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 a vapor pressure of at least about (760-x) mm Hg at 37.degree. C.,
where x is the vapor pressure of the second gas at 37.degree. C., and
wherein the vapor pressure of each of the first and second gases is
greater than about 75 mm Hg at 37.degree. C.; also disclosed are methods
for preparing microbubble compositions, including compositions that
rapidly shrink from a first average diameter to a second average diameter
less than about 75% of the first average diameter and are stabilized at
the second average diameter; kits for preparing microbubbles; and methods
for using such microbubbles as ultrasound contrast agents.
