Bioeffects of positive and negative acoustic pressures in mice infused with microbubbles

This study provided one test of the hypothesis that hemorrhage in tissues c ontaining ultrasound (US) contrast agents results from inertial cavitation. The test relied on the prediction of classical cavitation theory that the response of microbubbles to negative pressures is much greater than it is f or positive pressures. An endoscopic electrohydraulic lithotripter was used to generate a spherically diverging positive pressure pulse. A negative pr essure pulse was produced by reflection of the positive pulse from a pressu re release interface. Mice were injected with approximate to0.1 mL of Albun ex(R) and exposed to 100 pulses at either + 3.6 MPa or -3.6 MPa pressure am plitude. For comparison, mice were also exposed to the same acoustic fields without injection of contrast agents. Sham animals experienced the same pr otocols, with or without Albunex(R) injections, but were not exposed to the lithotripter fields. Following exposure, mice were scored for hemorrhage t o various organs and tissues. When Albunex(R) was present in the vasculatur e, negative pressure pulses produced significantly more hemorrhage than pos itive pressures in tissues such as the kidney, intestine, skin, muscle, fat , mesentery and stomach. (C) 2000 World Federation for Ultrasound in Medici ne & Biology.