Reconstruction of digits from 1951 USAF resolution target. Actual images of the objects taken with a IR camera are shown in the left column; reconstruction results are shown in the right. (Source: Optics Letters, Vol. 41, Issue 5, pp. 886-889)
An endoscopy is a vital technique for imaging the interior of the human body. Using a tube outfitted with a light and camera, a doctor can see, for example, whether you’re suffering from an ulcer, internal bleeding, or colon polyps. Though current endoscopic tools are effective, doctors and researchers are investigating micro-endoscopic tools to reduce both the invasiveness of the procedure and the potential for complications. Image resolution and field-of-view are critical to the viability of micro-endoscopy as a diagnostic tool. Without a clear picture, a doctor could get a diagnosis wrong, resulting in more suffering for their patient. However, as the tool tip gets smaller it becomes more and more difficult to collect high quality images.
To address these issue, engineers in the Department of Electrical and Computer Engineering at Johns Hopkins University have demonstrated a two-dimensional imaging technique using a single-mode fiber, which has the potential to improve visibility in a micro-endoscopy. The team reported their findings in the journal Optics Letters.
“What we showed is that by coating the tip of a single-mode fiber with a scattering medium—white paint—we can generate spatial patterns that randomly but deterministically measure many points in an image at once,” says Mark Foster, assistant professor of electrical and computer engineering at Johns Hopkins University and one of the authors on the paper. “Furthermore, by changing the wavelength of the illumination light the patterns change. We showed that by knowing what the patterns are and how they depend on wavelength we can compute an image of what we are observing without physically moving the fiber tip.”
Standard micro-endoscopes use a multi-core fiber, and each core transmits information from a single pixel of an object image. However, the image resolution is limited due to the number cores in a fiber bundle. Using a single-mode fiber is a novel approach, due to the fact that single-mode fibers do not convey spatial information and cannot be used to collect image information without mechanically scanning the fiber. The device developed by the team is mechanically scan-free.
“The mechanical devices used to scan a fiber tip are relatively large and if we can avoid needing them then we could make endoscopes much smaller,” says Foster.
Though the research represents a big step forward, there is still more work to be done.
“We still have work to do before we can apply this technique to endoscopy. Primarily, we need to come up with ways of efficiently collecting the light back through the fiber, but in principle it is possible,” says Foster.
This research was supported by funding from the National Science Foundation (ECCS-1254610). Other authors in the paper included Jaewook Shin and Bryan T. Bosworth, both with the Department of Electrical and Computer Engineering at Johns Hopkins University.