Water Content and Scatterers Dispersion Evaluation in Colorectal Tissues

Optical clearing treatments reduce light scattering in biological tissues. Due to the heterogeneous composition of tissues, such high scattering is created by the refractive index mismatch between tissue fluids and scatterers. With the objective of collecting experimental data to predict and characterize the magnitude of the refractive index matching in optical clearing treatments, a series of studies were performed with colorectal tissues. The free water content in normal mucosa, muscle and pathological colorectal tissues was estimated, showing similar values for normal tissues and about 5% more in pathological tissue. The refractive index of the tissues was measured at various wavelengths between UV and NIR. This data was used to estimate the refractive dispersion curves for the various tissues, which were then combined with the free water contents to calculate the dispersion of scatterers in these tissues. These dispersions remain unchanged during optical clearing and by obtaining such spectral data, it is possible to quantify and characterize the refractive index matching mechanism in any optical clearing treatment to be applied in these tissues. The differences obtained between the experimental data of healthy and pathological tissues can also be used as a marker for cancer progression in ex vivo analysis.