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22 February 2019 Index of refraction estimation using dual-angle optical coherence tomography
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The index of refraction (n) is an intrinsic parameter of materials and tissues that has recently been proven useful as a biomarker for the diagnosis disease. It can also serve as a source of optical contrast for imaging and provides invaluable information on disease and cell dynamics for studies in various fields such as hematology, oncology, etc. There are many methods to experimentally measure n, e.g. using prisms or interferometers. Optical coherence tomography (OCT) has also been used in the past to measure the index ex vivo. However, the methodologies reported to date are not appropriate for in vivo imaging since they require either a mirror below the sample or an otherwise complicated imaging setup and algorithm. In this summary, we propose a new measurement technique that could be deployed for in vivo estimation of n. This technique uses two OCT images obtained at different incidence angles. The path-lengths observed, in the sample, are different in the two images and directly depend on n. Measuring the path length changes and the incidence angles can provide an estimate of the index. The dual-angle method was validated experimentally using both clear and scattering samples. The resulting measurements of n were within a mean of ~1 % of the expected values. These initial results are promising and provide evidence that this method should be further investigated and validated on human tissues so that, in the future, it could be developed into a clinically useful diagnostic tool.
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Christos Photiou and Costas Pitris "Index of refraction estimation using dual-angle optical coherence tomography", Proc. SPIE 10867, Optical Coherence Tomography and Coherence Domain Optical Methods in Biomedicine XXIII, 108673S (22 February 2019);

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