High-speed and thermal imaging of the mechanism of action of the Cavitron Ultrasonic Surgical Aspirator (CUSA)

The Cavitron Ultrasonic Surgical Aspirator (CUSA) is being used, especially in neuro-and liver surgery, to resect selectively soft and hard tissue in favor of elastic tissues like blood vessels, enabling the removal of tumors with minimal loss of blood. In this study the phenomena associated with CUSA were visualized to expand the understanding of the mechanism of action of the CUSA. Real-time high-speed imaging techniques were applied to capture cavitation phenomena during application of the CUSA under physiological settings: in water, at tissue surfaces and inside artificial tissue. Close-up photography using a 1 μs flashlight showed the expanding and imploding cavitation bubbles around the rim of the ultrasonic vibrating hollow tip. Shock waves generated by imploding cavitation bubbles were observed using Schlieren techniques with a temporal resolution of 10 ns and synchronized with the duty cycle of the vibrating tip. In addition, thermal effects associated with friction between the vibrating tip and tissue were visualised using a thermal imaging technique. The CUSA mechanism has proven to be a combined effect of cavitation induced fragmentation, mechanical cutting and thermal deterioration of tissue depending on the irrigation/aspiration flow, intermittent vibration regime and degree of tissue contact. The impact of the shock waves observed is undetermined yet. These real-time imaging techniques will contribute to expand the understanding of the working mechanism of CUSA and to show the characteristics of probe designs and influence of driving frequency.