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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.

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From the Department of Mechanical Engineering and Materials Science (YZ, FHC, PZ), and Duke Comprehensive Kidney Stone Center, Division of Urology (GMP, PZ), Duke University, Durham, North Carolina

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