High intensity focused ultrasound: A method of hemostasis

Acoustic hemostasis is a new field of ultrasound research in which high int ensity focused ultrasound (HIFU) is used to induce hemostasis in actively b leeding, injured solid organs and blood vessels. In animal studies, moderat e to profuse bleeding from parenchymal and vascular injuries has been arres ted within approximately 1 minute of HIFU application, even when a large do se of heparin was administered Moreover, acoustic hemostasis has shown prom ise in cauterizing large regions of liver, providing a method for bloodless resectioning of abnormal tissue. Two distinct physical mechanisms of HIFU appear to contribute to hemostasis: (1) a thermal mechanism in which absorp tion of sound leads to temperature elevations, and (2) mechanical mechanism s (acoustic cavitation) in which gas and vapor-filled voids oscillate with large displacement amplitudes. White the thermal mechanism results in a tem perature increase in excess of 70 degreesC in about 1 second, the mechanica l mechanism appears to result in structural disruption of tissue and possib le release of coagulation-inducing tissue factors. Of utmost importance in further development of HIFU as a clinical tool is targeting and monitoring of the HIFU treatment. We have obtained initial success in, integrating HIF U with ultrasound imaging so as to develop an image-guided therapy system. Image-guided acoustic hemostasis may provide a valuable method of hemostasi s in surgical and prehospital settings with applications in trauma and elec tive surgery.