Engineers at Stanford have demonstrated a high-resolution endoscope that is as thin as a human hair with a resolution four times better than previous devices of similar design.

Their prototype can resolve objects about 2.5 microns in size, and a resolution of 0.3 microns is easily within reach. A micron is one thousandth of a millimeter. By comparison, today’s high-resolution endoscopes can resolve objects only to about 10 microns. The naked eye can see objects down to about 125 microns.

The opportunity and the challenge, Kahn and Solgaard knew, rested in multimode fibers in which light travels via many different paths, known in optics as modes; hence the name, multimode fiber. Light is very good at conveying complex information through such fibers—whether computer data or images—but it gets scrambled potentially beyond recognition along the way.

Kahn devised a way to undo the scrambling of information by using a miniature liquid crystal display called a spatial light modulator. To make this possible, Kahn and his graduate student, Reza Nasiri Mahalati, developed an adaptive algorithm—a specialized computer program—by which the spatial light modulator learned how to unscramble the light. Several years before, Kahn had set world records for transmission speeds using a similar trick to unscramble computer data transmitted through multimode fibers.

In Kahn’s 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, in turn, measures the reflected power of the light and uses algorithms developed by Nasiri Mahalati and fellow graduate student Ruo Yu Gu to reconstruct an image.

Kahn and his students were stunned to discover their endoscope could resolve four times as many image features as the number of modes in the fiber.

The team wrestled with the paradox for several weeks before they came up with an explanation. The random intensity patterns mix the modes that can propagate through the fiber, increasing the number of modes fourfold and producing four times as much detail in the image.

Kahn and team have created a working prototype. The main limiting factor at this point is that the fiber must remain rigid. Bending a multimode fiber scrambles the image beyond recognition. Instead, the fiber is placed in a thin needle to hold it rigid for insertion.

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.

This story is reprinted from material from
Stanford Engineering, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.