We propose a method for territorial segmentation and volumetric flow rate (VFR) measurement based on time-resolved contrast enhanced MR-angiography. Eight territories: right/left internal carotid arteries; the two anterior cerebral arteries (combined); the right/left external carotid arteries; the right/left posterior cerebral arteries; and the vertebrobasilar territory, were segmented using an iterative region-growing algorithm based on the bolus-arrival-time with increased temporal resolution. VFR was measured based on the territorial volume as a function of time. Healthy subjects' VFR results were similar to literature values. The clinical potential of this method is demonstrated on one patient with Moyamoya before and after surgery.