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

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 H-1 MRI has become an indispensable tool for the imaging of disease states, it frequently suffers from low contrast owing to background signal from intrinsic H-1. As a result, increasing attention is being directed at compounds containing F-19 as this nucleus has a similar NMR sensitivity to H-1 and, importantly, intrinsic F-19 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 F-19 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 F-19-MRI. Furthermore, examples of multimodal contrast agents containing F-19 nuclei are also starting to emerge. In this review we aim to summarise these exciting recent chemical developments.