Computer modeling of deployment and mechanical expansion of neurovascular flow diverter in patient-specific intracranial aneurysms
Introduction
Neurovascular flow diverter (FD) is an emerging paradigm for treating traditionally difficult intracranial aneurysm such as wide-necked or fusiform aneurysms (Nelson et al., 2011). It is a self-expandable, tube-shaped metallic stent with fine braided mesh delivered via a catheter. Owing to its low porosity and high pore density, FD is effective at reducing blood inflow to the aneurysm sac, promoting intra-aneurysm thrombosis while keeping the adjacent arterial perforators unblocked. Endothelialization on the stent inner surface forms a new blood flow conduit within months that bypasses the obliterated aneurysm (Szikora et al., 2010).
While this novel intervention has achieved clinical success in an increasing number of challenging aneurysm cases, serious complications such as delayed post-treatment hemorrhage have also been reported (Byrne and Beltechi, 2010, Siddiqui and Abla, 2012). Several contributing factors have been hypothesized including extended aneurysm occlusion time leading to thrombosis-related aneurysm wall weakening (Kulcsar et al., 2011) and post-treatment pressure increase inside the aneurysm dome (Cebral et al., 2011). These hypotheses essentially attribute the variability of clinical outcomes to the patient-specific modification of hemodynamics, which significantly influences endothelialization, thrombosis and wall remodeling. Therefore, knowledge of detailed hemodynamics modified by FD placement is critical to the prediction of treatment outcome.
Image-based computational fluid dynamics (CFD) analysis can potentially provide important insight for this purpose but requires realistic representations of FD in deployed states. This presents challenges to the numerical simulation of stent implantation, since previous methods do not capture clinically realistic FD deployment processes and cannot reproduce the highly variable deployed configurations.
In light of the increasing clinical need for accurate CFD analysis of FD treatment and the inability of current numerical methods to produce realistically expanded FD geometries, we have developed a virtual FD deployment method using finite element analysis (FEA). In this approach we model the main steps involved in FD stent deployment in patient-specific aneurysm geometry to obtain realistic final FD configuration. Aside from being a prerequisite in accurate CFD analysis, this method can investigate FD deployment strategies employed by operating clinicians, as well as evaluate the mechanical characteristics of FD stents.
Section snippets
Methods
Our FD deployment modeling workflow (Fig. 1) uses these strategies:
- (1).
FD stent is modeled by 3D finite beam element because of the slender shape of its helical component strands.
- (2).
The entire deployment process is modeled from stent crimping (packaging), fitting into a microcatheter, maneuver and delivery of the stent-microcatheter system, to stent release from the microcatherter.
- (3).
Several key components of the FD delivery system are also modeled (Fig. 2). They are found essential to the final deployed
Model validation
First, the grid sensitivity test shows that a beam element size of 0.09 mm was sufficient to accurately capture FD stent’s behavior (Supplement Part 2). Second, experimental validation using a modeled Wallstent (Fig. 6) shows excellent agreement of simulation experiment data. Third, modeling result of an F1 flow diverter in a simple scenario – free release from a sheath in unstrained space – recapitulated time-resolved x-ray imaging of an actual FD coming out of its microcatheter (Fig. 7). Both
Discussion
Initial clinical reports of FD treatment showed high success rates in aneurysm occlusions in six months to one year (Lylyk et al., 2009). However, several complications such as inadequate device apposition, periprocedural distal thrombo-embolization and prolonged occlusion time have been reported to cause morbidity and mortality (D'Urso et al., 2011). At Millard Fillmore Gates Hospital, applications of FD to aneurysms of the posterior fossa also encountered mortality and morbidity despite
Conclusion
The variability of FD treatment outcome requires knowledge of hemodynamic modifications by deployment-specific FD configurations in patient-specific aneurysm geometries. A FEA-based method of simulating mechanical deployment of FD has been developed and tested against available experimental data. The 3D finite beam element model, accounting for interactions between stent strands and between stent and other deployment components, is shown to capture the mechanical responses of braided stents
Acknowledgments
This study is partially supported by Toshiba Medical Systems. We thank Corvidien for Pipeline Embolization Device samples for this study and Debra Zimmer for editorial assistance.
References (27)
- et al.
Virtual optimization of self-expandable braided wire stents
Medical Engineering & Physics
(2009) - et al.
Numerical simulation of hemodynamics in stented internal carotid aneurysm based on patient-specific model
Journal of Biomechanics
(2010) - et al.
Stiffness and elastic behavior of human intracranial and extracranial arteries
Journal of Biomechanics
(1980) - et al.
Mechanical modeling of self-expandable stent fabricated using braiding technology
Journal of Biomechanics
(2008) - et al.
Comparative friction of orthodontic wires under dry and wet conditions
American Journal of Orthodontics
(1986) - et al.
Contact and friction between catheter and blood vessel
Tribology International
(2007) - et al.
Alteration of intra-aneurysmal hemodynamics for flow diversion using enterprise and vision stents
World Neurosurgery
(2010) - et al.
Delivery and release of nitinol stent in carotid artery and their interactions: a finite element analysis
Journal of Biomechanics
(2007) - et al.
Computational fluid dynamics of stented intracranial aneurysms using adaptive embedded unstructured grids
International Journal for Numerical Methods in Fluids
(2008) - et al.
Handbook of Biomaterial Properties
(1998)
Early experience in the treatment of intra-cranial aneurysms by endovascular flow diversion: a multicentre prospective study
PLoS One
Aneurysm rupture following treatment with flow-diverting stents: computational hemodynamics analysis of treatment
AJNR American Journal of Neuroradiology
Incomplete stent apposition and very late stent thrombosis after drug-eluting stent implantation
Circulation
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2022, Computers in Biology and MedicineCitation Excerpt :In particular, the virtual testing of devices on the specific anatomy of each patient is considered the most valuable application of simulation [16]. In the past few years, different methods have been proposed to simulate braided device deployment, such as stents and flow diverters (FD) [17–20]. The work of Larrabide et al. [21] validated in [22], allows predicting the foreshortening that a FD will suffer after deployed in the vasculature of a patient.