Optical Clearing and Tissue Imaging

Abstract

Imaging methods are a powerful tool for diagnostic purposes. In this chapter, the most important light-imaging methods, their advantages, and drawbacks are described. The advantages of radiation-free light-based imaging methods relative to traditional radiation methods, such as X-ray, magnetic resonance, or positron emission imaging, are indicated, and the recent advances to improve probing depth, contrast, and resolution in thick tissues are demonstrated. Some historical aspects and recent improvements in light-imaging methods, such as optical coherence tomography, speckle-imaging, second harmonic generation, or light-sheet microscopies, are presented. Due to the recent combination of optical immersion clearing with light-based imaging methods, several studies have been reported, where high-quality images and 3D reconstruction have been obtained for various tissues, providing an alternative to traditional histology or histopathology methods. The purpose of optical clearing is to reduce light scattering, but tissue clearing is obtained through three mechanisms: tissue dehydration, refractive index matching, and protein dissociation. This last mechanism leads to a reduction in the intensity of protein fluorescence, which can be a disadvantage in fluorescence imaging methods. The selection of certain clearing protocols that minimizes or eliminates protein dissociation has been made by some researchers, and a review of such literature is made in the various sections of this chapter.