Engineers at Stanford University have developed and demonstrated a prototype single-fiber endoscope that, they say, quadruples the resolution over existing designs, which might lead to the development of needle-thin, minimally invasive endoscopes able to view features out of reach of today’s instruments.

Fig. 1 – Professor Joseph Kahn (right), and graduate students Reza Nasiri Mahalati (left) and Ruo Yu Gu (center) with their prototype single-fiber endoscope. (Credit: John Todd)

The new micro-endoscope is as thin as a human hair and could lead to a significant improvement in high-resolution, minimally invasive bio-imaging with potential applications in research and clinical practice. Micro-endoscopy could enable new methods in diverse fields ranging from study of the brain to early cancer detection.

The device was developed by a team of researchers under the direction of Joseph Kahn, a professor of electrical engineering at the Stanford School of Engineering. Their results were published recently in the journal, Optics Express.

The prototype can resolve objects about 2.5 microns in size, and, they stated that a resolution of 0.3 microns is within reach. By comparison, currently available high-resolution endoscopes can resolve objects only to about 10 microns, and the naked eye can see objects down to about 125 microns.

Kahn’s work with endoscopy began two years ago after a discussion on biophotonics with another Stanford electrical engineer who wanted to know if it would it “be possible to send light through a single, hair-thin fiber, form a bright spot inside the body, and scan it to record images of living tissue,” he said.

The answer, they knew, must lie in multimode fibers in which light travels via many different (paths) modes. Light is very good at conveying complex information through such fibers but can get scrambled along the way. Kahn devised a way to unscramble the information by using a miniature liquid crystal display called a spatial light modulator. Kahn and graduate student, Reza Nasiri Mahalati, developed an adaptive algorithm to have the spatial light modulator unscramble the light. (See Figure 1)

In the micro-endoscope, the spatial light modulator projects random light patterns through the fiber into the body to illuminate the object under observation. The light reflecting off the object returns through the fiber to a computer. The computer then measures the reflected power of the light and uses algorithms developed by graduate students to reconstruct an image.

A rigid single-fiber micro-endoscope could enable myriad new procedures for microscopic imaging inside living organisms. These range from analyzing neuronal cellular biology in brain tissue to studying muscle physiology and disease to the early detection of various forms of cancer. Kahn hopes to now pursue the challenge of creating a flexible single-fiber endoscope.