Quantification of the tip movement of lithotripsy flexible pneumatic probes

Purpose: We developed an optical system to quantify in vitro tip movement of the Lithoclast flexible probe, and correlated various physical parameters of the vibrating probe tip with resultant stone fragmentation. Materials and Methods: A noncontact optical measurement system was developed to quantify in vitro tip movement of the Lithoclast flexible probe. This system and an in vitro fragmentation model were used to determine the tip displacement, velocity, impact momentum, impact energy and stone fragmentation of the flexible probe at 5 deflection angles between 0 and 48 degrees, and the 2 pneumatic pressure levels of 2.0 and 2.5 bar. Results: An increase in maximum probe tip displacement, velocity, impact momentum and energy, and stone fragmentation was seen as the pneumatic pressure was increased from 2.0 to 2.5 bar. A progressive decrease in these parameters was demonstrated as the probe tip was deflected, especially at deflection angles greater than 24 degrees. Impact momentum appears to be the physical parameter most closely correlated with stone fragmentation efficiency. Conclusions: The optical measurement system and in vitro fragmentation model developed allow one to quickly and reliably assess the performance of flexible pneumatic probes in vitro. This system can be used for general bench testing and basic research that can provide critical information for the design of more effective and efficient flexible pneumatic lithotripsy probes.