Parallel and spiral flow patterns of vertebral artery contributions to the basilar artery.

PURPOSE To demonstrate that the in vivo flow from individual vertebral arteries can be imaged and tracked in the basilar artery by use of saturation planes with three-dimensional time of flight MR angiography. METHODS Twenty volunteers were studied with intracranial three-dimensional time of flight angiography MR. The MR angiography was repeated with saturation of the individual vertebral arteries. Flow voids and signal intensity within the basilar and posterior cerebral arteries were evaluated for flow patterns. RESULTS Of 15 volunteers with a "normal" vertebrobasilar anatomy, 80% demonstrated a pattern of flow within the basilar artery in which the contributing vertebral components remained ipisilateral. This pattern was called "parallel." A "spiral" pattern of rotation of the contributing vertebral components was found in 20% of studies. The inflow to the posterior cerebral arteries could be identified from specific vertebral contributions and was related to the size-dominance of the vertebral artery. CONCLUSION There is nonadmixture of vertebral artery flows of variable duration within the basilar artery; at least two patterns of flow can be described within the basilar artery. The method presented is a simple technique for determining vertebral artery flow components with routine software and without secondary data manipulation.