During a colonoscopy or sigmoidoscopy as a screening test for colorectal cancer, the physician must often decide which polyp should be removed for histologic diagnosis. While hyperplastic polyps are considered benign without malignant potential, adenomatous polyps are thought to represent one of the earliest stages in the progression to a malignancy. Identification of these premalignant lesions is considered one of the cornerstones of colorectal cancer prevention. The physician must thus balance the time and potential morbidity of removing all polyps, many of which will be benign, versus removal of those polyps most likely to be adenomatous. Techniques have been developed as adjuncts to colonoscopy that are intended to distinguish between normal and precancerous tissue.
The first system developed was based on the observation that benign and malignant tissues emit different patterns and wavelengths of fluorescence after exposure to a laser light. One such device was approved by the U.S. Food and Drug Administration (FDA) in 2000, the Optical Biopsy System (SpectraScience, Minneapolis MN). This system consists of an optical fiber emitting a laser that is directed against three different regions of the same polyp. The subsequent fluorescent signal is collected, measured, and analyzed by a proprietary system software, and classifies a polyp as "suspicious" (i.e., adenomatous) or "not suspicious" (i.e., hyperplastic).
Narrow band imaging (NBI) is another technique that allows visualization of the mucosal surface and capillary vessels and thus may assist in the differentiation of abnormal from normal mucosa during colonoscopy. Two NBI systems are available. The NBI color chip system is used in the United States; in this system a single filter with a 2-band pass characteristic is used to generate central wavelengths at 415 nm (blue) and 540 nm (green and red). The NBI red-green-blue sequential illumination system uses narrow spectra of red, green, and blue light and a video endoscopic system with a frame sequential lighting method. The light source unit consists of a xenon lamp and a rotation disk with 3 optical filters. The rotation disk and monochrome charge-coupled device are synchronized and sequentially generate image in 3 optical filter bands. By use of all 3 band images, a single color endoscopic image is synthesized by the video processor. NBI has limited penetration into the mucosal surface and has enhanced visualization of capillary vessels and their fine structure on the surface layer of colonic tissue.
The FDA-labeled indication for the Optical Biopsy System reads as follows: "The SpectraScience Optical Biopsy System is indicated for use as an adjunct to lower gastrointestinal endoscopy. The device is intended for the evaluation of polyps less than 1 cm in diameter that the physician has not already elected to remove. The device is only to be used in deciding whether such polyps should be removed (which includes submission for histological examination)."
NBI received FDA clearance through the 510(k) process in 2005. This clearance (K051645) added NBI with the EVIS EXERA 160A System (Olympus Medical Systems Corp) to existing endoscopic equipment. FDA indications are for endoscopic diagnosis, treatment, and video observation.