A passive acoustic system for evaluating the in vivo performance of extracorporeal shockwave lithotripsy

The research has produced a sensor system for identifying the optimum positioning of extracorporeal shockwave lithotripsy (ESWL) equipment and for identifying the degree of fragmentation of the stone as the treatment proceeds. ESWL is a treatment used for patients suffering renal, ureteric, salivary duct and gall stone disease. An acoustic shockwave - generated outside the body - is used to fragment the stones to a small size so that they can more easily pass through the body or be dissolved using drugs. The intention of this invention is to allow the clinical operator of the lithotripter machine to determine more accurately when the treatment should be ended using a passive sensing technique. It consists of a passive acoustic pressure sensor that can be placed against the patient during treatment. The sensor picks up the acoustic signals generated by (and scattered from) the stone as the shockwave lithotripsy is progressed as well as signals resulting from an effect known as acoustic cavitation that occurs close to the stone. By monitoring characteristics of these signals it is possible to monitor whether the incident lithotripter shock is on-target and the degree to which stone cavitation has occurred.