Cavitation nucleation agents for nonthermal ultrasound therapy

The use of a nucleation-promoting agent can greatly enhance therapeutically useful nonthermal bioeffects. A blank agent (saline), Optison(TM) ultrasou nd contrast agent, a stabilized perfluoropentane droplet suspension (SDS), and retained air space were compared as nucleation agents in whole blood. F resh canine whole blood with added agent was exposed in 1.3-ml disposable p ipette bulbs to lithotripter shock waves (2-Hz rate; +24.4, -5.2 MPa peak p ressure amplitudes). Cavitation activity was assessed by measuring hemolysi s. The droplet suspension performed nearly as well as retained air when add ed at a concentration sufficient to provide a roughly equal volume of gas a fter vaporization. Optison(TM) also yielded nucleation, but a concentration of 10%-20% was needed for large enhancement of hemolysis comparable to 5% SDS. Exposure at room temperature, which was less than the 29 degrees C boi ling point of perfluoropentane, eliminated the enhancement of the hemolysis effect relative to the blank. Application of 100-kPa excess pressure durin g exposure reduced but did not eliminate the nucleation ability of Optison( TM), SDS, or retained air. However, this small pressure (relative to the pe ak positive pressure of the shock waves) eliminated the hemolysis induced w ith the blank agent. The stabilized perfluoropentane droplet suspension app ears to be a good nucleation agent for nonthermal ultrasound therapy applic ations. (C) 2000 Acoustical Society of America. [S0001-4966(00)01606-4].