A new site-targeted molecular imaging contrast agent based on a nanocolloidal suspension of lipid-encapsulated, organically soluble divalent copper has been developed. Concentrating a high payload of divalent copper ions per nanoparticle, this agent provides a high per-particle rl relaxivity, allowing sensitive detection in T1-weighted magnetic resonance imaging when targeted to fibrin clots in vitro. The particle also exhibits a defined clearance and safety profile in vivo.