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Research Papers

Numerical Investigation of Coil Configurations That Provide Ultrahigh Packing Density of Saccular Aneurysms

[+] Author and Article Information
Chander Sadasivan

Department of Biomedical Engineering, University of Miami, Coral Gables, FL 33146

Baruch B. Lieber1

Department of Biomedical Engineering and Department of Radiology, University of Miami, Miami, FL 33146blieber@miami.edu

1

Corresponding author.

J. Med. Devices 3(4), 041005 (Nov 20, 2009) (5 pages) doi:10.1115/1.4000453 History: Received June 25, 2009; Revised October 01, 2009; Published November 20, 2009; Online November 20, 2009

The long-term outcome of endovascular coiling of cerebral aneurysms is directly related to the packing density at the time of treatment. In general, the highest packing density achievable is only about 45% due to the quasirandom distribution of currently available coils within aneurysms. We investigated whether packing densities could be maximized via more ordered coil configurations. Three different coil configurations—circular loops, planar spirals, and spherical helices—were investigated. The packing densities achievable in maximally filling the volume of an exemplar human basilar aneurysm with each coil configuration were calculated numerically. Coil packing simulations were also carried out for aneurysms idealized as spheres over diameters ranging from 2 mm to 30 mm. The packing densities with the loop, spiral, and spherical helix configurations were 82%, 60%, and 73%, respectively, for the human aneurysm model; the numbers of coils required were 693, 34, and 13, respectively. Simulations within idealized aneurysms suggest that aneurysms cannot be packed to more than 91% with coils of constant circular cross section. The spherical helix configuration provides a constant packing density (coefficient of variation of 0.4%) over the range of aneurysm diameters studied as compared to the two other configurations (coefficients of variation of 9% and 8%). Coil configurations that allow for ordered filling of cerebral aneurysms can potentially provide packing densities that are twice those currently achieved. The spherical helix configuration seems to be the most technically feasible and stable configuration of the three coil types investigated.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

Grahic Jump Location
Figure 1

(a) Contours of the basilar aneurysm showing the line joining the centroids (dots) of each contour and the perpendicular line (dashed line) fitted to the centroids by linear regression; (b) the area of revolution (bounded by solid dotted line) is maximally filled with circles of 300 micron diameter. There are 646 circles in the packing; the dashed line on the left is the perpendicular axis of revolution from (a).

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Figure 2

Examples of coils (300 μm in diameter) within the exemplar basilar aneurysm: (a) the circular loop, (b) the planar spiral, and (c) the spherical helix configurations. Only half of the spherical helix coil is shown for visual clarity. Also for visual clarity, only half of the aneurysm surface is shown and the diameter of the coils is halved; entire aneurysm volume is filled with such coils but all the coils are not shown.

Grahic Jump Location
Figure 3

(a) Variation in maximum packing density with each of the three coil configurations for filling spheres ranging from 2 mm to 30 mm diameter with coils of 300 μm diameter; (b) variation in maximum packing density for filling a sphere of 10 mm in diameter with coils of 100 μm to 1000 μm in diameter.

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