Innovations in shock wave lithotripsy technology: updates in experimental studies.

Purpose: We developed innovations in shock wave lithotripsy (SWL) technology. Materials and Methods: Two technical upgrades were implemented in an original unmodified HM-3 lithotriptor (Dornier Medical Systems, Inc., Kennesaw, Georgia). First, a single unit ellipsoidal reflector insert was used to modify the profile of lithotriptor shock wave (LSW) to decrease the propensity of tissue injury in SWL. Second, a piezoelectric annular array (PEAA) generator (f 230 kHz and F 150 mm) was used to produce an auxiliary shock wave of approximately 13 MPa in peak pressure (at 4 kV output voltage) to intensify the collapse of LSW induced bubbles near the target stone for improved comminution efficiency. Results: Consistent rupture of a vessel phantom made of single cellulose hollow fiber (i.d. 0.2 mm) was produced after 30 shocks by the original HM-3 reflector at 20 kV. In comparison no vessel rupture could be produced after 200 shocks using the upgraded reflector at 22 kV or the PEAA generator at 4 kV. Using cylindrical BegoStone phantoms (Bego USA, Smithfield, Rhode Island) stone comminution efficiencies (mean sd) after 1,500 shocks produced by the original and upgraded HM-3 reflectors, and the combined PEAA/upgraded HM-3 system, were 81.3% 3.5%, 90.1% 4.3% and 95.2% 3.3%, respectively (p 0.05). Conclusions: Optimization of the pulse profile and sequence of LSW can significantly improve stone comminution while simultaneously decreasing the propensity of tissue injury during in vitro SWL. This novel concept and associated technologies may be used to upgrade other existing lithotriptors and to design new shock wave lithotriptors for improved performance and safety. In the last 2 decades shock wave lithotripsy (SWL) technology has evolved significantly in terms of the means of shock wave generation, focusing, patient coupling and stone localization. However, the fundamental principle of SWL remains unchanged. Independent of the technologies used almost all commercial lithotriptors produce a similar pressure waveform at the focus which can be characterized by a leading shock front with a compressive wave followed by a trailing tensile wave. The acoustic fields produced by different lithotriptors differ only in terms of peak amplitudes of the pressure waveform, pulse duration, beam size, total acoustic energy and, therefore, overall performance.1 To a large extent technical improvements in the second and third generation lithotriptors were made based on empirical experience to provide user convenience and device multifunctionality rather than a mechanistic understanding of stone comminution and tissue injury in SWL. Furthermore, the evolution of lithotriptor design thus far has overwhelmingly, and perhaps mistakenly, relied on the importance of the compressive wave component of the shock wave with almost total neglect of the contribution of the tensile component of the waveform. In contrast, significant progress in the basic research of SWL has been made in the last 5 years to improve our understanding of the primary mechanisms of stone comminution and tissue injury in SWL. It is now recognized that the disintegration of renal calculi in a lithotriptor field is the consequence of dynamic and synergistic interaction of 2 fun