Control of Acoustic Cavitation with Application to Lithotripsy

摘要

Control of acoustic cavitation (sound-induced bubble activity) is the subject ofthis dissertation. Application is to clinical lithotripsy where cavitation contributes to kidney stone comminution and tissue damage. An electrical spark at the near focus of an underwater ellipsoidal reflector was the acoustical source, as in the Dornier HM3 lithotripter. Experiments were done with rigid reflectors, pressure-release reflectors, and pairs of reflectors sharing a common focus and a controlled delay between sparks. Since a bubble hit by a single shock pulse can grow profoundly and then collapse violently, our hypothesis was that a second pulse timed to arrive during the collapse phase would intensify the ultimate collapse. Experiments and numerical calculations confirmed the hypothesis. Pitted by bubble collapses, aluminum foil placed along the reflector axis recorded the spatial cavitation field. Tempered collapse was also discovered; a sufficiently short delay between two pulses or a change in order of the positive and negative phases of a single pulse stifled bubble growth. Early collapse was detected acoustically. Computations of bubble radius and collapse pressure reinforced the observations.