Research Papers

Effect of Local Coil Density on Blood Flow Stagnation in Densely Coiled Cerebral Aneurysms: A Computational Study Using a Cartesian Grid Method

[+] Author and Article Information
Tomohiro Otani

Department of Mechanical Science
and Bioengineering,
Graduate School of Engineering Science,
Osaka University,
1-3 Machikaneyamacho,
Toyonaka-shi 560-8531, Osaka, Japan
e-mail: otani@me.es.osaka-u.ac.jp

Takuya Shindo

Department of Systems Science,
School of Engineering Science,
Osaka University,
1-3 Machikaneyamacho,
Toyonaka-shi 560-8531, Osaka, Japan
e-mail: t.shindo@biomech.me.es.osaka-u.ac.jp

Satoshi Ii

Department of Mechanical Science
and Bioengineering,
Graduate School of Engineering Science,
Osaka University,
1-3 Machikaneyamacho,
Toyonaka-shi 560-8531, Osaka, Japan
e-mail: sii@me.es.osaka-u.ac.jp

Masayuki Hirata

Department of Neurosurgery,
Graduate School of Medicine and
Global Center for Medical Engineering and
Informatics (MEI Center),
Osaka University,
2-2 Yamadaoka,
Suita-shi 560-0871, Osaka, Japan
e-mail: mhirata@nsurg.med.osaka-u.ac.jp

Shigeo Wada

Department of Mechanical Science
and Bioengineering,
Graduate School of Engineering Science,
Osaka University,
1-3 Machikaneyamacho,
Toyonaka-shi 560-8531, Osaka, Japan
e-mail: shigeo@me.es.osaka-u.ac.jp

1Corresponding author.

Manuscript received July 14, 2017; final manuscript received December 10, 2017; published online February 12, 2018. Assoc. Editor: Alison Marsden.

J Biomech Eng 140(4), 041013 (Feb 12, 2018) (8 pages) Paper No: BIO-17-1308; doi: 10.1115/1.4039150 History: Received July 14, 2017; Revised December 10, 2017

Aneurysm recurrence is the most critical concern following coil embolization of a cerebral aneurysm. Adequate packing density (PD) and coil uniformity are believed necessary to achieve sufficient flow stagnation, which decreases the risk of aneurysm recurrence. The effect of coil distribution on the extent of flow stagnation, however, especially in cases of dense packing (high PD), has received less attention. Thus, the cause of aneurysm recurrence despite dense packing is still an open question. The primary aim of this study is to evaluate the effect of local coil density on the extent of blood flow stagnation in densely coiled aneurysms. For this purpose, we developed a robust computational framework to determine blood flow using a Cartesian grid method, by which the complex fluid pathways in coiled aneurysms could be flexibly treated using an implicit function. This tool allowed us to conduct blood flow analyses in two patient-specific geometries with 50 coil distribution patterns in each aneurysm at clinically adequate PD. The results demonstrated that dense packing in the aneurysm may not necessarily block completely the inflow into the aneurysm and local flow that formed in the neck region, whose strength was inversely related to this local PD. This finding suggests that local coil density in the neck region still plays an important role in disturbing the remaining local flow, which possibly prevents thrombus formation in a whole aneurysm sac, increasing the risk of aneurysm regrowth and subsequent recurrence.

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Grahic Jump Location
Fig. 1

Workflow of blood flow simulation in the coiled aneurysm using Cartesian grid method. (a) and (b) The surface geometry of the aneurysm with parent arteries are reconstructed from medical images (a) and projected onto the Cartesian grid using the SDF (b). (c) Coil deployment simulation is conducted using the implicit surface of the aneurysm and balloon geometry (shown in green) modeled by the algorithm of Ford et al. [23]. (d) and (e) the coils in the aneurysm (d) are also projected onto the Cartesian grid, and the fluid domain is identified by the VOF function (e). The aneurysm surface in (e) shows the iso-surface of the VOF = 0.5.

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Fig. 2

Patient-specific aneurysm geometries of case A (left) and case B (right)

Grahic Jump Location
Fig. 3

Grid convergence test: fine (grid size 25 μm); medium (grid size 37.5 μm); and coarse (grid size 50 μm). (a) The velocity profile was measured along the red line, which is located along the y-direction. (b) Profiles of velocity components (ux, uy, uz).

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Fig. 4

Representative velocity fields in the cross-sectional plane of coiled aneurysms in case A (top) and case B (bottom)

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Fig. 5

Representative shear rate fields in the cross-sectional plane of coiled aneurysms in case A (top) and case B (bottom). Note that the color bars were set by log-scale.

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Fig. 6

SDF from the aneurysm neck to the fundus in case A (left) and case B (right)

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Fig. 7

Spatial proportion of kinetic energy in aneurysms from the aneurysm neck to the fundus in case A (top) and case B (bottom) before (left) and after (right) coiling. Error bars show maximum and minimum ranges.

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Fig. 8

Relations between the FER in the whole aneurysm and the local PD of coils in regions with the distance from neck of 0–0.5 mm (top), 0.5–1.0 mm (middle), and 1.0–1.5 mm (bottom) in case A (left) and case B (right). Lines show the results of the regression analysis using a log-linear model (lny = ax + b). R2 is the coefficient of determination; p indicates the significance of the coefficient.

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Fig. 9

Volume ratio of the low shear rate region (<50 s−1) against the distance from the aneurysm neck to its fundus in the aneurysms in case A (left) and case B (right). Error bars show the maximum and minimum ranges.



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