Doctor of Philosophy (PhD), Wright State University, 2023, Engineering PhD

Blood flow dynamics plays a critical role in maintaining tissue health, as it delivers nutrients and oxygen while removing waste products. It is especially important when there is a disruption in cerebral autoregulation due to trauma, which can induce ischemia or hyperemia and can lead to secondary brain injury. Thus, there is a need for noninvasive techniques that can allow continuous monitoring of blood flow during intervention. Optical techniques have become increasingly practical for measuring blood flow due to their non-invasive, continuous, and relatively lower-cost nature. This research focused on developing a low-cost, scalable optical technique for measuring blood flow by implementing speckle contrast optical spectroscopy using a fiber-camera-based approach. This technique is particularly well-suited for measuring blood flow in deep tissues, such as the brain, which is challenging to access using traditional optical methods. A two-channel continuous wave speckle contrast optical spectroscopy device was developed, and the device was rigorously tested using phantoms. Then, it is applied to monitor blood flow changes in the brain following traumatic brain injury (TBI) in mice. The results indicate that trauma-induced significant blood flow decreases consistent with the recent literature. Overall, this approach provides noninvasive continuous measurements of blood flow in preclinical models such as traumatic brain injury.

Committee: Ulas Sunar Ph.D. (Advisor); Tarun Goswami Ph.D. (Committee Member); Keiichiro Susuki Ph.D. (Committee Member); Robert Lober M.D., Ph.D. (Committee Member) Subjects: Biomedical Engineering; Biomedical Research; Biophysics; Engineering; Optics

Master of Science in Biomedical Engineering (MSBME), Wright State University, 2019, Biomedical Engineering

Neurovascular coupling is an important concept that indicates the direct link between neuronal electrical firing with the vascular hemodynamic changes. Functional Near Infrared Spectroscopy (fNIRS) can measure changes in cerebral vascular parameters of oxy-hemoglobin and deoxyhemoglobin concentrations and thus can provide neuronal activity through neurovascular coupling. Currently many commercial fNIRS devices are available, but they are limited by the number of channels (usually having only 8 detectors), which can limit the sensitivity, contrast, and resolution of imaging. High-density imaging can improve sensitivity, contrast, and resolution by providing many measurements and averaging the signals originating from the target cerebral focus area compared to background tissue. Here a multi-channel, low-cost, high-density imaging system based on scientific CMOS (Complementary Metal-Oxide-Semiconductor) detector will be presented. The CMOS camera is fiber-coupled such that on one end fibers are focused on the pixels on the CMOS camera, which allows individual pixels (or binned sub-pixels) to act as detectors, while the other end of the fibers can be positioned on a wearable optical probe. After the device details, I will show the device validation using a series of the dynamic flow phantom experiments mimicking the brain activation and finally human motor cortex experiments (finger tapping experiments). The results demonstrate that this system can obtain high-density data sets with higher contrast and resolution. This wearable, high-density optical neuroimaging technology is expected to find many applications including pediatric neuroimaging at clinics and assessing human cognitive performance.

Committee: Ulas Sunar Ph.D. (Advisor); Keiichiro Susuki Ph.D. (Committee Member); Tarun Goswami Ph.D. (Committee Member) Subjects: Biomedical Engineering; Biomedical Research; Engineering; Optics

Master of Science, Miami University, 2018, Physics

This thesis presents data from a series of experiments that investigate the ability of laser speckle contrast imaging (LSCI) to sense changes in flow in turbid media. I first provide a theoretical overview and a description of the experimental approach used in this flow imaging technique. Experimental validation of the technique's ability to sense induced changes in blood flow in the human forearm is demonstrated. Then, the technique's sensitivity to buried flow in controlled optical phantoms is examined. It is shown that the buried depth and optical properties of the media surrounding flow impact the measured flow indices. Lastly, a study shows how the polarization state of the imaged light impacts the flow measurements as a function of the buried depth and rate of the flow. The results demonstrate that the measurements are dependent on the flow rates and optical properties of the sample as well as the imaging setup used to capture the speckle.

Committee: Karthik Vishwanath (Advisor); Paul Urayama (Committee Member); E. Carlo Samson (Committee Member) Subjects: Biomedical Research; Biophysics; Medical Imaging; Optics; Physics