Blood flow dynamics in the vertebrobasilar system: correlation of a transparent elastic model and MR angiography

To describe the flow patterns in a model of the vertebrobasilar artery and use these observations to explain the appearance of the flow on the MR images.

We created an anatomically precise, transparent elastic model of the human vertebrobasilar artery containing a basilar tip aneurysm and perfused the model with non-Newtonian fluid which has similar rheologic properties to blood. Flow patterns in the vessels were directly observed. MR angiogram images were obtained with commercially available two-dimensional time-of-flight, three-dimensional time-of-flight, and 3-D phase-contrast MR angiographic pulse sequences, and they were correlated with the directly seen flow patterns. Quantitative flow velocity measurements were performed with 2-D cine phase-contrast MR angiography and correlated with the flow measured with an electromagnetic flow meter.

Visualization studies showed the dye stream patterns in the vertebrobasilar arteries to be extremely complex and variable. During the MR experiments we found that often the same segment of a vessel could appear very different depending on the pulse sequence. In some instances, the model experiments helped to explain the MR appearance of the vessels. Flow profiles measured with 2-D cine phase contrast were found to be consistent with those measured directly with an electromagnetic flow meter.

Clear elastic models can be used to duplicate the flow in human cranial vessels and thus provide a unique means to observe these flow patterns directly. The flow patterns helped to explain the variation in appearance of the vessels and the artifacts with different MR angiography pulse sequences. The artifacts depend on both the geometry of the vessel and the flow pattern within it. Two-dimensional cine phase-contrast MR provides temporal flow field information that is directly related to physiological information about flow volumes and velocity patterns.