Patent ID: RE39146

Claim:
A method of making a contrast agent having resistance against collapse from pressure increases when used in ultrasonic echography, said contrast agent consisting of gas-filled microvesicles suspended in an aqueous liquid carrier phase, the microvesicles being either microbubbles bounded by an evanescent gas/liquid interfacial closed surface, or microballoons bounded by a material envelope filled with a physiologically acceptable gas wherein the gas is bounded by a stabilizing layer of one or more film forming phospholipids in lamellar or laminar form at the gas/liquid interface , said method comprising the step of forming the microvesicles in the presence of a physiologically acceptable gas, or gas mixture comprising a physiologically acceptable gas, or filling preformed microvesicles with said gas, or said gas mixture, said the physiologically acceptable gas being selected from the group consisting of SF 6 , SeF 6 , CF 4 , CBrF 3 , C 4 F 8 , CClF 3 , CCl 2 F 2 , C 2 F 6 , C 2 ClF 5 , CBrClF 2 , C 2 Cl 2 F 4 , CBr 2 F 2 and C 4 F 10 , said microvesicles having resistance against collapse resulting, at least in part, from pressure increases effective when a suspension of said gas-filled microvesicles is in injected into the bloodstream of a patient.