The Role of Mechanical Compression in Human Skin Imaging Using Cross-Polarization Optical Coherence Tomography

Management of biotissue optical properties using cross-polarization optical coherence tomography (CP OCT) enables to acquire additional data on objects under study and can be achieved by applying mechanical compression due to different mechanical and elastic properties of various biotissue layers.

The aim of the investigation was to study the effect of mechanical compression on the formation of in vivo human thin skin CP OCT-images acquired in registered parallel and orthogonal polarizations in relation to initial polarization.

Materials and Methods. In vivo human thin skin was chosen as test object. A series of experiments was carried out to study the effect of skin compression caused by OCT-probe end pressure on contrast of CP OCT-images acquired in parallel and orthogonal polarizations. A group consisted of 7 male volunteers aged 20–50 years with normal skin type, with no pathological changes.

The experiment was performed using an optical coherence tomograph developed by Institute of Applied Physics of the Russian Academy of Sciences (Nizhny Novgorod). Central wavelength of probing radiation was 910 nm, longitudinal resolution — 20 µm, transverse resolution — 25 µm. Probe design enabled to control the force on biotissue at compression using a conjugate dynamometer. A probe diameter was 2.7 mm.

Results. The experiments showed the boundary contrast between layers on CP OCT-images of skin to increase from 3 to 12 dB in parallel and orthogonal polarizations, and from 5 to 12 dB — in orthogonal polarization. Contrast difference at reference time might be related to linear polarization of probing radiation, due to which epidermal and dermal signals are poorly depolarized in relation to initial radiation. In compression, there is a concentration increase of scattering centers in derma resulting in the enhancement of this layer signal and boundary contrast increase, as well as probing radiation depolarization increase due to scattering in this layer, which, in its turn, leads to equalization of contrast values on CP OCT-images in parallel and orthogonal polarizations.
The findings should be taken into consideration when developing the techniques of OCT-diagnosis and interpretation of diagnostic images.

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Agrba P.D., Bakshaeva Е.А., Ellinsky D.О., Shlivko I.L., Kirillin М.Yu. The Role of Mechanical Compression in Human Skin Imaging Using Cross-Polarization Optical Coherence Tomography. Sovremennye tehnologii v medicine 2014; 6(1): 75