Background and Purpose-Carotid endarterectomy (CEA) has become a routine procedure to treat symptomatic carotid artery disease and reduce the risk of recurrent cerebral ischemic events. The purpose of this study was to use an arterial spin labeling dynamic magnetic resonance angiography technique to characterize intracranial hemodynamics before and after CEA. Methods-Thirty-seven carotid artery disease patients participated in this study, of whom 24 underwent magnetic resonance imaging before and after CEA. Seventeen control subjects spanning 5 decades underwent magnetic resonance imaging to assess age-related changes. Hemodynamic metrics (that is, relative time to peak and amplitude) were calculated with a ␥-variate model. Linear regression was used to relate carotid artery disease burden to downstream hemodynamics in the circle of Willis. Results-Relative time to peak increased with age in controls (PϽ0.020). For patients, relative time to peak was positively correlated with percent stenosis (PϽ0.050), independent of age. At 1 day after CEA, the middle cerebral artery ipsilateral to the CEA showed significant dynamic magnetic resonance angiography changes: relative time to peak decreased (PϽ0.017) and the flow amplitude increased (PϽ0.009). No pre-versus post-CEA changes were significant in the contralateral middle cerebral artery or posterior segments. Conclusions-This noninvasive, arterial spin labeling-based method produced time-resolved images that were used to characterize intracranial arterial flow associated with aging, extracranial carotid artery disease, and CEA. Results demonstrate that the technique has the sensitivity to detect hemodynamic changes after CEA. (Stroke. 2011;42:979-984.)Key Words: endarterectomy Ⅲ carotid stenosis Ⅲ arterial spin labeling Ⅲ angiography Ⅲ dynamic Ⅲ blood flow Ⅲ aging A therosclerosis is a major risk factor for ischemic cerebrovascular events. Extracranial steno-occlusive disease influences hemodynamics and physiology in the brain. 1 Therefore, carotid endarterectomy (CEA) is a standard treatment for patients with symptomatic stenosis Ͼ70% because surgical therapy is associated with higher event-free survival compared with medical therapy. 2 However, CEA is not without risk; 1 study reported a 4.3% increase in the risk of stroke or death within 30 days of CEA. 2 Other studies report silent infarcts, evident postoperatively on diffusion-weighted images in 17% to 33% of CEA patients. 3,4 Therefore, there is merit in developing imaging techniques that can be used to assess the downstream impact of extracranial steno-occlusive disease. phase encoding, nor does it require that slices be perpendicular to the vessels of interest. The purpose of this study was to determine whether ASL-based DynAngio could be used to characterize circle of Willis hemodynamics, as it provides the primary means of collateral blood supply in the brain. We collected data from control subjects and patients with carotid artery disease to test the hypotheses that DynAngio hemodynamic measures are capab...