Last updated: 02/17/2009

Lithotripsy uses the technique of focused shock waves to fragment a stone in the kidney or the ureter. The affected person is placed in a tub of water or in contact with a water-filled cushion. A sophisticated machine called Lithotripter produces the...

focused shock waves. A high-voltage electrical discharge is passed through a spark gap under water. The shock waves thus produced are focused on the stone inside the person's body. The shock waves are created and focused on the stone with the help of a machine called C-Arm Image Intensifier. The wave shatters and fragments the stone. The resulting debris, called gravel, can then pass through the remainder of the ureter, through the bladder, and through the urethra during urination. There is minimal chance of damage to skin or internal organs because biologic tissues are resilient, not brittle, and because the shock waves are not focused on them.

The shock wave is characterized by a very rapid pressure increase in the transmission medium and is quite different from ultrasound. The shock waves are transmitted through a person's skin and pass harmlessly through soft tissues. The shock wave passes through the kidney and strikes the stone. At the edge of the stone, energy is transferred into the stone, causing small cracks to form on the edge of the stone. The same effect occurs when the shock wave exits the stone. With successive shock waves, the cracks open up. As more cracks form, the size of the stone is reduced. Eventually, the stone is reduced to small particles, which are then flushed out of the kidneys or ureter naturally during urination.