The acoustic field of a lithotripter is intense enough to rip apart the fluid through which it propagates. The vapour bubbles (or cavities) formed by the tearing of the liquid are refered to as cavitation bubbles.
In the case of
lithotripsy the cavitation bubbles emit a characteristic "double-bang"
acoustic signal. Coleman et al used a focused hydrophone to detect
the double bang signal from a lithotripter. It is called a passive
cavitation detector (PCD) because it detects cavitation events
by listening to acoustic emissions from the bubble. It does not
have to send in a probing beam.
We have developed a dual PCD which uses two focused hydrophones at 90 degrees to detect acoustics emissions. The dual PCD has the advantage that coincidence detection between the two hydrophones allow us to detect acoustic emissions from a very small volume; typically 5 mm in diameter.
Figure 1 shows the dual PCD in the HM3 at Methodist Hospital, Indianapolis, IN. A needle hydrophone is placed at the focus of the lithotripter so that the foci of the hydrophones can be precisely aligned with the focus of the lithotripter.
Figure 2 shows
the dual PCD configured to take in vivo cavitation measurements
from the kidney of the pig.
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Last Updated February 5, 1998