Precancerous Lesions: New 3-D Colonoscopy Eases Detection

Photo: 3-D image

A new type of endoscopy can produce three-dimensional images of the surface of the colon; © MIT

Researchers at the Massachusetts Institute of Technology have developed a new endoscopy technology that could make it easier for doctors to detect precancerous lesions in the colon. Early detection of such lesions has been shown to reduce death rates from colorectal cancer, which kills about 50,000 people per year in the United States.

The new technique, known as photometric stereo endoscopy, can capture topographical images of the colon surface along with traditional two-dimensional images. Such images make it easier to see precancerous growths, including flatter lesions that traditional endoscopy usually misses, says Nicholas Durr, a research fellow in the Madrid-MIT M+Vision Consortium.

"In conventional colonoscopy screening, you look for these characteristic large polyps that grow into the lumen of the colon, which are relatively easy to see," Durr says. "However, a lot of studies in the last few years have shown that more subtle, nonpolypoid lesions can also cause cancer."

In the United States, colonoscopies are recommended beginning at age 50, and are credited with reducing the risk of death from colorectal cancer by about half. Traditional colonoscopy uses endoscopes with fiber-optic cameras to capture images.

Durr and his colleagues, seeking medical problems that could be solved with new optical technology, realized that there was a need to detect lesions that colonoscopy can miss. A technique called chromoendoscopy, in which a dye is sprayed in the colon to highlight topographical changes, offers better sensitivity but is not routinely used because it takes too long.

"Photometric stereo endoscopy can potentially provide similar contrast to chromoendoscopy," Durr says. "And because it is an all-optical technique, it can give the contrast at the push of a button."

Originally developed as a computer vision technique, photometric stereo imaging can reproduce the topography of a surface by measuring the distances between multiple light sources and the surface. Those distances are used to calculate the slope of the surface relative to the light source, generating a representation of any bumps or other surface features.

However, the researchers had to modify the original technology for endoscopy because there is no way to know the precise distance between the tip of the endoscope and the surface of the colon. Because of this, the images generated during their first attempts contained distortions, particularly in locations where the surface height changes gradually.; Source: Massachusetts Institute of Technology