Download Angular scattering properties of human epidermal layers

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)
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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
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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)
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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
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