Journal of Ultrasound in Medicine, Vol 11, Issue 8 419-424, Copyright © 1992 by American Institute of Ultrasound in Medicine
Gallstone movement during lithotripsy: mechanisms and effects on fragmentation
N. Vakil, E. C. Everbach and S. M. Gracewski
Department of Medicine, University of Rochester, New York.
We sought to examine the mechanisms of gallstone movement and its effect on
gallstone fragmentation in vitro. Two experiments were performed in four
specially constructed phantoms that allowed decreasing degrees of movement
during the application of shock waves. Shock waves caused displacement of
the stone from the focus, but the stone and its fragments were returned to
the focus by streaming movements in the coupling liquid when the volume of
surrounding fluid was small. Streaming movements were ineffective in large
volumes. Restraining movements of the gallstone did not improve the results
of fragmentation. We conclude that radiation force and the streaming motion
of the surrounding liquid account for movements of the stone and fragments
during lithotripsy. Lithotripsy is more effective when smaller volumes are
used because streaming brings fragments back to the focus of the
lithotripter. Total immobilization of the stone in the focus of the
lithotripter, however, offers no benefit, probably because it inhibits
rotational movement of the stone.
