Wireless coils based on resonant and nonresonant coupled-wire structure for small animal multinuclear imaging

International audienceEarlier work on radiofrequency (RF) metasurfaces for preclinical MRI has targeted applications such aswhole-body imaging and dual-frequency coils. In these studies, a non-resonant surface coil was used toinduce currents into a metasurface that was operated as a passive inductively powered resonator. As weshow in this study, the strategy of using a resonant metasurface, however, reduces the impact of thesurface coil on the global performance of the whole coil. To mitigate this deficiency, we developed anew approach that relies on the combination of a commercial surface coil coupled to a non-resonantcoupled-wire structure. A wireless coil based on two parallel coupled-wire structure was designed andelectromagnetic field simulations were carried out with different levels of matching and couplingbetween both components of the coil. For experimental characterization, a prototype was built andtested at two frequencies, 300 MHz for $^1$H and 282.6 MHz for $^{19}$F at 7 T. Phantom and in vivo MRIexperiments were done in different configurations to study signal and noise figures of the structure. Theresults showed that the proposed strategy improves the overall sensitive volume while simultaneouslymaintaining a high signal-to-noise ratio (SNR). Metasurfaces based on coupled wires are thereforeshown here as promising and versatile elements in the MRI RF chain, as they allow customizedadjustment of the sensitive volume as a function of SNR yield. In addition, they can be easily adaptedto different Larmor frequencies without loss of performanc