We present an ultra-simple miniature fiber optic probe to measure spatially and spectrally resolved diffuse reflectance in the sub-diffuse regime (i.e. measurements with source-detector separation less than a transport mean free path) in-vivo. This probe has a robust and simple design with a small footprint (<.5 mm diameter). We show that our probe has sensitivity to structures scattering light an order of magnitude smaller than the diffraction limit, and thus can be used to quantify alterations in the very smallest structures in tissue (e.g. organelles, chromatin, collagen fibers, etc.). Specifically, the probe samples the spatial profile of diffuse reflectance in the sub-diffusion regime (P(r), r<<1 mm). P(r) can be used to quantify the entire shape of the phase function, F(θ). The shape of the refractive index correlation function Bn(rd) (through which the spatial distribution of mass is defined) can be analytically derived from the shape of F(θ) through application of the Born approximation. Therefor measurements of P(r) can elucidate F(θ) and Bn(rd). This ability has tremendous potential for use as a diagnostic tool and broad applications for probing the nanoscale environment of tissue in-vivo.
Adam Eshein, Wenli Wu, The-Quyen Nguyen, Andrew J. Radosevich, and Vadim Backman, "A fiber optic probe to measure spatially resolved diffuse reflectance in the sub-diffusion regime for in-vivo use
(Conference Presentation)," Proc. SPIE 9703, Optical Biopsy XIV: Toward Real-Time Spectroscopic Imaging and Diagnosis, 970317 (Presented at SPIE BiOS: February 17, 2016; Published: 26 April 2016); https://doi.org/10.1117/12.2211432.4848650685001.
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