Abstract: The present invention provides a method for chemically modifying non-ionic, water soluble particulate contrast agents so that they degrade in vivo to their non-ionic parent contrast material and carbon dioxide. According to the present invention, known particulate, non-ionic contrast agents are chemically modified to form a precursor or "prodrug" comprising cyclic carbonates and carbamates of the parent compound. The resulting cyclic carbonates and carbamates are lipid soluble, biodegradable, and can be prepared in large quantities using well-established methods. These cyclic carbonates and carbamates can be converted to particulate contrast media using simple, well known techniques, such as solvent-extraction or solvent evaporation.

Abstract: The present invention relates to a highly efficient method of preparing modified microcapsules exhibiting selective targeting. These microcapsules are suitable for encapsulation surface attachment of therapeutic and diagnostic agents. In one aspect of the invention, surface charge of the polymeric material is altered by conjugation of an amino acid ester to the providing improved targeting of encapsulated agents to specific tissue cells. Examples include encapsulation of radiodiagnostic agents in 1 .mu.m capsules to provide improved opacification and encapsulation of cytotoxic agents in 100 .mu.m capsules for chemoembolization procedures. The microcapsules are suitable for attachment of a wide range of targeting agents, including antibodies, steroids and drugs, which may be attached to the microcapsule polymer before or after formation of suitably sized microcapsules. The invention also includes microcapsules surface modified with hydroxyl groups.