Stones can either be localized with ultrasound or X-ray. The main benefits of ultrasound are real time monitoring of the disintegration process and the absence of ionizing radiation. Fluoroscopic imaging usually is very fast and precise. It visualizes areas that are not seen with ultrasound. Dornier lithotripters are designed for dual-mode imaging offering the choice to apply both imaging modalities simultaneously.
Stone fragmentation is primarily caused by high local tensile and shear waves created by the focused shock waves hitting the stone. Spherical shock wave fronts contribute to compression-induced tensile cracks or spalling at the posterior surface of the stone. Cavitation is also important for stone comminution. The rapid collapse of cavitation bubbles on the surface of the stone or in liquid-filled cracks within the stone produces shock waves that cause microfractures in the stone.