Regional Aneurysm Wall Enhancement is Affected by Local Hemodynamics: A 7T MRI Study

S. Hadad, F. Mut, B.J. Chung, J.A. Roa, A.M. Robertson, D.M. Hasan, E.A. Samaniego and J.R. Cebral - Departments of Bioengineering and Mechanical Engineering (S.H., F.M., J.R.C.), George Mason University ; Department of Applied Mathematics and Statistics (B.J.C.), Mountclair State University ; Departments of Neurology, Neurosurgery, and Radiology (J.A.R., E.A.S.) ; Department of Mechanical Engineering and Material Science (A.M.R.), University of Pittsburgh ; Neurosurgery (D.M.H.), University of Iowa ;

Aneurysm wall enhancement has been proposed as a biomarker for inflammation and instability. However, the mechanisms of aneurysm wall enhancement remain unclear. We used 7T MR imaging to determine the effect of flow in different regions of the wall.

Twenty-three intracranial aneurysms imaged with 7T MR imaging and 3D angiography were studied with computational fluid dynamics. Local flow conditions were compared between aneurysm wall enhancement and nonenhanced regions. Aneurysm wall enhancement regions were subdivided according to their location on the aneurysm and relative to the inflow and were further compared.

Aneurysm wall enhancement regions tend to have lower wall shear stress than nonenhanced regions of the same aneurysm. Moreover, the association between flow conditions and aneurysm wall enhancement seems to depend on the location of the region on the aneurysm sac. Regions at the neck and close to the inflow tend to be exposed to higher wall shear stress and wall shear stress gradients. Regions at the body, dome, or far from the inflow tend to be exposed to uniformly low wall shear stress and have more aneurysm wall enhancement.

How Amira-Avizo Software is used

The high spatial resolution of 7T imaging allows visual determination of areas of enhancement within the aneurysmal wall. In step four, 3D surfaces are recovered by extracting isosurfaces in Amira. These AWE region surfaces were thus already aligned with the 3D vascular model and were then projected onto the vascular model and used to label its surface elements as “enhanced” or “nonenhanced”. Finally, AWE regions are split into connected components and assigned different labels (colors). Note that in cases in which the vascular model was constructed from the TOF-MRA images, the AWE regions are automatically aligned and step 2 is skipped.