Surgeons may one day treat chronic back pain by vaporizing the bone away from pinched nerves with lasers, a physicist said today at the American Physical Society Division of Plasma Physics Meeting in Pittsburgh. The same computer models that predict how lasers pound fuel pellets to trigger nuclear fusion have now shown that high-power lasers can also destroy bone--without endangering nearby nerves.
In laser fusion, high-intensity laser pulses heat a tiny pellet of hydrogen isotopes to tens of millions of degrees, while squeezing it to high density to spark a nuclear reaction. During the last 25 years, physicists have not solved the world's energy headaches, but they have created detailed computer simulations of exactly how the laser light is absorbed. And remarkably, it turns out that "the equations are quite similar, if not the same," for a laser striking human tissue, says physicist Richard London of Lawrence Livermore National Laboratory (LLNL) in California.
So London, encouraged by a handful of medical researchers, developed a new simulation called LATIS for modeling what happens when light from a laser strikes tissue. The calculations suggested that a burst of very intense laser light lasting less than one-trillionth of a second would ionize atoms in the bone and turn it into a hot gas called a plasma. And since the plasma is an electrical conductor, the laser light only penetrates a short distance, removing just a micrometer of bone. "The electrons oscillate in phase and re-radiate in a backwards direction," so most of the light is reflected, London explains.
Testing a Ti-Sapphire laser on pig bones from a slaughterhouse, the researchers have now shown that they can target just bone. The trick was monitoring the wavelengths of light bouncing off the sample. When the laser zapped bone, the calcium atoms in the bone tissue emitted photons at a certain wavelength. They set the laser to shut itself off if those wavelengths disappeared--say if the beam had hit a nerve, which doesn't have much calcium.
Experts say the computer model strengthens the technical foundation for laser surgery. "This is a solid, scientific approach," says Rodney White, chief of vascular surgery at Harbor University of California Medical Center in Los Angeles. Luiz Da Silva, a physicist at LLNL who worked on the project, says they expect to have a working prototype available within a year.