Ultrasound localization of kidney stones in shock wave treatment preliminary results

Abstract

Extracorporeal shock wave lithotripsy is now accepted as a method of choice for treatment of most renal stones. Shock waves can be generated by an underwater spark gap discharge at the first focal point of a hemi-ellipsoid. Resulting acoustic waves are reflected from the walls of the ellipsoid and converge at the second focal point, outside the ellipsoid. Any concretion placed at this point, provided that it is surrounded by a medium with transmission characteristics similar to those of water (e.g. human soft tissues) will be disintegrated. This physical principle has been used to disintegrate renal concretions (1). Prerequisites for extracorporeal shock wave lithotripsy are: (a) shock wave generation: (b) stone localization: and (c) a positioning device enabling the kidney stone position to coincide with the second focus of the ellipsoid (site of maximum energy density). Stone localization by two independent fluoroscopy tubes and patient positioning by a hydraulic overhead gantry were used by Chaussy. This system allows treatment of most opaque stones with a success rate of approximately 90%. However, the price of the system in addition to its size make it prohibitive for most health care institutions.