Abstract
We present flow-based results from the early stage design cycle, based on computational modeling, of a prototype flow-diverter device, known as the ‘Sphere’, intended to treat bifurcation aneurysms of the cerebral vasculature. The device is available in a range of diameters and geometries and is constructed from a single loop of NITINOL® wire. The ‘Sphere’ reduces aneurysm inflow by means of a high-density, patterned, elliptical surface that partially occludes the aneurysm neck. The device is secured in the healthy parent vessel by two armatures in the shape of open loops, resulting in negligible disruption of parent or daughter vessel flow. The device is virtually deployed in six anatomically accurate bifurcation aneurysms: three located at the Basilar tip and three located at the terminus bifurcation of the Internal Carotid artery (at the meeting of the middle cerebral and anterior cerebral arteries). Both steady state and transient flow simulations reveal that the device presents with a range of aneurysm inflow reductions, with mean flow reductions falling in the range of 30.6–71.8% across the different geometries. A significant difference is noted between steady state and transient simulations in one geometry, where a zone of flow recirculation is not captured in the steady state simulation. Across all six aneurysms, the device reduces the WSS magnitude within the aneurysm sac, resulting in a hemodynamic environment closer to that of a healthy vessel. We conclude from extensive CFD analysis that the ‘Sphere’ device offers very significant levels of flow reduction in a number of anatomically accurate aneurysm sizes and locations, with many advantages compared to current clinical cylindrical flow-diverter designs. Analysis of the device’s mechanical properties and deployability will follow in future publications.
Highlights
The frequency of intracranial aneurysms in the general population is considered to be between 1 and 5%.47 In the vast majority of cases, these aneurysms are asymptomatic, posing no health risk to the patient
Governing Equations and Solution Procedure Six anatomically accurate, bifurcation aneurysm geometries are selected: three examples of a Basilar tip blood is in general non-Newtonian, it has been shown that the non-Newtonian effects can be assumed secondary in arteries with a diameter greater than 0.5 mm.[29]
An entry plane meeting the criteria previously set out is projected across each aneurysm neck, and the aneurysm inflow at each time step of the transient solution and for the steady state solution is calculated
Summary
The frequency of intracranial aneurysms in the general population is considered to be between 1 and 5%.47 In the vast majority of cases, these aneurysms are asymptomatic, posing no health risk to the patient. Intracranial aneurysm rupture is a major cause of stroke, resulting in hemorrhagic stroke or subarachnoid hemorrhage. Aneurysm rupture can lead to significant brain damage and even death in around 25% of hemorrhage cases.[8] As diagnostic imaging use becomes more widespread, an increasing number of asymptomatic aneurysms are being identified during imaging scans (CT, MRI) requested for other conditions.[47]. This has lead to marked increase in the need for effective treatment options to stabilize the ever-increasing number of aneurysms identified as being at risk of rupture or complications. Treatments focus on reducing the rupture risk by excluding the aneurysm from the circulation, which induces stable thrombus formation within the aneurysm sac, and vascular remodeling
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