Visualizing Epithelial Expression in Vertical and Horizontal Planes With Dual Axes Confocal Endomicroscope Using Compact Distal Scanner

The epithelium is a thin layer of tissue that lines hollow organs, such as colon. Visualizing in vertical cross sections with sub-cellular resolution is essential to understanding early disease mechanisms that progress naturally in the plane perpendicular to the tissue surface. The dual axes confocal architecture collects optical sections in tissue by directing light at an angle incident to the surface using separate illumination and collection beams to reduce effects of scattering, enhance dynamic range, and increase imaging depth. This configuration allows for images to be collected in the vertical as well as horizontal planes. We designed a fast, compact monolithic scanner based on the principle of parametric resonance. The mirrors were fabricated using microelectromechanical systems (MEMS) technology and were coated with aluminum to maximize near-infrared reflectivity. We achieved large axial displacements <inline-formula> <tex-math notation="LaTeX">$> 400~\mu \text{m}$ </tex-math></inline-formula> and wide lateral deflections >20°. The MEMS chip has a <inline-formula> <tex-math notation="LaTeX">$3.2\times2.9$ </tex-math></inline-formula> mm² form factor that allows for efficient packaging in the distal end of an endomicroscope. Imaging can be performed in either the vertical or horizontal planes with <inline-formula> <tex-math notation="LaTeX">$430~\mu \text{m}$ </tex-math></inline-formula> depth or <inline-formula> <tex-math notation="LaTeX">$1 \times 1$ </tex-math></inline-formula> mm² area, respectively, at 5 frames/s. We systemically administered a Cy5.5-labeled peptide that is specific for EGFR, and collected near-infrared fluorescence images ex vivo from pre-malignant mouse colonic epithelium to reveal the spatial distribution of this molecular target. Here, we demonstrate a novel scanning mechanism in a dual axes confocal endomicroscope that collects optical sections of near-infrared fluorescence in either vertical or horizontal planes to visualize molecular expression in the epithelium.