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RESEARCH PAPERS

In Vitro Evaluation of Flow Divertors in an Elastase-Induced Saccular Aneurysm Model in Rabbit

[+] Author and Article Information
Jaehoon Seong

Department of Biomedical Engineering, University of Miami, 1251 Memorial Drive, Coral Gables, FL 33146j.seong@miami.edu

Ajay K. Wakhloo

Department of Radiology, University of Massachusetts Medical School, 55 Lake Avenue, Worchester, MA 01655wakhlooa@ummhc.org

Baruch B. Lieber

Department of Biomedical Engineering, and Department of Radiology, University of Miami, 1251 Memorial Drive, Coral Gables, FL 33146blieber@miami.edu

J Biomech Eng 129(6), 863-872 (Mar 07, 2007) (10 pages) doi:10.1115/1.2800787 History: Received July 26, 2006; Revised March 07, 2007

Endovascular coiling is an acceptable treatment of intracranial aneurysms, yet long term follow-ups suggest that endovascular coiling fails to achieve complete aneurysm occlusions particularly in wide-neck and giant aneurysms. Placing of a stentlike device across the aneurysm neck may be sufficient to occlude the aneurysm by promoting intra-aneurysmal thrombosis; however, conclusive evidence of its efficacy is still lacking. In this study, we investigate in vitro the efficacy of custom designed flow divertors that will be subsequently implanted in a large cohort of animals. The aim of this study is to provide a detailed database against which in vivo results can be analyzed. Six custom designed flow divertors were fabricated and tested in vitro. The design matrix included three different porosities (75%, 70%, and 65%). For each porosity, there were two divertors with one having a nominal pore density double than that of the other. To quantify efficacy, the divertors were implanted in a compliant elastomeric model of an elastase-induced aneurysm model in rabbit and intra-aneurysmal flow changes were evaluated by particle image velocimetry (PIV). PIV results indicate a marked reduction in intra-aneurysmal flow activity after divertor implantation in the innominate artery across the aneurysm neck. The mean hydrodynamic circulation after divertor implantation was reduced to 14% or less of the mean circulation in the control and the mean intra-aneurysmal kinetic energy was reduced to 29% or less of its value in the control. The intra-aneurysmal wall shear rate in this model is low and implantation of the flow divertor did not change the wall shear rate magnitude appreciably. This in vitro experiment evaluates the characteristics of local flow phenomena such as hydrodynamic circulation, kinetic energy, wall shear rate, perforator flow, and changes of these parameters as a result of implantation of stentlike flow divertors in an elastomeric replica of elastase-induced saccular aneurysm model in rabbit. These initial findings offer a database for evaluation of in vivo implantations of such devices in the animal model and help in further development of cerebral aneurysm bypass devices.

Copyright © 2007 by American Society of Mechanical Engineers
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References

Figures

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Figure 9

Peak kinetic energy inside the aneurysm before and after implantation of flow divertors. Error bars denote SEM (n=3) (ns: P>0.05,  *: P<0.05,  **: P<0.01, and  ***: P<0.001).

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Figure 10

(A) Local WSR measurements at five different locations inside the sac: (a) proximal neck, (b) proximal wall, (c) dome, (d) distal wall, and (e) distal neck of the aneurysm. (B) Coordinate system of positive WSR in the aneurysm and the parent artery.

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Figure 11

WSR at the proximal neck of the aneurysm (Location (a)) for all cases: (A) control and Divertor Nos. 1, 3, and 5 and (B) control and Divertor Nos. 2, 4, and 6. Error bars denote SEM (n=3).

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Figure 12

WSR at the dome of the aneurysm (Location (c)) for all cases: (A) control and Divertor Nos. 1, 3, and 5 and (B) control Divertor Nos. 2, 4, and 6. Error bars denote SEM (n=3).

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Figure 13

WSR at the distal neck of the aneurysm (Location (e)) for all cases: (A) control and Divertor Nos. 1, 3, and 5 and (B) control and Divertor Nos. 2, 4, and 6. Error bars denote SEM (n=3).

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Figure 14

Velocity vectors in vertebral artery of the silicone model: (A) pre-implantation of a divertor and (B) post-implantation of a divertor

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Figure 1

(A) Silicone replica of elastase-induced aneurysm model in rabbit and (B) a silicone model placed in a Plexiglas box

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Figure 2

Modified flow rate in the ascending aorta of the anesthetized rabbit (— —) and flow rate in the ascending aorta of the flow model (—) (error bars denote SEM (n=3))

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Figure 15

Flow rates in the vertebral artery in all cases: (A) control and cases after flow divertors implanted (Divertor Nos. 1, 3, and 5) and (B) control and cases after flow divertors implanted (Divertor Nos. 2, 4, and 6). Error bars denote SEM (n=3).

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Figure 3

Schematic of mock circulation loop and PIV system

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Figure 4

PIV results of flow patterns in the aneurysm of the silicone model during a cardiac cycle (control)

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Figure 5

PIV results of flow patterns in the aneurysm of the silicone model with flow Divertor No. 6 during a cardiac cycle

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Figure 6

Temporal evolution of intra-aneurysmal circulation: (A) control, (B) after flow divertors implanted (Divertor Nos. 1, 3, and 5), and (C) after flow divertors implanted (Divertor Nos. 2, 4, and 6). Error bars denote SEM (n=3).

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Figure 7

Mean hydrodynamic circulation inside the aneurysm before and after implantation of flow divertors. Error bars denote SEM (n=3). (ns: P>0.05,  *: P<0.05,  **: P<0.01, and  ***: P<0.001).

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Figure 8

Mean kinetic energy inside the aneurysm before and after implantation of flow divertors. Error bars denote SEM (n=3) (ns: P>0.05,  *: P<0.05,  **: P<0.01, and  ***: P<0.001).

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