The transcranial doppler is a kind of pulsed doppler (frequency 2 Mhz) which, by arrangement of the probe in particular regions of the skull (temporal, orbital, and occipital fenestra), permits the assessment of the flow velocity on the level of the main intracranial arteris, giving information about the perviety and the characteristics of the flow and about Willis polygon being functional. This non-invasive vascular diagnostic is methodology concerned, and, therefore, fundamental in the evaluation of patients suffering from cerebral-vascular insufficiency and likely to be operated by carotid-TEA.