| Imaging of biological tissues with optical coherence tomography (OCT) poses a great interest for its capability to noninvasively outline subsurface microstructures within tissues. However, a major limitation for many optical imaging techniques is inadequate depth penetration of light in turbid media, which is bounded to just a few millimeters. There have been several attempts to improve light penetration depth in biological tissues, including application of different tissue optical clearing methods.Photonic technology in medical imaging, diagnosis and treatment is the current international hot spots of research. The main limiting factor is the light scattering of the biological tissue that restricts light to penetrate the depth of tissue, limiting the scope of application, reducing the optical (microscopic) imaging depth, resolution, contrast ratio and the efficiency of laser treatment.The effect of ultrasound [surgeon-performed (SP)] on the changes in optical properties and some possible mechanism was investigated. In the paper, Clearing capability of glycerol was much improved with the simultaneous application of ultrasound with a frequency of 1 MHz and a power of 0.75W over a 3 cm probe. Adult cavy'skin of abdomen was chosen to comparatively studied by Optical coherence tomography (OCT) and scanning electronic microscope (SEM) with optical clearing agents in combination with ultrasound. The OCT results found that the 1/e light penetration depth of epidermis and dermis increases by roughly 8.61% from the native to the optically cleared state with 60% G at 30 min,The most significant effect was seen where skin was treated with the combination of 60%G and ultrasound, resulting in a 18.61% increase of optical clearing, meanwhile, the results derived from the OCT signal slope also demonstrate the similar conclusion. The results show that ultrasound enhanced the optical clearing of the cavy skin greatly. The SEM results demonstrated that ultrasound disrupts the highly ordered lipid structure of stratum corneum (SC) and makes the structure of SC loose, which causes the outermost cell of SC easy to exfoliate and decreases the barrier function of skin for the transdermal absorption of optical clearing agents (OCA),which enhances the effect of optical clearing of skin tissue.Functional imaging, monitoring and quantitative description of glucose diffusion in epithelial and underlying stromal tissues in vivo and controlling of the optical properties of tissues are extremely important for many biomedical applications including the development of noninvasive or minimally invasive glucose sensors as well as for therapy and diagnostics of various diseases, such as cancer, diabetic retinopathy, and glaucoma. The diffusion of glucose was studied in pig sclera tissues in vitro. Because OCT provides depth-resolved imaging of tissues with high in-depth resolution, the glucose diffusion is described as a function of depth.We demonstrate the capability of the optical coherence tomography (OCT) technique for depth-resolved monitoring and quantifying of glucose diffusion in pig sclera tissues. The depth-resolved and average permeability coefficients of glucose were calculated. We found that the glucose diffusion rate is not uniform and nonlinear throughout the tissue in the lateral depth and is decreased from approximately (3.5±0.062)×10-6m/s at the start point of lateral diffusion to (1.9887±0.049)×10-6m/s close to the inner side of the sclera with the topical application of 10% glycerol(10%G), from (3.5417±0.061)×10-6m/s to (1.2333±0.041)×10-6m/s with the topical application of 20%G, from (4.0833±0.075)×10-6m/s to (1.1984±0.061)×10-6m/s with the topical application of 40%G . Results demonstrated that the OCT technique is capable of depth-resolved monitoring and quantification of glucose diffusion in sclera.In this study, optical coherence tomography(OCT) was utilized in the functional imaging of glucose axial diffusion through scleral tissues. Permeability coefficients for different concentrations of glucose were quantified nondestructively. Obtained results indicate an inverse proportionality between the permeability coefficnt and the concentration of the analyte in epithelial tissues: in-depth diffusion of solutions with lower glucose concentration was faster than those with a higher concentration. The permeability coefficient decreased from (1.596±0.051)×10-5 cm/s of 10% glucose solution to (4.247±0.504)×10-6 cm/s of 40% glucose solution. The dependence of the permeability on the concentration of hyperosmotic analytes could potentially be used in various basic sciences and clinical fields, such as optical clearing of tissues and cells as well as in clinical pharmacology.The presented results encourage us to believe that OCT is an effective tool for studying permeability and analytes (including drug) diffusion in tissues, both in specified regions and at different tissue depths. Our future studies will be focused on development of a theoretical model of analyte diffusion in different scleral compartments (based on the size, distribution, and orientation of collagen fibrils). However, since it has been previously shown that hydration plays a key role in the study of the diffusion rate, our future experiments will be conducted in vivo to eliminate the hydration factor. |
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