| Speaker : |
Dr. Michael R. Bailey (Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington) |
| Subject : |
Behavior and Application of Cavitation in Lithotripsy and High Intensity Focused Ultrasound |
| Date : |
June 18, 2004 (Lecture room 27, Faculty of Engineering bldg.2, Hongo campus) |
| Abstract : |
Cavitation appears to play an important role in shock wave lithotripsy (SWL) and high
intensity focused ultrasound (HIFU). In both medical therapies, cavitation can play both
a beneficial and detrimental role. In lithotripsy, in which shock waves (SWs) are used to
break kidney stones, a cavitation cloud created by one shock wave can shield the stone
from subsequent SWs. Accordingly, faster application rates appear to be less effective.
However, stones do not break in in vitro experiments designed to suppress cavitation.
Cavitation appears to be necessary to initiate cracks in the stone, and µCT images show
cracks in stones form from the outside of the stone. Cavitation also appears necessary to
erode stone fragments to passable size. A model of stresses created in stones by
lithotripsy and experimental results testing the roles of various mechanisms of stone
fragmentation will be discussed. In HIFU, particularly for acoustic hemostasis, where
ultrasound is used to cauterize bleeds or close vessels, cavitation appears to play a role in
emulsifying and heating tissue that forms a paste, which seals open incisions in body
organs. Lung tissue with air present seals more quickly than liver or spleen, and adding
micro-bubbles enhances heat deposition. Much as Prof. Matsumoto's group has done in
lithotripsy, we report here a technique to alter the HIFU waveform to generate and
oscillate bubbles to enhance heating and accelerate hemostasis. Work supported by NIH
DK43881 and NSBRI SMS00203. Visit supported by the University of Tokyo, School of
Engineering. |
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