Supramolecular aggregates containing lipophilic Gd(III) complexes as contrast agents in MRI

Magnetic resonance imaging (MRI) contrast agents based on paramagnetic gadolinium complexes are widely used in biomedical research and diagnosis. Their application is intended to improve efficacy of MRI providing physiological information along with the impressive anatomical detail already obtained by images without contrast. The classical gadolinium complexes currently used for MRI contrast enhancement are all lowmolecularweightcompounds that rapidly equilibrate between the intra and extravascular spaces after intravenous administration. In order to obtain gadolinium-based agents with different pharmacokinetic properties, supramolecular aggregates such as micelles and liposomes have been recently proposed. Micelles and liposomes, obtained by the aggregation of lipophilic gadolinium complexes are here described, with the aim to correlate their structural and relaxometric properties.We report on the state of the art in the development of supramolecular aggregates obtained by self-assembly of lipophilic gadolinium complexes and aggregates in which lipophilic gadolinium complexes are assembled with surfactants. Moreover aggregates derivatized with bioactive molecules, such as peptides and antibodies, acting as target selective MRI contrast agents are described.