Assessment of Brain Perfusion and Vascular Compliance with Magnetic Resonance Imaging
Brain perfusion is an index that reflects the amount of blood received by the brain tissue in a given time period. Normal brain perfusion ensures that sufficient oxygen, glucose, and other nutrients are delivered to the neurons and glial cells in the brain. While perfusion is relatively static index of brain vascular function, vascular compliance represents the dynamic ability of arteries to dilate or retract in response to blood pressure alternations. An artery vessel with high compliance can better buffer the pulsatility of blood flow, thereby protecting the downstream arterioles and capillaries from damage. Consequently, brain perfusion and vascular compliance are complementary properties of brain's vascular system and may be important indicators of cerebrovascular health. Therefore, noninvasive imaging of brain perfusion and vascular compliance will provide valuable biomarkers to study cerebral physiology and function. Furthermore, these biomarkers may also yield crucial pathophysiological knowledge and guide therapies in brain disorders, such as stroke, small-vessel disease, and neurodegenerative disease. This thesis consists of three novel tools toward brain perfusion and vascular compliance imaging. I first developed a cardiac-triggered Arterial-Spin-Labeling (ASL) technique to enhance the sensitivity of brain perfusion MRI without using exogenous contrast agent. I demonstrated its utility in several experimental settings, including single-shot acquisition, multi-shot acquisition, and detection of cerebral blood flow (CBF) changes. Next, I worked on the analysis strategies of perfusion MRI data. I developed a cloud-based tool for ASL data processing that is free from any software installation, compatible with file formats from all major MRI manufacturers, and publicly accessible. Quantitative CBF maps and region-specific reports are available for download within minutes. I have launched this cloud service recently and received initial feedback from researchers around the world. Finally, I developed a technique to measure vascular compliance in larger cerebral arteries. I used a time-resolved vascular-space-occupancy technique to obtain 3D maps of cerebral arterial compliance and then applied the technique to study arterial stiffness in aging.