface.

• Functional at field strengths >7T
• Tunable for compatibility at multiple frequencies
• Thin, flexible, durable, and inexpensive compared to dielectric pads