There is no doubt that cutting of stones is one of the oldest of surgical procedures since time immemorial. Today kidney stones account for about 350,000 U.S. hospital admissions a year. But not all of these people are cut. When conditions are favorable, therapists use noninvasive options for breaking up the stones inside the body and removing them by natural elimination or other means that don't involve cutting.

One recently developed option is treatment by a device called a lithotripter, which generates sound waves to crush the stones. Worldwide, about 100,000 patients a year use this treatment though it has its limitations. Now a new technique that uses laser light is about to enter clinical use, offering several potential advantages over the lithotripter.

Studies in which laser light successfully treated 76 out of 77 patients with kidney stones have recently been clinically approved. This method's versatility will eventually take its place as an alternate, noninvasive therapy that will be less expensive and less cumbersome than the lithotripter and will be able to treat patients lithotripter cannot. The pelvic bones block the sound waves, which makes the lithotripter useful only for stones lying above the waist.

This is an application of plasma physics to medicine. Laboratory experiments were carried out wherein stones were held in little wire baskets. These baskets are also used therapeutically: On the end of a catheter they can grasp and crush a stone. The experimenters put an optical fiber into contact with the stone and send the laser light through the fiber, just as if they were treating a patient. Whenever a pulse of light hit a stone, there was a spark like flash. The experimenters wanted to know what this flash was and whether it was necessary to the destruction of the stone, so they studied the spectrum of the flash. It was not a blackbody spectrum but a line spectrum. The line spectrum indicated that something more than simple heating was taking place.

The researchers believe that the light vaporized and ionized a small part of the surface of the stone, producing an ionized gas, plasma. The plasma absorbed energy from the light and so expanded. Expansion of the plasma, they believe, generated an acoustic wave that shattered the stone.

The work on kidney stones was begun by a urologist, who experimented on pigs. He then treated 34 patients the same way. Later, a hospital staff member treated 43 more. In all but one of the patients, the shattered stones were passed in urine or removed with the basket. Kidneys sometimes produce stones, and these stones can lodge in places that are difficult to reach. Laser light guided by optical fibers promises to be a nonsurgical means of breaking and removing some of these kidney stones be it below or above the waist.