Advances in Distal-Scanning Two-Photon Endomicroscopy for Biomedical Imaging

Two-photon endomicroscopy (2PEM), an endomicroscopic imaging technique based on the two-photon excitation effect, provides several technical benefits, including high spatiotemporal resolution, label-free structural and metabolic imaging, and optical sectioning. These characteristics make it extremely promising for biomedical imaging applications. This paper classifies distal-scanning 2PEMs based on their actuation mechanism (PZT or MEMS) and excitation–collection optical path configuration (common or separate path). Recent representative advancements are reviewed. Furthermore, we introduce its biomedical applications in tissue, organ, and brain imaging with free-behaving mice. Finally, future development directions for distal-scanning 2PEM are discussed.