A Dual-Band Metasurface for Functional and Anatomical 1.5 T MRI

In this work, a dual-band passive metasurface, excited by an RF coil and able to homogenize the magnetic field distribution for 1.5 T magnetic resonance imaging is presented. In particular, the metasurface is composed by a 5×5 passive array, covering a 15 cm x 15 cm area. Each unit-cell consists of two concentric spiral coils resonating at different Larmor frequencies: the internal coil at 64 MHz and the external one at 17 MHz, respectively. The two frequencies have been chosen to simultaneously combine the anatomical (
¹
H, 64 MHz) and functional
²³
Na, 17 MHz) imaging for 1.5 T MRI scanners within the same hardware system. To validate the theoretical approach, we performed preliminary numerical full-wave simulations with and without the metasurface presence. Specifically, we compared the magnetic field distributions in terms of uniformity within the Field of View for the two configurations and at different distances from the radiating system. A superior magnetic field uniformity and, thus, a high signal-to-noise ratio, has been observed in the presence of the metasurface for both the frequencies. Therefore, these preliminary results demonstrated the possibility to use the proposed system for both anatomical and functional 1.5 T MRI.