Angle-resolved low coherence interferometry (a/LCI) enables depth-resolved measurements of scattered light that can be used to recover subsurface structural information, such as the size of cell nuclei. Measurements of nuclear morphology, however, can be complicated by coherent scattering between adjacent cell nuclei. Previous studies have eliminated this component by applying a window filter to Fourier transformed angular data, based on the justification that the coherent scattering must necessarily occur over length scales greater than the cell size. To fully study this effect, results of experiments designed to test the validity of this approach are now presented. The a/LCI technique is used to examine light scattered by regular cell arrays, created using stamped adhesive micropatterned substrates. By varying the array spacing, it is demonstrated that cell-to-cell correlations have a predictable effect on light scattering distributions. These results are compared to image analysis of fluorescence micrographs of the cell array samples. The a/LCI results show that the impact of coherent scattering on nuclear morphology measurements can be eliminated through data filtering.
"Notably, the two distributions for samples with ensemble scatterers contain a high frequency modulation of the Mie scattering pattern, a form of coherent interference that contains information about the distance between scatterers. In contrast to speckle phenomena, the modulation term here presents well defined frequencies which do not overlap with the frequency seen for the individual scatterer patterns, provided the mean scatterer separation is greater than the scatterer diameter . In all three scans, excellent qualitative agreement is obtained between the scans. "
[Show abstract][Hide abstract] ABSTRACT: We demonstrate accurate determination of the size and shape of spherical and spheroidal scatterers through inverse analysis of two-dimensional solid-angle and depth resolved backscattered light intensities. Intensity of scattered light is measured over a wide range of solid angles using a novel scanning fiber optic interferometer from both individual and ensembles of scatterers. T-matrix based inverse analysis of these two-dimensional angular measurements yields completely unique size and aspect ratio determinations with subwavelength precision over a large range of possible scatterer geometries.
"Physically, this step removes the contribution to angular scattering arising from coherent scattering by neighboring cell nuclei, which are necessarily spaced at distances greater than the cell size. This effect was explored and characterized in a previous study , which systematically varied cell spacing to show that the a/LCI analysis method was able to make accurate size determinations in the presence of coherent scattering by adjacent cell nuclei. In the human tissue studies described later, the filtering step is accomplished automatically by the analysis software. "
[Show abstract][Hide abstract] ABSTRACT: The combination of low-coherence interferometry with angle-resolved light scattering measurements has been shown to be a powerful method for determining the structure of cell nuclei within intact tissue samples. The nuclear morphology data have been used as a biomarker of neoplastic change in a wide range of settings. Here, we review the development of angle-resolved low-coherence interferometry (a/LCI) for assessing the health status of human esophageal epithelial tissues based on depth-resolved measurements of the morphology of cell nuclei. The design and implementation of clinical instrumentation are reviewed, and results from ex vivo human tissue measurements are presented to validate the capabilities of the technique. In addition to the review of earlier papers, new results are presented, which demonstrate the first application of a portable a/LCI system with a flexible endoscopic probe to assessing depth-resolved nuclear morphology in a clinical setting. High sensitivity for the detection of precancerous tissues is demonstrated.
IEEE Journal of Selected Topics in Quantum Electronics 02/2008; 14(1-14):88 - 97. DOI:10.1109/JSTQE.2007.913969 · 2.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present spectroscopic swept-source optical coherence tomography (OCT) measurements of the phase-dispersion of cell samples. We have previously demonstrated that the phase of the scattered field is, in general, independent of the intensity, and both must be measured for a complete characterization of the sample. In this paper, we show that, in addition to providing a measurement of the size of the cell nuclei, the phase spectrum provides a very sensitive indication of the separations between the cells. Epithelial cancers are characterized by many factors, including enlarged nuclei and a significant loss in the architectural orientation of the cells. Therefore, an in vivo diagnostic tool that analyzes multiple properties of the sample instead of focusing on cellular nuclei sizes alone could provide a better assessment of tissue health. We show that the phase spectrum of the scattered light appears to be more sensitive to cell spacing than the intensity spectrum. It is possible to determine simultaneously the cell nuclei sizes from the intensity spectrum and the nuclei spacing from the phase spectrum. We measure cell monolayer samples with high and low cell density and compare measured results with histograms of the cell separations calculated from microscope images of the samples. We show qualitative agreement between the predicted histograms and the interferometric results.
Proceedings of SPIE - The International Society for Optical Engineering 01/2007; DOI:10.1117/12.701239 · 0.20 Impact Factor
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