Characterization of Light Transport in Scattering Media at Subdiffusion Length Scales with Low-Coherence Enhanced Backscattering

Abstract

Low-coherence enhanced backscattering (LEBS) is a technique that has recently shown promise for tissue characterization and the detection of early pre-cancer. Although several Monte Carlo models of LEBS have been described, these models have not been accurate enough to predict all of the experimentally observed LEBS features. We present an appropriate Monte Carlo model to simulate LEBS peak properties from polystyrene microsphere suspensions in water. Results show that the choice of the phase function greatly impacts the accuracy of the simulation when the transport mean free path (ls*) is much greater than the spatial coherence length (L SC ). When ls* < L SC , a diffusion approximation based model of LEBS is sufficiently accurate. We also use the Monte Carlo model to validate that LEBS can be used to measure the radial scattering probability distribution (radial point spread function), p(r), at small length scales and demonstrate LEBS measurements of p(r) from biological tissue. In particular, we show that pre-cancerous and benign mucosal tissues have different small length scale light transport properties.

Measurement of optical scattering properties with low-coherence enhanced backscattering spectroscopy

“…(1) because a number of experimentally obtained results are in good agreement with the approach. 17,18 In a typical LEBS experiment, a circular aperture acts as the secondary source resulting in a first order Bessel function of the first kind as the coherence function. The two-dimensional backscattering distribution p(r, ϕ) [p( r ) = p(r, ϕ)], where ϕ is the polar azimuth angle in the interface plane, is therefore sampled by c(r, ϕ).…”

“…LEBS is capable of measuring the reflectance distribution at small scattering distances (i.e., separations between incident and collected ray pairs well below the transport mean free path length or even the mean free path length) resulting in a high sensitivity to the phase function. 17 Furthermore, the capability for spectroscopic measurements allow LEBS to measure optical properties such as μ a with depth selectivity. 18 In this work, we will present a methodology for how LEBS can be used to measure μ * s and two parameters of the scattering phase function (g and m).…”

Mechanical assessment of bovine pericardium using Müeller matrix imaging, enhanced backscattering and digital image correlation analysis

“…This contraction leads to a rearrangement of the collagen fibers along the horizontal direction thus increasing the number of scatterers (fibers) per unit of volume. Hence, the scattering force within the sample increases along with the MFP [10]. This may be related to the intrafibrillar structure of collagen, and has been directly observed during mechanical tests by means of small-angle X-ray scattering (SAXs) measurements [20].…”

“…The EBS cone is then registered using a lens with a focal length of 45 mm and the 1024x768 CCD. This configuration provides a resolution of 0.1 mrad with no moving parts once adjustments on the alignment have been completed [10]. Conventional images are recorded using white light illumination for subsequent processing using DIC.…”

“…This allows for obtaining an experimental measurement of the MFP for a sample upon evaluation of the width of the angular distribution of the backscattered intensity. In our experiments, the intensity recorded in each pixel of the CCD was mapped to the scattering angle considering both, the pixel width and the focal length as described in [10]. Subsequently, Eq.…”