Gadolinium-labeled liposomes containing various amphiphilic Gd-DTPA derivatives: targeted MRI contrast enhancement agents for the liver.

Unique paramagnetic liposomal contrast agents were synthesized and utilized for selective augmentation of T1 MR imaging of the livers of normal Balb/c mice. A series of amphipathic gadolinium complexes, which mimic phospholipids, was incorporated into the lamella of small unilamellar liposomes such that they become an integral part of its surface. The amphipathic complexing agents consisted of DTPA reagents in which two stearyl chains are attached via amide, ester, and thioester linkages. The in vitro stability and the in vivo lifetimes of the new amphipathic agents were dependent on the method used to attach the long-chain alkyl groups.