Figure 4.

Each set of images shows (left) a high-speed photograph of bubbles on the stone surface from a single lithotripter pulse and (right) the average of four binary images from repeated lithotripter pulses for A) a COM stone and B) a BegoStone. In A), a chain of bubbles arose on the right side of the stone with every pulse, as indicated by the black bubble outline in the binary image. While not every bubble arose with each lithotripter pulse, bubbles repeatedly arose from certain locations on the stone surface. The magnified image shows the dark outline of a bubble that arose in one particular location in all four lithotripter pulses. In B), the bubble distribution was variable with successive lithotripter pulses, as evidenced by the grey as opposed to black scattered across the stone surface in the binary image. Blue arrows indicate the four locations on the BegoStone surface with noticeable imperfections that could not be filtered out of the binary image.