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Technical Brief

In Vitro Investigation of a New Thin Film Nitinol-Based Neurovascular Flow Diverter

[+] Author and Article Information
M. H. Babiker

Endovantage, LLC,
Skysong,
Ste. 200, 1475 N. Scottsdale Road,
Scottsdale, AZ 85257
e-mail: haithem.babiker@endovantage.com

Y. Chun

Department of Industrial Engineering,
Swanson School of Engineering,
University of Pittsburgh,
1034 Benedum Hall,
Pittsburgh, PA 15261;
Department of Bioengineering,
Swanson School of Engineering,
University of Pittsburgh,
1034 Benedum Hall,
Pittsburgh, PA 15261
e-mail: yjchun@pitt.edu

B. Roszelle

Department of Mechanical and Materials Engineering,
University of Denver,
2390 S. York Street,
Denver, CO 80208
e-mail: Breigh.Roszelle@du.edu

W. Hafner

Department of Physical Medicine and Rehabilitation,
University of Colorado,
12631 East 17th Avenue,
Aurora, CO 80045
e-mail: walt.hafner@gmail.com

H. Y. Farsani

School of Biological and Health Systems Engineering,
ECG 334,
Tempe, AZ 85287-9707
e-mail: hyadolla@asu.edu

L. F. Gonzalez

Duke University Hospital,
2301 Erwin Road,
Durham, NC 27710
e-mail: Fernando.gonzalez@duke.edu

F. Albuquerque

Barrow Neurological Institute,
Saint Joseph's Hospital and Medical Center,
350 W. Thomas Road,
Phoenix, AZ 85013
e-mail: Felipe.Albuquerque@bnaneuro.net

C. Kealey

Business Development,
NeuroSigma, Inc.,
10960 Wilshire Boulevard, Suite 1910,
Los Angeles, CA 90024
e-mail: ckealey@neurosigma.com

D. S. Levi

Pediatric Cardiology,
Mattel Children's Hospital,
UCLA,
B2-427, 10833 Le Conte Avenue,
Los Angeles, CA 90095-1743
e-mail: dlevi@ucla.edu

G. P. Carman

Department of Mechanical and Aerospace Engineering,
University of California, Los Angeles,
38-137M, Engineering IV,
Los Angeles, CA 90095
e-mail: carman@seas.ucla.edu

D. H. Frakes

School of Biological and Health Systems Engineering,
ECG 334,
Tempe, AZ 85287-9707
e-mail: dfrakes@asu.edu

1Corresponding author.

Manuscript received March 27, 2015; final manuscript received February 26, 2016; published online September 12, 2016. Assoc. Editor: Rupak K. Banerjee.

J. Med. Devices 10(4), 044506 (Sep 12, 2016) (7 pages) Paper No: MED-15-1153; doi: 10.1115/1.4033015 History: Received March 27, 2015; Revised February 26, 2016

Fusiform and wide-neck cerebral aneurysms (CAs) can be challenging to treat with conventional endovascular or surgical approaches. Recently, flow diverters have been developed to treat these cases by diverting flow away from the aneurysm rather than occluding it. The pipeline embolization device (PED), which embodies a single-layer braided design, is best known among available flow diverters. While the device has demonstrated success in recent trials, late aneurysmal rupture after PED treatment has been a concern. More recently, a new generation of dual-layer devices has emerged that includes a novel hyperelastic thin film nitinol (HE-TFN)-covered design. In this study, we compare fluid dynamic performance between the PED and HE-TFN devices using particle image velocimetry (PIV). The PED has a pore density of 12.5–20 pores/mm2 and a porosity of 65–70%. The two HE-TFN flow diverters have pore densities of 14.75 pores/mm2 and 40 pores/mm2, and porosities of 82% and 77%, respectively. Conventional wisdom suggests that the lower porosity PED would decrease intra-aneurysmal flow to the greatest degree. However, under physiologically realistic pulsatile flow conditions, average drops in root-mean-square (RMS) velocity (VRMS) within the aneurysm of an idealized physical flow model were 42.8–73.7% for the PED and 68.9–82.7% for the HE-TFN device with the highest pore density. Interestingly, examination of collateral vessel flows in the same model also showed that the HE-TFN design allowed for greater collateral perfusion than the PED. Similar trends were observed under steady flow conditions in the idealized model. In a more clinically realistic scenario wherein an anatomical aneurysm model was investigated, the PED affected intra-aneurysmal VRMS reductions of 64.3% and 56.3% under steady and pulsatile flow conditions, respectively. In comparison, the high pore density HE-TFN device reduced intra-aneurysmal VRMS by 88% and 71.3% under steady and pulsatile flow conditions, respectively. We attribute the superior performance of the HE-TFN device to higher pore density, which may play a more important role in modifying aneurysmal fluid dynamics than the conventional flow diverter design parameter of greatest general interest, absolute porosity. Finally, the PED led to more elevated intra-aneurysmal pressures after deployment, which provides insight into a potential mechanism for late rupture following treatment with the device.

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References

Figures

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Fig. 1

Three-dimensional reconstruction of a typical sidewall CA from medical image data [1]

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Fig. 2

The thin film nitinol mesh covering of the HE-TFN flow diverter is indicated along with its laser-cut stent backbone. A standard U.S. currency penny is shown for scale.

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Fig. 3

The idealized model (a) with the PED, and the anatomical model (b) without any devices deployed. The perforating vessel in the idealized model is visible at the left of (a) and a pressure tap into the fundus of the anatomical model is visible at the top of (b). Note that the model images are at similar but not identical scales.

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Fig. 4

Bar graphs of aneurysmal VRMS after treatment with various stents and flow diverters in the idealized CA model under steady and pulsatile flow conditions. The percentages reported above each bar represent reductions in VRMS as compared to the no device case.

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Fig. 5

Flow velocity vector fields after treatment with various stents and flow diverters in the idealized CA model under pulsatile flow conditions. Data for the early systolic and mid-diastolic phases of the cardiac cycle are shown. The parent vessel flow direction is from left to right.

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Fig. 6

Bar graphs of aneurysmal VRMS after treatment with the PED and HE-TFN-300 flow diverters in the anatomical CA model under steady and pulsatile flow conditions. The percentages reported above each bar represent reductions in VRMS as compared to the no device case.

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Fig. 7

Flow velocity vector fields after treatment with the PED and HE-TFN-300 flow diverters in the anatomical CA model under pulsatile flow conditions. Data for the early systolic and mid-diastolic phases of the cardiac cycle are shown. The parent vessel flow direction is from left to right.

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Fig. 8

Bar graphs of perforator VRMS after treatment with various stents and flow diverters in the idealized CA model under steady and pulsatile flow conditions. The percentages reported above each bar represent reductions in VRMS as compared to the no device case.

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Fig. 9

Aneurysmal pressure measurements after treatment with the PED and HE-TFN-300 flow diverters in the anatomical CA model under pulsatile flow conditions

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