Flexible-type ultrathin holographic endoscope for microscopic imaging of unstained biological tissues

Abstract

Lensless fibre endoscopes are minimally invasive, but are often rigid and require calibration and fluorescence labelling. Here, the authors present a flexible endoscope based on a bare fibre bundle and a lensless Fourier holographic imaging configuration to detect weak reflections from unstained biological tissues. Ultrathin lensless fibre endoscopes offer minimally invasive investigation, but they mostly operate as a rigid type due to the need for prior calibration of a fibre probe. Furthermore, most implementations work in fluorescence mode rather than label-free imaging mode, making them unsuitable for general medical diagnosis. Herein, we report a fully flexible ultrathin fibre endoscope taking 3D holographic images of unstained tissues with 0.85-mu m spatial resolution. Using a bare fibre bundle as thin as 200-mu m diameter, we design a lensless Fourier holographic imaging configuration to selectively detect weak reflections from biological tissues, a critical step for label-free endoscopic reflectance imaging. A unique algorithm is developed for calibration-free holographic image reconstruction, allowing us to image through a narrow and curved passage regardless of fibre bending. We demonstrate endoscopic reflectance imaging of unstained rat intestine tissues that are completely invisible to conventional endoscopes. The proposed endoscope will expedite a more accurate and earlier diagnosis than before with minimal complications.