1. A method for detecting a vascular occlusion from a set of angiographic data relating to the brain of a patient, the method including: (i) locating the mid-sagittal plane within the set of angiographic data; (ii) mapping the angiographic data to a pre-existing atlas of blood supply territories, thereby obtaining the portion of the angiographic data corresponding to each of one or more blood supply territories; (iii) for each of the blood supply territories, evaluating the asymmetry of the corresponding portion of the angiographic data about the identified mid-sagittal plane; and (iv) according to the evaluated asymmetry of the portion of the angiographic data corresponding to each blood supply territory, detecting the presence of an occlusion in any of the blood supply territories.