Measurement of Cerebral Blood Flow Using Arterial Spin Labeling Magnetic Resonance Imaging
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Cerebral Blood Flow (CBF) reflects the amount of blood perfusion in the brain, often defined as ml of blood per 100 gram of brain per minute. CBF is an important measure in understanding brain physiology and pathophysiology. Thus, it is important to establish a robust method suitable for longitudinal and cross-sectional studies of neurovascular and neurodegenerative diseases non-invasively. Pseudo-Continuous Arterial Spin Labeling (pCASL) MRI is a new MRI technique that is able to detect blood flow changes, non-invasively. The blood flow change detected by pCASL MRI is relative and it is expressed in terms of arbitrary MRI units which does not have any physiological meaning. Thus, quantifying absolute CBF map is of a great interest. In the first part of this study, I quantified absolute CBF (aCBF) map by utilizing phase contrast MRI as a normalization factor. Next, I provided a systematic investigation into the detection power of ASL and the optimal strategies for data analysis. The power of ASL MRI in detecting CBF differences between patient and control subjects is hampered by inter-subject variations in global CBF, which are associated with non-neural factors and may contribute to the noise in the across-group comparison. I found that when normalizing the CBF with whole-brain CBF or CBF in a reference region (termed relative CBF, rCBF), the statistical significance was improved considerably (p<0.003). In the last part of this study, the aCBF of ten major brain human fibers were estimated for the first time and the relationship between Fractional Anisotropy (FA) and aCBF was investigated. The inverse association between aCBF and FA suggests that higher myelination restricted the blood flow to the center of the fiber or higher myelination made the conductance of the action potential more efficient. In summary, ASL MRI has become the method of choice for measuring cerebral blood flow and it has a great potential in clinical settings for diagnosis of most neurological disorders before anatomical changes are observed.