A microbubble preparation formed of a plurality of microbubbles comprising a first gas and a second gas surrounded by a membrane such as a surfactant, wherein the first gas and the second gas are present in a molar ratio of from about 1:100 to about 1000:1, and wherein the first gas has...http://www.google.ca/patents/US5720938?utm_source=gb-gplus-sharePatent US5720938 - Systems for the formation of microbubbles
