Today, OCT is used in optometry to image the retina for signs of glaucoma and macular degeneration. That technology, used to scan outside the body, involves bulky equipment requiring a lot of power. Only recently have researchers looked into shrinking the technology down to a microscale that can be threaded within the human body. The challenge has been to make the technology small enough to fit through human airways while using very small amounts of voltage to scan infrared light.
Xie’s prototype uses a MEMS-based (microelectromechanical system) approach, centered on a tiny, one-by-one-millimeter mirror. Xie and his students designed the mirror with tiny actuators, or mechanical supports, which pivot the mirror. As infrared light beams down the endoscope, the mirror steers the light back and forth, illuminating a slice of tissue. The reflected light bounces back up the endoscope, and is analyzed and depicted on a screen in real time.
The mirror can pivot 200 turns per second, at a 100-degree angle, enabling the scope to perform fast, real-time imaging. Xie tested the scope in rats, taking 3-D images of rat and mouse tongues.
The prototype is still too big to use in humans–it requires a total diameter of 5 millimeters to fit all its parts. However, Xie plans to further miniaturize the design, and will test the model in larger animals like pigs and goats in the next year. He recently started a company, WiOptix, and is seeking funding from the National Institutes of Health to help commercialize the technology.
Eric Seibel, research associate professor of mechanical engineering and director of the Human Photonics Lab at the University of Washington, says clinicians would have to be trained to interpret OCT images, which look more like ultrasound images than the visual images obtained from video cameras. He adds that size will determine whether OCT-based endoscopes work. “[This design] is a little bit more space-efficient, but it’s still more than five millimeters in size,” says Seibel. “It’s not quite there yet, but it’s a step in the right direction.”