CAVITATION DETECTION IN EX VIVO BOVINE LIVER TISSUE EXPOSED TO HIGH INTENSITY FOCUED ULTRASOUND (HIFU)

A study of the feasibility of detecting broadband high frequency emissions (6-12 MHz) generated by acoustic cavitation activity during clinical high intensity focused ultrasound (HIFU) exposures are presented. The ability to monitor acoustic emissions, drive power fluctuations and audible (1-20 kHz) emissions is demonstrated in ex vivo tissue, and the utility of active cavitation detection (ACD) is shown. It is shown that power fluctuations, ACD and audible emissions are most sensitive to large boiling bubbles due to acoustic scattering. A significant difference is observed between the amplitude of high frequency broadband emissions detected from cavitation activity in degassed water and those emanating from 2.5 cm below the surface of bovine liver tissue ex vivo due, in part at least, to the greater attenuation of higher frequency signals in tissue. This, and the noise level in the detection system, suggests that it may be impractical to detect acoustic cavitation using these emissions at clinically relevant depths in tissue (up to 15 cm)