Nonlinear spectroscopic multimodal instrumentation for tissue imaging

Abstract

Multimodal nonlinear imaging techniques have proven to be a versatile tool to understand morpho-chemical properties of tissues and biomaterials. Illuminating a sample with strong laser fields gives rise to a variety of nonlinear processes. The corresponding imaging modalities are inherently label-free, non-invasive, and have intrinsic z-sectioning capabilities. By choosing appropriate wavelengths, the resulting signals can be assigned to specific molecules and structures and a combination of techniques thus provides deep insight into a samples structure and composition. Our research focuses on implementations of two-photon excited fluorescence (TPEF) arising from autofluorophores such as NADH, second harmonic generation (SHG) which can be used to specifically address non-centrosymmetric compounds like collagen/myosin, and coherent anti-Stokes Raman scattering (CARS) as a tool for imaging lipids and certain biomolecules like vitamin A. \nParticularly interesting is the establishment of multimodal nonlinear microscopy for medical purposes. Investigating tissues of different morpho-chemistry like human spinal disk, dura mater, liver, and colon underlines the versatility and high potential of this imaging approach, e.g. to distinguish between healthy tissue and tissue altered by mechanical stress, drugs, diseases, or tumors.\nTranslating the knowledge gained from pathological sections and in-vitro measurements to bulk and in-vivo samples eventually helps to overcome the boundary between research and diagnostics/intraoperative application. To bring multimodal nonlinear imaging from university to clinics, setups adapted to clinical needs will be introduced within this presenation. In the past years, miniaturization and innovative optical components promoted rapid progress in custom-designed small, flexible, and sterilizable setups for fast, easy, and high-resolution imaging applicable to a broad scope of questions. Examples from our group are the compact microscope MediCARS as well as our recent developments in the field of endoscopic fiber probe designs for multimodal nonlinear microscopy such as all-optical multi-core, or piezo-tube controlled double-core-double-cladding scanning fiber probes.