1. Date of download: 6/2/2016 Copyright © 2016 SPIE. All rights reserved. Drawing of the distal face of the fiber ferrule. The OIR source fiber is located at the 12:00 position at a center-to-center spacing from the central fiber bundle of 0.6 mm. Four single-mode fibers (placed around the circumference of the fiber bundle allow for the possibility of other imaging modalities such as optical coherence tomography (OCT). Figure Legend: From: Oblique incidence reflectometry: optical models and measurements using a side- viewing gradient index lens-based endoscopic imaging system J. Biomed. Opt. 2014;19(6):067002. doi:10.1117/1.JBO.19.6.067002

2. Date of download: 6/2/2016 Copyright © 2016 SPIE. All rights reserved. Top-down illumination-imaging geometry for the OIR endoscope. Light incident on the tissue (gray dot, red online) refracts into the turbid media, and results in a diffuse reflectance profile centered (black cross) some distance, Δr, away. Diffuse reflectance imaged onto the middle 50% of the fiber bundle (left diagonals, shaded blue online) was used to calculate Δr, after which the fiber area was masked with a circular mask (gray circle, red online) of radius 0.6 mm, centered at the point of incident illumination. The resulting fiber area (right diagonals, shaded red online) was used to extract μeff. Figure Legend: From: Oblique incidence reflectometry: optical models and measurements using a side- viewing gradient index lens-based endoscopic imaging system J. Biomed. Opt. 2014;19(6):067002. doi:10.1117/1.JBO.19.6.067002

3. Date of download: 6/2/2016 Copyright © 2016 SPIE. All rights reserved. Simulated FRED analysis plot of diffuse reflectance from a tissue (μa=1 mm−1, μs′=2.5 mm−1, g=0.9) shows irradiance collected by fiber bundle in both longitudinal and azimuthal directions. Figure Legend: From: Oblique incidence reflectometry: optical models and measurements using a side- viewing gradient index lens-based endoscopic imaging system J. Biomed. Opt. 2014;19(6):067002. doi:10.1117/1.JBO.19.6.067002

4. Date of download: 6/2/2016 Copyright © 2016 SPIE. All rights reserved. Optical model of oblique incidence reflectometry (OIR) illumination and collection. The source fiber is moved to a position resulting in 638 nm incident illumination (dark gray, blue online) at 18 deg away from the fiber bundle imaging field-of-view (light gray, pink online) and focused 30 μm inside the tissue with an NA=0.14. Figure Legend: From: Oblique incidence reflectometry: optical models and measurements using a side- viewing gradient index lens-based endoscopic imaging system J. Biomed. Opt. 2014;19(6):067002. doi:10.1117/1.JBO.19.6.067002

5. Date of download: 6/2/2016 Copyright © 2016 SPIE. All rights reserved. For a non-normally incident source, photons travel an average distance, three-dimensional, at a refracted angle, θt, before they are scattered. The peak of the diffuse reflectance profile is shifted by some distance, Δr, and can be sampled at various distances, r, away from the peak, after which Eq. (2) can be fit to the profile. Figure Legend: From: Oblique incidence reflectometry: optical models and measurements using a side- viewing gradient index lens-based endoscopic imaging system J. Biomed. Opt. 2014;19(6):067002. doi:10.1117/1.JBO.19.6.067002

6. Date of download: 6/2/2016 Copyright © 2016 SPIE. All rights reserved. Expected versus calculated effective attenuation coefficients (μeff), offsets, and absorption (μa) and reduced scattering coefficients (μs′) for FRED-simulated tissue optical phantoms and the full OIR endoscope. Measurements of phantoms with mean free paths (mfp′)>0.8 mm (outside design limits) are marked with diamonds, while measurements for those with an mfp′<0.8 mm are marked by squares. Figure Legend: From: Oblique incidence reflectometry: optical models and measurements using a side- viewing gradient index lens-based endoscopic imaging system J. Biomed. Opt. 2014;19(6):067002. doi:10.1117/1.JBO.19.6.067002

7. Date of download: 6/2/2016 Copyright © 2016 SPIE. All rights reserved. Expected versus calculated effective attenuation coefficients (μeff) for tissue optical phantoms experimentally measured with the bare fiber bundle and obliquely incident fiber setup. Measurements of phantoms with mean free paths (mfp′)<0.8 mm are marked with diamonds, while measurements for those with an mfp′<0.8 mm are marked by squares. Figure Legend: From: Oblique incidence reflectometry: optical models and measurements using a side- viewing gradient index lens-based endoscopic imaging system J. Biomed. Opt. 2014;19(6):067002. doi:10.1117/1.JBO.19.6.067002

8. Date of download: 6/2/2016 Copyright © 2016 SPIE. All rights reserved. Expected versus calculated offsets, effective attenuation coefficients (μeff), and absorption (μa) and reduced scattering coefficients (μs′) for tissue optical phantoms experimentally measured with the full OIR endoscope. Measurements of phantoms with mean free paths (mfp′)<0.8 mm are marked with blue diamonds, while measurements for those with an mfp′<0.8 are marked by red squares. Figure Legend: From: Oblique incidence reflectometry: optical models and measurements using a side- viewing gradient index lens-based endoscopic imaging system J. Biomed. Opt. 2014;19(6):067002. doi:10.1117/1.JBO.19.6.067002

9. Date of download: 6/2/2016 Copyright © 2016 SPIE. All rights reserved. Section of 30 mm in vivo mouse colon imaged with OCT and coregistered with OIR measurements. Image is colored with effective attenuation coefficients between 1.35 (blue) and 2.15 mm−1 (red). Figure Legend: From: Oblique incidence reflectometry: optical models and measurements using a side- viewing gradient index lens-based endoscopic imaging system J. Biomed. Opt. 2014;19(6):067002. doi:10.1117/1.JBO.19.6.067002