Magnetic Resonance Imaging at ultra-high field strengths (17-22 T) provides both opportunities and challenges for non-invasive imaging of biological specimens. As low sensitivity is the most common drawback of MRI applications, the most apparent opportunity of ultra-high field imaging manifests itself by an augmentation in the Signal-to-Noise ratio (SNR). To this end, using similar RF coils, we found that the SNR increased by a factor of 6 when going from 14.1 T to 22.3 T. This SNR increase can be used for faster imaging (a factor of 32), higher resolution imaging reaching (5.5 µm)3 for an acquisition time of 58 h 35 min (3D FLASH, field-of-view 1.6 x 1.1 x 1.1 mm3), and direct metabolite detection by localized spectroscopy (10 mM acetate in a voxel volume of 27 nL in 18 min). In addition to spectroscopy, the increased chemical shift dispersion offered by ultra-high magnetic fields also benefits chemical exchange techniques such as Chemical Exchange Saturation Transfer (CEST) imaging which allows indirect metabolite detection by making use of the exchange of labile metabolite protons with water protons. We show that CEST at 17 T outperforms CEST at 7 T not only in terms of sensitivity but also by better separating the contributions of individual metabolites (glutamate vs. glucose). Lastly, concerning the challenges of MRI at ultra-high field, the increase of susceptibility artifacts caused by air spaces and paramagnetic ions is detrimental to image quality. We will show such effects and discuss possible solutions by examples of in vivo root specimens of M. truncatula and electrode materials.
 Krug et al., High spatial and temporal resolutions with increasing B0 and decreasing transceiver coil dimensions, (manuscript in preparation).