Ultrasound contrast agents nucleate inertial cavitation in vitro

Some ultrasound contrast agents contain stable bodies of gas, and this study was undertaken to determine if these agents could provide nuclei for inertial cavitation. Inertial cavitation was detected and assessed by the measurement of the sonochemical hydrogen peroxide after exposure to 2.17-, 2.95- or 3.8-MHz ultrasound. A noncavitating system was obtained by removing cavitation nuclei from the rotating tube exposure chambers by vacuum degassing, and from the phosphate-buffered saline medium by filtering. Albunex added at 10-2, 10-3 or 10-4 dilutions, or Levovist added at 2 mg mL-1, 0.2 mg mL-1 or 0.02 mg mL-1 all initiated significant H2O2 production for 2.17-MHz ultrasound at 0.41 MPa or higher spatial peak pressure amplitude for 5 min exposure gated at 0.25 s on and off with 60-rpm rotation. Not rotating the tube virtually eliminated H2O2 production. For 2.5-min continuous exposure, both agents initiated significant H2O2 production for 2.95-MHz exposure at 0.58 MPa or higher, but not for 3.8-MHz exposure up to 1.16 MPa. Bubble-based ultrasound contrast agents therefore appear to be able to provide nuclei for inertial cavitation in the rotating tube exposure system.