Computational study of acoustic streaming and heating during acoustic hemostasis

Abstract

High intensity focused ultrasound (HIFU) has many applications ranging from thermal ablation of cancer to hemostasis. Although focused ultrasound can seal a bleeding site, physical mechanism of acoustic hemostasis is not fully understood yet. To understand better the interaction between different physical mechanisms involved in hemostasis a mathematical model for acoustic hemostasis is developed. This model comprises the nonlinear Westervelt equation and the bioheat equations in tissue and blood vessel. In a three dimensional domain, the nonlinear hemodynamic equations are coupled with the acoustic and thermal equations. Convective cooling and acoustic streaming effects are incorporated in the modeling study. Effect of acoustic streaming on the blood flow out of the wound has been studied for two wound shapes and different sonication angles. It was theoretically shown that if focused ultrasound beam is applied directly to the bleeding site, the flow out of the wound can be reduced due to the acoustic streaming effect. Bleeding can be completely stopped even for a big wound, if the focal point location, ultrasound power and sonication angle are appropriately chosen. The sonication angles should be chosen in the range between 45° and 90°. The temperature around 70°C can be achieved within a second on the blood vessel wall, thus showing the theoretical possibility of sealing the bleeding site by focused ultrasound.