Progress in Lithotriptor Technology

Abstract

Introduction: Based on own experiences and the review of the recent literature, this paper focusses on actual theories about the physics of shock waves (i.e. mechanism of stone disintegration and tissue trauma), actual lithotriptor concepts, new technological developments, and the comparison of lithotriptors. Material and Methods: We performed a MEDLINE research, evaluating more than 50 articles on extracorporeal shock wave lithotripsy. In addition, the results of recent experimental and clinical studies performed in collaboration with manufacturers and acoustic phycisists were included in this survey. Results: Today mainly two types of lithotriptors are provided by the companies: an economic ESWL-table or a more sophisticated urolithotriptor. Stone localization is predominantly based on fluoroscopy (isocentric C-arm). There are four discussed mechanisms of stone disintegration: the tear-and-shear forces by reflection of shock waves at acoustical interphases play a major role in the initiation of stone comminution, whereas the role of cavitation is limited to the final process of stone disintegration (together with dynamic fatigue). Recent studies did not support the theory of quasistatic squeezing. Nevertheless, larger focal zones seem to be advantageous, since shock wave energy (not peak pressure) represents the most important parameter for stone fragmentation. Energy density is responsible for shock wave induced tissue trauma, which is mainly caused by cavitation. Electromagnetic sources are used most frequently in new lithotriptors (Siemens, Storz, Dornier, Direx), because of the variabilty of focal zone (i.e. different focussing principles, dual focus), constancy of the impulses, and long-term reliability (more than 1 Mio. shock waves). The clinical comparison of different lithotriptors should be based on modified Efficacy Quotients (i.e. distinguishing between curative and adjuvant auxiliary measures). Recent studies indicate, that actual lithotriptors are able to meet the “gold standard” of the Dornier HM3, however with all advantages of a multifunctional table, high patient comfort (i.e. treatment without general anesthesia) and significantly lower costs. Conclusions: After a decade of minimal changes and progress, exciting technological developments based on a better understanding of shock wave physics are taking place, which will definitively stimulate further research and thus improve the results of extracorporeal shock wave lithotripsy.