It has been discovered that the incorporation of fluorinated gases, especially a perfluorocarbon such as octafluoropropane, into synthetic polymeric microparticles, significantly enhances echogenicity as compared with microparticles having air incorporated therein. The microencapsulated perfluorocarbon is manufactured with a diameter suitable for the targeted tissue to be imaged, for example, for intravenous or oral administration. In one embodiment, bioadhesive microparticles are formed for enhanced imaging of mucosal surfaces.