Browsing by Author "Yu, Linhui"

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    A Single Fiber System for Monitoring Tissue Oxygen Saturation
    (2015-09-28) Yu, Linhui; Murari, Kartikeya
    Oxygen saturation is an important biological marker in tissue and is often quantified using optical imaging of intrinsic signals. However, due to the scattering property of biological tissue, most optical functional imaging methods are limited to the surface of the brain or have poor resolution. In this work, a single fiber optical system with zero source-detector separation is presented. The system is designed for measuring the oxygen saturation of deep brain structures by implanting the small diameter fiber probe into the tissue of interest. The system measures oxygen saturation using a steady-state spectroscopy method based on the absorption properties of oxy-hemoglobin and deoxy-hemoglobin. This thesis covers: (a) system design, including the optical simulation, system components and performance; (b) Monte Carlo simulations for wavelength determination, depth penetration and the received signal; (c) quantification method for the single fiber system; and (d) experimental results in a tissue phantom.
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    Instrumentation for Functional Brain Monitoring with Intrinsic Optical Signals
    (2019-12-05) Yu, Linhui; Murari, Kartikeya; Dunn, Jeff F.; Fear, Elise C.; Kiss, Zelma H. T.; Curiel, Laura; Côté, Daniel C.
    Intrinsic optical signals are widely used in functional brain imaging techniques for measuring hemodynamic parameters, such as oxygen saturation and blood volume. These parameters indicate brain metabolism and serve as an indirect measurement of neural activity. In this thesis, I describe two techniques for hemodynamic monitoring from freely-moving animals. The first technique is single fiber spectroscopy, which enables measurements from a highly-localized volume in deep brain structures. I describe the optical system design for measuring reflectance spectra, Monte Carlo simulations for estimating the sampling volume, phantom experiments for rating the accuracy of hemodynamic parameter quantification, and finally, animal experiments for evaluating system performance in in-vivo experiments. I demonstrate that the single fiber spectroscopic system is capable of measuring spontaneous and stimulus-evoked hemodynamic response through a small diameter multimode fiber from non-line-of-sight brain regions in anesthetized and freely-moving animals. The second system is a miniaturized intrinsic optical sensing system (MiniIOS), a cost-effective, integrated system for measurement from the brain surface. The thesis covers the design and characterization of two versions of MiniIOS, the development of an empirical model for extracting hemodynamic parameters from the measured reflectance, as well as system validation in optical phantoms and animal experiments. The final system has a dimension of 5.5 mm×4.7 mm×1.8 mm and weight of 0.12 g. The system can be powered with a battery and operated as a stand-alone device integrating light source, detector, power supply, data acquisition and storage. Phantom experiments showed that the system was sensitive to both changes in oxygen saturation and blood volume fraction. A pilot animal experiment showed the system can be mounted on the head of a mouse without affecting its movement.