Shock-induced collapse of a gas bubble in shockwave lithotripsy

TLDR

The study investigates shock‑induced collapse of a gas bubble near a solid surface in the focal region of a lithotripter. The collapse is modeled with a high‑order shock‑ and interface‑capturing simulation, using wall pressure as a damage indicator. Simulations reveal that a re‑entrant jet generates a water‑hammer shock, producing wall pressures up to ~1 GPa that exceed the incoming shock for bubbles close to the wall, with pressure decreasing with stand‑off distance and pulse width and increasing with pulse amplitude, underscoring the high damage potential of shock‑induced collapse.

Abstract

The shock-induced collapse of a pre-existing nucleus near a solid surface in the focal region of a lithotripter is investigated. The entire flow field of the collapse of a single gas bubble subjected to a lithotripter pulse is simulated using a high-order accurate shock- and interface-capturing scheme, and the wall pressure is considered as an indication of potential damage. Results from the computations show the same qualitative behavior as that observed in experiments: a re-entrant jet forms in the direction of propagation of the pulse and penetrates the bubble during collapse, ultimately hitting the distal side and generating a water-hammer shock. As a result of the propagation of this wave, wall pressures on the order of 1 GPa may be achieved for bubbles collapsing close to the wall. The wall pressure decreases with initial stand-off distance and pulse width and increases with pulse amplitude. For the stand-off distances considered in the present work, the wall pressure due to bubble collapse is larger than that due to the incoming shockwave; the region over which this holds may extend to ten initial radii. The present results indicate that shock-induced collapse is a mechanism with high potential for damage in shockwave lithotripsy.