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Angular scattering properties of human epidermal layers A.N.Yaroslavskaya1 , S.R.Utz1'2, S.N.Tatarintsev1, V.V.Tuchin1 1 - Saratov State University, Astrakhanskaya Str. ,83, Saratov 410071 , Russia; 2 -- Laboratory of Optical and Laser Methods of Diagnostics and Therapy, Institute of Rural Hygiene, Chemyshevskogo Str., 1 35, Saratov 410071 , Russia 1 .INTRODUCTION There is a defmite need to determine accurately optical parameters of tissues. It is required either when planning a laser treatment or trying to make diagnostic conclusions, based on differences in optical properties of healthy and pathological tissues. Scattering phase function is an important characteristic of medium optical properties1.Knowledge of scattering phase function of epidermal layers is necessary for direct calculations of light propagation through skin2. Changes in angular properties of scattered light may reflect pathology of tissue and can be used in investigation of skin diseases, like psoriasis3. Besides the self4mportance measurements of scattering phase function can be used in combination with integrating sphere measurements to determine absorption and scattering coefficients of tissue4. This combination can also be useful for testing of photoprotectors. Direct gomometric measurements of the angular distribution of radiation, scattered by human samples have been reported by several authors5'6. However, known literature data on angular scattering properties of human epidermis are still liniited7'8. In present paper we concentrate on outermost epidermal layers and report measurements, performed on samples, obtained by the novel technique3. We investigated also influence of various chemical's applications to skin surface on scattering phase function of epidermal layers. 2.MATERIALS AND METHODS The measurements have been performed on the set-up, principal scheme of which is presented in Fig.l. He-Ne laser (A.=632.8 mm, model LGN 201A, Russia) was used as a light source. Detector was a photon-counting system, based on the photomultiplying tube FEU-79 (Russia). The whole system was controlled by a personal computer. Epidermal sample was placed between quartz hemisphere in order to avoid refraction of both incident and scattered lights. The measurements have been performed in the range O06O0 with step 10. Used epidermal samples were selected to satisfy the following requirements: 1 .diameter > 2 cm; 2. no visible defects. Thickness of the samples was measured by a micrometer and varied from 20-30 xm (accuracy 2 p.m). All investigated epidermal samples have been obtained from internal surface of forearm of healthy volunteers. 38 ISPIE Vol. 2100 Cell and Biotissue Optics(1994) 0-8194-1383-6/94/$6.00 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/18/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx 1 2 3 Fig. 1 . Scheme of the set-up for scattering phase function measurements. 1 He-Ne laser; 2 - quartz slide; 3 - epidermal sample; 4 - quartz hemisphere; 5- detector. The amsotropy factor (mean value of scattering cosine) g was estimated for each sample by of fitting experimentaldata with the Henyey-Greeej function, which has been proven to be a good approximationfor scattering phase function of tissues: (1—g2) p(e)HG=_L_ 4ic (1 + g2 2g cos0)3/2' — where ® is scattering angle. Because of steep decrease of intensity of scattered light with increase of ®, only OO3Øo angle range was used for fitting. ,RESULTS AND jM$çjjssjos Fig.2 a-d exemplifies results on scattering phase function measurements for a normal epidermal sample and for epidermal samples after application of various chemicals. Table SUflimarjzeS collected data for subsequent epidermal layers. Obtained average value of g for normal epidermis is slightly higher, than it was reported in 8 One possible explanation for this fact is that we used thimier samples in our experiments, so contribution of multiple scattering was lower. As one can see from Table, there is no visible dependence of g on depth, excluding higher value of g for Stratum corneum. However, more investigations are required for final conclusion on this matter. The results show that application of psoralen or Vaseline to skin surface leads to reducing of anisotropy factor, which is probably caused by decreasing of effective refractive index of scatters in respect to surrounding medium. At the same time, application of 1 % Metilen blue water solution does not change angular charactestics of scattering, but just increase's absorption coefficient of epidermis. SP1E Vol. 2100 Ce/land Biotissue Optics (1994) / 39 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/18/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx I(e)/I(2) I(e)/I(2) 0.8 gO.89 gO.84 0.6 0.4 0 I 5 15 10 20 25 0 30 5 10 15 0, deg 0 deg a b 20 25 30 I/I(2) I)/1(2) 1 0 0.8 g=O.85 g*O.86 0.6 0.4 0 0.2 0 5 10 15 20 25 0 deg C 30 5 15 10 20 0, deg d Fig.2. Measured scattering phase functions of epidermal samples. 0 experimental; --R-- Henyey-Greenstein function approximation. a - normal epidermis; b - epidermis after vaseline application; c - epidermis after 1% metilene blue application; d - epidermis after psoralen application. 40 ISPIE Vol. 2100 Ce/land Biotissue Optics (1994) Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/18/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx 25 30 Table Mean value of scattering cosine for different epidermal layers Number of Normal epidermis Epidermis with psoralen Epidermis with Vaseline Epidermis with 1% Metilen blue ith 0.91 0.87 0.88 0.90 2nd 3rd 4th 5th Mean 0.89 0.85 0.88 0.87 0.85 0.84 0.85 0.91 0.86 0.85 0.92 0.87 0.86 0.85 0.86 0.89 0.86 0.85 0.89 epidermal strippigs 0.87 We have performed our measurements on a set-up that enables also polarization-.dependent measurements of scattered light. This allows to determine full Muller-matrix of the sample. The work in this direction is now in progress. 4.REFERENCES A.Ishimaru,"Wave propagation and scattering in random media", New York : Academic Press, 1978. 1. 2. M.Keijzer, J.M.Pickering, M.J.C.van Gemert, "Laser beam diameter for port wine stain treatment", Las.Surg.Med., vol.11, pp.601-605, 1991. 3. V.V.Tuchin, S.R.Utz, I.V.Yaroslavsky, "Skin optics: modeling of light transport and measuring of optical parameters", In: Medical Optical Tomography:Functionai Imaging and Monitoring (G.Muller, ed.), SPIEInst. 5cr., vol. IS 11, pp.234-258, 1993. P.van der Zee, "Methods for measuring the optical properties of tissue samples in the visible and near-infrared wavelength range", Ibid., pp. 166-192. 4. 5. W.A.Bruls, J.C. van der Leun, "Forward scattering properties of human epidermal layers", Photochem.PhotobjoJ. , vol.40, pp.23 1 —242, 1984. 6. S.L.Jacques, C.A.Alter, S.A.PhaKl, "Angular dependence of He-Ne laser light scattering by human dermis", Las.Life ScL, vol.1, pp.309-333, 1987. W.-F. Cheong, S.A.Prahl, A.J. Welch, "A review of the optical properties of biological tissues", IEEEJ.Quantum Electr., vol.26, pp.2166-2185, 1990. 8. M.J.C. van Gemert, S.L.Jacques, H.J.C.M. Sterenbogr, W.M.Star, "Skin Optics", IEEE Trans. 7. Biomed.Eng., vol.36, pp.1146-1154, 1989. SPIE Vol. 2 1 00 Cell and Biotissue Optics (1 994) I 41 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 02/18/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx