INTERSTITIAL MATRIX PREVENTS THERAPEUTIC ULTRASOUND FROM CAUSING INERTIAL CAVITATION IN TUMESCENT SUBCUTANEOUS TISSUE

We search for cavitation in tumescent subcutaneous tissue of a live pig under application of pulsed, 1-MHz ultrasound at 8 Wcm(-2) spatial peak and pulse-averaged intensity. We find no evidence of broadband acoustic emission indicative of inertial cavitation. These acoustic parameters are representative of those used in external ultrasound-assisted lipoplasty and in physical therapy and our null result brings into question the role of cavitation in those applications. Acomparison of broadband acoustic emission from a suspension of ultrasound contrast agent in bulk water with a suspension injected subcutaneously indicates that the interstitial matrix suppresses cavitation and provides an additional mechanism behind the apparent lack of in-vivo cavitation to supplement the absence of nuclei explanation offered in the literature. We also find a short-lived cavitation signal in normal, non-tumesced tissue that disappears after the first pulse, consistent with cavitation nuclei depletion in vivo. (E-mail: koulakis@physics.ucla.edu) (C) 2018 World Federation for Ultrasound in Medicine & Biology. All rights reserved.