Combined Metasurface and Metamaterial Passive Transmit Lens and Receive Array for 3 T

PURPOSE: Metasurfaces (MSs) and metamaterials (MMs) can reduce transmit field nulls caused by wavelength effects at higher MR field strengths. We present a layered MM and MS resonant structure that improves transmit field performance when used as a combined slab (i.e., the metaslab), while also operating as a receive array. METHODS: The MS structure consists of cross-shaped traces joined by capacitors on a PCB. It is embedded between two layers of a MM consisting of inductively coupled longitudinal strips acting as a 2D transmission line. The two structures are intrinsically decoupled and support connection ports to create an 8-element receive array. Simulations were performed with a realistic body phantom, and imaging experiments were performed at 3 T on a large water phantom and in vivo on an adult male's abdomen. RESULTS: Transmit efficiency is improved by a factor of 1.45 in simulation over body coil alone using a realistic body model and by a factor of 1.55 from in vivo measurement. Inhomogeneity is reduced from 24.1% to 17.5% in simulation with realistic human body models, and from 18.5% to 13.9% in phantom measurements. Furthermore, the SAR efficiency is improved by 26% in simulation. In receive, the measured SNR is improved by a factor of 1.48 at the center, compared to a 1.76 improvement with equivalent channel count conventional surface coil array. CONCLUSION: The proposed combination of MS and MM operating dually as a passive field lens and receive array improves homogeneity, SAR efficiency, and receive sensitivity for 3 T abdominal MRI.