Flow territories normalization was observed in patients underwent carotid endarterectomy (CEA). To investigate whether collateral flow associated with the redistribution of blood we performed 3D ASL and tASL on 25 patients prior to (PRE) and after (POST) surgery. Collateral flow was read as the presence of arterial transit artifact (ATA) on 3D ASL images. Alteration of flow territories was determined by comparing the PRE and POST tASL images. Our study demonstrated that good collateral compensation shown in ASL was associated with normalization of tASL flow territories after CEA.