Researchers from TU Dresden in Germany have developed a new ultrathin lensless endoscope for biomedical applications. Their work demonstrates that the endoscope, only 200 microns in diameter, can self-calibrate and adjust its focus to perform 3D imaging. This exciting development can be used for optogenetic applications, as well as monitoring cells and tissues.
Typical endoscopes use a combination of cameras, lenses, optical fibers, and light sources in order to visualize internal body structures. New technology has enabled researchers to develop ultra-thin lensless endoscopes. Yet, these new optical designs are very prone to temperature fluctuations and bending / twisting of the optical fiber. In order address these limitations, the TU Dresden researchers developed a novel method for calibrating such ultra-thin endoscopes.
The way that the endoscope and calibration method work is as follows: The endoscope consists of an optical fiber bundle that is about 350 microns wide, and has 10,000 optical fiber cores. The researchers stimulate a central optical fiber core, which illuminates a thin glass plate at the tip of the endoscope. This light is then collected by the other optical fibers in the bundle, allowing the researchers to quantify how light is being emitted and collected by the scope. This feature of the scope, dubbed the “optical transfer function,” can change due to positioning and bending of the scope, and has to be calibrated and checked on the fly during imaging experiments.
The team coupled their self-calibrating method with an adaptive lens and a galvanometer mirror to adjust the focal length of the endoscope. This allows them to not only image one point in front of the scope, but to scan around it as well.
The researchers utilized their device to image a 3D specimen. They scanned the image plane in 13 steps over 400 microns. While they were able to successfully image particles at the top and bottom of the specimen, the focus of the device deteriorated to image particles in the middle of the sample. Future work will focus on addressing this limitation.
According to Juergen W. Czarske, professor at TU Dresden and lead author on the paper, “The lensless fiber endoscope is approximately the size of a needle, allowing it to have minimally invasive access and high-contrast imaging as well as stimulation with a robust calibration against bending or twisting of the fiber. The novel approach enables both real-time calibration and imaging with minimal invasiveness, important for in-situ 3D imaging, lab-on-a-chip-based mechanical cell manipulation, deep tissue in vivo optogenetics, and key-hole technical inspections”.
The technology is slated to be presented at the Frontiers in Optics + Laser Science (FIO + LS) conference next month in Washington, D.C.