We developed techniques in low coherence enhanced backscattering spectroscopy (LEBS) that can probe low order scattering events (1, 2, 3 order events events) in disordered dielectric medium (including tissue). 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, 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.

Application of LEBS technique to cancer detection:
We have applied LEBS technique to charecterize the nano-scale morphological changes in a cell in early carnimegenesis and we are also designing probes for in-vivo cancer detection for different types of cancers: Colon, pancreatic, etc.

Some important basic results Using LEBS technique:
(1) It is well known in the theoretical literature that a double scattering event is the minimum event for the coherent backscattering effect to occur. However, there has been no experimental proof of this fundamental theoretical claim, even though the coherent backscattering effect has been known for three decades. We have recently demonstrated this prediction for the first time by using a low coherence light source in very weakly scattering media. Using co- and cross-polarized light in our LEBS configuration, we isolated a parameter regime where we were able to isolate double scattering events from the higher order scattering.
(2) Furthermore, we were able to plot a phase diagram in the relevant parameter space which shows a fixed point that separates the double scattering events from the multiple scattering events. The low order scattering events, such as double scatterings, are the most important events for cancer detection in epithelial tissues. This is because light backscattering from epithelial carcinogenic layers is effectively within the double scattering regime. Furthermore, we have derived an analytical expression that gives penetration depth as a function of sample and source parameters.

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Representative Publications

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1. Low-coherence enhanced backscattering of light: characteristics and applications for colon cancer screening
   Y. Kim, Prabhakar Pradhan, V. Turzhitsky, H. Subramanian, Y. Liu, R. K. Wali, H. K. Roy, and V. Backman
   Proc. SPIE 6446 , 644606 (2007)
   Link to the journal   /   PDF
   
   
2. Low-coherence enhanced backscattering: review of principles and applications for cancer screening
   Y. Kim, V. M. Turzhitksy, Yang Liu, Hemant. K. Roy, Ramesh K. Wali, H. Subramanian, Prabhakar Pradhan, and V. Backman
   J. Biomed. Opt 11, 041125 (2006)
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3. Association between Rectal Optical Signatures and Colonic Neoplasia: Potential Applications for Screening
   H. K. Roy, V. Turzhitsky, Y. Kim, M. J. Goldberg, P. Watson, J. D. Rogers, A. J. Gomes, A. Kromine, R. E. Brand, M. Jameel1, A. Bogovejic1, P. Pradhan, and V. Backman
   Cancer Research 69 , 4476 (2009)
   Link to the journal   /   PDF
   
   
4. Circular polarization memory effect in low-coherence enhanced backscattering of light
   Y. Kim, Prabhakar Pradhan, Min H. Kim, and V. Backman
   Opt. Lett. 31, 2744 (2006)
   Link to the journal   /   PDF   /   cond-mat/0607307
   
   
5. Photon random walk model of low-coherence enhanced backscattering (LEBS) from anisotropic disordered media: a Monte Carlo simulation
   H. Subramanian, Prabhakar Pradhan, Y. Kim, Y. Liu, X. Li, V. Backman
   Applied Optics 45, 6292 (2006)
   Link to the journal   /   PDF   /   cond-mat/0508538
   
   
6. Origin of low-coherence enhanced backscattering
   Y. L. Kim, Prabhakar Pradhan, H. Subramanian, Y. Liu, M. Kim, and V. Backman
   Opt. Lett. 31 , 1459(2006);   The Virtual Journal for Biomedical Optics, Vol.1, Iss. 6, (2006);
   Link to the journal   /   PDF