Pressure Measurements in a Wolf Piezolith 2200 Lithotripter

Abstract

We have developed a PC-based system and a measurement protocol to study characteristics of acoustic shock waves generated by a extracorporeal shock wave lithotripter. * The system has the following capabilities: data acquisition, data transfer, mass storage, wave form analysis, and graphics display. Using this system, we measured the peak pressure distribution within a cylindrical region of 120 × 70 mm (diameter × height) surrounding the geometric focal point of a Richard Wolf Piezolith 2200 lithotripter. At a given point, we aligned the transducer along the local radial line from the focal point so that its sensing element would capture the incident wave front. Due to the axisymmetric nature of the wave-generator geometry and of the pressure loadings generated, measurement from one meridian plane was deemed sufficient. On a meridian plane, a total of 105 measurements were made with 15 taken from each of the seven radial lines at θ = 0, 15, 30, 45, 60, 75, 90 degrees, respectively. We repeated measurements at meridian planes at every 90 degrees to make a total of four measurements for one location. Results were mapped and displayed with a three-dimensional surface plot to show the spatial distribution of peak pressure within the region of measurement. We also made a two-dimensional contour plot to show the shape and size of the focal zone within the region. The peak pressure at the geometrical focal point was measured to be 8.6 Kpsi (600 bar). An ellipsoidal shaped focal zone with peak pressure of 6 Kpsi or higher was found to have major and minor axes of 9.8 and 2.6 mm, respectively. We may have underestimated peak pressures due to the transducers used. Experiments with new probes are currently underway.