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 &# 34 ; prodrug &# 34 ; 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 .