Yu, T.Zhu, DanGenina, Elina A.Oliveira, LuísBashkatov, A.NTuchin, V.V2022-02-242022Yu T., Zhu D., Oliveira L., Genina E.A., Bashkatov A.N., Tuchin V.V. (2021) Tissue optical clearing mechanisms. In: Tuchin V.V., Zhu D., Genina E.A. (eds). Handbook of Tissue Clearing: New Prospects in Optical Imaging. (Ch. 1, pp. 3-29). CRC Press, London 2021. ISBN 9780367895099, ISBN 9781003025252 (ebook), Chapter DOI: 10.1201/9781003025252.9780367895099http://hdl.handle.net/10400.22/20053The high scattering and absorption of opaque tissues limit the penetration of light into deep tissues, limiting the imaging depth of various optical imaging techniques. The proposed tissue optical clearing technique provides an innovative way to perform deep-tissue imaging. Recently, various optical clearing methods have been developed. They result in tissue clearing with similar physical principles but different chemical approaches. This chapter will introduce the mechanisms of the current tissue optical clearing methods, ranging from fundamental physical to chemical perspectives, including the main physical principle, refractive index matching; and chemical approaches such as dissociation of collagen, dehydration, delipidation, decalcification, and hyperhydration to reduce scattering, as well as the use of decolorization to reduce absorption.engOptical clearingDeep-tissue imagingbook part10.1201/97810030252529781003025252