Abstract
We present a novel angle-resolved low coherence interferometry scheme for rapid measurement of depth-resolved angular scattering distributions to enable determination of scatterer size via elastic scattering properties. Depth resolution is achieved using a superluminescent diode in a modified Mach-Zehnder interferometer with the mixed signal and reference fields dispersed by an imaging spectrograph. The spectrograph slit is located in a Fourier transform plane of the scattering sample, enabling angle-resolved measurements over a 0.21 radian range. The capabilities of the new technique are demonstrated by recording the distribution of light scattered by a sub-surface layer of polystyrene microspheres in 40 milliseconds. The data are used to determine the microsphere size with good accuracy. Future clinical application to measuring the size of cell nuclei in living epithelial tissues using backscattered light is discussed.
Highlights
Angle-resolved low coherence interferometry (a/LCI) has been developed as a means to obtain sub-surface structural information by examining the angular distribution of scattered light [1,2,3]
The a/LCI technique combines the ability of low coherence interferometry to detect singly scattered light from sub-surface sites with the capability of light scattering methods to obtain structural information with sub-wavelength precision and accuracy [2,4]. a/LCI has been successfully applied to measuring cellular morphology in tissues [3] and in vitro [4] as well as diagnosing intraepithelial neoplasia [5] and assessing the efficacy of chemopreventive agents [6] in an animal model of carcinogenesis
The data are ensemble averaged by integrating over one mean free path (MFP)
Summary
Angle-resolved low coherence interferometry (a/LCI) has been developed as a means to obtain sub-surface structural information by examining the angular distribution of scattered light [1,2,3]. Recent implementations of Fourier (spectral) domain optical coherence tomography (OCT) have obtained high quality images with high frame rates [10,11,12] While these new OCT implementations achieve 2–3 μm resolution, which is insufficient for quantitative comparisons of cellular features, light scattering based techniques can obtain structural information with sub-wavelength precision and accuracy [2,4]. The use of an imaging spectrograph to examine the angular distribution of light scattered by biological tissues was introduced by Kim, et al [13] and later applied to Pyhtila and Wax study neoplasia in an animal model of carcinogenesis [14] These studies did not achieve depth resolution, as they only detected scattered intensity and focused on bulk tissue properties and absorptive spectral features. The results are discussed in the context of future application of faLCI to probe nuclear morphology of sub-surface cells
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