Originally Published August 2000
Among the distinguishing characteristics of human ingenuity is that we manage to come up with new uses for old inventions. One of the most venerable inventions of all, according to Genesis—and the first to be subject to quality control—is light, and light is increasingly being employed in novel and fascinating ways, both for device manufacturing and in a variety of clinical settings.
Of course, spectrographic analysis has long been a classic technique of materials and surface characterization. As a processing tool in the fabrication of medical parts and devices, light is a critical element in operations ranging from the curing of adhesives and coatings to the most exacting laser micromachining. Strain testing of transparent plastics uses light to measure birefringence, while powerful bursts of visible light can serve as a means of sterilization.
Clinically, fiber-optic illuminators are a key component in endoscopic equipment and in systems designed to trigger light-activated drugs. Therapeutic lasers figure prominently in dermatological and ophthalmic procedures, and bright-light therapy is used to alleviate conditions that include seasonal affective disorder, insomnia, and migraine. An elegant combination of diagnostics and treatment is the use of light with jaundiced infants, whose hyperbilirubinemia can be verified via noninvasive devices that analyze skin color and addressed with UV phototherapy.
A recent collaboration between researchers and clinicians in Scotland is taking advantage of several light-based technologies in an attempt to develop a new diagnostic instrument to screen for early, heretofore-undetectable intestinal cancers and precancerous lesions. The work is based on the fact that cancer cells metabolize and excrete a certain compound called protoporphyrin IX (PpIX) less efficiently than do normal cells. A few hours after patients drink a glass of orange juice that contains a chemical precursor to PpIX, the tissues under examination are exposed to a high-energy violet light, which elicits another PpIX characteristic: its tendency to fluoresce in the red spectrum.
The violet-light source is an endoscope-mounted mercury arc lamp, prefiltered to remove all red light and equipped with a night-vision-type image intensifier. The endoscope also has two separate camera units, one providing a standard color image of the intestinal tract and the second providing an intensified image of only the fluorescent cancer cells, which is then superimposed on the "base map" of the color image. The system is thus designed to identify and transmit precise visual data on suspicious areas too small to be picked up by the naked eye or with conventional color video endoscopes.
To this point, the system has been tested only on patients with known malignancies, where it appears to function quite well; a new, third-generation version of the device is about to enter clinical trials for the diagnosis of early-stage cancers. According to participants in the development project, an important objective is to improve diagnostic accuracy for individuals in high-risk groups who are currently subjected to multiple random biopsies and the attendant waiting for histology reports.
Perhaps the most intriguing aspect of the system is that when a high concentration of PpIX is photoirradiated it exhibits an additional property: the production of cytotoxins that could presumably destroy a cell from within. Although this light-induced auto-destruct mechanism has yet to be tested with human subjects, the future for many potential cancer victims would seem to be brightening.
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