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. In this study, an aqueous solution of glucose (40%) is added to rabbit sclera in vitro, where depth-resolved permeability coefficients and optical clearing are calculated with OCT. The permeability rate in regions in the upper 80- to 100-microm region is found to be different from that of regions in the deeper 100-microm region: (6.01+/-0.37)x10(-6) cmsec and (2.84+/-0.68)x10(-5) cmsec, respectively. A difference in percent clearing is also noted. Optical clearing of the upper region is about 10% and increased to 17 to 22% in the one beneath. These results demonstrate the capability of OCT-based methods to not only measure the diffusion rate and optical clearing of a tissue, but also its ability of functional differentiation between layers of epithelial tissues.

Abstract. Noninvasive cardiovascular imaging could lead to the early detection and timely treatment of complex atherosclerotic lesions responsible for major cardiovascular events. Recent investigations have suggested that optical coherence tomography ͑OCT͒ is an ideal diagnostic tool due to the high resolution this technology achieves in discriminating the different features of atherosclerotic lesions based on structural imaging. We explore the capability of OCT for functional imaging of normal and atherosclerotic aortic tissues based on time-and depth-resolved quantification of the permeability of biomolecules through these tissues. The permeability coefficient of 20% aqueous solution of glucose was found to be ͑6.80± 0.18͒ ϫ 10 −6 cm/ s in normal aortas and ͑2.69± 0.42͒ ϫ 10 −5 cm/ s in aortas with atherosclerotic disease. The results suggest that this new OCT functional imaging method-the assessment of the permeability coefficients of various physiologically neutral biomolecules in vascular tissues-could assist in early diagnosing and detecting the different components of atherosclerotic lesions.

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Noninvasive assessments of optical clearing and permeability coefficients of tissues pose great possibilities in advanced diagnostics and medical applications. In order for both of these to become utilized in common practice, a greater understanding of molecular diffusivity in multi-layered tissues is required. In biological tissues, the different layers are comprised of differentiated cells and/or collagen fibrils which come together to form that specific layer. Therefore, a patchwork of layers is created each with its own set of properties. In our current study we analyze and describe the dynamics of matter diffusion and its underlying non-linear character in various epithelial tissues. For instance, the permeability coefficient (PC) of 20% concentrated mannitol in the rabbit eye sclera showed an increasing trend as it was measured deeper into the tissue. The PC was found to be 2.18 × 10 -6 cm/sec at 50 µm away from the epithelial layer. It increased to about 7.33 × 10 -6 cm/sec when it was computed at 210 µm from the epithelial layer. Different layers in the sclera showed different clearing response to glucose solution as well. The first 100 µm region from the epithelial layer cleared about 10% whereas the next 100 µm cleared about 17-22%. The importance of this study is that it may offer a novel explanation to how a layer's composition affects optical clearing and the permeability coefficient of analytes and solutions.