Destruction of gallstones and model stones by extracorporeal shock waves.

The disintegration effectivity of an electrohydraulic lithotripter was evaluated by determining the acoustic energy that had to be applied, until all fragments of three artificial materials and human gallstones were cleared from a basket of 2.8 mm mesh size. The lithotripter had either an open ellipsoid, or the ellipsoidal axis was covered with a metal cage as used in clinical lithotripters to house the ultrasound scanner. Fragmentation was assessed at a low, medium and high voltage setting using 9 and 16 mm breeze block marbles, considered to be primarily fragmented by a cavitation-mediated mechanism; 16 mm glass marbles, considered to be primarily fragmented by a direct shock wave effect; 12 and 15 mm plaster balls as commonly used to monitor lithotripter output; and gallstones with a mean diameter of 16 mm. As a result, the acoustic energy for the disintegration of 9 and 16 mm breeze block marbles was 620 and 670 mJ cm-3, of glass marbles 3369 mJ cm-3, of 12 and 15 mm plaster balls 1599 and 1764 mJ cm-3 and of gallstones 8050 mJ cm-3. It was largely independent of pulse energy, specimen size and configuration of the shock wave source. It is concluded that acoustic energy is a major determinant of disintegration, independent of the presumed mechanism of destruction.