Major Optical Clearing Mechanisms
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The optical immersion clearing is an effective method to reduce light scattering in tissues, but to optimize each treatment, it is necessary to understand the mechanisms involved. Since these treatments are intended to be temporary, it is also important to know if the mechanisms involved are reversible. Various studies have been made to evaluate and characterize the mechanisms of optical clearing. In all cases studied, two major mechanisms were observed—the tissue dehydration and the refractive index matching mechanisms. Some particular studies have reported that the agents used in treatments also dissolve proteins and suggested that protein dissolution is also a clearing mechanism. All these mechanisms have been reported as reversible, both on ex vivo or on in vivo studies. We make an analysis on these studies and present a method based on ex vivo collimated transmittance and thickness measurements to characterize the major clearing mechanisms—tissue dehydration and refractive index matching. Although this method can only be made with ex vivo tissues, alternative measurements are suggested for in vivo characterization of the clearing mechanisms.
KeywordsOptical clearing agents Dehydration mechanism Refractive index matching Collagen solubility Water flux out OCA flux in
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