Influence of refractive index matching on the photon diffuse reflectance

Abstract

Photon migration in a randomly inhomogeneous, highly scattering and absorbing semi-infinite medium with a plane boundary is considered by a Monte Carlo (MC) technique. The employed MC technique combines the statistical weight scheme and real photon paths simulation, allowing the exclusion of the energy conservation problem. The internal reflection of the scattered radiation on the medium interface is taken into account by allowing the trajectories of photon packets to be split into reflected and transmitted parts. The spatial photon sensitivity profile (SPSP), spatially resolved diffuse reflectance and angular and spatial photon detector weight distributions are considered in terms of Fresnel's reflection/refraction on the boundary of the medium. The effect of the refractive index match is predicted correctly by the MC method and by the diffusion approximation. The results demonstrate that matching of the refractive index of the medium significantly improves the contrast and spatial resolution of the spatial photon sensitivity profile (SPSP). The results of simulation of the spatially resolved diffuse reflectance agree well with the results predicted by the diffusion approximation and the experimental results reported earlier.

Analysis of skin tissues spatial fluorescence distribution by the Monte Carlo simulation

“…The internal photon packet reflection/refraction on the medium boundary are taken into account by splitting the photon packet into the reflected and the transmitted parts [30,32]. This procedure is important for the shallow probing of skin tissues [29,32].…”

Photon-cell interactive Monte Carlo model based on the geometric optics theory for photon migration in blood by incorporating both extra- and intracellular pathways

“…(8) are stored in the look-up table. For example, if the table contains only k = 1, reflection occurs at the entry point and the photon does not enter the intra-cellular space giving Q 1 = R 1 .…”

“…If k is 2 or greater, Q k indicates the probability of photon escaping from the intracellular space at the k'th interaction point. The internal reflection profile reported by Churmakov et al 8 is applied to calculate Q k (k 2) as follows:…”

“…[2][3][4][5][6][7] Among them, the MCML (MC maximum likelihood) developed by Wang et al 7 simulated migration process of photons in multilayered tissues that comprised of homogeneous layers with different optical properties, where the internal reflection at the plane boundaries was expressed using geometric optics. Similarly, Churmakov et al 8 in 2002 verified the importance of refractive index matching at the boundary to model diffuse reflectance by splitting the photon packets into reflection and refraction at the boundary based on the geometric optics. For randomly inhomogeneous polydisperse scattering media, such as sprays, aerosols, smoke, fog, and foams, Berrocal and Meglinski 9 in 2005 characterized the medium by different extinction coefficients and phase functions.…”

“…28 The interaction of photons at the plasmacell boundary of a randomly oriented three-dimensional (3-D) biconcave RBC is modeled using the geometric optics. A single photon-cell interaction model of Lugovtsov et al, 29 who applied the Snell's and Fresnel's laws to model interactions at the boundary of an optically soft spheroidal particle, and the MC code of Churmakov et al, 8 who compiled the internal reflection profile at the plane boundary, are utilized to model interactions between photons and biconcave RBCs. We developed MC code pciMC without requiring macroscopic scattering phase function and the anisotropy factor g to compute photon migration time and optical density for a given blood medium by accounting for both the intra-and extracellular migration pathways.…”