Stroke is a condition with an high mortality rate and a relevant burden of disability and social costs. Indeed it is the third cause of death and the first cause of disability in western countries. About 80% of strokes is ischemic and due to the occlusion of a large or small cerebral artery. Therefore the rationale of thrombolysis is the reopening of the occluded vessel within a short time window from symptoms onset, mainly by using iv rtPA but also by using local delivery of rtPA and/or mechanical disruption of the thrombus. The basic assumption is simple and clear: a large vessel was abruptly occluded and the corresponding brain territory was deprived of oxygenated blood and nutrients. The brain metabolism during ischemia is flowand time-dependent; there are precise perfusional thresholds for maintaining membrane pump activity; therefore the cell integrity and the duration of neuronal life is related to the time from the vessel occlusion, in a variable combination of individual ischemic tolerance and activation of the collateral circulation. The irreversibly damaged brain tissue is known as ischemic core and the suffering, but still viable, tissue is known as penumbra. The penumbra to core ratio is affected by several factors, but it is widely recognized that both occlusive pattern and time from symptoms onset are strong predictors of the presence of as much viable tissue as needed for the success of the reperfusion treatment. The clinical data and the neurological severity scales, as NIHSS (National Institute of Health Stroke Scale), do not reliably predict if there is a large vessel occlusion and for which extent in single cases. The clinical presentation can be the same for a very proximal large arterial occlusion and for a small perforating artery involvement, but the recanalization rate is strictly dependent on the occlusive pattern. Therefore, because the recanalization is a strong predictor of a good outcome, the prognosis depends on it and it can be early inferred by the diagnosis of the occlusive pattern. All efforts should be made to achieve the diagnosis of vessel occlusion ad brain perfusion condition as early as possible, in order not only to predict the prognosis but also to tailor the treatment. In acute stroke time is brain, and therefore the diagnostic steps should be reliable, fast and not time consuming. Ultrasound techniques have these features for other body districts, also for extracranial vessels, but their use for the examination of the intracranial circulation has been hampered for many years, because of the attenuation effect of the skull. In the last twenty years this limitation has been demonstrated to be passed by neurosonological