Absorption spectra and light penetration depth of normal and pathologically altered human skin |
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Authors: | V V Barun A P Ivanov A V Volotovskaya V S Ulashchik |
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Institution: | (1) B. I. Stepanov Institute of Physics, National Academy of Sciences of Belarus, 68 Nezavisimosti Ave., 220072 Minsk, Belarus;(2) Belarus Medical Academy of Post-Graduate Education, Minsk |
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Abstract: | A three-layered skin model (stratum corneum, epidermis, and dermis) and engineering formulas for radiative transfer theory
are used to study absorption spectra and light penetration depths of normal and pathologically altered skin. The formulas
include small-angle and asymptotic approximations and a layer-addition method. These characteristics are calculated for wavelengths
used for low-intensity laser therapy. We examined several pathologies such as vitiligo, edema, erythematosus lupus, and subcutaneous
wound, for which the bulk concentrations of melanin and blood vessels or tissue structure (for subcutaneous wound) change
compared with normal skin. The penetration depth spectrum is very similar to the inverted blood absorption spectrum. In other
words, the depth is minimal at blood absorption maxima. The calculated absorption spectra enable the power and irradiation
wavelength providing the required light effect to be selected. Relationships between the penetration depth and the diffuse
reflectance coefficient of skin (unambiguously expressed through the absorption coefficient) are analyzed at different wavelengths.
This makes it possible to find relationships between the light fields inside and outside the tissue.
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Translated from Zhurnal Prikladnoi Spektroskopii Vol. 74, No. 3, pp. 387–394, May–June, 2007. |
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Keywords: | biological tissue skin laser light absorption spectrum penetration depth radiative transfer theory melanin blood |
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