From Academic Kids

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A lithotriptor with integrated fluoroscope (upper head) and ultrasound generator (lower head)

A lithotriptor is a medical device used in the non-invasive treatment of kidney stones (urinary calculosis) and gallstones (stones in the gallbladder in the liver). The scientific name of this procedure is Extracorporeal Shock Wave Lithotripsy (ESWL). Lithotripsy was developed in 1985 and revolutionized treatment of calculosis. It is estimated that more than one million patients are treated annually with ESWL in the USA alone.

How it works

Lithotripsy attempts to break up the stones without harming body tissues by using externally-applied, focused high-intensity ultrasound (inaudible sound waves). The sedated or anesthesized patient lies down in the apparatus' bed, with his back supported by a water-filled cushion placed at the level of kidneys, for instance. A fluoroscopic x-ray imaging system or an ultrasound imaging system are used to locate the stone and aim the apparatus ultrasound-generating head precisely on it. When irradiation is turned on, several ultrasound beams converge into the stone and their intensities are summed.

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Diagram of focused ultrasound waves into a kidney stone

The successive shock wave pressure pulses fragment the stones in smaller pieces, which then can pass easily through the ureters or the cystic duct. The process takes about an hour. An ureteral stent (a kind of expandable hollow tube) may be used with stones larger than 2.5 cm. The stent prevents blockage of the ureter and helps the small stone pieces to pass more easily.

Extracorporeal lithotropsy works best with stones between 4 mm and 2 cm in diameter, that are still located in the kidney. It can be used to break up stones which are located in a ureter, too, but with less success.

Since lithotripsy avoids invasive surgery, the treatment starts very quickly after diagnosis, and recovery is generally more rapid, as well. The passage of stone fragments may take a few days or a week and may cause mild pain. It is a very safe procedure and can be used with children.

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