The use of a nucleation-promoting agent can greatly enhance therapeutically useful nonthermal bioeffects. A blank agent (saline),
Optison ultrasound
contrast agent, a stabilized
perfluoropentane droplet
suspension (SDS), and retained air space were compared as nucleation agents in whole blood. Fresh canine whole blood with added agent was exposed in 1.3-ml disposable pipette bulbs to lithotripter
shock waves (2-Hz rate; +24.4, -5.2 MPa peak pressure amplitudes). Cavitation activity was assessed by measuring
hemolysis. The droplet
suspension performed nearly as well as retained air when added at a concentration sufficient to provide a roughly equal volume of gas after vaporization.
Optison 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 boiling point of
perfluoropentane, eliminated the enhancement of the
hemolysis effect relative to the blank. Application of 100-kPa excess pressure during exposure reduced but did not eliminate the nucleation ability of
Optison, SDS, or retained air. However, this small pressure (relative to the peak positive pressure of the
shock waves) eliminated the
hemolysis induced with the blank agent. The stabilized
perfluoropentane droplet
suspension appears to be a good nucleation agent for nonthermal
ultrasound therapy applications.