The functional imaging of perfusion enables the study of its properties such as the vasoreactivity to circulating gases, the autoregulation and the neurovascular coupling. Downstream from arterial stenosis, this imaging can estimate the vascular reserve and the risk of ischemia in order to adapt the therapeutic strategy. This method reveals the hemodynamic disorders in patients suffering from Alzheimer's disease or with arteriovenous malformations revealed by epilepsy. Functional MRI of the

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... reactivity also helps to better interpret the functional MRI activation in practice and in clinical research. The study of cerebral perfusion provides critical information to understand the functioning of the central nervous system and apprehend its dysfunction, among the main causes of morbidity and mortality in the West. In neurology and psychiatry, the identification of these microvascular pathophysiological disorders may provide information that may help to better characterize a several diseases, or even assess individual vulnerability. Above all, cerebral perfusion allows for the transfer of appropriate quantities of glucose and oxygen for the functional needs of the brain, while eliminating heat and some catabolites such as CO 2 [1]. Perfusion is a dynamic physiological phenomenon able to respond to changes in the homoeostasis of the vascularized organ and the entire body. Like any biological function, general and local factors are likely to not only modify its state of equilibrium but also its adaptive properties. This adjustment is both passive, due to the Abbreviations: ASL, arterial spin labeling; BOLD, blood oxygenation level dependent; CBF, cerebral blood flow; CBV, cerebral blood volume; CVR, cerebral vasoreactivity; fMRI, functional MRI; MRA, magnetic resonance angiography; P a CO 2 , arterial pressure in CO 2 ; P e CO 2 , expiratory pressure in CO 2 .