Wireless coils based on resonant and nonresonant coupled-wire structure for small animal multinuclear imaging
Résumé
Earlier work on radiofrequency (RF) metasurfaces for preclinical MRI has targeted applications such as
whole-body imaging and dual-frequency coils. In these studies, a non-resonant surface coil was used to
induce currents into a metasurface that was operated as a passive inductively powered resonator. As we
show in this study, the strategy of using a resonant metasurface, however, reduces the impact of the
surface coil on the global performance of the whole coil. To mitigate this deficiency, we developed a
new approach that relies on the combination of a commercial surface coil coupled to a non-resonant
coupled-wire structure. A wireless coil based on two parallel coupled-wire structure was designed and
electromagnetic field simulations were carried out with different levels of matching and coupling
between both components of the coil. For experimental characterization, a prototype was built and
tested at two frequencies, 300 MHz for $^1$H and 282.6 MHz for $^{19}$F at 7 T. Phantom and in vivo MRI
experiments were done in different configurations to study signal and noise figures of the structure. The
results showed that the proposed strategy improves the overall sensitive volume while simultaneously
maintaining a high signal-to-noise ratio (SNR). Metasurfaces based on coupled wires are therefore
shown here as promising and versatile elements in the MRI RF chain, as they allow customized
adjustment of the sensitive volume as a function of SNR yield. In addition, they can be easily adapted
to different Larmor frequencies without loss of performance
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