Anisotropy of light propagation in biological tissue

Abstract

We investigated the propagation of light in biological tissues that have aligned cylindrical microstructures (e.g., muscle, skin, bone, tooth). Because of pronounced anisotropic light scattering by cylindrical structures (e.g., myofibrils and collagen fibers) the spatially resolved reflectance exhibits a directional dependence that is different close to and far from the incident source. We applied Monte Carlo simulations, using the phase function of an infinitely long cylinder, to explain quantitatively the experimental results. These observations have consequences for noninvasive determination of the optical properties of tissue as well as for the diagnosis of early tissue alterations.

Imaging 2D optical diffuse reflectance in skeletal muscle

“…A previous model [4] based on Mie scattering of infinite cylinder can produce similar rhombus patterns. However, in their simulation the pattern became elliptic when the measurement location was only ~2 mm away from the light incident point.…”

“…This is likely caused by the aforementioned method we applied to handle the fibrous effects, which may only be valid in the diffuse region. Better results might be produced if the cylindrical geometry [4] of muscle fiber is considered. …”

“…Several methods have been developed to study light propagation in such anisotropic media. Kienle et al applied the Mie scattering of infinite cylinder in a Monte Carlo model to study photon migration in dentin and artery tissues [3,4]. Heino et al [5] introduced a diffuse tensor to replace the usual scalar coefficient in diffuse equation to describe the anisotropic diffusion process.…”

Lateral light transfer ensures efficient resource distribution in symbiont-bearing corals

“…Anisotropic light transfer results from light travelling between discrete tissue layers (i.e. optical boundaries) of different refractive indices, where photons crossing these boundaries are redirected because of Fresnel reflection (Kienle et al, 2004). If photons are travelling at very low angles relative to the boundaries, they can be total internally reflected in cases where tissue layers differ in their refractive index.…”

Lateral light scattering in fibrous media

“…Anisotropic directional dependent scattering can for example be modelled by using phase functions derived from an analytical solution of electromagnetic scattering by an infinite cylinder [7]. This was first proposed by Kienle et al [8,9] who observed the anisotropic shapes of backscattered point spread functions (PSF) for different stochastic representations of the cylinder alignments. Similar Monte Carlo simulations have since then been used to model light scattering in anisotropic structures such as biological tissue [10,11], softwood [12] and textile [13].…”