Tara M. Urner
BME PhD Defense Presentation
Date: 2025-01-15
Time: 2:00 pm
Location / Meeting Link: In person: HSRB II N100; Via zoom: https://emory.zoom.us/j/95133571891
Committee Members:
Erin M. Buckley, PhD (Advisor); Brandon Dixon, PhD; Francisco Robles, PhD; Shella Keilholz, PhD; Ofer Sadan, PhD/MD
Title: Noninvasive assessment of pulsatile hemodynamics in the cerebral microcirculation with diffuse correlation spectroscopy
Abstract:
The heart propels blood through the circulatory system as a series of compression waves, causing cerebral blood flow (CBF) to be pulsatile in nature. CBF waveform morphology is determined by the dual effects of attenuation along the vascular bed and interference with back reflections from vascular branch points and other sites of changing cross sectional area. Physiological factors such as cerebrovascular tone and intracranial pressure impact the degree of attenuation/back reflection and, therefore, the shape of the CBF waveform. State-of-the-art measurement techniques can capture CBF waveforms in the large cerebral arteries but not the arterioles and capillary beds that collectively make up the microvasculature and are responsible for delivering oxygen and nutrients directly to tissue. This densely branching network represents the majority of the cerebral circulation, its primary bottleneck, and the setting in which many neurovascular pathologies develop and persist even after treatment. As the relationship between macro- and microvascular CBF is variable and altered in injury and disease, direct assessment of microvascular CBF waveforms would offer a more complete picture of cerebrovascular health, facilitating targeted and timely clinical intervention when abnormalities are detected. In this work I investigate and enhance the utility of diffuse correlation spectroscopy (DCS), a noninvasive optical technique, for characterizing CBF waveforms in healthy and diseased populations. First, I systematically characterize DCS-derived CBF waveforms in 30 healthy adults, revealing sensitivity of waveform morphology to changes in vascular tone. Next, I present a refined waveform analysis method that eliminates the need for an external physiological reference signal, enhancing the feasibility of clinical translation. Finally, I apply the improved method in a pilot clinical study of 25 subarachnoid hemorrhage (SAH) patients with vasospasm, revealing significant CBF waveform morphology alterations associated with both brain injury and vasodilatory treatment. Together, these results highlight the potential of DCS-derived pulsatile hemodynamics as a biomarker of microvascular function in health and disease.