Radiative transfer equation and its diffusion approximation in the frequency domain technique: a comparison

Ilya V. Yaroslavsky; Hans-Joachim Schwarzmaier M.D.; Anna N. Yaroslavsky; Valery V. Tuchin

doi:10.1117/12.200856

31 January 1995 Radiative transfer equation and its diffusion approximation in the frequency domain technique: a comparison

Ilya V. Yaroslavsky, Hans-Joachim Schwarzmaier M.D., Anna N. Yaroslavsky, Valery V. Tuchin

Author Affiliations +

Proceedings Volume 2326, Photon Transport in Highly Scattering Tissue; (1995) https://doi.org/10.1117/12.200856
Event: International Symposium on Biomedical Optics Europe '94, 1994, Lille, France

Abstract

In this work, we present a comparison of two approaches (the rigorous transfer equation and its diffusion approximation) to describe the frequency dependence of the modulation and the phase shift of scattered light for the problem of diffuse reflection form a semi-infinite medium with isotropic scattering. It is shown that both approaches lead to the same results, when the modulation frequency of the incident light is low with respect to the inverse time-of-flight between two interaction sites. At increased frequencies, however, these two models reveal differences in their predictions. Besides, the diffusion approximation fails even qualitatively to describe angular dependence of the modulation and the phase shift of back scattered radiation. The photon migration process in tissue is also influenced by the finite (non-zero) life-time of photons in the virtually absorbed state during the scattering process. Most of the existing models assume that this life-time is neglectably short. However, in dense scattering media, like in most biological tissues, this time can be comparable with the time-of-flight between two interaction sites. We also investigated this effect on the frequency dependence of the modulation and the phase shift. The results let us conclude that both -- the diffusion approximation and the assumption of short life-times in the virtually absorbed state -- should be applied with caution when using frequency domain data to determine optical properties of biological tissues especially when using high modulation frequencies. This is also true for the application of this technique in optical tomography.

Citation Download Citation

Ilya V. Yaroslavsky, Hans-Joachim Schwarzmaier M.D., Anna N. Yaroslavsky, and Valery V. Tuchin "Radiative transfer equation and its diffusion approximation in the frequency domain technique: a comparison", Proc. SPIE 2326, Photon Transport in Highly Scattering Tissue, (31 January 1995); https://doi.org/10.1117/12.200856

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