Fluorinated contrast agents for magnetic resonance imaging; a review of recent developments

Abstract

The development of medical imaging probes for magnetic resonance imaging (MRI) is a particularly dynamic area of research. At present, many prominent groups are dedicating significant resources to tailoring and optimising the performance of potential contrast agents. Whilst ¹H MRI has become an indispensable tool for the imaging of disease states, it frequently suffers from low contrast owing to background signal from intrinsic ¹H. As a result, increasing attention is being directed at compounds containing ¹⁹F as this nucleus has a similar NMR sensitivity to ¹H and, importantly, intrinsic ¹⁹F signals are virtually undetectable in vivo. For several decades, perfluorinated molecules (in which all of the C–H bonds in the parent molecule have been replaced with C–F bonds) and highly fluorous gases such as SF₆ have traditionally been used for these kinds of investigations and there have been some excellent reviews of these compounds and their applications. However, recently ¹⁹F imaging is showing signs of evolution, particularly as there have been several reports of fluorinated responsive (smart) agents, micelles, dendrimers and hyperbranched polymers being investigated as targets for ¹⁹F-MRI. Furthermore, examples of multimodal contrast agents containing ¹⁹F nuclei are also starting to emerge. In this review we aim to summarise these exciting recent chemical developments.