R King

The impact of coil shape design on angiographic occlusion, packing density and coil mass uniformity in aneurysm embolization: an in vitro study

Objective To investigate the impact of coil design on the distribution of the coil mass in a controlled in vitro experiment. A secondary objective was to study the relationship between angiographic occlusion, packing density and coil mass uniformity. Methods Seven silicon side wall aneurysm models were embolized in each arm with a different coil design under fluoroscopic guidance. Packing density calculations and scoring of the angiographic occlusion were made. The models were embedded in epoxy and sectioned through the aneurysm neck and the dome. The sections were imaged and processed to derive the fractional surface area of coil material over the coil free area, a quantitative endpoint representing the percentage of the given region of interest consumed by coils. The SD of the surface area fractions is inversely proportional to the uniformity of coil distribution. Results The novel triangular primary wind design of the Deltapaq achieved a more homogenous distribution of coils within the aneurysm dome compared with the helical and complex microcoil systems (p=0.018). The packing density achieved by the Deltapaq (39.1±1.6%) was significantly higher than the complex (35.2±2.8%) and the helical (32.2±3.3%) coils. Angiographically, aneurysms coiled by the Deltapaq were more likely to obtain a Raymond score of class I. Conclusion Evaluation of emerging coil technologies with respect to treatment durability may be well served by an assessment of their uniformity of distribution within an aneurysm in addition of the traditional packing density and angiographic occlusion scoring methods.

The Effect of Intracranial Stent Implantation on the Curvature of the Cerebrovasculature

BACKGROUND AND PURPOSE: Recently, the use of stents to assist in the coiling and repair of wide-neck aneurysms has been shown to be highly effective; however, the effect of these stents on the RC of the parent vessel has not been quantified. The purpose of this study was to quantify the effect of intracranial stenting on the RC of the implanted artery using 3D datasets. MATERIALS AND METHODS: Twenty-four patients receiving FDA-approved neurovascular stents to support coil embolization of brain aneurysms were chosen for this study. The stents were located in the ICA, ACA, or MCA. We analyzed C-arm rotational angiography and contrast-enhanced cone beam CT datasets before and after stent implantation, respectively, to ascertain changes in vessel curvature. The images were reconstructed, and the vessel centerline was extracted. From the centerline, the RC was calculated. RESULTS: The average implanted stent length was 25.4 ± 5.8 mm, with a pre-implantation RC of 7.1 ± 2.1 mm and a postimplantation RC of 10.7 ± 3.5 mm. This resulted in a 3.6 ± 2.7 mm change in the RC due to implantation (P < .0001), more than a 50% increase from the pre-implantation value. There was no difference in the change of RC for the different locations studied. The change in RC was not impacted by the extent of coil packing within the aneurysm. CONCLUSIONS: The implantation of neurovascular stents can be shown to have a large impact on the RC of the vessel. This will lead to a change in the local hemodynamics and flow pattern within the aneurysm.

Grading of Regional Apposition after Flow-Diverter Treatment (GRAFT): a comparative evaluation of VasoCT and intravascular OCT

Background Poor vessel wall apposition of flow diverter (FD) stents poses risks for stroke-related complications when treating intracranial aneurysms, necessitating long-term surveillance imaging. To facilitate quantitative evaluation of deployed devices, a novel algorithm is presented that generates intuitive two-dimensional representations of wall apposition from either high-resolution contrast-enhanced cone-beam CT (VasoCT) or intravascular optical coherence tomography (OCT) images. Methods VasoCT and OCT images were obtained after FD implant (n=8 aneurysms) in an experimental sidewall aneurysm model in canines. Surface models of the vessel wall and FD device were extracted, and the distance between them was presented on a two-dimensional flattened map. Maps and cross-sections at potential locations of malapposition detected on VasoCT-based maps were compared. The performance of OCT-based apposition detection was evaluated on manually labeled cross-sections using logistic regression against a thresholded (≥0.25 mm) apposition measure. Results VasoCT and OCT acquisitions yielded similar Grading of Regional Apposition after Flow-Diverter Treatment (GRAFT) apposition maps. GRAFT maps from VasoCT highlighted 16 potential locations of malapposition, of which two were found to represent malapposed device struts. Logistic regression showed that OCT could detect malapposition with a sensitivity of 98% and a specificity of 81%. Conclusions GRAFT delivered quantitative and visually convenient representations of potential FD malapposition and occasional acute thrombus formation. A powerful combination for future neuroendovascular applications is foreseen with the superior resolution delivered by intravascular OCT.

Quantitative assessment of device–clot interaction for stent retriever thrombectomy

Purpose Rapid revascularization in emergent large vessel occlusion with endovascular embolectomy has proven clinical benefit. We sought to measure device–clot interaction as a potential mechanism for efficient embolectomy. Methods Two different radiopaque clot models were injected to create a middle cerebral artery occlusion in a patient-specific vascular phantom. A radiopaque stent retriever was deployed within the clot by unsheathing the device or a combination of unsheathing followed by pushing the device (n=8/group). High-resolution cone beam CT was performed immediately after device deployment and repeated after 5 min. An image processing pipeline was created to quantitatively evaluate the volume of clot that integrates with the stent, termed the clot integration factor (CIF). Results The CIF was significantly different for the two deployment variations when the device engaged the hard clot (p=0.041), but not the soft clot (p=0.764). In the hard clot, CIF increased significantly between post-deployment and final imaging datasets when using the pushing technique (p=0.019), but not when using the unsheathing technique (p=0.067). When we investigated the effect of time on CIF in the different clot models disregarding the technique, the CIF was significantly increased in the final dataset relative to the post-deployment dataset in both clot models (p=0.004–0.007). Conclusions This study demonstrates in an in vitro system the benefit of pushing the Trevo stent during device delivery in hard clot to enhance integration. Regardless of delivery technique, clot–device integration increased in both clot models by waiting 5 min.

Acute thrombus formation on phosphorilcholine surface modified flow diverters

Purpose Thromboembolic complications remain a limitation of flow diverting stents. We hypothesize that phosphorilcholine surface modified flow diverters (Pipeline Flex with Shield Technology, sPED) would have less acute thrombus formation on the device surface compared with the classic Pipeline Embolization device (cPED). Methods Elastase-induced aneurysms were created in 40 rabbits and randomly assigned to receive cPED or sPED devices with and without dual antiplatelet therapy (DAPT) (four groups, n=10/group). Angioplasty was performed to enhance apposition and create intimal injury for a pro-thrombotic environment. Both before and after angioplasty, the flow diverter was imaged with intravascular optical coherence tomography. The outcome measure was the number of predefined segments along the implant relative to the location of the aneurysm with a minimum of 0 (no clot formation) and maximum of 3 (all segments with thrombus). Clot formation over the device at ostia of branch arteries was assessed as either present or absent. Results Following angioplasty, the number of flow diverter segments with clots was significantly associated with the flow diverter (p<0.0001), but not with DAPT (p=0.3872) or aneurysm neck size (p=0.8555). The incidence rate for clots with cPED was 1.72 times more than with sPED. The clots on the flow diverter at the location corresponding to side branch ostia was significantly lower with sPED than with cPED (OR 0.180; 95% CI 0.044 to 0.734; p=0.0168), but was not associated with DAPT (p=0.3198). Conclusion In the rabbit model, phosphorilcholine surface modified flow diverters are associated with less thrombus formation on the surface of the device.

Temporal Evolution of Susceptibility Artifacts from Coiled Aneurysms on MR Angiography: An In Vivo Canine Study

BACKGROUND AND PURPOSE: Intracranial aneurysms treated by coiling have a risk for recurrence, requiring surveillance imaging. MRA has emerged as an attractive technique for postcoiling aneurysm imaging. Previous research has evaluated MR imaging artifacts of the coil mass in vitro. Our aim in this study was to evaluate MR imaging artifacts of coiled aneurysms in vivo with time. MATERIALS AND METHODS: Four sidewall aneurysms were created in each of 4 dogs. Aneurysms were embolized receiving only 1 type of coils. After embolization, the animals were transferred to MR imaging, which included axial 3D TOF MRA (TEs, 3.5, 5, and 6.9 ms), phase-contrast MRA, and coronal CE-MRA. MR imaging studies were repeated at 1, 4, 6, 8, 14, and 28 weeks. We calculated an OEF: OEF = VA/VCM, where the numerator represents the volume of the MR imaging artifacts and the denominator is the true volume of the coil mass measured by 3D RA. RESULTS: OEFs were largest immediately after embolization and showed a gradual decay until approximately 4 weeks, when there was stabilization of the size of the artifacts. By 4 weeks, there was mild coil compaction (average coil mass volume decrease of 7.8%); however, the OEFs decreased by 25% after 4 weeks (P < .001). CONCLUSIONS: MR imaging susceptibility artifacts change with time, being maximal in the postembolization setting and decaying until 4 weeks. The clinical implications of this study are that baseline MRA for comparison with future imaging should be acquired at a minimum of 1 week after the procedure.

Novel Distal Emboli Protection Technology: The EmboTrap

Background: Over the course of the thrombectomy procedure, clot fragments may become dislodged and lead to downstream emboli due to manipulation of an endovascular device. The EmboTrap thrombectomy system features an inner stent channel with an outer stent trap design that may potentially reduce the risk of distal clot fragmentation during clot removal. We tested the hypothesis that distal emboli to both the same and new territory generated during mechanical thrombectomy are a function of device design. Methods: EmboTrap and Solitaire thrombectomy were conducted in an in vitro model system that mimicked a middle-cerebral artery (MCA) occlusion within a complete circle of Willis vascular replica and a contrast-enhanced clot analog. Emboli generated during the procedure with a size >1,000 μm were collected and measured with calipers. The Coulter principle was used to characterize emboli with a size between 200 and 1,000 µm. Results: EmboTrap thrombectomy resulted in a significant reduction in the risk of large emboli (>1,000 μm) formation as compared to first-generation stent retriever thrombectomy (p = 0.031, Fisher exact test). The majority of emboli >1,000 μm (∼80%) were found in the MCA, regardless of device type. There was no significant difference between the EmboTrap and Solitaire in 200 to 1,000 μm emboli formation (p = 0.89, Mann-Whitney test). When combining all emboli in the most dangerous range (>200 μm), EmboTrap offered a size reduction of emboli (p = 0.022). Conclusion: The risk of distal embolization can be altered with improved stent retriever design. When encountering fragment-prone clots, EmboTrap thrombectomy may lower the risk of distal embolization.

P-001 High-Resolution Optical and Angiographic CT Imaging of Flow-Diverter Stents for Assessment of Vessel Wall Apposition

Introduction Intracranial placement of flow-diverter (FD) stents provides a safe and effective treatment for aneurysms.1 However, long-term angiographic follow-up is indicated, since in-stent stenosis and late thrombosis as a consequence of poor vessel wall apposition increase the risks of stroke-related complications.1,2 In addition to conventional angiography, high-resolution contrast-enhanced cone-beam CT (VasoCT) may provide improved three-dimensional visualization of stent deployment and apposition.2,3 Here we explored the use of VasoCT for the assessment of FD vessel wall apposition in comparison to concurrent optical coherence tomography (OCT) endoscopy. Catheter-based OCT delivers near-infrared images at a spatial resolution in the order of 10–50 μm, which enables superior intravascular tissue and device visualization.4 This work was performed in an experimental sidewall aneurysm model in canines. Materials and methods Two sidewall aneurysms were created on each common carotid artery (CCA) in female canines by anastomosis of sections of the detached right external jugular vein, as described before.5 Under fluoroscopic guidance (Allura Xper FD20, Philips, Best, The Netherlands), FD stents (Pipeline Embolization Device, EV3-MTI, Irvine, CA; Surpass, Stryker, Fremont, CA) were placed and apposition was assessed bilaterally using VasoCT, and in the right CCA using OCT (C7 System/Dragonfly Catheter, St Jude Medical, Westford, MA). Results Figure 1 shows an example of poor apposition, approximately 7.5 mm proximal to the aneurysm on the right CCA. With OCT (right), the distance between the FD and vessel wall measured 0.39 mm. The vessel diameter in this plane was 3.24–3.53 mm, and the area between the stent and the vessel wall was 15% of the lumen area. A similar distance 0.35 mm could be observed in a 67 μm VasoCT reconstruction (left), although lumen and stent struts are rendered more smoothly as compared to OCT. Abstract P-001 Figure 1 Conclusion Due to its superior in-plane resolution, OCT clearly visualised the distinction between the vessel wall and the FD stent struts. Nevertheless, our example showed that VasoCT enables identification of apposition distances in the order of 0.5mm. Although OCT is clinically used in interventional cardiology, its neurovascular application is currently limited to the experimental setting. Here we showed that OCT can provide a gold-standard for the validation of VasoCT assessments of FD apposition. References Pierot L, Wakhloo AK. Stroke 2013;44:2046–2054 Kizilkilic O, et al. J Neurosurg 2012;117:45–49 Flood TF, et al. J NeuroIntervent Surg 2014;doi:10.1136/neurintsurg-2013-010950 Bezerra HG, et al. J Am Coll Cardiol Intv 2009;2:1035–1046 Wakhloo AK, et al. Am J Neuroradiol 1994;15:493–502 Disclosures K. van der Marel: None. M. Gounis: 1; C; eV3/Covidien, Philips Healthcare, NIH, Silk Road, Stryker Neurovascular. 2; C; Stryker Neurovascular, Codman Neurovascular. R. King: None. A. Wakhloo: 1; C; NIH, Philips Healthcare. 2; C; Stryker Neurovascular. A. Puri: None.

Phosphorylcholine surface modified flow diverter associated with reduced intimal hyperplasia

Background Optical coherence tomography (OCT) is a high-resolution, intra-vascular diagnostic technique widely used for the characterization of vascular pathologies and optimization of stent implantation during percutaneous coronary intervention. OCT was used to investigate the in vivo vascular response to a new phosphorylcholine surface modified flow diverter (sPED). Methods In an in vivo rabbit aneurysmal model, we used two different types of flow diverters (classic Pipeline – cPED; and sPED) with or without dual antiplatelet therapy (four groups, n=10 per group). OCT cross-sectional area measurements were compared with histology in all animals. Neointimal hyperplasia (NIH) ratio was compared between OCT and histology at five different levels for each stent. The severity of NIH was also compared between the different stents, antiplatelet protocols, and vessel locations. Results OCT was used to calculate in-stent hyperplasia in 227 different locations corresponding to histology sections. OCT measurement strongly correlated with gold standard histology (r2=0.83; slope=0.988; P<0.0001). sPED had significantly less in-stent NIH than non-treated flow diverters (mean percent of lumen reduction 5.7% for sPED versus 8.9% for cPED; P<0.0001). The NIH ratio was slightly higher with dual antiplatelet therapy (DAPT) (NIH ratio=7.9% with DAPT versus 6.8% without DAPT; P<0.05). Complete and near complete occlusion rates of the aneurysms were not different with the cPED or sPED. Conclusion OCT is a promising technique for immediate and long-term evaluation of flow diverter stent treatments. In an animal model, phosphorylcholine surface modified flow diverters induces less NIH after stent implant without reducing aneurysm occlusion rates.

Communicating malapposition of flow diverters assessed with optical coherence tomography correlates with delayed aneurysm occlusion

Background Optical coherence tomography (OCT) is a high resolution intravascular imaging method that allows visualization of flow diverter struts and the vessel wall. In this study, malapposition of the flow diverter that continues into the neck of the aneurysm, named communicating malapposition (CM), was investigated as a potential factor for delayed aneurysm healing. Methods 40 New Zealand White rabbits underwent elastase induced aneurysm creation, and were subsequently assigned to one of four treatment groups based on flow diverter type and administration of antiplatelet therapy. All animals underwent post device deployment balloon angioplasty and subsequent OCT to assess device/vessel apposition. The incidence of CM seen on OCT was assessed with a binary scoring system: 0–CM present; 1–CM absent. At 30 days, DSA was acquired to assess aneurysm healing. Aneurysm healing on terminal DSA was measured using a previously developed 5 point scale, with a score of 3 or 4 considered a positive outcome. Results All animals were grouped into a single cohort for analysis as no difference in the rate of CM or healing was seen in the four treatment groups. Significant interaction between the absence of CM and a positive outcome was confirmed by Fisher exact test (P=0.0034). Angioplasty was shown to treat 33% of the cases of CM seen at implant, and these treated cases overwhelmingly had a positive outcome (P<0.001). Conclusion The use of OCT to assess CM of flow diverters has been shown to be predictive of the 30 day healing rate of an animal model of aneurysms.