Organic Radical Contrast Agents for Magnetic Resonance Imaging

摘要

We report a molecular design that provides an intravenously injectable organic radical contrast agent (ORCA) for which the molecular ~1H water relaxivity (r_1) is ca. 5 mM~(-1) s~(-1). The ORCA is based on spirocyclohexyl nitroxide radicals and poly(ethylene glycol) chains conjugated to a fourth-generation polypropylenimine dendrimer scaffold. The metal-free ORCA has a long shelf life and provides selectively enhanced magnetic resonance imaging in mice for over 1 h.