A Lithotriptor is a medical device used in the non-invasive treatment of kidney stones (urinary calculosis) and biliary calculi (stones in the gallbladder or in the liver).Lithotripsy attempts to break up the stone with minimal collateral damage by using an externally applied, focused, high-intensity acoustic pulse. The sedated or anesthesized patient lies down in the apparatus' bed, with his back supported by a water-filled coupling device placed at the level of kidneys, for instance. A fluoroscopic x-ray imaging system or an ultrasound imaging system is used to locate the stone and aim the treatment head so that the F1 of the shock wave is focused on the stone. The treatment usually starts at the equipment's lowest power level, with a long gap between pulses, in order to accustom the patient to the sensation. The frequency of pulses and the power level will then be gradually increased, in order to break up the stone more effectively. The final power level will usually depend on the patient's pain threshold. If the stone is positioned near a bone (usually a rib in the case of kidney stones), this treatment may be more uncomfortable because the shock waves can cause a mild resonance in the bone which can be felt by the patient. The sensation of the treatment is likened to an elastic band twanging off the skin, and the patient is shocked in time with his heartbeat (he will be hooked up to an ECG).