A fiber optic probe design to measure depth- limited optical properties in-vivo with Low-coherence Enhanced Backscattering (LEBS) Spectroscopy

Abstract

Low-coherence enhanced backscattering (LEBS) spectroscopy is an angular resolved backscattering technique that is sensitive to sub-diffusion light transport length scales in which information about scattering phase function is preserved. Our group has shown the ability to measure the spatial backscattering impulse response function along with depth-selective optical properties in tissue ex-vivo using LEBS. Here we report the design and implementation of a lens-free fiber optic LEBS probe capable of providing depth-limited measurements of the reduced scattering coefficient in-vivo. Experimental measurements combined with Monte Carlo simulation of scattering phantoms consisting of polystyrene microspheres in water are used to validate the performance of the probe. Additionally, depth-limited capabilities are demonstrated using Monte Carlo modeling and experimental measurements from a two-layered phantom.

Rectal Optical Markers for In Vivo Risk Stratification of Premalignant Colorectal Lesions

“…1C have previously been described in other publications (30, 31). In short, the LEBS probe (assembled by OFS, Avon, CT; schematic in Fig.…”

“…We next established that this diagnostic signal is the result of synergistic changes in the epithelial cells and surrounding stroma (i.e., $\downarrow {\mu }_s^{\ast }$ and $\uparrow D$ in both compartments) (23). Armed with these observations ex-vivo , we developed the minimally invasive LEBS probe to optimally interrogate the alterations in-vivo (30) .…”

“…In order to control the spatial coherence (L sc ) of the illumination and thereby limit the tissue depths that are interrogated, the illumination fiber core diameter is set to 50 μm and a 9 mm glass rod separates the fiber array from the tissue surface. This configuration results in L sc = 27 μm at 700 nm illumination corresponding to superficial penetration depths between ~100-150 μm (30, 32). …”

“…To calculate ${\mu }_s^{\ast }$, we make the assumption that the anisotropy factor g = 0.9 in colonic mucosa (36). We then employ empirical relations derived using Monte Carlo simulation to calculate ${\mu }_s^{\ast }=-7133c{m}^{-1}\cdot E^{\prime }+3762.5c{m}^{-1}\cdot E^{\prime }\cdot D-4.53c{m}^{-1}$ (35), where E ' is the average of the intensities measured at −0.6° and +0.6° minus the intensity at +1.12° (30, 35). Before applying these equations, the value of E ' was first multiplied by a constant calibration factor of 0.31 to achieve agreement between experiment and Monte Carlo simulation.…”

“…Moreover, we demonstrated that these optical changes contained excellent diagnostic potential with an overall accuracy of 89.5% for advanced adenomas (21). In order to translate these findings into the clinic for in-vivo application, we developed a minimally invasive 3.4 mm diameter fiber-optic LEBS probe optimized for detecting the previously observed changes (30). We therefore hypothesize that the changes previously measured ex-vivo should also be detectable in-vivo .…”