The critical barrier to stratifying stroke risk rests with a lack of (i) methodology for measuring multiple hemodynamic factors with high specificity and (ii) noninvasive approaches capable of monitoring longitudinal progression of impairment. The investigators have demonstrated the clinical utility of relatively new, noninvasive MRI approaches for assessing cerebrovascular reactivity (CVR), aCBV, and collateral CBF. These approaches have been optimized and feasibility assessed in healthy volunteers or isolated clinical studies, however comparatively little information is available regarding the relationship between these collective measures and stroke risk. Therefore, the investigators propose to complement established angiographic and structural imaging with more novel, validated hemodynamic measurements to assess tissue-level impairment and compensation strategies in patients with IC stenosis. Using a collective approach combining measurements of collateral CBF, aCBV and CVR in multiple brain regions, in conjunction with a statistical model incorporating the above parameters as possible prognostic factors, the investigators will quantify the extent to which two-year stroke risk is associated with hemodynamic compensation mechanisms in a population of symptomatic IC stenosis patients. The noninvasive and multi-faceted scope of this investigation is intended to expand the diagnostic stroke infrastructure and elucidate new hemodynamic prognostic indicators of stroke in this high-risk population.