Almost everyone gets occasional heartburn, that painful sensation in the chest or throat caused by the reflux of stomach acid back into the esophagus. When it happens too frequently, however, such as in patients with gastroesophageal reflux disease, it can result in a condition known as Barrett’s esophagus. An estimated 3 million Americans suffer from this disorder, where the tissue that lines the esophagus accumulates abnormal changes over time, increasing the risk for esophageal cancer.

Barrett’s esophagus often goes undiagnosed because it causes minor or nonexistent symptoms, and because of the procedure required to identify it. Currently, doctors must sedate a patient, insert a long, flexible camera known as an endoscope down the esophagus to look for abnormal tissue, and then cut off a small piece for analysis in a laboratory. The procedure is invasive, expensive and uncomfortable.

Now, researchers at the Massachusetts General Hospital (MGH) in Boston have invented a tethered, pill-sized endoscope that that allows doctors to construct an image of a person’s esophagus in microscopic detail within a few minutes—and all without anesthesia, intense training or causing pain. Their work was published today in Nature Medicine.

“A lot of people have reflux but don’t feel the pain of heartburn,” says MGH pathologist Gary Tearney, who led the study. These patients are at high risk for developing cancer, because they usually have no reason to get their esophagus inspected. “[Our device] really opens up screening to many more people,” Tearney says.

The new experimental endomicroscope device looks like a penny-sized, clear plastic pill, attached to a long piano wire that runs to a computer console. It can be swallowed with a cup of water. Because it is tethered, the pill can then be sent up and down the length of the esophagus, where it scans and generates an image.

The device works via optical frequency domain imaging (OFDI), a technique similar to ultrasound but using infrared light. The researchers first generate a beam of light, and then split it into two with mirrors. One beam is sent into a detector where it serves as a reference; the other is sent through the tether, into the pill, where it is directed into the tissue.

In the esophagus, the light beam is focused on an area roughly the diameter of a human hair and then spun around axially 20 times per second. Like in ultrasounds, the properties of the light after it reflects off tissue can be measured. When it is sent back to a detector and compared with the reference beam, the difference between the two can be used to reconstruct a thin cross section of the esophagus in microscopic detail. By stacking these cross-sections together, researchers can create a three-dimensional image of the esophagus in a method similar to CT scan reconstructions.

The device gives doctors the ability to see the detailed surface of a patient’s esophagus, but also can penetrate and image at a depth of around 10 microns—enough to allow the diagnosis of abnormal growth patterns in esophageal tissue, which are potentially a precursor to cancer.

“We also can potentially see other esophageal diseases,” says Tearney, who previously described a probe for imaging blocked arteries in the December 2011 issue of Nature Medicine. “Moving toward the future, we’re going to be building pills that can diagnose diseases of the stomach, diseases of the small intestine and even diseases of the colon.”

To hear an interview with Tearney about the new device, stay tuned for the February 2013 episode of the Nature Medicine podcast. Subscribe now in iTunes to ensure you don’t miss the show. And if you’re already a subscriber, be sure to leave a review on the iTunes store.