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RESEARCH PAPERS

Modeling the Interaction of Coils With the Local Blood Flow After Coil Embolization of Intracranial Aneurysms

[+] Author and Article Information
Kyung Se Cha

Department of Mechanical Engineering, University of Maryland, College Park, MD 20742

Elias Balaras1

Department of Mechanical Engineering, University of Maryland, College Park, MD 20742

Baruch B. Lieber, Chander Sadasivan

Department of Biomedical Engineering, and Department of Radiology, University of Miami, Miami, FL 33146

Ajay K. Wakhloo

Department of Radiology, Neurosurgery, and Neurology, University of Massachusetts Medical School, Worcester, MA 01655

1

Corresponding author.

J Biomech Eng 129(6), 873-879 (Apr 23, 2007) (7 pages) doi:10.1115/1.2800773 History: Received July 30, 2006; Revised April 23, 2007

Aneurysmal recanalization and coil compaction after coil embolization of intracranial aneurysms are seen in as many as 40% of cases. Higher packing density has been suggested to reduce both coil compaction and recanalization. Basilar bifurcation aneurysms remain a challenge due possibly to the hemodynamics of this specific aneurysm/parent vessel architecture, which subjects the coil mass at the aneurysm neck to elevated and repetitive impingement forces. In the present study, we propose a new modeling strategy that facilitates a better understanding of the complex interactions between detachable coils and the local blood flow. In particular, a semiheuristic porous media set of equations used to describe the intra-aneurysmal flow is coupled to the incompressible Navier–Stokes equations governing the dynamics of the flow in the involved vessels. The resulting system of equations is solved in a strongly coupled manner using a finite element formulation. Our results suggest that there is a complex interaction between the local hemodynamics and intra-aneurysmal flow that induces significant forces on the coil mass. Although higher packing densities have previously been advocated to reduce coil compaction, our simulations suggest that lower permeability of the coil mass at a given packing density could also promote faster intra-aneurysmal thrombosis due to increased residence times.

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Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 7

Temporal variation of (a) average pressure in the aneurysm normalized with the peak pressure from Case 4; (b) Flow rate into the aneurysm normalized with the average flow rate into the aneurysm from Case 4. (—) Case 5 (ϵ=0.7,Da=10−3); (----) Case 2 (ϵ=0.7,Da=10−4).

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Figure 8

Variation of the hemodynamic force on the coil during the pulsatile cycle. (----) Case 5 (Dn∕Dp=1.0,ϵ=0.7,Da=10−3); (—) Case 2 (Dn∕Dp=1.0,ϵ=0.7,Da=10−4); (–∙–∙) Case 7, (Dn∕Dp=0.5,ϵ=0.7,Da=10−4).

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Figure 6

Velocity profiles at an (y-z) plane at x=0 near the peak flow rate (t∕T=0.2) for three different grids (Cases 1, 2, and 3 in Table 1). (a) Location at the neck of the aneurysms; (b) location in the middle of the sac.

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Figure 5

Instantaneous streamlines near the peak flow rate t∕T=0.2. (a) Case 5; (b) Case 4.

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Figure 4

Instantaneous velocity contours and velocity vectors near the minimum flow rate t∕T=0.5. Velocity is normalized with the average bulk velocity ⟨Ub⟩.

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Figure 3

Instantaneous velocity contours and velocity vectors near peak flow rate t∕T=0.2. Velocity is normalized with the average bulk velocity ⟨Ub⟩.

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Figure 2

Three-dimensional geometry in the vicinity of the aneurysm. The flow rate variation imposed at the inflow plane is also shown.

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Figure 1

(a) Schematic of a terminal aneurysm and the surrounding vessels. Dn and Dp are the diameters of the aneurysm neck and parent vessel, respectively, and the shaded area denotes the coil(s). (b) Zoom in of the shaded area in Part (a). A schematic of the pore structure after coil embolization is shown. l is the averaging length and d is the characteristic length scale at the pore level.

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