Stereoscopic PIV measurement in cerebral artery model.

 Stereoscopic PIV measurement in cerebral artery model with rigid wall

In this research, we make in vitro model (Fig. 1) that has realistic vessel geometry, and we visualized velocity field in cerebral aneurysm and velocity near the wall using in vitro model at the steady state. And we investigate the distribution of wall shear stress, which plays an important role in formation, growth and rupture of the cerebral aneurysm. To visualize the velocity field and calculate the wall shear stress, we use stereoscopic particle image velocimetry (stereo-PIV)(Fig. 2), to noninvasively measure the flow and obtain the information on three velocity components simultaneously at many points in any plane.

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Fig. 1 In vitro model with an aneurysm.

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Fig. 2 Stereo PIV system

The measurement geometry (Fig. 3(a)) is MCA with cerebral aneurysm at bifurcation area, and we measured 36 slices from near branching to top of aneurysm (Fig. 3(b)).

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Fig.3 (a) Coordinate system and inflow and outflow direction. (b) Measurement slices.

Because we measured the flow in detail, we can make the 3D velocity map in the aneurysm. So we can make the distribution of velocity form any direction (Fig. 4), we can understand the flow structure intuitively.

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Fig. 4 Vector of in plane velocities and distribution of out plane velocity.

We visualized the streamline to investigate the flow structure in the aneurysm (Fig. 5). In these results, the flow mostly goes into the aneurysm rather than into the branching arteries, and two vortices along the aneurysm are observed

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Fig. 5 Flow structure in the aneurysm

And we calculated the wall shear stress using velocity data and geometry data, which is reconstructed from raw data of the CT angiography (Fig. 6). The value are normalized the averaged wall shear stress at the z=0mm. The result shows that the magnitude of WSS averaged over the aneurysm is lower than that of WSS averaged over the rest of the blood vessels.

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Fig.6 Distribution of wall shear stress.

References
Y. Akedo, M. Oshima, M. Oishi and T. Saga, Visualization of Flow Structure In Cerebral Aneurysm Model, The 8th Asian Symposium on Visualization, 2005, Thailand, pp. 177-179
Y. Akedo, M. Oshima, M. Oishi , T. Saga and T. Kobayashi, Stereoscopic PIV Measurement in Cerebral Artery Model, Nihon Kikai Gakkai Ronbunshu, B (T-ransactions of the Japan Society of Mechanical Engineers, Series B), 72-722 (2006), 2386-2393