Magnetic resonance imaging (MRI) is a leading clinical diagnostic technique that is able to provide whole body imaging, and when individual cells are imaged in living animals, it can provide new insights into the biology of cell trafficking and migration. For cells to be visualised by MRI, they generally must be labelled to enable their discrimination from surrounding tissue. The development of magnetic resonance imaging (MRI) contrast agents is therefore an active area of research, where the basis for this interest is the expansion of MRI as a high-resolution and non-invasive important preclinical and clinical imaging modality. Moreover, there are now new opportunities to developing smart materials with multifunctional abilities including MRI contrast in-built within biomaterial structures, functionalisation with targeting ligands and the carrying of a therapeutic payload. This move towards a new generation of MRI contrast reagents has also been spurred on by the mounting evidence against gadolinium-based contrast agents (GBCAs). They are currently the agents of choice and were considered historically safe and well tolerated until recently. However, they have been found to accumulate in various tissues of patients who do not have renal impairment, including bone, brain and kidneys. Furthermore, in 2015, the FDA released a new safety announcement regarding GBCAs and the risk of accumulated deposits in the brain following repeated use. Whilst GBCAs are being investigated, they can still be administered but healthcare professionals have been advised to limit the use of GBCA to situations in which contrast is deemed absolutely necessary.This has opened the door to the novelty of using perfluorocarbon (19F) being incorporated inside smart nanoparticles, which can offer unique quantitative signatures for molecular MRI with no competing background signal.

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