The most used experimental headache model is the glyceryl trinitrate model (GTN). Where infusion of the NO donor GTN induces headache and changes in the cerebral arteries. On the other hand injection of Diamox (Acetazolamide) apparently causes increase of the cerebral blod flow with out dilation of the arteries. We wish to study the precise effect of GTN and diamox on the cerebral haemodynamics such as Cerebral blod flow (CBF) and Cerebral blod volume (CBV) via a 3-Tesla MRI.