Mechanisms of action for ultrasound surgical instruments.

Abstract

Ultrasound devices operating at kilohertz frequencies have been used in surgery for over 40 years. Examples range from cataract removal (phacoemulsification) to adipocyte extraction (ultrasound assisted liposuction). These devices make direct contact to erode tissue and work via a number of mechanisms including cavitation (both inertial and stable) and acoustic (micro)streaming. This talk will describe recent research into various factors which affect the mechanisms of tissue erosion. While all these devices operate in the frequency range of 23 to about 43 kHz, the exact combination of frequency, vibration amplitude and mode, and tip configuration creates a range of acoustic source strengths and thus acoustic outputs. Some devices work principally through inertial cavitation action, and experiments to demonstrate this will be reviewed. Other systems tend to favor stable cavitation, permitting, for example, the extraction of viable fat cells which can be re-implanted or harvested for other purposes, such as adipose-derived regenerative (stem) cells. Still other devices rely mostly on acoustic microstreaming and physical macromotion to dissolve blood clots. The range of device types and mechanisms creates difficulties in making direct comparisons between systems, even between those with similar overall design and clinical purpose. Potential solutions to this issue will also be presented.