Design and test of a rigid endomicroscopic system for multimodal imaging and femtosecond laser ablation

Abstract

Significance: Conventional diagnosis of laryngeal cancer is normally made by a combination of endoscopic examination, a subsequent biopsy, and histopathology, but this requires several days and unnecessary biopsies can increase pathologist workload. Nonlinear imaging implemented through endoscopy can shorten this diagnosis time, and localize the margin of the cancerous area with high resolution.

Aim: Develop a rigid endomicroscope for the head and neck region, aiming for in-vivo multimodal imaging with a large field of view (FOV) and tissue ablation.

Approach: Three nonlinear imaging modalities, which are coherent anti-Stokes Raman scattering, two-photon excitation fluorescence, and second harmonic generation, as well as the single photon fluorescence of indocyanine green, are applied for multimodal endomicroscopic imaging. High-energy femtosecond laser pulses are transmitted for tissue ablation.

Results: This endomicroscopic system consists of two major parts, one is the rigid endomicroscopic tube 250 mm in length and 6 mm in diameter, and the other is the scan-head ($10\times 12\times 6{\mathrm{cm}}^3$ in size) for quasi-static scanning imaging. The final multimodal image accomplishes a maximum FOV up to $650\mu m$, and a resolution of $1\mu m$ is achieved over $560\mu m$ FOV. The optics can easily guide sub-picosecond pulses for ablation.

Conclusions: The system exhibits large potential for helping real-time tissue diagnosis in surgery, by providing histological tissue information with a large FOV and high resolution, label-free. By guiding high-energy fs laser pulses, the system is even able to remove suspicious tissue areas, as has been shown for thin tissue sections in this study.

Keywords: endomicroscope; indocyanine green imaging; microsurgery probe; nonlinear imaging; optical biopsy; tissue ablation.