<p>Diffuse reflectance spectroscopy (DRS) is a simple, yet powerful technique that has the potential to offer practical, non-invasive, and cost effective information for op- tical diagnostics and therapeutics guidance. Any progress towards moving DRS systems from their current laboratory settings to clinical settings, field settings and ambitiously to home settings, is a significant contribution to society in terms of reducing ever growing healthcare expenditures of an aging society. Additionally, im- proving on the existing mathematical models used to analyze DRS signals; in terms of speed, robustness, accuracy, and capability in accounting for larger feature space dimensionality (i.e. extraction of more tissue-relevant information) is equally im- portant for real-time diagnosis in the desired settings and to enable use of DRS in as many biomedical applications (e.g. skin cancer diagnosis, diabetics care, tissue oxygenation monitoring) as possible. Improving the reflectance signal complexity and density through novel DRS instrumentation, would facilitate development of the desired models or put the existing ones built on simulations in practical use; which otherwise could not go beyond being a theoretical demonstration.</p><p>DRS studies tissue morphology and composition through quantification of one or more (ideally all of them) of the tissue- and wavelength-specific optical properties: absorption coefficient (μa), reduced scattering coefficient (μ1s), scattering anisotropy (g), tissue thickness, and scattering phase function details (e.g. higher order moments of the scattering phase function). DRS involves sampling of diffusely reflected photons which experience multiple scattering and absorption as they travel within the tissue, at the tissue surface. Spatially resolved diffuse reflectance spectroscopy (SRDRS) is a subset of general DRS technique, which involves sampling of diffuse reflectance signals at multiple distances to an illumination source. SRDRS provides additional spatial information about the photon path; yielding depth-resolved tissue information critical to layered tissue analysis and early cancer diagnostics. Exist- ing SRDRS systems use fiber optic probes, which are limited in accommodation of large number and high-density collection fibers (i.e. yielding more and dense spa- tially resolved diffuse reflectance (SRDR) measurement data) due to difficulty of fiber multiplexing. The circular shape of the fibers restricts the implementable probe ge- ometries and reduces the fill factor for a given source to detector (i.e. collection fiber) separation (SDS); resulting in reduced light collection efficiency. The finite fiber nu- merical aperture (NA) reduces the light collection efficiency well as; and prevents selective interrogation of superficial tissues where most cancers emerge. Addition- ally, SRDR systems using fiber optic probes for photon collection, require one or more photodetectors (i.e. a cooled CCD); which are often expensive components of the systems.</p><p>This thesis deals with development of an innovative silicon SRDRS probe, which partially addresses the challenge of realizing high measurement density, miniaturized, and inexpensive SRDRS systems. The probe is fabricated by conventional, flexible and inexpensive silicon fabrication technology, which demonstrates the feasibility of developing SRDRS probes in any desired geometry and complexity. Although this approach is simple and straightforward, it has been overlooked by the DRS community due to availability of the conventional fiber optic probe technology. This new probe accommodates large number and high density of detectors; and it is in the form of a concentric semi-annular photodiode (PD) array (CMPA) with a central illumination aperture. This is the first multiple source-detector spacing Si SRDRS probe reported to date, and the most densely packed SRDRS probe reported to date for all types of SRDRS systems. The closely spaced and densely packed detectors enable higher density SRDR measurements compared to fiber-based SRDR probes, and the higher PD NA compared to that of fibers results in a higher SNR increasing light collection efficiency. The higher NA of the PDs and the presence of PDs positioned at very short distances from the illumination aperture center enable superficial tissue analysis as well as depth analysis.</p> / Dissertation
| Identifer | oai:union.ndltd.org:DUKE/oai:dukespace.lib.duke.edu:10161/13375 |
| Date | January 2016 |
| Creators | SENLIK, OZLEM |
| Contributors | Jokerst, Nan M |
| Source Sets | Duke University |
| Detected Language | English |
| Type | Dissertation |
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