Schlieren photography study of energy absorption by uric acid nuclei

Previous studies using microfocus x-ray radiography on concentric laminated uric acid calculi following in vitro extracorporeal shock-wave lithotripsy (ESWL) has demonstrated the enlargement of the matrix layers. The Schlieren technique was used to verify the hypothesis that the incident energy would be concentrated in the matrix layers by total internal reflection. Because of the rough surface of the stone, the ultrasonic beam (4 MHz) was incident at various angles. At the critical Rayleigh angle (45.9 degrees +/- 0.5 degrees ), the reflected beam consisted of a spectacularly reflected lobe and a reradiated leaky Rayleigh wave. Different critical Lamb angles, theta(L), of 30.8 degrees, 38.1 degrees and 50.8 degrees (experimental uncertainty 0.5 degrees ) were also determined. Depending on the angle of incidence on the stone surface, a Rayleigh wave can be produced and/or one or more layers, as a whole, are set into vibration (Lamb excitation), with the result that shell-like fragments consisting of one or more layers, break off the stones at sites of weaker bonding, as has been noted in previous in vitro lithotripsy experiments by our group.