Ethanol injection induced cavitation and heating in tissue exposed to high intensity focused ultrasound

Abstract

High Intensity Focused Ultrasound (HIFU) can ablate tumors located deep in the body through highly localized energy deposition and tissue heating at the target location. The volume of a HIFU-induced thermal lesion can be increased in the presence of cavitation. This study explores the effect of ethanol injection on cavitation and heating in tissue-mimicking phantoms and bovine liver tissues exposed to HIFU. The HIFU transducer (0.825 MHz) operated at seven acoustic power levels ranging from 1.3 W to 26.8 W. The cavitation events were quantified by B-mode ultrasound imaging, needle hydrophone measurements, and passive cavitation detection (PCD). Temperature in or near the focal zone was measured by thermocouples embedded in the samples. The onset of inertial cavitation in ethanol-treated phantoms and bovine liver tissues occurred at a lower power level than in the untreated samples (control). The cavitation occurrence in turn resulted in a sudden rise of temperature in ethanol-treated samples at a lower acoustic power than that in control. The results of this work indicate that the use of percutaneous ethanol injection prior to HIFU exposure may improve the HIFU therapeutic efficiency.