Low-coherence enhanced backscattering (LEBS) is a depth-selective self-interference phenomenon that originates from light traveling time-reversed paths in a scattering medium. The depth selectivity of LEBS and its sensitivity to optical properties of the scattering medium has made it a promising technique for probing the structure of biological tissue with applications to disease diagnosis and, in particular, precancerous conditions. The ability to accurately predict the penetration depth of the LEBS signal is important in targeting an optimal tissue depth for detecting precancerous cells. This prediction is further complicated by the variation in optical properties of different tissue types. In this paper, the effects of the reduced scattering coefficient (μs'), the phase function and the instrument spatial coherence length (Lsc) on the LEBS penetration depth are quantified. It is determined that the LEBS penetration depth is primarily dependent on Lsc, μs', and the anisotropy factor (g), but has minimal dependence on higher moments of the phase function. An empirical expression, having a similar form as the double scattering approximation for LEBS, is found to accurately predict the average penetration depth in the multiple scattering regime. The expression is shown to be accurate for a broad range of experimentally relevant optical properties and spatial coherence lengths.
Low-coherence enhanced backscattering (LEBS) is a depth selective technique that allows noninvasive characterization of turbid media such as biological tissue. LEBS provides a spectral measurement of the tissue reflectance distribution as a function of distance between incident and reflected ray pairs through the use of partial spatial coherence broadband illumination. We present LEBS as a new depth-selective technique to measure optical properties of tissue in situ. Because LEBS enables measurements of reflectance due to initial scattering events, LEBS is sensitive to the shape of the phase function in addition to the reduced scattering coefficient (μs*). We introduce a simulation of LEBS that implements a two parameter phase function based on the Whittle-Matérn refractive index correlation function model. We show that the LEBS enhancement factor (E) primarily depends on μs*, the normalized spectral dependence of E (Sn) depends on one of the two parameters of the phase function that also defines the functional type of the refractive index correlation function (m), and the LEBS peak width depends on both the anisotropy factor (g) and m. Three inverse models for calculating these optical properties are described and the calculations are validated with an experimental measurement from a tissue phantom.
The phenomenon of enhanced backscattering (EBS) of light, also known as coherent backscattering (CBS) of light, is a
spectacular manifestation of self-interference effects in elastic light scattering, which gives rise to an enhanced scattered
intensity in the backward direction. Although EBS has been the object of intensive investigation in non-biological
media over the last two decades, there have been only a few attempts to explore EBS for tissue characterization and
diagnosis. We have recently made progress in the EBS measurements of biological tissue by taking advantage of lowcoherence
(or partially coherent) illumination, which is referred to as low-coherence EBS (LEBS) of light. LEBS
possess novel and intriguing properties such as speckle reduction, self-averaging effect, broadening of the EBS width,
depth-selectivity, double scattering, and circular polarization memory effect. After we review the current state of
research on LEBS, we discuss how these characteristics apply for early cancer detection, especially in colorectal cancer
(CRC), which is the second leading cause of cancer mortality in the United States. Although colonoscopy remains the
gold standard for CRC screening, resource constraints and potential complications make it impractical to perform
colonoscopy on the entire population at risk (age > 50). Thus, identifying patients who are most likely to benefit from
colonoscopy is of paramount importance. We demonstrate that LEBS measurements in easily accessible colonoscopically normal mucosa (e.g., in the rectum of the colon) can be used for predicting the risk of CRC, and thus
LEBS has the potential to serve as accurate markers of the risk of neoplasia elsewhere in the colon.
The phenomenon of enhanced backscattering (EBS) of light, also known as coherent backscattering (CBS) of light, has been the object of intensive investigation in nonbiological media over the last two decades. However, there have been only a few attempts to explore EBS for tissue characterization and diagnosis. We have recently made progress in the EBS measurements in tissue by taking advantage of low spatial coherence illumination, which has led us to the development of low-coherence enhanced backscattering (LEBS) spectroscopy. In this work, we review the current state of research on LEBS. After a brief discussion of the basic principle of EBS and LEBS, we present an overview of the unique features of LEBS for tissue characterization, and show that LEBS enables depth-selective spectroscopic assessment of mucosal tissue. Then, we demonstrate the potential of LEBS spectroscopy for predicting the risk of colon carcinogenesis and colonoscopy-free screening for colorectal cancer (CRC).
Although the phenomenon of coherent backscattering (CBS) in non-biological media has generated substantial research interest, observing CBS in biological tissue has been extremely difficult. Thus, this phenomenon has awaited its applications in tissue optics over the last two decades. Here we demonstrate depth-resolved spectroscopic elastic-light scattering measurements in tissue by use of low-coherent backscattering (LCBS) spectroscopy. The depth resolution is achieved by exploiting the nature of the LCBS peak that contains information about a wide range of tissue depths. We further
demonstrate that the depth-resolved LCBS spectroscopy has the potential for identifying the location of the origin of precancerous transformations in the colon at an early, previously undetectable stage.
Coherent backscattering (CBS) is a photon weak-localization phenomenon that gives rise to an enhanced backscattering of light by random media. Although this effect has been previously studied in nonbiological media, there have been only few attempts to use CBS for diagnosis and characterization in living tissue. Here we report spectroscopic CBS measurements (low-coherence CBS spectroscopy) by combining broadband illumination and low-coherence detection. We demonstrate that low-coherence CBS spectroscopy substantially simplifies CBS measurements in biological tissue and enables depth-resolved spectroscopic analysis of CBS. Low-coherence CBS spectroscopy may find important applications in probing biological tissue where depth-selective measurements are crucial. As an example of the potential of CBS for tissue diagnosis, we show that low-coherence CBS spectroscopy can be used to detect the earliest, previously undetectable, preadenomatous stages of colorectal carcinogenesis.
Accelerated proliferation of smooth muscle cells (SMC) is known to play an integral role in atherosclerotic lesion formation. Thus, there has been significant interest in defining both positive and negative regulators of SMC growth. We have applied a novel optical technique referred to as four-dimensional light scattering fingerprinting (4D-ELF) that enables non-invasive assessment of living cells. 4D-ELF can serve for highly sensitive detection of slight alterations in cellular and subcellular microstructure. Using 4D-ELF, we characterized the proliferation of SMC grown on two different substrates: laminin and fibronectin. Fibronectin-grown SMC have been previously shown to be more proliferative. Our results indicate that light scattering can be used to monitor the changes in the intracellular structure caused by the cell-substrate interaction and differentiate between more and less proliferative SMCs. Thus, light scattering fingerprinting may potentially provide a quick, inexpensive, and accurate means to noninvasively characterize the proliferation of living cells as well as cell-biomaterial interaction.
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