Diminishing comminution of urinary stones with subsequent laser pulses

Abstract

Ureteroscopic lithotripsy with Holmium:YAG lasers is a common treatment for urinary stones but the physical mechanisms of stone comminution are still under investigation. The dominant mechanisms were reported to be associated with the direct action of light on the stone surface causing the photothermal decomposition of stones and explosive vaporization of interstitial water. The objective of this study was to better understand stone fragmentation by the direct action of light and other potential mechanisms (cavitation) using ultra-high-speed video microscopy. Stone fragmentation was quantitatively assessed using an Open-source library of Computer Vision algorithms (OpenCV) with programs written in Python. Stone fragments were identified by detecting difference between the images and tracked with identification numbers considering cross-section areas and velocities of the fragments. Images of stone comminution were collected using a Shimadzu HPV-X2 camera at 200 000–500 000 fps with dry stones in air and those hydrated in water. Stone fragmentation by the direct action of light was observed to diminish with subsequent laser pulses. The diminishing fragmentation, however, was offset by the action of cavitation bubbles that continued to erode and fragment stone surface, augmenting stone breakage with subsequent laser pulses. [Work supported by the NIDDK of the NIH under Award R43DK129104.]