A Novel Metamaterial-Inspired RF-coil for Preclinical Dual-Nuclei MRI

In this paper we propose, design and test a new dual-nuclei RF-coil inspired by wire metamaterial structures. The coil operates due to resonant excitation of hybridized eigenmodes in multimode flat periodic structures comprising several coupled thin metal strips. It was shown that the field distribution of the coil (i.e. penetration depth) can be controlled independently at two different Larmor frequencies by selecting a proper eigenmode in each of two mutually orthogonal periodic structures. The proposed coil requires no lumped capacitors for tuning and matching. In order to demonstrate the performance of the new design, an experimental preclinical coil for $^{19}$F/$^{1}$H imaging of small animals at 7.05T was engineered and tested on a homogeneous liquid phantom and in-vivo. The presented results demonstrate that the coil was well tuned and matched simultaneously at two Larmor frequencies and capable of image acquisition with both the nuclei reaching large homogeneity area along with a sufficient signal-to-noise ratio. In an in-vivo experiment it has been shown that without retuning the setup it was possible to obtain anatomical $^{1}$H images of a mouse under anesthesia consecutively with $^{19}$F images of a tiny tube filled with a fluorine-containing liquid and attached to the body of the mouse.