Depth-resolved measurement of mucosal microvascular blood content using 
low-coherence enhanced backscattering spectroscopy

Abstract

Low-coherence enhanced backscattering (LEBS) spectroscopy is a light scattering technique which uses partial spatial coherence broadband illumination to interrogate the optical properties at sub-diffusion length scales. In this work, we present a post-processing technique which isolates the hemoglobin concentration at different depths within a sample using a single spectroscopic LEBS measurement with a fixed spatial coherence of illumination. We verify the method with scattering (spectralon reflectance standard and polystyrene microspheres) and absorbing (hemoglobin) phantoms. We then demonstrate the relevance of this method for quantifying hemoglobin content as a function of depth within biological tissue using the azoxymethane treated animal model of colorectal cancer.

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

“…A discussion of how absorption measurements can be obtained from an LEBS peak is presented elsewhere. 18 The LEBS angular distribution can be calculated as the twodimensional Fourier transform of the radial reflectance intensity distribution, p( r ):…”

“…18,26 Equation (1) is a generalization of the conventionally known Fourier transform relationship between the enhanced backscattering angular distribution and the spatial distribution of light backscattered from a random medium illuminated by an infinitely narrow collimated beam [ p( r )]. 27,28 Therefore, a simulation of LEBS can be accomplished by utilizing the Monte Carlo method to obtain p( r ) and then applying Eq.…”

“…(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).…”

“…The measurement of absorption from LEBS is a separate topic that is described elsewhere. 18 This results in P(r )dr = 1 for any value of l * s , constraining the values of P(r ) at r < l * s to be approximately inversely proportional to l * s . In other words, a medium with a longer l * s will have a broader and shorter P(r ) with identical area.…”

“…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). LEBS spectroscopy has previously been shown to have promise for the detection of several types of epithelial cancers.…”