Optical immersion as a new tool for controlling the optical properties of tissues and blood

This paper aims to review the basic principles, recent results, advantages, limitations, and future of the optical immersion method as applied to clearing of the naturally turbid biological tissues and blood. The refractive index matching concept for enhancement of in-depth light and laser beam penetration into tissues and blood is discussed on the basis of in vitro and in vivo studies using optical spectroscopy and polarization and coherence-domain techniques. The optical properties of tissues with basic multiple scattering, which are transformed to a low scattering mode, are analyzed. It is shown that light reflection, transmission, scattering, and polarization can be effectively controlled. The diagnostic abilities of the method based on contrasting abnormalities, on the in-depth profiling of tissue and blood, and on the monitoring of endogenous and exogenous matter diffusion within tissues are demonstrated.