Abstract:Background and Objectives: Optical clearing of dura mater caused by hyperosmotic immersion liquids is important for the development of noninvasive methods of brain optical tomography and for the study of microcirculation and homeostasis of tissue fluids. It allows significantly increasing the spatial resolution and the probing depth of brain. Obviously, a quantitative description of the optical clearing processes requires the development of reliable physicomathematical models, which in turn requires the knowledge of the diffusion rate parameters of immersion agents in tissues. In spite of the fact that diffusion of many biocompatible chemicals, in particular glucose, in aqueous solutions is well described, their diffusion in tissues continues to be poorly investigated. Thus, the goal of the study is estimation of the relative glucose diffusion coefficient in the human dura mater in vitro. Materials and Methods: The method of estimating the relative diffusion coefficient of immersion liquids in tissues was based on the analysis of the kinetics of the change in the collimated transmittance of a tissue sample under the action of these liquids. The kinetics of the interstitial fluid replacement by immersion liquid was measured by successive recording of collimated transmittance spectra in the spectral range of 400–700 nm. For a quantitative description of the process, a corresponding model that assumed a constant diffusion coefficient in the entire volume of the tissue sample was developed. Results: In the study the results of the experiments, performed for a 40%-glucose solution, are presented. The relative diffusion coefficient of glucose in dura mater obtained using the approximation of the experimental data within the framework of the proposed model, was 6.08$\times$10$^{-6} \pm$ 2.26$\times$10$^{-8}$ cm$^2$/s. Based on Fick's first law, the coefficient of permeability of the dura mater for the glucose solution was calculated, the value of which was (1.3$\pm$0.13)$^{-4}$ cm/s. Conclusion: The obtained results can be used in the development of new and optimization of existing non-invasive methods of optical tomography as well as for the development of methods of laser therapy and surgery of various brain diseases.
Keywords:diffusion coefficient, dura mater, glucose, control of tissue optical properties.
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