Purpose : Ultrasonically activated scalpels are used widely in laparoscope assisted surgery, but there is concern that they may dam age tissue at sites other than the site of the surgical procedure. Cavitation has been cited as a cause of such damage. In this paper, we examined the possibility that the cavitation effect spreads beyond the ultrasonic vibration source. Subjects and methods : We mea sured the vibration distribution of the blade with a laser Doppler vibrometer, and the sound

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... e distribution near the blade with a hydrophone. We also observed the generation of cavitation bubbles underwater using high speed digital video. Results and Discussion : From the relation between the vibration distribution on the blade and the observed position of bubble generation, it be came obvious that cavitation bubbles are mainly generated at the large vibration amplitude region on the blade. We examined the re gion where cavitation bubbles might be generated from the sound pressure measurement and frequency analysis around the blade in the water. The bubble generation region showed a strong correlation with measurement results of acoustic pressure. It was estimated that bubble generation was localized to the region within several mm from the blade. Conclusion : Cavitation bubbles are generated locally near the blade. It is supposed that the direct effect of cavitation is limited to the vicinity of the blade. Abstract Keywords ultrasonically activated scalpel, cavitation, ultrasonic therapy, laser Doppler vibrometer, bubble