New optical technique boosts prospect of virtual biopsy

Volumetric images generated with a new optical imaging technique may provide unprecedented diagnostic detail of blood vessels and gastrointestinal organs.

The technique, pioneered at the Wellman Center for Photomedicine at Massachusetts General Hospital in Boston, has been used successfully to visualize large areas of the esophagus and coronary arteries in living pigs. These studies indicate that optical frequency domain imaging (OFDI) might help in identifying precancerous lesions in the GI tract and plaque deposits in the coronary arteries, Bouma said.

Using a new type of laser developed at MGH-Wellman, OFDI can be used to examine more than 1000 points simultaneously. By comparison, the better known and more widely used optical coherence tomography (OCT) is constrained to tightly focused areas.

Sampling only a few microscopic points of an organ, as is done with OCT, is not enough when trying to spot early-stage disease, according to Brett Bouma, Ph.D., an associate professor of dermatology at Harvard Medical School.

"With optical frequency domain imaging, we can now perform microscopy throughout very large volumes of tissue without missing any locations," he said.

A rotating laser tip inside the fiberoptic catheter probe emits a light beam with constantly changing wavelengths. As the probe moves through the cavity, the light examines the GI or arterial surfaces, providing the data needed to create detailed microscopic images.

In a paper scheduled for publication in Nature Medicine, lead author Bouma and others from the MGH-Wellman team report that preclinical applications of OFDI revealed structural details of a 4.5-cm length of pig esophagus. Scans were accomplished in under six minutes.

Coronary artery surfaces were similarly mapped, producing 3D images of segments 24 mm to 63 mm long. An experiment designed to evaluate OFDI's ability to detect damage to arterial surfaces confirmed that the technique could differentiate between healthy and damaged tissue.

Potential applications for OFDI include the diagnosis of Barrett's esophagus, a precursor to esophageal cancer. Another major application may be examining coronary arteries for vulnerable plaque that could rupture and produce heart attacks.

A 2005 study from the division of cardiology at MGH found that OCT could identify vulnerable plaques in symptomatic patients. The OCT-developed scanning criteria could be used with OFDI to further study the vulnerable plaque hypothesis, potentially to diagnose dangerous plaques and guide their treatment.

Researchers might add other possibilities. Some go well beyond the traditional bounds of diagnosis. Bouma speculated that OFDI might be leveraged by therapies that involve the use of lasers. One is the use of laser light to treat early cancer.

"Our hope is that, through one minimally invasive probe, clinicians will be able to diagnose and precisely treat diseased tissue, while sparing adjacent healthy tissue," Bouma said.