BME PhD Defense Announcement for Jinxia Yao (Y. Tong, advisor) Everyone is invited to attend the public presentation beginning at 2:30pm. Title: An investigation of fMRI-based perfusion biomarkers in resting state and physiological stimuli Advisory committee: Dr. Yunjie Tong (Chair), Dr. Vitaliy Rayz, Dr. Ulrike Dydak, Dr. Jean Chen Date: September 15, 2022 Time: 2:30pm Location: MJIS 2001 and Zoom (link follows) https://purdue-edu.zoom.us/j/94745595165?pwd=NXhHekhKbXJJMzJGUTBvQ0Y4ZVpnUT0... Meeting ID: 947 4559 5165 Passcode: 411944 Abstract: Cerebrovascular disease is the most common life-threatening neurological disease in the United States. For example, stroke is the third leading cause of death in the U.S. To support normal brain function, maintaining adequate brain perfusion (i.e., cerebral blood flow (CBF)) is important. Therefore, it is crucial to assess the brain perfusion so that early intervention can be applied if abnormal perfusion is observed. The goal of my study is to develop metrics to measure the brain perfusion by understand the brain physiology using blood-oxygen-level-dependent (BOLD) functional MRI (fMRI) under resting state and physiological stimulus. My first and second studies focused on deriving the blood arrival time using the BOLD under resting state. In the first study, we extracted the systemic low-frequency oscillations (sLFOs) fMRI signals from the internal carotid arteries (ICA) and the superior sagittal sinus (SSS). Consistent and robust results of the ICA signals leading the SSS signals by about 5 seconds among 400 fMRI scans. This delay time could be considered as an effective perfusion biomarker that associates with the cerebral circulation time (CCT). To further explore sLFO in assessing dynamic blood flow changes during the scan, in my second study, a "carpet plot", a 2-dimensional plot (time vs. voxel) of scaled fMRI signal intensity, was reconstructed and paired with a developed slope-detection algorithm. Tilted vertical edges across which a sudden signal intensity change was observed. The edges were successfully detected by the algorithm and the averaged propagation time derived from the carpet plot matches the cerebral circulation time. Given that CO2 is a vasodilator, controlling of inhaled CO2 is able to modulate the BOLD signal, therefore, as a follow-up study, we focused on investigating the feasibility of using the CO2 modulated sLFO signal as a "natural" bolus to track the CBF with the tool developed from the second study. Meaningful and comparable transit times were derived from the CO2-MRI carpet plots. Not only the timing, the BOLD signal deformation (the waveform change) under CO2 challenge is also a very useful perfusion information, which represents how the brain react to stimulus. Therefore, my fourth study focused on characterizing the brain reaction to the CO2 stimulus to better measure the brain health. Overall, these studies deepen our understanding of fMRI signal and the derived perfusion parameters can potentially be used to assess some cerebrovascular diseases, such as stroke, ischemic brain damage, and steno-occlusive arterial disease in addition to functional activations.