Sensitive Multichannel F Magnetic Resonance Imaging Enabled by Paramagnetic Fluorinated Ionic Liquid-Based Probes

Owing to its negligible biological background and high magnetic resonance sensitivity, F magnetic resonance imaging (MRI) has emerged as a competitive complement for H MRI, which is already widely used in biomedical research and clinical practice. The performance of F MRI is greatly reliant on imaging probes, the development of which poses considerable demands on F sources. Fluorinated ionic liquids (FILs) have recently attracted increasing attention as alternative F sources because of their good aqueous solubility, ease of chemical modification, and high fluorine contents. However, the imaging performance of FIL-based probes is significantly restricted by their unfavorable F relaxation times. Herein, we developed a strategy to modulate the F relaxation times (including both and ) of FILs by exploiting the paramagnetic relaxation enhancement effect of Mn ions to promote their imaging capacity. The F relaxation times of three FILs including EMIMBF, BMIMOTf, and BMIMPF are appropriately tuned with paramagnetic Mn ions at optimized concentrations, resulting in significant signal enhancement over 5-fold. We further utilized liposils to encapsulate these FILs with Mn ions to construct F MRI probes, which enables fast and clear F MRI as illustrated by a series of experiments. Moreover, we made a F MRI probe containing all three FILs and Mn ions at the optimized concentration, whose capacity for multiplexed F MRI is also validated with experiments. Our study demonstrates the promising potential of paramagnetic FIL-based probes for "hot spot" F MRI, and more importantly, the feasibility of relaxation modulation for the construction of high-performance F MRI probes.