Depth-resolved measurements in multi-layer scattering media using linearly and elliptically polarized reflectance spectroscopy
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Optical reflectance spectroscopy is a non-invasive tool that can provide quantitative information on tissue morphology and biochemistry. However, interpreting the depth-dependent signals from multi-layer tissue can be challenging as optical signatures are from a range of depths. The focus of this dissertation is on the development of light-based systems for the depth-resolved characterization of multi-layered tissue. Specifically, this dissertation concentrates on the assessment of polarized reflectance spectroscopy (PRS) with linearly and elliptically polarized light. PRS is a form of elastic scattering spectroscopy that relies on polarization gating to selectively isolate polarization maintaining photons in order to probe superficial depths. Polarization gating relies on the observation that as light travels deeper into a turbid medium and undergoes scattering, the incident polarization will become depolarized. Polarization-sensitive techniques for imaging and spectroscopy have received attention for their relatively simple and low-cost instrumentation to favorably collect either superficial or deep penetration photons. In this dissertation, I will present a fiber optic probe that combines polarization gating with linearly polarized light and an oblique detection geometry via multiple beveled collection fibers to detect scattering within various depths in tissue. The performance of the oblique polarized reflectance spectroscopy (OPRS) probe was evaluated in a clinical trial of oral cavity cancer. I will also discuss in this dissertation a new system based on elliptical polarization. The probing depth of elliptical polarized reflectance spectroscopy (EPRS) was assessed in turbid media by tuning the ellipticity of polarized light.