Color and pulsed-wave Doppler showing flow in right carotid and vertebral arteries. (a) To- and- fro with mainly retrograde blood flow in right common carotid artery. (b) Right external carotid artery with reversal of blood flow. (c) To- and- fro with mainly retrograde blood flow in right internal carotid artery. (d) Bidirectional and primarily reversed blood flow in right vertebral artery. Flow in the vertebral vein and the vertebral artery are in the same direction (toward the heart) and shown in blue. Note all arterial color Doppler flows are retrograde in these images.
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