Investigation of frequency characteristics in cutting of soft tissue using prototype ultrasonic knives

Recently, ultrasonic surgical knives have been applied in a variety of surgical operations. In this paper, the operation frequency of a surgical knife is focused on. Prototype ultrasonic knives operated at 24.3, 44.3, and 71.9 kHz were constructed. Differences in the effects on soft tissue depending on the operation frequency were investigated using these knives. Frequency characteristics were measured using two parameters: coagulation ratio and coagulated depth. For the same vibration velocity, at a lower frequency, the distribution of the coagulated tissue was deep and in a narrower region around the center of the tip. For the same vibration amplitude, the coagulated depth at each frequency was similar for all these frequencies. Furthermore, the dependences of tissue coagulation on the vibration velocity, pressure load, contact of the tip with tissue, and direction of vibration were investigated. From these investigations, it was found that the mechanical effect, rather than ultrasound absorption, is the dominant factor in tissue coagulation.