878 Table 1 Demographic and clinical characteristics of the study groups Eur Radiol (2011) 21:875–881 Healthy controls Patients with internal carotid stenosis Number Male (%) Age (mean years ± SD) Degree of ICA stenosis (n) 0–49% 50–69% 70–99% Occluded Presenting events (n) Transient ischemic attack Ischemic stroke Retinal ischemia 18 11 (61.1%) 67.4±6.5 18 0 0 0 – – – Symptomatic 15 9 (60.0%) 70.9±7.2 0 3 12 0 9 3 3 Asymptomatic 20 12 (60.0%) 68.7±6.6 0 10 10 0 – – – the contralateral ICA to the caudate nucleus in these patients is accompanied with anterior collateral flow, confirming that blood is being diverted from the contralateral ICA via the circle of Willis. We did not find differences between the three groups with respect to the feeding arteries of the lentiform nucleus and the thalamus. Knowledge of the perfusion territories of the brain- feeding arteries in the deep brain structures is largely based on post-mortem studies in which dyed resins were injected into the brain-feeding arteries [2, 5]. With modern imaging modalities such as CT and MR angiography the cerebral vasculature and corresponding perfusion territories can be visualized in vivo. These techniques however can only visualize the vascular tree. Selective ASL-MRI has shown to reliably image the cortical supply of individual major brain-feeding arteries [21]. With the introduction of perfusion territory selective ASL-MRI, the perfusion territories of the brain-feeding arteries can now be visualized at brain tissue level. Our findings dispute the textbook concept of a fixed pattern of the perfusion territories from the brain-feeding arteries. In a symptomatic patient with steno-occlusive carotid artery disease, information about the individual perfusion territories might be used complementary to the type and anatomical location of ischemic infarction for determining the involved artery. With respect to the deep brain structures, perfusion territory selective ASL-MRI could show if an ischemic area receives blood from the ipsilateral or contralateral ICA (anterior circulation), or from the basilar artery (posterior circulation). Knowledge on the artery perfusing the ischemic area may have consequences for treatment. For instance if a severe stenosis is present that may be amenable by endarterectomy or stenting. Fig. 2 Perfusion territory image a of a patient with a right-sided symptomatic ICA stenosis. Colors represent the perfusion territories of the right ICA (blue), left ICA (red) and the basilar artery (green). The caudate nucleus on the right side is supplied by the contralateral ICA (besides white star). The lentiform nuclei on both sides are supplied by their respective ipsilateral ICA. Furthermore, both thalami are partially supplied by their ipsilateral ICA and basilar artery. Circle of Willis on 2D phase-contrast MR angiogram (MRA), phase encoded in the right-left direction b and anterior-posterior direction c. Blood flowing to the patient’s right and anterior direction is black and blood flowing to the patient’s left and posterior direction is white. There is collateral flow towards the right hemisphere via the right A1 segment (retrograde flow, black in B, white in C, indicated by white star). Maximum intensity projection d shows the anatomy of the circle of Willis