Low-coherence enhanced backscattering (LEBS) spectroscopy

Enhanced backscattering (EBS) otherwise known as coherent backscattering is a fascinating optical phenomenon that gives rise to the enhancement of light backscattering in random media in directions close to the backscattering. EBS originates from the weak localization of light in random medium leading to the constructive interference of photons traveling time-reversed paths. Although EBS in non-biological media has generated substantial research interest, observing EBS in biological tissue has been extremely difficult. Thus, this phenomenon has awaited its applications in tissue optics over the last two decades. Our group was the first to report an experimental observation of an extension of EBS, enhanced backscattering with spatially low coherent illumination (LEBS). LEBS occurs when the spatial coherence length of illumination is smaller than the mean free path length of light in the medium. We found that the use of low-coherent light lifts all main limitations so far impeding the use of EBS for tissue characterization.

We can record LEBS as a function of wavelength and develop LEBS spectroscopy for tissue characterization. LEBS offers unique advantages including non-invasive tissue analysis, depth-resolution (it is particularly useful to interrogate mucosae, the origin of 90% of cancers), and unique sensitivity to tissue microarchitecture. We are developing LEBS spectroscopy and LEBS tomography for the detection and diagnosis of some of the earliest precancerous changes in tissue.

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Backman's Biophotonics Laboratory at Northwestern University

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