Lasers Illuminate New Frontiers in Medicine

Medical Device & Diagnostic Industry Magazine
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An MD&DI October 1997 Column

R&D HORIZONS

Working on a microscopic level, new laser applications perforate, move, cut, and map human cells.

Long a mainstay of surgical applications, medical lasers are finding their way into ever more diverse niches. Some of these applications are within the medical mainstream; others are found outside, in the distant regions of bioscience, where their uses are guided by quantum theory.

This span of applications is bridged by the nature of laser light itself­a beam composed of nearly massless particles imparting energy that in one instance explodes cells and in another harmlessly holds them in place like a pair of subatomic tweezers. Laser light can map the topographical surfaces of wounds or­potentially­distinguish between cancerous and healthy tissue.

The Lasette (Cell Robotics, Albuquerque) uses MCR technology to decrease its size.

LASER-BASED LANCETS

A new product that is near at hand is the laser-based lancet, a battery-powered laser designed to replace the stainless-steel products jabbed daily into countless fingers around the globe. Two companies are jockeying for the lead in this new marketplace. Both received FDA clearance this year.

TransMedica International, Inc. (Little Rock, AR), offers the Laser Lancet; Cell Robotics, Inc. (Albuquerque), the Lasette. Both are extensions of the laser scalpels first used by surgeons years ago. But this new breed of laser is distinguished by its limited cutting power and greater portability. These battery-powered lasers penetrate only to the capillary level, freeing a drop or two of blood in the process­enough to allow simple blood tests.

Using these lasers, health-care workers can reduce the risk of infection by bloodborne diseases, including HIV and hepatitis. But it is the patient who will reap the everyday reward­avoiding pain. "The sensation is gone before you see the blood," says Charles Vestal, president of TransMedica.

The Laser Lancet (TransMedica International, Little Rock, AR) penetrates human skin almost painlessly.A laser-assisted egg-hatching technique may improve the success of in vitro fertilization (Cell Robotics).Lasers weaken the ovum's shell without injuring its contents.

Laser-based lancets are virtually painless because the light beam vaporizes tissue rather than tearing it. Energy carried by photons excited with an erbium: YAG laser is absorbed by the water inside cells. The water turns instantly to steam, causing the cells to explode along the narrow path of the beam.

The device is expected to be especially appealing to diabetics, particularly the 800,000 Americans who have Type I diabetes. These patients require daily insulin injections and are advised to check blood glucose levels at least four times a day to help control the disease.

The device that promises to make this daily regimen less onerous was started not in the United States but in Russia, where Vestal, a hard-core entrepreneur, was exploring opportunities to distribute chicken from Little Rock's Tyson Foods. "I wasn't there more than a couple of days when this top expert in lasers walked in the door and asked if I would like to look at lasers that had never been seen before in the West," Vestal recalls. "I said, 'Yeah, cool.' "

The basic laser device was available, but Vestal still needed to add the electronics and other components that would make it a medical product. Those were designed by engineers in Little Rock, with the assistance of experts at Massachusetts General Hospital in Boston. As currently constructed, the Laser Lancet sends a laser pulse through a disposable plastic tube, creating a small slit, usually in the fingertip of the patient.

Size, however, is a problem. "Right now it is about as big as a loaf of bread­but we're working to get products that are much, much smaller," Vestal says.

Cell Robotics has an edge in the race to miniaturize. Its Lasette is just 7 in. long and fits in a zipper notebook similar to those used to carry daily planners.

The Lasette is also very light, less than 2 lb. It has an adjustable power setting to penetrate different skin types, as well as the necessary safety features. But the feature that really stands out about this new product is its use of rugged, solid-state technology.

The Albuquerque company achieved the laser's size and durability by using the multifaceted crystal resonator (MCR), a technology that permits the design and cost-effective manufacture of compact but powerful solid-state or crystal lasers. MCR, which Cell Robotics acquired in early 1996 from Tecnal Products, Inc. (Albuquerque), is a way of making laser crystals that act as their own resonators. Without mirrors, the laser can be made smaller and is less likely to malfunction from being jostled. "You can just put the crystals in and not spend a lot of time tuning up the laser," says David Costello, Lasette product manager. "Basically it's a way to make one laser after another very quickly and have them all work pretty much the same."

WOUND MAPPING

Just as lasers can create wounds, they can also map them. In much the same way lasers probe the earth's surface from orbit, laser light is being harnessed to scan the topography of torn human tissue. Using an off-the-shelf diode laser and legacy PC, Daniel Smith, PhD, and his colleagues at the University of Akron (Akron, OH) have constructed a device that profiles superficial injuries in three dimensions. These profiles might be used to evaluate wound repair or burn depth, to assess surgical reconstructions, to treat scarring, or to perform cosmetic surgery.

"Right now, determining whether a wound is healing on a day-to-day or week-to-week basis is reasonably subjective," says Smith, a professor of chemistry and biomedical engineering. His laser system would remedy that.

Red laser light emitted by a diode scans the surface of the wound, reflecting light to a sensor that generates a signal corresponding to the wound's topography. A sound generator, mounted beside the diode laser, emits high-pitch waves that complement the laser light, reflecting off the tissue and demonstrating surface texture. This texture indicates rate of healing, as the wound goes from a jelly to a progressively more ordered state. The data are represented in a kind of three-dimensional map constructed and displayed on a PC screen.

This three-dimensional measurement system could help people evaluate the wound-healing products now being developed, Smith says. "There's going to be a cost/benefit question," he explains. "Is it worth putting a lot of money into this product? Probably, if it makes the person heal 50% faster."

Modeling surfaces in three dimensions, says Smith, is already widely used outside of health care. For example, makers of extruded pipe and tubing use such systems to monitor product quality. But in that application, the products whiz by on an assembly line and the laser shoots them as they pass. In a medical application, the patient is stationary, which makes conducting a scan problematic.

Smith solved the problem by setting the laser and its accompanying sound generator in motion along the x and y planes of a table positioned above the wound. "It just goes back and forth­bam, bam, bam," explains Smith. A 30-second scan can cover a wound about two inches square, he says. Processing the image takes about 4 minutes.

The next engineering challenge is to eliminate the positioning table by electronically or mechanically steering the laser and sound generator. Ideally, the two energy sources would be mounted on a robotic arm, relaying spatial coordinates to the computer.

TWEEZERS AND SCISSORS

Somewhere between the effect of a laser-based lancet that penetrates tissue and light beams that bounce inconsequentially off wound surfaces are the LaserTweezers and LaserScissors, both developed by Cell Robotics.

The tweezers use a technique called optical trapping to catch and hold living cells and particles. Optical trapping is accomplished by photons that go through, rather than bounce off, a target. The photons are refracted slightly, imparting momentum to the surface that has bent their trajectory. The surface moves opposite the photons, like a backlash, pulling the cell toward the source of the laser light and effectively trapping it in the beam. The LaserScissors, essentially a highly focused and targeted laser beam, is then used to remove selected parts of the target.

These technologies have been used in the pursuit of basic science­to tease apart cells or document the functions of different organelles. But recently, engineers at Cell Robotics have applied these advanced techniques to medicine.

IVF WORKSTATIONS

Using the company's in vitro fertilization (IVF) workstation, a fertilized human egg can be held in place by the LaserTweezers while a computer aims and then focuses a laser to weaken the shell of the ovum. Weakening the egg improves the chance that a viable embryo will hatch.

"Much of the problem that women in their late 30s and early 40s have becoming pregnant is not so much getting an embryo started but getting the embryo to break out," says Ronald Lohrding, PhD, chairman, CEO, and president of Cell Robotics. "When women approach 40, the shells become tougher."

Preliminary clinical results indicate that the laser-assisted hatching technique developed by Cell Robotics may triple the IVF success rate of these women. "We're able to cut little trenches in the shell so the embryo can crack the egg," Lohrding says.

The chief technical challenge facing engineers developing this workstation was to accomplish the critical weakening of the shell without injuring the fragile contents. "There had to be no possibility of damaging the DNA or the proteins associated with the embryo," Lohrding says. That meant choosing wavelengths shorter than visible light but capable of passing through the objective of a microscope.

Ultimately, the design task was simplified by having already developed technologies capable of optical trapping and optical cutting­the LaserTweezers and LaserScissors. "We already had the precision with which we could move and position the egg and accurately score the shell," he says.

The IVF workstation has everything needed to perform in vitro fertilization, from injecting sperm into the egg to improving the chance of hatching the egg. The product is already approved for use in Europe and has entered FDA-sanctioned clinical trials in Europe, Israel, and the United States.

TISSUE HEALTH

Laser light unleashed inside the human body may provide information about the health of tissue, indicated by its fluorescence. Xillix Technologies Corp. (Richmond, BC, Canada) has developed a laser-induced fluorescence endoscopy (LIFE) system for detecting lung and gastrointestinal cancers. Bruno Jaggi, Xillix cofounder and chief engineer, believes that diseased tissue as small as 1 mm can be accurately identified with this technology.

The process begins with ultraviolet light emitted by an HeCd laser and fired through an endoscope or bronchoscope. The light is absorbed by tissue and causes a fluorescence that is picked up by a bundle of optical fibers feeding into mirrors and spectral filters. The light is split into red and green bands, each recorded by a charge-coupled device, processed by computer, and output in real time on a video monitor.

Healthy tissue returns a signal in the green band about eight times stronger than that of diseased tissue, says Jaggi. But distance from the fluorescing tissue also affects the strength of the green band, which could skew results. That, says Jaggi, is the reason for recording the red band, which shows very little difference between healthy or diseased tissue and thereby serves as a benchmark. "If you have a large change in the green due to an actual change in the spectrum, the ratio between green and red will change," he says. "If you have a change just because you go farther or closer to the tissue (with the endoscope), the ratio will not change."

Scientists working in this promising area must take a tentative approach, however. Whether cancerous and healthy tissues demonstrate such clear-cut differences in fluorescence is still debated by researchers.

The signals retrieved from fluorescence are very small. "You don't have that many photons to work with," Jaggi says. And human tissue is not the only source of fluorescence. Some bacteria fluoresce, as do the bits of feces and partially digested foods within the gastrointestinal tract.

It is not surprising, therefore, that a white-light endoscope has been tied into this system as a kind of medical fail-safe. "We think the way to introduce this new technology is in small steps," Jaggi says. "Physicians have used white light for the last 20 years. They are very good at looking at these images. What we're really saying is, 'Look, we're just providing you with new information in addition to what you already have.' "

So it is with the most far-reaching laser applications. Their true value relies as much on increased understanding of the human body as on technological development. Where these niche applications­and the technologies that drive them­will ultimately take medicine is one of the unknowns that drive pioneers in this industry.

Copyright ©1997 Medical Device & Diagnostic Industry