Frontiers in 19 F-MR imaging: nanofluorides and 19 F-CEST as novel extensions to the 19 F-MRI toolbox.

Fluorine-containing materials have enriched the field of molecular and cellular MRI with unambiguous and quantitative detection capabilities. The background-free "hot-spot" display and the large range of chemical shifts of the broad palette of F-formulations are now used for a variety of applications. The common features of these formulations are: (i) they are based on organic molecular backbones (, organofluorines); and (ii) their F-MRI detectability relies on a well-defined and clearly observed F-MR signal. During the last few years, our lab aimed to expand the F-MR toolbox with new capabilities that were, thus far, not used in molecular and cellular F-MRI. This Feature Article summarizes our developments and implementations in the field of F-MRI emphasizing (i) the introduction of ultrasmall inorganic fluoride-based nanocrystals (nanofluorides) as nano-sized (<10 nm) agents for F-MRI, and (ii) the use of Chemical Exchange Saturation Transfer (CEST) in the F-MRI framework to indirectly amplify F-MR signals of otherwise-undetected fluorinated entities.