Stimuli-Responsive Partially Fluorinated Polymers as ¹⁹F Switchable Magnetic Resonance Imaging Tracers

Fluorine magnetic resonance imaging (¹⁹F MRI) has emerged as a promising imaging technique. Unlike conventional ¹H MRI, there is no detectable endogenous background signal in soft tissue. Perfluorocarbon (PFCs) nanoemulsions, with a high number of equivalent fluorine atoms, are perhaps the most common reported examples for ¹⁹F MRI applications. Nevertheless, the large size and inadequate emulsion stability limit their efficiency. This review provides a comprehensive overview of partially fluorinated polymers as a promising new class of ¹⁹F MRI tracers, offering an attractive alternative to traditional perfluorocarbon-based systems. It examines how polymer composition, fluorine content, and macromolecular architecture play critical roles in regulating relaxation properties and signal intensity. Special consideration is given to recent advancements in stimuli-responsive fluorinated polymers, which can undergo conformational transition in response to specific stimuli (e.g., pH, redox, or temperature). These confirmational transitions can result in "switchable" ¹⁹F MRI signals, which hold significant potential for targeted imaging and early disease diagnosis, particularly in cancer and inflammatory disorders.