Flow modification in canine intracranial aneurysm model by an asymmetric stent: studies using digital subtraction angiography (DSA) and image-based computational fluid dynamics (CFD) analyses

Abstract

An asymmetric stent with low porosity patch across the intracranial aneurysm neck and high porosity elsewhere is designed to modify the flow to result in thrombogenesis and occlusion of the aneurysm and yet to reduce the possibility of also occluding adjacent perforator vessels. The purposes of this study are to evaluate the flow field induced by an asymmetric stent using both numerical and digital subtraction angiography (DSA) methods and to quantify the flow dynamics of an asymmetric stent in an in vivo aneurysm model. We created a vein-pouch aneurysm model on the canine carotid artery. An asymmetric stent was implanted at the aneurysm, with 25% porosity across the aneurysm neck and 80% porosity elsewhere. The aneurysm geometry, before and after stent implantation, was acquired using cone beam CT and reconstructed for computational fluid dynamics (CFD) analysis. Both steady-state and pulsatile flow conditions using the measured waveforms from the aneurysm model were studied. To reduce computational costs, we modeled the asymmetric stent effect by specifying a pressure drop over the layer across the aneurysm orifice where the low porosity patch was located. From the CFD results, we found the asymmetric stent reduced the inflow into the aneurysm by 51%, and appeared to create a stasis-like environment which favors thrombus formation. The DSA sequences also showed substantial flow reduction into the aneurysm. Asymmetric stents may be a viable image guided intervention for treating intracranial aneurysms with desired flow modification features.

The Expanding Realm of Endovascular Neurosurgery: Flow Diversion for Cerebral Aneurysm Management

“…22,23 However, computational fluid dynamics analyses suggested that placement of the stent in the parent vessel itself may alter flow within the aneurysm, potentially accelerating the rate of aneurysm thrombosis. 24,25 Flow diversion for the treatment of intracranial aneurysms was conceived through a combination of ingenuity and serendipity. While performing animal studies, researchers discovered that covering an aneurysm with a stent changed the flow dynamic into the aneurysm, in some instances leading to obliteration of the aneurysm.…”

Asymmetric Vascular Stent

“…Various groups have reported both in vitro and in vivo aneurysm treatment results with commercially available stents, 1,5,6,12,13 whereas our group has been developing specially designed stents. 2,3,7,8,14 Hemodynamic conditions in an IA dome vary significantly depending on aneurysm geometry, 15 and hence may require different treatments. Aneurysm thrombogenesis might be achievable through hemodynamic modification via a stent, regardless of initial flow conditions or IA dome geometry.…”

“…In vitro experiments with AVS-treated aneurysm phantoms using particle image velocimetry demonstrate a 2-order of magnitude drop in intraaneurysmal velocity and vorticity. 3 Hoi et al used a pressure reduction model with computational fluid dynamics to simulate a low-porosity patch covering the neck of a side-wall aneurysm 2 and also indicated drastic decreases in aneurysm-dome wall shear stress and vorticity. The benefit of using an AVS (over a fully covered stent) is that the nonpatch area of the stent has a high porosity (Ն80%), ensuring a low probability of perforator blockage.…”

“…2,3,8,14 Our asymmetric vascular stent (AVS) has a low-porosity mesh patch grafted to a standard high-porosity stent. The AVS is then deployed with the small dense area covering the aneurysm neck, thus significantly modifying aneurysm flow.…”

“…[1][2][3][4][5][6][7][8][9][10][11] Development may yield such potential benefits as reduced surgery time, lower dome perforation risk, shorter recovery time, reduced aneurysm recanalization, increased numbers of treatable aneurysms, and reduced costs. Various groups have reported both in vitro and in vivo aneurysm treatment results with commercially available stents, 1,5,6,12,13 whereas our group has been developing specially designed stents.…”