Improved methods for detecting dysplasia, or pre-cancerous growth, are a current clinical need. Random biopsy and
subsequent diagnosis through histological analysis is the current gold standard in endoscopic surveillance for
dysplasia. However, this approach only allows limited examination of the at-risk tissue and has the drawback of a
long delay in time-to-diagnosis. In contrast, optical scattering spectroscopy methods offer the potential to assess
cellular structure and organization in vivo, thus allowing for instantaneous diagnosis and increased coverage of the
at-risk tissue. Angle-resolved low coherence interferometry (a/LCI), a novel scattering spectroscopy technique,
combines the ability of low-coherence interferometry to isolate scattered light from sub-surface tissue layers with
the ability of light scattering spectroscopy to obtain structural information on sub-wavelength scales, specifically by
analyzing the angular distribution of the backscattered light. In application to examining tissue, a/LCI enables depthresolved
quantitative measurements of changes in the size and texture of cell nuclei, which are characteristic
biomarkers of dysplasia. The capabilities of a/LCI were demonstrated initially by detecting pre-cancerous changes in
epithelial cells within intact, unprocessed, animal tissues. Recently, we have developed a new frequency-domain
a/LCI system, with sub-second acquisition time and a novel fiber optic probe. Preliminary results using the fa/LCI
system to examine human esophageal tissue in Barrett's esophagus patients demonstrate the clinical viability of the
approach. In this paper, we present a new portable system which improves upon the design of the fa/LCI system to
allow for higher quality data to be collected in the clinic. Accurate sizing of polystyrene microspheres and cell
nuclei from ex vivo human esophageal tissue is presented. These results demonstrate the promise of a/LCI as a
clinically viable diagnostic tool.
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.
Angle-resolved low-coherence interferometry (a/LCI) is used to obtain quantitative, depth-resolved nuclear morphology measurements. We compare the average diameter and texture of cell nuclei in rat esophagus epithelial tissue to grading criteria established in a previous a/LCI study to prospectively grade neoplastic progression. We exploit the depth resolution of a/LCI to exclusively examine the basal layer of the epithelium, approximately 50 to 100 µm beneath the tissue surface, without the need for exogenous contrast agents, tissue sectioning, or fixation. The results of two studies are presented that compare the performance of two a/LCI modalities. Overall, the combined studies show 91% sensitivity and 97% specificity for detecting dysplasia, using histopathology as the standard. In addition, the studies enable the effects of dietary chemopreventive agents, difluoromethylornithine (DFMO) and curcumin, to be assessed by observing modulation in the incidence of neoplastic change. We demonstrate that a/LCI is highly effective for monitoring neoplastic change and can be applied to assessing the efficacy of chemopreventive agents in the rat esophagus.
We have developed a novel angle-resolved low coherence interferometry scheme for rapid measurement of depth-resolved angular scattering distributions. These measurements enable the determination of scatterer size via elastic scattering properties. The scheme uses spectral domain measurements where the mixed signal and reference fields are dispersed by an imaging spectrograph to achieve depth-resolved measurements upon Fourier transform of the spectral data. Angle-resolved measurements are obtained by locating the spectrograph slit in a Fourier transform plane of the scattering sample. We discuss the theoretical basis for the measurements and demonstrate the capabilities of the new technique by recording the distribution of light scattered by polystyrene microspheres. The important features of the system include the ability to detect sub-surface scattering distributions and rapid data acquisition with the entire scattering distribution recorded in 40 milliseconds. The data are used to determine the microsphere size with good accuracy. Potential application of the technique to measuring cell nuclei size in living epithelial tissues is discussed.
Angle-resolved low coherence interferometry enables depth-resolved measurements of scattered light. The scattered light measurements can be used to recover structural information from sub-surface layers, 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 data based upon the justification that the coherent scattering must necessarily occur over length scales greater than the cell nucleus size. To fully study this effect, we now present results of experiments designed to test the validity of this approach. We examine light scattered by regular cell arrays, created using stamped adhesive micro-patterned substrates. By varying the array spacing, the influence of cell-to-cell correlations on light scattering distributions is determined. The impact on nuclear morphology measurements within intact tissue samples is discussed.
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