Development of A Wet-Coupling Device for Shock Wave Lithotripsy

Abstract

The primary goal of this study is to verify the applicability of a miniature wet-coupling device specifically designed for shock wave lithotripsy (SWL) and its effect on improving the stone comminution efficiency. Despite the technical and functional improvements implemented in the recent years, modern shock wave lithotripters have failed to re-achieve the treatment outcome of their ancestor, the original Dornier HM3. The defects of the dry-coupling approach used in contemporary lithotripters have been considered as one of the key factors that contribute to their reduced stone fragmentation efficiency. Therefore, this study aims at addressing this drawback by designing and developing a new coupling device to substitute the contemporary dry-coupling device. The idea of the miniature wet-coupling design is to combine the strengths of the water-bath coupling and the dry coupling to produce a high-quality coupling while still ensuring great user convenience. In this study, the wet-coupling device was designed for a contemporary electromagnetic (EM) lithotripter with an acoustical lens, consisting of a patient-interface component, a water-filled bellow, and a connecting unit in between. Through 3D printing of customized molds and downstream mold casting with polyurethane rubber, these components were built individually and then assembled together. To verify the performance of this wet-coupling device, in vitro stone fragmentation tests and coupling quality tests were performed with two coupling setups on the same EM lithotripter and a PVC torso model to mimic a clinical SWL treatment. Soft cylindrical BegoStone phantoms (10 mm × 10 mm, D × H) were treated by shock waves delivered at a pulse repetition frequency (PRF) = 1.5 Hz and a power output set of E2.5. The coupling interface condition and subsequent changes during the shock wave treatment were captured after every 500 shocks.The wet-coupling setup has successfully maintained a steady and uniform coupling interface with minimal coupling defects. In contrast, the dry-coupling setup resulted in an initial bubble formation and a subsequent bubble aggregation within the coupling medium that impeded the energy delivery. The wet-coupling setup resulted in a significantly-improved comminution efficiency (41.5% vs. 27.3%) after 2000 shocks. Based on the modular design, the wet-coupling device can be easily modified for other dry-coupling lithotripters and serve as a promising optimization for clinical SWL.