IMPORTANCE OF THE IMPLOSION OF ESWL-INDUCED CAVITATION BUBBLES

The damage induced by an extracorporeal shock wave lithotripter is obs erved with a fiber optic stress sensing technique. When a stone is pla ced in the focus, besides the expected stress induced by the incoming shock wave emitted by the ESWL apparatus, a second delayed stress is o bserved some hundreds of microseconds later. The second stress is indu ced by a shock wave generated at the collapse of a cavitation bubble. Partial reflection of the incoming shock wave at the stone boundary is at the origin of the large cavitation bubble formation. Sensing fiber fracture results always from the second shock wave due to the collaps e of the cavitation bubble. Thus the largest stress is generated at th e collapse. When no target is placed in the focus of the lithotripter, no large cavitation bubble is formed and no delayed shock wave is obs erved. Our results demonstrate unambiguously the decisive role of cavi tation in ESWL procedures.