B1 inhomogeneity correction of RARE MRI at low SNR: Quantitative in vivo 19 F MRI of mouse neuroinflammation with a cryogenically-cooled transceive surface radiofrequency probe

How to 19F MRI: applications, technique, and getting started

Magnetic resonance imaging (MRI) plays a significant role in the routine imaging workflow, providing both anatomical and functional information. 19F MRI is an evolving imaging modality where instead of 1H, 19F nuclei are excited. As the signal from endogenous 19F in the body is negligible, exogenous 19F signals obtained by 19F radiofrequency coils are exceptionally specific. Highly fluorinated agents targeting particular biological processes (i.e., the presence of immune cells) have been visualised using 19F MRI, highlighting its potential for non-invasive and longitudinal molecular imaging. This article aims to provide both a broad overview of the various applications of 19F MRI, with cancer imaging as a focus, as well as a practical guide to 19F imaging. We will discuss the essential elements of a 19F system and address common pitfalls during acquisition. Last but not least, we will highlight future perspectives that will enhance the role of this modality. While not an exhaustive exploration of all 19F literature, we endeavour to encapsulate the broad themes of the field and introduce the world of 19F molecular imaging to newcomers. 19F MRI bridges several domains, imaging, physics, chemistry, and biology, necessitating multidisciplinary teams to be able to harness this technology effectively. As further technical developments allow for greater sensitivity, we envision that 19F MRI can help unlock insight into biological processes non-invasively and longitudinally.

Exploiting the Fluxionality of Lanthanide Complexes in the Design of Paramagnetic Fluorine Probes

Fluorine-19 MRI is increasingly being considered as a tool for biomolecular imaging, but the very poor sensitivity of this technique has limited most applications. Previous studies have long established that increasing the sensitivity of ¹⁹F molecular probes requires increasing the number of fluorine nuclei per probe as well as decreasing their longitudinal relaxation time. The latter is easily achieved by positioning the fluorine atoms in close proximity to a paramagnetic metal ion such as a lanthanide(III). Increasing the number of fluorine atoms per molecule, however, is only useful inasmuch as all of the fluorine nuclei are chemically equivalent. Previous attempts to achieve this equivalency have focused on designing highly symmetric and rigid fluorinated macrocyclic ligands. A much simpler approach consists of exploiting highly fluxional lanthanide complexes with open coordination sites that have a high affinity for phosphated and phosphonated species. Computational studies indicate that Ln^III-TREN-MAM is highly fluxional, rapidly interconverting between at least six distinct isomers. In neutral water at room temperature, Ln^III-TREN-MAM binds two or three equivalents of fluorinated phosphonates. The close proximity of the ¹⁹F nuclei to the Ln^III center in the ternary complex decreases the relaxation times of the fluorine nuclei up to 40-fold. Advantageously, the fluorophosphonate-bound lanthanide complex is also highly fluxional such that all ¹⁹F nuclei are chemically equivalent and display a single ¹⁹F signal with a small LIS. Dynamic averaging of fluxional fluorinated supramolecular assemblies thus produces effective ¹⁹F MR systems.