Abstract
An extremely compact all-fiber-optic scanning endomicroscopy system was developed for two-photon fluorescence (TPF) and second harmonic generation (SHG) imaging of biological samples. A conventional double-clad fiber (DCF) was employed in the endomicroscope for single-mode femtosecond pulse delivery, multimode nonlinear optical signals collection and fast two-dimensional scanning. A single photonic bandgap fiber (PBF) with negative group velocity dispersion at two-photon excitation wavelength (i.e. approximately 810 nm) was used for pulse prechirping in replacement of a bulky grating/lens-based pulse stretcher. The combined use of DCF and PBF in the endomicroscopy system made the endomicroscope basically a plug-and-play unit. The excellent imaging ability of the extremely compact all-fiber-optic nonlinear optical endomicroscopy system was demonstrated by SHG imaging of rat tail tendon and depth-resolved TPF imaging of epithelial tissues stained with acridine orange. The preliminary results suggested the promising potential of this extremely compact all-fiber-optic endomicroscopy system for real-time assessment of both epithelial and stromal structures in luminal organs.
Highlights
Two-photon fluorescence (TPF) and second harmonic generation (SHG) microscopy has become a powerful tool for three-dimensional (3D) deep tissue imaging [1,2,3]
This compact all-fiber-optic SHG endomicroscopy system can be potentially used for real-time assessment of collagen fiber network morphology under various clinically relevant conditions for diagnosis and treatment monitoring
A commercially available double-clad fiber was employed in the endomicroscope for femtosecond pulse delivery, nonlinear optical signals collection and fast beam scanning
Summary
Two-photon fluorescence (TPF) and second harmonic generation (SHG) microscopy has become a powerful tool for three-dimensional (3D) deep tissue imaging [1,2,3]. The use of near-infrared radiation in TPF/SHG microscopy, combined with wide-field detection, enhances the sampling depth in highly scattering biological tissues. Despite these attractive features, in vivo TPF and SHG imaging of biological tissues has been mainly limited to skin due to the lack of proper miniature probes to access internal organs. We conducted 3D TPF imaging of pig corneal tissue and rat oral tissue ex vivo (stained with acridine orange) with the rapid 2D en face scanning achieved by a miniature fiber-optic scanner built in the endomicroscope and the slow axial scan achieved by moving the probe with respect to the sample with a precision translation stage. The preliminary results strongly suggested the potential of the all-fiber-optic scanning endomicroscopy system for realtime and in vivo imaging of internal organs
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