Science / Medicine : SURGICAL LASERS

When Columbia University graduate student Gordon Gould developed the idea in 1957 of producing a beam of pure light that could deliver a high amount of energy to a spot as small as the point of a pin, he had no working model and no idea how it might be used. He named his invention after its process: Light Amplification by Stimulated Emission of Radiation, or LASER.

Gould developed the idea from a suggestion by Albert Einstein in 1917. As the molecules of the “medium” used in a laser--usually a gas such as carbon dioxide, a chemical or a crystal--are stimulated by heat, light or electricity into a higher energy state and then return to their normal state, they spontaneously emit energy particles called photons. Mirrors at both ends of the tube, or resonator, in which the medium is stored bounce the photons back and forth until the amplification is intense enough for light to escape from one end of the tube. Thus a laser beam is born.

But the light of a laser beam is not like ordinary light, which spreads out, as has been suggested, the way a football team moves after the ball is snapped. The light of a laser beam is more like a precision band marching tightly in step. That is why a television camera on the Moon was able to pick up the intense light of a laser beam from Earth but could not pick out the lights of an area the size of Los Angeles. And that is why the laser packs the power it does.

But there is something else about the light of the laser beam that makes it particularly useful in medicine.

Different mediums emit light beams that differ in intensity and in color, from ultraviolet to visible to infrared. Since intensity and color determine the effects of a laser beam on tissue, different lasers, change tissue differently.

Thus the heat of one laser beam can cauterize and fuse tissue together, while another can turn tissue into a vapor and remove growths and other lesions on the skin. Still another produces acoustic shock waves or chemical changes that selectively destroy tissue.

And the beam of a laser is sharper than a scalpel.

A physician delivers the laser beam to a targeted area through a hand piece about the size of a penlight, much as a dentist uses a drill. Different hand pieces are used for different procedures, and in critically minute operations, the laser beam can be manipulated with an adapter attached to a microscope.

Fiber-optic strands as thin as a hair that carry laser beams can be inserted into catheters or endoscopes to reach areas that were once inaccessible. The incision is so small it can be closed with a bandage.

The laser hand piece, or light scalpel, as it is sometimes called, is attached to a resonator kept on the periphery of the operating area. Many surgical laser procedures can be performed in a doctor’s office with little or no anesthesia.

Today, lasers cost from $30,000 to $50,000. At least half of the hospitals in the United States, as well as practitioners in almost every medical specialty, use lasers.

Some studies predict that laser surgery will grow by 25% a year, and worldwide annual sales of medical lasers are expected to reach $750 million by 1990, 70% of them in the United States. That compares with the $600 million in sales forecast for the entire laser industry this year.

But lasers are not quite the miracle makers they were once believed to be. More often, they supplement rather than replace conventional procedures. Not all physicians are comfortable with them. Some refuse to spend money on them; others will not take the time necessary to learn to use them. And the adequacy of existing training programs has also been questioned.

Furthermore, at least one established authority in the field has questioned whether the proliferation of medical lasers has become a means for physicians to compete against each other and against hospitals for patients, rather than a result of the lasers’ demonstrated superiority.

But despite these doubts, lasers continue to find new applications in a variety of medical specialties.

The laser surgery that has been around longest and is used by more specialists than any other is the carbon dioxide (C02) laser, according to Ron Wolpa, marketing manager for Coherent Medical Group of Palo Alto, Calif., the leading manufacturer of ophthalmic lasers and the No. 2 manufacturer of surgical lasers.

The carbon dioxide of the device emits an invisible infrared beam that vaporizes tissue without affecting adjacent tissue that might be damaged by a scalpel. It also fuses as it cuts, leaving a relatively “bloodless” surgical field. This can eliminate much of the time taken during surgery to suction off blood and debris.

“Virtually every leading teaching institution in the world uses the C02 (device),” Wolpa said.

It is the principal laser used in gynecology for destroying precancerous and cancerous tissue in the cervix, vagina and vulva, and can be performed in a doctor’s office, avoiding hospital costs.

It has significantly reduced menstrual pain by severing nerves to the uterus in women who cannot get relief from over-the-counter painkillers, and has been employed on an outpatient basis to treat infertility by opening blocked Fallopian tubes. Bladder tumors are removed with the C02, as are various malignant growths on the genitals.

In podiatry, the C02 laser is used to remove ingrown and fungus toenails and warts, and people can literally get back on their feet in less than half the time it takes with traditional procedures.

The argon laser is used almost as widely as the C02. Its visible blue-green light also avoids adjacent tissue, but because its energy is absorbed only by blood, it passes through bloodless tissue harmlessly and destroys only blood vessels.

Because it can clot blood vessels without vaporizing the tissue, it is becoming the preferred treatment for removing purplish-red birthmarks called port-wine stains, tattoos, warts and other skin blemishes and basal cell carcinomas, a form of skin cancer common on the faces of older people. Studies have shown that laser removal has several advantages over other methods, including lower infection rates, little or no post-operative pain, and smaller scars.

In ophthalmology, where medical lasers were first developed in the early 1960s, the most frequent procedure utilizes the argon in outpatient settings to treat diabetic retinopathy, the leading cause of blindness in young adults in the United States. It is also used for outpatient treatment of glaucoma.

A third major medical laser, the YAG (so called after its medium: yttrium-aluminum-garnet), reaches seven or eight times deeper into tissue than the C02, which has made it useful in getting to blood vessel abnormalities in the brain and spinal cord. However, “because the surgeon cannot see beyond the surface of tissue, the YAG can sometimes damage important tissues,” Dr. Henry Garretson, professor and chairman of neurological surgery at the University of Louisville, said in a telephone interview.

The YAG has special application for patients with massive bleeding who are at high risk because of other complications, such as hemophilia. Its success rate in stopping bleeding ulcers is reported to be 80% to 90%. By using endoscopes, the YAG’s infrared beam can reach into the gastrointestinal tract, lungs, vocal cords, urogenital tract and other sites that are often avoided by conventional surgery because they can easily be damaged.

A more recent model of the YAG, which uses shock waves rather than heat, removes secondary cataracts (those behind rather than on the lens of the eye). And now, a 15-pound, battery-operated YAG is saving the eyesight of people in remote areas who might otherwise go blind. The portable YAG also has the potential to treat glaucoma in older people who cannot be moved to a hospital. The procedure takes only minutes and requires no anesthesia.

Both the YAG and carbon dioxide lasers can remove hemorrhoids, and the C02 and argon can treat abnormal narrowing of the urethra. Lasers are also being used to cut out cancerous tissue in the prostate without removing the entire gland, preserving sexual function.

A fourth major medical laser is the dye laser, so-called because it uses different kinds of dye as the emitting medium. The dye laser can be “tuned” by matching its emitting dye, which is initially stimulated by an argon laser, to a dye that concentrates in cancer tissue but is excreted by normal tissue. The beam will then hit only the cancerous tissue and kill it.

“Laser cancer surgery can sometimes produce a total kill of cancerous tissue where radiation and chemotherapy cannot,” said Dr. Geza Jako, past president of the American Society for Laser Medicine and Surgery.

When the dye laser beam is rapidly switched on and off, rather than beamed constantly, it will disintegrate urinary stones and reach stones shielded by pelvic bones that conventional lithotripsy, which pulverizes stones with sound waves, has difficulty reaching.

The dye laser’s ability to be “tuned” enabled researchers at the Baylor Research Foundation in Texas to dissolve two viruses that had been mixed in blood with red dye without damaging the healthy blood cells. The procedure at some point will be tested with the HIV virus believed to cause AIDS.

In some procedures, lasers are combined. Surgeons at University Hospital in Cincinnati, for example, recently removed a large tangled mass of blood vessels from the brain stem of a 22-year-old patient by first using a YAG to clot the malformation and then a C02 to vaporize it.

Even more exciting possibilities might be just around the corner with a fifth laser, still mostly in preclinical trials. What sets that laser, the excimer, apart is its lack of heat. It can cut through a match without igniting it. This “cool” laser can also vaporize a chip of tissue as small as one-hundredth of a micron (one-millionth of a meter), and it will cut through bone.

The excimer is being tested for opening fat-clogged human arteries by a team of cardiologists headed by Dr. James Forrester at Cedars-Sinai Medical Center in Los Angeles. Unlike current procedures that remove arterial fat but leave debris behind, the excimer vaporizes the fat into a gas that is carried off by the blood. But it does that without the heat damage caused by other lasers. Because the vaporizing action is so thorough, recurrence of the clogging--always a factor in unblocking arteries--is significantly reduced, Forrester said.

Also at Cedars, ophthalmologist August Reader is leading a team that is exploring the use of the excimer in transplanting corneas and actually sculpting corneas to correct farsightedness. The research is only in its infancy, but if successful it could mean an end to reading glasses and bifocals.

Despite widespread optimism, one laser expert has reservations. Michael Berns Ph.D., current president of the laser medicine society and director of the Beckman Laser Institute at UC Irvine, said that advances in laser medicine are being overemphasized, not by the media but as a result of the new competitiveness in medicine and among laser manufacturers. The overemphasis has created “an alarmingly high rate of increase” in the use of laser surgery, he said recently. “They are being pushed too fast.”

Berns is willing to leave it to clinicians to decide when and when not to use lasers, and maintained that it would be “bad medicine to not use a laser for secondary cataracts, retinopathy, removing most port-wine stains, removing precancerous tissue in gynecology, and for certain head and neck tumors.”

But beyond that, he said, the use of lasers should be either optional or experimental. And even in those specialties in which its use is firmly established, there can be reasons not to use laser, he contends.

At present, Berns said, no one oversees the purchase of lasers for use in physicians’ offices or ambulatory surgical centers, and he suspects that some physicians who use them have not been properly trained.

The subject of laser surgery training is still a matter of controversy, he said. He recommends a minimum two-day training period, with half a day of hands-on experience followed by a program under the supervision of a training physician.

However, countered Dr. Arlen Meyers, associate professor of otolaryngology and head and neck surgery at the University of Colorado’s Health Sciences Center and former director of the Institute for Laser Medicine in Denver, it would be a mistake to think there are “lots of people using lasers willy nilly.”

“Hospital laser committees have been relatively stringent in limiting the use of lasers to qualified individuals,” he said. But he admitted that there is the potential for laser use by persons outside the jurisdiction of a hospital or certifying body.

In the meantime, Coherent’s Wolpa reported, laser-related questions are beginning to appear on specialty board exams, and many graduates from residency and gynecology programs are learning how to work with lasers.

BUILDING THE RIGHT LASER TO DO THE JOB

A Liquid Laser has a dye filled tube, the dye atoms excited by flash tubes to produce laser light. Different dyes produce light of different frequency.

A Crystal Laser has a fluorescent crystal, such as a ruby, for its light-amplifying substance. Excited by a flash of light from the flash tube, the laser produces short burst of very powerful light beams. The YAG laser is a crystal laser.

A Gas Laser such as the CO2and argon lasers relies on a tube filled with gas as its light-amplifying substance. Atoms of the gas are excited by an electric current to produce a beam of laser light, which shoots out the partially mirrored surface.