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Effect of Flow Diverter Porosity on Intraaneurysmal Blood Flow

Effekt der Porosität von „flow diverters“ auf den intraaneurysmatischen Blutfluss

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Abstract

Background and Purpose:

Growth and rupture, the two events that dominate the evolution of an intracranial aneurysm, are both dependent on intraaneurysmal flow. Decrease of intraaneurysmal flow is considered an attractive alternative for treating intracranial aneurysms by minimally invasive techniques. Such modification can be achieved by inserting stents or flow diverters alone. In the present paper, the effect of different commercial and innovative flow diverters’ porosity was studied in intracranial aneurysm models.

Material and Methods:

Single and stent-in-stent combination of Neuroform II as well as single and stent-in-stent combination of a new innovative, low-porosity, intracranial stent device (D1, D2, D1 + D2) were inserted in models of intracranial aneurysms under shear-driven flow and inertia-driven flow configurations. Steady and pulsating flow rates were applied using a blood-like fluid. Particle image velocimetry was used to measure velocity vector fields in the aneurysm midplane along the vessel axis. Flow and vorticity patterns, velocity and vorticity magnitudes were quantified and their value compared with the same flows in absence of the flow diverter.

Results:

In absence of flow diverters, a solid-like rotation could be observed in both shear-driven and inertia-driven models under steady and pulsatile flow conditions. The flow effects due to the insertion of low-porous devices such as D1 or D2 provoked a complete alteration of the flow patterns and massive reduction of velocity or vorticity magnitudes, whereas the introduction of clinically adopted high-porous devices provoked less effect in the aneurysm cavity. As expected, results showed that the lower the porosity the larger the reduction in velocity and vorticity within the aneurysm cavity. The lowest-porosity device combination (D1 and D2) reached an averaged reduction of flow parameters of 80% and 88% under steady and pulsatile flow conditions, respectively. The reduction in mean velocity and vorticity was much more significant in the shear-driven flows as compared to the inertia-driven flows.

Conclusion:

Although device porosity is the main parameter influencing flow reduction, other parameters such as device design and local flow conditions may influence the level of flow reduction within intracranial aneurysms.

Zusammenfassung

Hintergrund und Ziel:

Die zwei wichtigsten Faktoren für die Entwicklung intrazerebraler Aneurysmen, nämlich Wachstum und Ruptur, hängen vom intraaneurysmatischen Blutfluss ab. Eine Verminderung des intraaneurysmatischen Blutflusses durch minimalinvasive Techniken wird als attraktive Behandlungsmethode erachtet. Eine solche Modifikation des Blutflusses kann durch das Einbringen eines Stents oder „flow diverter“ allein erzielt werden. In der vorliegenden Arbeit untersuchten die Autoren den Effekt der Porosität verschiedener handelsüblicher und innovativer „flow diverters“ an Modellen intrakranieller Aneurysmen.

Material und Methodik:

Sowohl einzelne oder Stent-in-Stent-Kombinationen des Neuroform II (NF) als auch einzelne oder Stent-in-Stent-Kombinationen von neuen innovativen, niedrigporösen intrakraniellen Stents (D1, D2, D1 + D2) wurden in Modellen intrakranieller Aneurysmen mit Eigenschaften von „shear-driven“ und „inertia-driven“ Fluss platziert. Flächen mit Geschwindigkeitsvektoren in der mittleren Ebene des Aneurysmas parallel zur Achse des Gefäßes wurden mit Hilfe der „particle image velocimetry“ (PIV) ermittelt. Eigenschaften von Fluss und Verwirbelungen, Geschwindigkeit und Ausmaß von Verwirbelungen wurden gemessen und mit Messwerten des gleichen Modells ohne „flow diverter“ verglichen.

Ergebnisse:

Ohne „flow diverter“ konnte eine beständige Rotation in beiden – „shear-driven“ und „inertia-driven“ – Flussmodellen beobachtet werden. Die Auswirkungen nach Platzierung eines niedrigporösen Modells wie D1 oder D2 riefen eine komplette Änderung der Flusseigenschaften und eine massive Verringerung der Geschwindigkeit und des Ausmaßes von Verwirbelungen hervor, wohingegen die Platzierung klinisch angewendeter hochporöser Modelle geringere Auswirkungen auf die Kavität des Aneurysmas hatte. Erwartungsgemäß haben die Ergebnisse gezeigt: Je kleiner die Porosität ist, desto größer sind die Auswirkungen auf Blutflussgeschwindigkeit und Verwirbelungen im Aneurysma. Die Kombination mit der geringsten Porosität (D1 und D2) erzielte eine durchschnittliche Reduktion der Flussparameter um 80% bzw. 88% bei konstanten und pulsatilen Flüssen. Die Verminderung von mittlerer Geschwindigkeit und von Verwirbelungen war beim „shear-driven“ Fluss deutlich signifikanter als beim „inertia-driven“ Fluss.

Schlussfolgerung:

Obwohl die Porosität der wichtigste Parameter zur Senkung des Flusses ist, können andere Parameter wie das Design des jeweiligen Modells oder lokale Flusseigenschaften die Wirksamkeit der Flussreduktion in intrakraniellen Aneurysmen beeinflussen.

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Correspondence to Luca Augsburger.

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Augsburger, L., Farhat, M., Reymond, P. et al. Effect of Flow Diverter Porosity on Intraaneurysmal Blood Flow. Clin Neuroradiol 19, 204–214 (2009). https://doi.org/10.1007/s00062-009-9005-0

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  • DOI: https://doi.org/10.1007/s00062-009-9005-0

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