Effect of high‐intensity focused ultrasound on platelet activation, aggregation, and adhesion Free

High‐intensity focused ultrasound (HIFU) has been examined as a noninvasive means for achieving acoustic hemostasis [Delon‐Martin et al., UMB 21, 113–119 (1995); Hynynen et al., UMB 22, 193–201 (1996); Vaezy et al., UMB 24, 903–910 (1998)]. Our own efforts in acoustic hemostasis are directed toward using diagnostic ultrasound to locate a hemorrhage and HIFU to halt the bleeding. To enhance the imaging of blood, the use of ultrasound contrast agents (UCAs; gas‐filled microbubbles that increase the echogenicity of fluids) has been proposed as a means to locate internal bleeding; however, the combination of UCAs and ultrasound has been found to cause bioeffects in whole blood [Miller et al., UMB 23, 625–633 (1997); Poliachik et al., UMB 25, 991–998 (1999)]. Our results have shown that HIFU can cause platelets in a platelet rich plasma (PRP) sample to activate, aggregate, and adhere to a collagen‐coated surface. Furthermore, UCAs can increase the amount of cavitation induced by HIFU, and thus lead to an increase in platelet activity. Although HIFU exposure alone can induce platelet activity, the addition of UCAs increases the amount and the rate of cavitation (cavitation dose); therefore, cavitation is the likely mechanism of HIFU‐induced platelet activity. [Research supported by DARPA.]