Low‐boiling Point Perfluorocarbon Nanodroplets as Dual‐Phase Dual‐Modality MR/US Contrast Agent

Detection of bare gas microbubbles by magnetic resonance (MR) at low concentrations typically used in clinical contrast‐ultrasound studies was recently demonstrated using hyperCEST. Despite the enhanced sensitivity achieved with hyperCEST, in vivo translation is challenging as on‐resonance saturation of the gas‐phase core of microbubbles consequently results in saturation of the gas‐phase hyperpolarized (129)Xe within the lungs. Alternatively, microbubbles can be condensed into the liquid phase to form perfluorocarbon nanodroplets, where (129)Xe resonates at a chemical shift that is separated from the gas‐phase signal in the lungs. For ultrasound applications, nanodroplets can be acoustically reverted back into their microbubble form to act as a phase‐change contrast agent. Here, we show that low‐boiling point perfluorocarbons, both in their liquid and gas form, generate phase‐dependent hyperCEST contrast. Magnetic resonance detection of ultrasound‐mediated phase transition demonstrates that these perfluorocarbons could be used as a dual‐phase dual‐modality MR/US contrast agent.