Abstract
The evaluation of the optical clearing mechanisms in tissues provides information about the efficiency of the clearing treatment. One of such mechanisms is the refractive index matching, which is created by the partial replacement of tissue water by an optical clearing agent with higher refractive index, better matched to the index of tissue scatterers. With the objective of evaluating the refractive index matching mechanism for a wide spectral range and comparing its magnitude between treatments with different clearing agent osmolarities, thickness and collimated transmittance measurements were obtained from human colorectal muscle samples under treatment with 20%-, 40% and 60%-glycerol. Such measurements were used in a calculation model to obtain the refractive index kinetics for the interstitial fluid and for the whole tissue. The calculation results show that the refractive index matching has a stronger effect in the ultraviolet and that such matching is more effective for higher agent concentrations in the treating solutions.
Highlights
Introduction and theoretical backgroundSince its rediscovery about 30 years ago [1], the research related to the Optical immersion Clearing (OC) technique has produced a large number of publications [2], which continues to grow significantly
This study demonstrated that the magnitude of these windows increases with the optical clearing agents (OCAs) concentration in the treating solution [37], which suggests that higher OCA concentrations provide a higher magnitude refractive index (RI) matching in the UV range
In a previous study by our group [39], we have evaluated the RI matching mechanism in the visibleNIR range in skeletal muscle under treatment with glucose and ethylene glycol solutions, showing that both the RI of the interstitial fluid (ISF) and of the whole tissue increase as a result of the applied OC treatments
Summary
Since its rediscovery about 30 years ago [1], the research related to the Optical immersion Clearing (OC) technique has produced a large number of publications [2], which continues to grow significantly Some of those studies were made to evaluate, discriminate and characterize the mechanisms of OC [2,3,4,5,6,7,8], while others evaluated the diffusion properties of the optical clearing agents (OCAs) in tissues [9,10,11,12,13,14,15,16], or described such diffusion as a molecular-based model [17,18]. One of such studies was reported by Lagerweijt et al [26], where fluorescence confocal imaging, two-photon imaging, photoacoustic imaging and image reconstruction of optically cleared tissues have allowed to discriminate between normal and infiltrating glioblastoma brain tumors in rats
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