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Investigation of Cerebrovascular Reactivity Using Hypercapnia and Optical Brain Imaging

Wednesday, June 8, 2022

9:30 AM-11:30 AM

BIOMED PhD Research Proposal

Investigation of Cerebrovascular Reactivity Using Hypercapnia and Optical Brain Imaging
Pratusha Reddy, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University

Kurtulus Izzetoglu, PhD
Associate Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University

Ramon R. Diaz- Arrastia, MD, PhD
Clinical Traumatic Brain Injury (TBI) Research Center
Department of Neurology
Perelman School of Medicine
University of Pennsylvania

Damage to the cerebral microvasculature network that regulates cerebral blood flow (CBF) is a universal feature of traumatic brain injury (TBI). One way to quantify this damage is to assess cerebrovascular reactivity (CVR), which is the ability of cerebral microvasculature to increase or decrease CBF in response to a vasoactive stimulus, such as hypercapnia (i.e., increasing partial arterial carbon dioxide-PaCO2 levels). In comparison to CBF, CVR offers increased sensitivity to disease progression and greater precision in quantifying effects of therapeutic intervention aimed at improving cerebrovascular function. Despite these advantages, CVR has not been implemented into the routine clinical settings yet due to the prohibitive cost of existing techniques and the lack of practical methods and sensors. Functional near infrared spectroscopy (fNIRS) is a noninvasive and wearable neuroimaging modality that offers the potential to assess CVR in routine clinical settings. Few studies have explored the utility of fNIRS to measure hemodynamic changes during hypercapnic stimulus and assess CVR in healthy and TBI patients. However, large variability in fNIRS-derived CVR measures was observed across these studies. This variability has been proposed to be due to inadequate removal of fNIRS signal components arising from extracerebral tissue layers and those associated with systemic factors such as Mayer waves, which share similar time and frequency characteristics as the signal of interest - PaCO2. Therefore, the primary goal of this thesis is to investigate and develop an approach to further our understanding of fNIRS signal components and evaluate fNIRS measure’s ability to assess CVR in healthy adults and TBI patients. To accomplish this goal, I plan on using a combination of short source detector separation (SDS) optode, multi-channel methods and wavelet transform technique to identify, extract, and compare time, frequency and spatially varying fNIRS signal components.

The first specific aim will focus on investigating time, frequency, and spatial characteristics of fNIRS measures from healthy adults during resting, cognitive and hypercapnic conditions. This aim will improve our understanding of how signal components confounding fNIRS measures vary with stimulus type and provide quantitative evidence of the source of variability observed in CVR measures. Second, I plan on developing a signal-processing methodology to extract PaCO2-related effects from cerebral layers and testing the resulting fNIRS-derived CVR measures against those derived from commonly used signal-processing methodologies. This aim will improve reliability of fNIRS-derived CVR measures. Lastly, I plan on investigating fNIRS-derived features during hypercapnic stimulus to differentiate between healthy controls and TBI patients. This aim will provide evidence of fNIRS ability to assess CVR and other systemic deficits occurring because of TBI.

In summary, this thesis studies cerebral hemodynamics and investigates whether optical brain imaging is an effective and viable modality to assess cortical changes during hypercapnic stimulus in healthy controls and TBI patients. Broadly, the approach (i.e., combination of features, methods, and techniques) developed in this thesis can be utilized to enable a practical and cost-effective way to identify and monitor microvascular dysfunctions in not only TBI, but also in other neurological disorders such as Alzheimer’s, small vessel disease, stroke, and others.

Contact Information

Natalia Broz

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