Assessment of tissue viability by polarization spectroscopy |
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Authors: | G Nilsson C Anderson J Henricson M Leahy J O’Doherty F Sjöberg |
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Institution: | 1.Department of Biomedical Engineering,Link?pings Universitet,Link?ping,Sweden;2.Department of Biomedicine and Surgery,Link?ping University Hospital,Link?ping,Sweden;3.Department of Medicine and Care,Link?ping University Hospital,Link?ping,Sweden;4.Department of Physics,University of Limerick,Limerick,Ireland |
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Abstract: | A new and versatile method for tissue viability imaging based on polarization spectroscopy of blood in superficial tissue
structures such as the skin is presented in this paper. Linearly polarized light in the visible wavelength region is partly
reflected directly by the skin surface and partly diffusely backscattered from the dermal tissue matrix. Most of the directly
reflected light preserves its polarization state while the light returning from the deeper tissue layers is depolarized. By
the use of a polarization filter positioned in front of a sensitive CCD-array, the light directly reflected from the tissue
surface is blocked, while the depolarized light returning from the deeper tissue layers reaches the detector array. By separating
the colour planes of the detected image, spectroscopic information about the amount of red blood cells (RBCs) in the microvascular
network of the tissue under investigation can be derived. A theory that utilizes the differences in light absorption of RBCs
and bloodless tissue in the red and green wavelength region forms the basis of an algorithm for displaying a colour coded
map of the RBC distribution in a tissue. Using a fluid model, a linear relationship (cc. = 0.99) between RBC concentration
and the output signal was demonstrated within the physiological range 0–4%. In-vivo evaluation using transepidermal application
of acetylcholine by the way of iontophoresis displayed the heterogeneity pattern of the vasodilatation produced by the vasoactive
agent. Applications of this novel technology are likely to be found in drug and skin care product development as well as in
the assessment of skin irritation and tissue repair processes and even ultimately in a clinic case situation. |
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Keywords: | tissue viability imaging red blood cells polarization spectroscopy vasodilatation vasoconstriction |
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