Photoacoustic endoscopy

Collaboration yields better view of Barrett's esophagus

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Harnessing light and sound to visually penetrate biological tissue, photoacoustic endoscopy, invented by biomedical engineer Lihong Wang, PhD, right, may provide surgeon Brent D. Matthews, MD, a powerful new tool to screen for Barrett’s esophagus.  ROBERT BOSTON

BY Greg Barnett

People with Barrett’s esophagus — a disorder in which the lining of the esophagus is damaged by stomach acid or bile — must undergo periodic endoscopic examinations with biopsies because they have a risk for cancer. But because this surveillance technique may miss precancerous tissue, a better screening method is needed. That’s why a Washington University minimally invasive surgeon was very interested when a biomedical engineer at Washington University’s Danforth Campus called him about a new imaging technology that could visually penetrate biological tissue safely.

“Once you have Barrett’s esophagus, you must undergo regular screening endoscopy for a lifetime,” says Brent D. Matthews, MD, chief of the Section of Minimally Invasive Surgery. “Four-quadrant biopsies every centimeter along the area where the Barrett’s is located are required. But there could be areas between the biopsy sites that actually could show a higher-grade Barrett’s esophagus, and you wouldn’t necessarily know that.”

"Photoacoustic endoscopy could be a more accurate way to map out the entire esophageal mucosa as part of a surveillace program." — Brent D. Matthews, MD

Lihong Wang, PhD, the Gene K. Beare Distinguished Professor of Biomedical Engineering, contacted Matthews about the possible use of the 3D imaging method photoacoustic tomography in the diagnosis of gastrointestinal disease. Wang invented photoacoustic endoscopy, which applies photoacoustic tomography by way of an endoscope; with this technology, an endoscope pulses light into tissue, generating a sound wave that is then converted to an image. Wang and postdoctoral fellow Joon-Mo Yang, PhD, have been fitting a standard endoscope with the instrumentation to view the esophagus.

In the images above acquired from rabbit esophagus, top, and rat colon, photoacoustic signals in red indicate blood vasculature and ultrasonic signals in green reveal tissue density. LIHONG WANG, PHD

“There is a rotating mirror, which we spin to reflect light and sound,” says Wang. “We get a 360-degree perspective with dual contrasts — both optical and ultrasound. If there are lesions beyond 1 milimeter in depth, you cannot see them using standard optical endoscopy. In the current version, we can penetrate to about 7 millimeters in depth.”

Photoacoustic tomography can also measure concentration and oxygen saturation of hemoglobin to assess blood vessel development and hypermetabolism, respectively, which are hallmarks of cancer. The next step is to test the endoscope in animals, and ultimately to assess the technique in humans.

Barrett’s esophagus is commonly found in people with gastroesophageal reflux disease. “Photoacoustic endoscopy could be a more accurate way to map out the entire esophageal mucosa as part of a surveillance program,” says Matthews.

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