Tiny Souped-Up Scope

For doctors, endoscopes are like eyes that can see far into the body. But today’s endoscopes don’t have the combination of small size and good image quality required for delicate procedures. Now, researchers at Massachusetts General Hospital (MGH) have made the first hair-thin scope to image in 3-D. They say if it’s good in humans, it could change diagnostics and minimally invasive surgery.

Today’s endoscopes suffer from a size-versus-image problem, says Guillermo Tearney, professor of dermatology at Harvard Medical School and leader of the MGH team. Scopes that image clearly, usually using a millimeter-size camera, are too big to go many places in the body. But smaller scopes, which can be as thin as a human hair, provide poor pictures.

Doctors who do the most delicate work need small scopes and good pictures. When endoscopes are penetrating layers into the brain, looking at a fetus, or threading through a tiny duct, size is important: big scopes can plow big holes through sensitive tissues. But good images are also needed for sure navigation of these areas. No scope does it all. So doctors performing these procedures must choose between bigger holes and clumsier movements.

That’s why the new scope is optimal, Tearney says. It’s as thin as a human hair and nearly as flexible, but it also shows doctors 3-D images of patients’ bodies.

The trick to the device, which is described in the October 19 issue of Nature, is better use of light, Tearney says. Today’s smallest endoscopes work like periscopes, shining white light down a bundle of glass fibers. The light bounces off tissues and returns to the doctor’s eye, creating an image that looks like a photograph. It’s good, says Tearney, but “suboptimal.”

With the new scope, white light shines down a single glass fiber, then breaks into a rainbow of colors. Each color hits a different area of tissue. The colors reflect back to a spectrometer outside the patient’s body. The spectrometer then measures two qualities of the reflected rays. First is intensity, which in the final image translates as shadows. Next, it measures how the returning rays compare with rays bounced off a flat reference object, creating topography. A computer then combines the shadows and topography into a 3-D image that looks like a computer model of the tissue.

To demonstrate the new device’s “proof of concept,” the researchers imaged tumors in the abdomen of a live mouse. They punctured the mouse’s underside with a tiny needle and threaded the scope into its gut. The scope’s 3-D scans clearly showed tiny bumps–tumors–on the abdominal wall. The researchers reported said that tumors this small wouldn’t be visible with any existing scope of the same size.

If doctors could look for tumors that small and in structures that delicate in humans, they might catch cases of breast or pancreatic cancer sooner, Tearney says.

The device could also make new procedures possible, he says. With such a small, sure instrument, doctors could burrow deeper into the brain or poke safely through an amniotic membrane to examine a fetus. They might also be able to conduct endoscopic exams without administering anesthesia.

“The technology looks extremely promising to me,” says Wayne Lencer, chief of gastroenterology and nutrition at Children’s Hospital Boston. Lencer knows the size-versus-image problem firsthand because he uses endoscopes to look for gastrointestinal problems in children. A scope as thin as a hair could explore the smallest, most fragile ducts of the pancreas “that are now not accessible,” he says. And with 3-D imaging, he might see “diseases not readily apparent” in his scopes’ 2-D images, he says.

But the new scope, still a prototype, has a long way to go before reaching humans, Tearney says. The team must test safety. And it would like to add color and increase the resolution, or add more pixels, to the 3-D images. The resolution–now only slightly better than that of small scopes used by doctors today–could be boosted tenfold by tweaking the optics, Tearney’s colleague Dvir Yelin says. A big challenge, Tearney points out, will be equipping the now-flimsy scope to route around twists and turns in the body without adding bulk.

If it all comes together in the hair-thin device, Tearney says, doctors could get a safe and clear look at any tissue in the body. “No one has ever had these capabilities before,” he says.