Measuring bubble dynamics in lithotripsy using a high-speed camera

Abstract

The primary goal of this study was to examine bubble dynamics in shock wave lithotripsy and experimentally obtain the radius-time (r-t) profile. A piezoelectric array was employed as a shock wave (SW) source. The focal waveform (as measured with a fiber optic probe hydrophone) was double-peaked with two shocks: leading peak pressure 65±3 MPa and second peak 30±3 MPa. The negative phase in between had a peak p−=−16±2 MPa. The cavitation field was monitored using a dual passive cavitation detector consisting of two 1-MHz focused transducers. The second peak of the SW inhibited cavitation limiting the characteristic time to less than 60 μs. A high-speed camera (up to 10 million frames per second) with a spatial resolution of 2 μm/pixel was used to measure bubble dynamics. The camera could record 14 frames that were timed to measure the growth and collapse phases of the bubbles. The bubbles were initially spherical but became aspherical and exhibited jetting as they collapsed. The bubble radius was estimated from the area of bubble in each snapshot from which r-t curves were constructed and compared to calculations using the Gilmore formulation. The maximum radius ranged from 150 to 300 μm. [Work supported by NIH.]