Pii: S0301-5629(01)00444-6

Using platelet-rich plasma, we investigated the effect of 1.1-MHz continuous wave high-intensity focused ultrasound (HIFU) on platelet activation, aggregation and adhesion to a collagen-coated surface. Platelets were exposed for durations of 10–500 s at spatial average intensities of up to 4860 W/cm. To avoid heating effects, the average temperature in the HIFU tank was maintained at 33.8 4.0°C during platelet experiments. Flow cytometry, laser aggregometry, environmental scanning electron microscopy and passive cavitation detection were used to observe and to quantify platelet activation, aggregation, adhesion to a collagen-coated surface and associated cavitation. It was determined that HIFU can activate platelets, stimulate them to aggregate and promote their adherence to a collagen-coated surface. In principle, HIFU can stimulate primary, or plateletrelated, hemostasis. Cavitation was monitored by a passive cavitation detector during aggregation trials and was quantified to provide a relative measure of the amount of cavitation that occurred in each aggregation trial. Regression analysis shows a weak correlation (r 0.11) between aggregation and ultrasound intensity, but a substantial correlation (r 0.76) between aggregation and cavitation occurrence. (E-mail: poliachi@u. washington.edu) © 2001 World Federation for Ultrasound in Medicine & Biology.