Frontiers in ¹⁹F-MR imaging: nanofluorides and ¹⁹F-CEST as novel extensions to the ¹⁹F-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 ¹⁹F-formulations are now used for a variety of applications. The common features of these formulations are: (i) they are based on organic molecular backbones (i.e., organofluorines); and (ii) their ¹⁹F-MRI detectability relies on a well-defined and clearly observed ¹⁹F-MR signal. During the last few years, our lab aimed to expand the ¹⁹F-MR toolbox with new capabilities that were, thus far, not used in molecular and cellular ¹⁹F-MRI. This Feature Article summarizes our developments and implementations in the field of ¹⁹F-MRI emphasizing (i) the introduction of ultrasmall inorganic fluoride-based nanocrystals (nanofluorides) as nano-sized (<10 nm) agents for ¹⁹F-MRI, and (ii) the use of Chemical Exchange Saturation Transfer (CEST) in the ¹⁹F-MRI framework to indirectly amplify ¹⁹F-MR signals of otherwise-undetected fluorinated entities.