Abstract

The effect of a clear layer at the surface of a diffusive medium on measurements of reflectance and transmittance has been investigated with Monte Carlo simulations. To quantify the effect of the clear layer Monte Carlo results have been fitted with the solution of the diffusion equation for the homogeneous medium in order to reconstruct the optical properties of the diffusive medium. The results showed that the clear layer has a small effect on measurements of transmittance. On the contrary measurements of reflectance are greatly perturbed and the accurate reconstruction of the optical properties of the diffusive medium becomes almost impossible.

© 2004 Optical Society of America

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References

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Appl. Opt. (1)

J Opt Soc Am A (2)

J. Ripoll, M. Nieto-Vesperinas, S. R. Arridge, and H. Dehghani, �??Boundary conditions for light propagation in diffusive media with nonscattering regions,�?? J Opt Soc Am A 17, 1671-1681 (2000).
[CrossRef]

H. Dehghani, S. R. Arridge, M. Schweiger, and D. T. Delpy, �??Optical tomography in the presence of void regions,�?? J Opt Soc Am A 17, 1659-1670 (2000).
[CrossRef]

J. Opt. Soc. Am. A (1)

Opt. Express (1)

Phys. Med. Biol. (4)

M. Firbank, S. R. Arridge, M. Schweiger, and D. Delpy, �??An investigation of light transport through scattering bodies with non-scattering regions,�?? Phys. Med. Biol. 41, 767-783 (1996).
[CrossRef] [PubMed]

H. Kawaguchi, T. Hayashi, T. Kato, and E. Okada, �??Theoretical evaluation of accuracy in position and size of brain activity obtained by near-infrared topography,�?? Phys. Med. Biol. 49, 2753-2765 (2004).
[CrossRef] [PubMed]

F. Martelli, M. Bassani, L. Alianelli, L. Zangheri, and G. Zaccanti, �??Accuracy of the diffusion equation to describe photon migration through an infinite medium: numerical and experimental investigation,�?? Phys. Med. Biol. 45, 1359-1374 (2000).
[CrossRef] [PubMed]

S. R. Arridge, M. Cope, and D. T. Delpy, �??The theoretical basis for the determination of optical pathlengths in tissue: temporal and frequency analysis,�?? Phys. Med. Biol. 37, 1531-60 (1992).
[CrossRef] [PubMed]

Phys. Rev. A (1)

J. X. Zhu, D. J. Pine, and D. A. Weitz, �??Internal reflection and diffusive light in random media,�?? Phys. Rev. A 44, 3948-59 (1991).
[CrossRef] [PubMed]

Phys. Rev. E (1)

D. J. Durian, �??Influence of boundary reflection and refraction on diffusive photon transport,�?? Phys. Rev. E 50, 857-66 (1994).
[CrossRef]

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Figures (6)

Fig. 1.
Fig. 1.

Dependence of the time resolved transmittance on the thickness of the transparent walls of the cell containing the diffusive medium. The medium has sd =40 mm, µs =1 mm-1, µa =0.003 mm-1, nd =1.33, ncl =1.49, and ne =1.

Fig. 2.
Fig. 2.

Absorption and reduced scattering coefficients retrieved from data of Fig. 1 by the fit with the solution of the DE for the homogeneous medium as a function of the thickness of the transparent walls.

Fig. 3.
Fig. 3.

Dependence of the time resolved reflectance on the thickness of a clear layer at the surface of a semi-infinite diffusive medium having: µ s =1 mm-1, µa =0.01 mm-1, nd =1.33, ncl =1.49, and ne =1. The results have been reported for four values of the distance of the receiver from the light beam.

Fig. 4.
Fig. 4.

Absorption and reduced scattering coefficients retrieved from data of Fig. 3 by the fit with the solution of the DE for the homogeneous medium as a function of the thickness of the clear layer.

Fig. 5.
Fig. 5.

Dependence of the time resolved reflectance on the optical properties of a clear layer 10 mm thick at the surface of a semi-infinite diffusive medium having: µ s =1 mm-1, µa =0.01 mm-1, nd =1.33, ncl =1.49, and ne =1. The results have been reported for three combinations of µ scl and µacl , and for two values of the distance of the receiver from the light beam.

Fig. 6.
Fig. 6.

Absorption and reduced scattering coefficients retrieved from simulations for a diffusive medium having µ s =0.5 mm-1 and µa =0.01 mm-1 by the fit with the solution of the DE for the homogeneous medium as a function of the thickness of the clear layer.

Equations (2)

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z e = 2 3 μ s 1 + 3 0 1 R ( μ ) μ 2 d μ 1 2 0 1 R ( μ ) μ d μ
R ( μ ) = R 12 + R 23 + 2 R 12 R 23 1 R 12 R 23

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