880 thalamus in both the patients and healthy control subjects. The thalamus is predominantly supplied via the basilar artery, but may also receive blood from the ipsilateral ICA. In a few subjects, the contralateral ICA also contributed to the perfusion of the thalamus. Textbook-based perfusion territory maps do not give this unique perfusion territory information in individual subjects. Because the supply routes of the thalamus varied the most of all the nuclei in our study, perfusion territory selective ASL-MRI may be particularly useful for the thalamus. A limitation of this study is that in patients with an ICA stenosis, there may be a delayed arrival of the bolus of magnetically labeled blood. As the perfusion-weighted images in ASL are acquired after a fixed amount of time, this may potentially lead to reduced sensitivity for delayed perfusion via collaterals. In order to compensate for underestimation of collateral blood flow we employed a pseudo-continuous ASL labeling technique, where the protons labeled directly after the start of the labeling have an effective delay time of more than 3 s. As the collateral blood flow paths via the circle of Willis are relatively fast and have shown to not result in a measurable delayed arrival of the magnetically labeled blood bolus in a previous ASL-MRI study using multiple time intervals [25], this should be adequate. Another limitation of this study is the relatively small group sizes. With a larger study population smaller differences in prevalence of perfusion contributions to the various nuclei may have been detected between the patient groups and healthy control subjects. Still, with the size of the current study we could demonstrate a difference in perfusion contributions to the caudate nucleus between patients with a symptomatic carotid artery stenosis and healthy control subjects. 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