Internal stress wave measurements in solids subjected to lithotripter pulses

Semiconductor strain gauges were used to measure the internal strain along the axes of spherical and disk plaster specimens when subjected to lithotripter shock pulses. The pulses were produced by one of two lithotripters. The first source generates spherically diverging shock waves of peak pressure approximately 1 MPa at the surface of the specimen. For this source, the incident and first reflected pressure (P) waves in both sphere and disk specimens were identified. In addition, waves reflected by the disk circumference were found to contribute significantly to the strain fields along the disk axis. Experimental results compared favorably to a ray theory analysis of a spherically diverging shock wave striking either concretion. For the sphere, pressure contours for the incident P wave and caustic lines were determined theoretically for an incident spherical shock wave. These caustic lines indicate the location of the highest stresses within the sphere and therefore the areas where damage may occur. Results were also presented for a second source that uses an ellipsoidal reflector to generate a 30-MPa focused shock wave, more closely approximating the wave fields of a clinical extracorporeal lithotripter

Gallstone movement during lithotripsy: mechanisms and effects on fragmentation

We sought to examine the mechanisms of gallstone movement and its effect on gallstone fragmentation in vitro. Two experiments were performed in four specially constructed phantoms that allowed decreasing degrees of movement during the application of shock waves. Shock waves caused displacement of the stone from the focus, but the stone and its fragments were returned to the focus by streaming movements in the coupling liquid when the volume of surrounding fluid was small. Streaming movements were ineffective in large volumes. Restraining movements of the gallstone did not improve the results of fragmentation. We conclude that radiation force and the streaming motion of the surrounding liquid account for movements of the stone and fragments during lithotripsy. Lithotripsy is more effective when smaller volumes are used because streaming brings fragments back to the focus of the lithotripter. Total immobilization of the stone in the focus of the lithotripter, however, offers no benefit, probably because it inhibits rotational movement of the stone

Development of a 25 W TEM\u2080\u2080diode-pumped Nd:YLF laser

We report the design and the operation of a novel two-head, side-pumped Nd:YLF laser that generates up to 25 W TEM\u2080\u2080 output power at 1.053 \u3bcm. The anisotropic thermal lensing of each laser head has been examined and compensated with cylindrical lenses. The output power of this two-head laser exhibits excellent dynamic range with a typical optical\u2013optical conversion efficiency of 18%.Peer reviewed: YesNRC publication: Ye