Method of preparing gas and gaseous precursor-filled microspheres

Gaseous precursor-filled liposomes prepared by a gel state shaking gaseous precursor instillation method, said method comprising adding a lipid to an aqueous solution or suspension, shaking said lipid-containing aqueous solution or suspension in the presence of a temperature activated gaseous precursor at a temperature below the gel state to liquid crystalline state phase transition temperature of the lipid, wherein said gaseous precursor is a fluorine-containing gaseous precursor, said fluorine-containing gaseous precursor selected from the group consisting of perfluorocarbons, fluorohydrocarbons, and sulfur hexafluoride, wherein upon activation of said gaseous precursor to a gas said liposomes have at least about a 90% volume of gas in the interior thereof.