Preclinical model of anterior circulation intracranial stenting

BACKGROUND

Preclinical testing of intracranial stents is currently performed in the peripheral circulation, and rarely in the basilar artery of the dog.

OBJECTIVE

To test the feasibility of intracranial stenting in the middle cerebral artery (MCA) of the dog and explore the use of MRI to detect thromboembolic complications.

METHODS

Six purpose-bred cross-hound dogs were used for proof-of-concept stenting of both MCAs in each animal. Immediately following the procedure, the animals were imaged with MRI. MRI was repeated weekly for 1 month. After the final angiography at 30 days, the animals were euthanized for pathological assessment of the stents and the brain.

RESULTS

We successfully deployed 12 stents in the MCAs of all animals. We deployed three techniques for microcatheterization of the MCA-namely, directly through the internal carotid artery (ICA), using anastomotic arteries from the external carotid artery, or via the contralateral ICA through the anterior communicating artery. Two iatrogenic perforations of the ICA with formation of an arteriovenous fistula occurred, without clinical sequelae, which spontaneously resolved on follow-up. All animals tolerated the procedure and completed the follow-up surveillance. MRI revealed procedural thromboembolic induced areas of restricted diffusion, and only one instance of a delayed thromboembolic lesion during surveillance. At follow-up angiography, the devices were all patent.

CONCLUSION

We describe a new preclinical model of intracranial stenting in the MCA. Such a model may prove useful for evaluating new surface modifications.

Molecular Magnetic Resonance Imaging of Aneurysmal Inflammation Using a Redox Active Iron Complex

OBJECTIVES

Inflammation plays a key role in driving brain aneurysmal instability and rupture, but clinical tools to noninvasively differentiate between inflamed and stable aneurysms are lacking. We hypothesize that imaging oxidative changes in the aneurysmal microenvironment driven by myeloid inflammatory cells may represent a noninvasive biomarker to evaluate rupture risk. In this study, we performed initial evaluation of the oxidatively activated probe Fe-PyC3A as a tool for magnetic resonance imaging (MRI) of inflammation in a rabbit model of saccular aneurysm.

MATERIALS AND METHODS

The difference in longitudinal relaxivity ( r1 ) in reduced and oxidized states of Fe-PyC3A was measured in water and blood plasma phantoms at 3 T. A rabbit saccular aneurysm model was created by endovascular intervention/elastinolysis with subsequent decellularization in situ. Rabbits were imaged at 4 weeks (n = 4) or 12 weeks (n = 4) after aneurysmal induction, when luminal levels of inflammation reflected by the presence of myeloperoxidase positive cells are relatively high and low, respectively, using a 3 T clinical scanner. Both groups were imaged dynamically using a 2-dimensional T1-weighted fast field echo pulse MRI sequence before and up to 4 minutes postinjection of Fe-PyC3A. Dynamic imaging was then repeated after an injection of gadobutrol (0.1 mmol/kg) as negative control probe. Rabbits from the 12-week aneurysm group were also imaged before and 20 minutes and 3 hours after injection of Fe-PyC3A using an axial respiratory gated turbo-spin echo (TSE) pulse sequence with motion-sensitized driven equilibrium (MSDE) preparation. The MSDE/TSE imaging was repeated before, immediately after dynamic acquisition (20 minutes postinjection), and 3 hours after injection of gadobutrol. Aneurysmal enhancement ratios (ERs) were calculated by dividing the postinjection aneurysm versus skeletal muscle contrast ratio by the preinjection contrast ratio. After imaging, the aneurysms were excised and inflammatory infiltrate was characterized by fluorometric detection of myeloperoxidase activity and calprotectin immunostaining, respectively.

RESULTS

In vitro relaxometry showed that oxidation of Fe-PyC3A by hydrogen peroxide resulted in a 15-fold increase of r1 at 3 T. Relaxometry in the presence of blood plasma showed no more than a 10% increase of r1 , indicating the absence of strong interaction of Fe-PyC3A with plasma proteins. Dynamic imaging with Fe-PyC3A generated little signal enhancement within the blood pool or adjacent muscle but did generate a transient increase in aneurysmal ER that was significantly greater 4 weeks versus 12 weeks after aneurysm induction (1.6 ± 0.30 vs 1.2 ± 0.03, P < 0.05). Dynamic imaging with gadobutrol generated strong aneurysmal enhancement, but also strong enhancement of the blood and muscle resulting in smaller relative ER change. In the 12-week group of rabbits, MSDE/TSE imaging showed that ER values measured immediately after dynamic MRI (20 minutes postinjection) were significantly higher ( P < 0.05) in the case of Fe-PyC3A (1.25 ± 0.06) than for gadobutrol injection (1.03 ± 0.03). Immunohistochemical corroboration using anticalprotectin antibody showed that leukocyte infiltration into the vessel walls and luminal thrombi was significantly higher in the 4-week group versus 12-week aneurysms (123 ± 37 vs 18 ± 7 cells/mm 2 , P < 0.05).

CONCLUSIONS

Magnetic resonance imaging using Fe-PyC3A injection in dynamic or delayed acquisition modes was shown to generate a higher magnetic resonance signal enhancement in aneurysms that exhibit higher degree of inflammation. The results of our pilot experiments support further evaluation of MRI using Fe-PyC3A as a noninvasive marker of aneurysmal inflammation.

High-frequency optical coherence tomography predictors of aneurysm occlusion following flow diverter treatment in a preclinical model

BACKGROUND

High-frequency optical coherence tomography (HF-OCT) is an intravascular imaging method that allows for volumetric imaging of flow diverters in vivo.

OBJECTIVE

To examine the hypothesis that a threshold for both volume and area of communicating malapposition can be predictive of early aneurysm occlusion.

METHODS

Fifty-two rabbits underwent elastase aneurysm formation, followed by treatment with a flow diverter. At the time of implant, HF-OCT was acquired to study the rate and degree of communicating malapposition. Treated aneurysms were allowed to heal for either 90 or 180 days and euthanized following catheter angiography. Healing was dichotomized into aneurysm remnant or neck remnant/complete occlusion. Communicating malapposition was measured by HF-OCT using a semi-automatic algorithm able to detect any points where the flow diverter was more than 50 µm from the vessel wall. This was then summed across image slices to either a volume or area. Finally, a subsampled population was used to train a statistical classifier for the larger dataset.

RESULTS

No difference in occlusion rate was found between device type or follow-up time (p=0.28 and p=0.67, respectively). Both volume and area of malapposition were significantly lower in aneurysms with a good outcome (p<0.001, both). From the statistical model, a volume of less than 0.56 mm3 or a normalized area less than 0.69 as quantified by HF-OCT was predictive of occlusion (p<0.001, each).

CONCLUSIONS

HF-OCT allows for measurements of both volume and area of malapposition and, from these measurements, an accurate prediction for early aneurysm occlusion can be made.

A novel intrasaccular aneurysm device with high complete occlusion rate: initial results in a rabbit model

BACKGROUND

Intrasaccular flow-disrupting devices are a safe and effective treatment strategy for intracranial aneurysms. We utilized high-frequency optical coherence tomography (HF-OCT) and digital subtraction angiography (DSA) to evaluate SEAL Arc, a new intrasaccular device, and compare the findings with the well-established Woven EndoBridge (WEB) device in an animal model of saccular aneurysms.

METHODS

In a rabbit model, elastase-induced aneurysms were treated with SEAL Arc (n=11) devices. HF-OCT and DSA were performed after implant and repeated after 12 weeks. Device protrusion and malapposition were assessed at implant time and scored on a binary system. Aneurysm occlusion was assessed at 12 weeks with the WEB Occlusion Scale and dichotomized to complete (A and B) or incomplete (C and D) occlusion. The percentage of neointimal coverage after 12 weeks was quantified using HF-OCT. We compared these data to previously published historical controls treated with the gold-standard WEB device (n=24) in the same model.

RESULTS

Aneurysm size and device placement were not significantly different between the two groups. Complete occlusion was demonstrated in 80% of the SEAL Arc devices, which compared favorably to the 21% of the aneurysms treated with WEB devices (P=0.002). Neointimal coverage across SEAL Arc devices was 86±15% compared with 49±27% for WEB (P=0.001). Protruding devices had significantly less neointimal coverage (P<0.001) as did incompletely occluded aneurysms (P<0.001). Histologically, all aneurysms treated with SEAL Arc devices were completely healed.

CONCLUSION

Complete early aneurysm occlusion was frequently observed in the SEAL Arc treated aneurysms, with significant neointimal coverage after 12 weeks.

Longitudinal healing flow diverting stents with phosphorylcholine surface modification

BACKGROUND

Flow diversion has become a standard treatment for cerebral aneurysms. However, major drawbacks include the need for dual antiplatelet therapy after implant and delayed complete occlusion of the aneurysm, which occurs when new tissue growth excludes the aneurysm from the parent artery. Biomimetic surface modifications such as the phosphorylcholine polymer (Shield surface modification) represent major advances in reducing thrombogenicity of these devices. However, in vitro studies have raised concerns that this modification may also delay endothelialization of flow diverters.

METHODS

Bare metal Pipeline, Pipeline Shield, and Vantage with Shield devices were implanted in the common carotid arteries (CCAs) of 10 rabbits (two in the left CCA, one in the right CCA). Following implant and at 5, 10, 15, and 30 days, the devices were imaged with high-frequency optical coherence tomography and conventional angiography to evaluate tissue growth. At 30 days the devices were explanted and their endothelial growth was assessed with scanning electron microscopy (SEM) at five locations along their length using a semi-quantitative score.

RESULTS

The average tissue growth thickness (ATGT) was not different between the three devices. Neointima was apparent at 5 days and all devices demonstrated similar ATGT at each time point. On SEM, no difference was found in the endothelium scores between the device types.

CONCLUSION

In vivo, neither the Shield surface modification nor the device design (Vantage) altered the longitudinal healing of the flow diverter.

Active drug-coated flow diverter in a preclinical model of intracranial stenting

BACKGROUND

Flow diverters carry the risk of thromboembolic complications (TEC). We tested a coating with covalently bound heparin that activates antithrombin to address TEC by locally downregulating the coagulation cascade. We hypothesized that the neuroimaging evidence of TEC would be reduced by the coating.

METHODS

16 dogs were implanted with overlapping flow diverters in the basilar artery, separated into two groups: heparin-coated (n=9) and uncoated (n=7). Following implantation, high-frequency optical coherence tomography (HF-OCT) was acquired to quantify acute thrombus (AT) formation on the flow diverters. MRI was performed postoperatively and repeated at 1, 2, 3, 4, and 8 weeks, consisting of T1-weighted imaging, time-0f-flight (ToF), diffusion weighted imaging (DWI), susceptibility weighted imaging (SWI), and fluid attenuated inversion recovery (FLAIR) sequences. Neurological examinations were performed throughout the 8-week duration of the study.

RESULTS

The mean AT volume on coated devices was lower than uncoated (0.014 vs 0.018 mm³); however, this was not significant (P=0.3). The mean number of foci of magnetic susceptibility artifacts (MSAs) on SWI was significantly different between the uncoated and coated groups at the 1-week follow-up (P<0.02), and remained statistically different throughout the duration of the study. The AT volume showed a direct linear correlation with the MSA count and 80% of the variance in the MSA could be explained by the AT volume (P<0.001). Pathological analysis showed evidence of ischemic injury at locations of MSA.

CONCLUSIONS

Heparin-coated flow diverters significantly reduced the number of new MSAs after 1 week follow-up, showing the potential to reduce TEC.

Assessment of thrombectomy procedure difficulty by neurointerventionalists based on vessel geometry parameters from carotid artery 3D reconstructions

BACKGROUND

Diagnosing and treating acute ischemic stroke patients within a narrow timeframe is challenging. Time needed to access the occluded vessel and initiate thrombectomy is dictated by the availability of information regarding vascular anatomy and trajectory. Absence of such information potentially impacts device selection, procedure success, and stroke outcomes. While the cervical vessels allow neurointerventionalists to navigate devices to the occlusion site, procedures are often encumbered due to tortuous pathways. The purpose of this retrospective study was to determine how neurointerventionalists consider the physical nature of carotid segments when evaluating a procedure's difficulty.

METHODS

Seven neurointerventionalists reviewed 3D reconstructions of CT angiograms of left and right carotid arteries from 49 subjects and rated the perceived procedural difficulty on a three-point scale (easy, medium, difficult) to reach the targeted M1. Twenty-two vessel metrics were quantified by dividing the carotids into 5 segments and measuring the radius of curvature, tortuosity, vessel radius, and vessel length of each segment.

RESULTS

The tortuosity and length of the arch-cervical and cervical regions significantly impacted difficulty ratings. Additionally, two-way interaction between the radius of curvature and tortuosity on the arch-cervical region was significant (p < 0.0001) wherein, for example, at a given arch-cervical tortuosity, an increased radius of curvature reduced the perceived case difficulty.

CONCLUSIONS

Examining the vessel metrics and providing detailed vascular data tailored to patient characteristics may result in better procedure preparation, facilitate faster vessel access time, and improve thrombectomy outcomes. Additionally, documenting these correlations can enhance device design to ensure they suitably function under various vessel conditions.

Tectonic infarct analysis: A computational tool for automated whole-brain infarct analysis from TTC-stained tissue

Background

Infarct volume measured from 2,3,5-triphenyltetrazolium chloride (TTC)-stained brain slices is critical to in vivo stroke models. In this study, we developed an interactive, tunable, software that automatically computes whole-brain infarct metrics from serial TTC-stained brain sections.

Methods

Three rat ischemic stroke cohorts were used in this study (Total n = 91 rats; Cohort 1 n = 21, Cohort 2 n = 40, Cohort 3 n = 30). For each, brains were serially-sliced, stained with TTC and scanned on both anterior and posterior sides. Ground truth annotation and infarct morphometric analysis (e.g., brain-V_brain, infarct-V_infarct, and non-infarct-V_non-infarct volumes) were completed by domain experts. We used Cohort 1 for brain and infarct segmentation model development (n = 3 training cases with 36 slices [18 anterior and posterior faces], n = 18 testing cases with 218 slices [109 anterior and posterior faces]), as well as infarct morphometrics automation. The infarct quantification pipeline and pre-trained model were packaged as a standalone software and applied to Cohort 2, an internal validation dataset. Finally, software and model trainability were tested as a use-case with Cohort 3, a dataset from a separate institute.

Results

Both high segmentation and statistically significant quantification performance (correlation between manual and software) were observed across all datasets. Segmentation performance: Cohort 1 brain accuracy = 0.95/f1-score = 0.90, infarct accuracy = 0.96/f1-score = 0.89; Cohort 2 brain accuracy = 0.97/f1-score = 0.90, infarct accuracy = 0.97/f1-score = 0.80; Cohort 3 brain accuracy = 0.96/f1-score = 0.92, infarct accuracy = 0.95/f1-score = 0.82. Infarct quantification (cohort average): V_brain (ρ = 0.87, p < 0.001), V_infarct (0.92, p < 0.001), V_non-infarct (0.80, p < 0.001), %infarct (0.87, p = 0.001), and infarct:non-infact ratio (ρ = 0.92, p < 0.001).

Conclusion

Tectonic Infarct Analysis software offers a robust and adaptable approach for rapid TTC-based stroke assessment.

Development of an in-vitro model based on patient vessel geometry for simulated use testing in neurointerventional surgery

BACKGROUND

Neurointerventionalists use in-vitro vascular models to train for worst-case scenarios and test new devices in a simulated use environment to predict clinical performance. According to the Food and Drug Administration (FDA), any neurovascular navigation device should be able to successfully navigate two 360-degree turns and two 180-degree turns at the distal portion of the anatomical model. Here, we present a device benchmarking vascular model that complies with FDA recommendations.

METHODS

Our vascular model was assembled from quantitative characterization of 49 patients who underwent CT angiography either for acute ischemic stroke caused by large vessel occlusion or for aneurysm treatment. Following complete characterization of these data, the vascular segments were 3D reconstructed from CT angiograms of 6 selected patients that presented with challenging anatomy. The curvature and total rotational angle were calculated for each segment and the anatomical parts that complied with FDA recommendations were fused together into a single in-vitro model.

RESULTS

The model was constructed containing two common carotid branches arising from a type two aortic arch and the dimensions of the overall model exceeded the recommendations of the FDA. Two experienced neurointerventionalists tested the model for navigation difficulty using several devices on an in-vitro perfusion system and concluded that the model provided a realistic, challenging scenario.

CONCLUSIONS

This model provides a first prototype designed according to FDA recommendations of cumulative angle while also integrating an aggregation of actual patient-specific anatomy. The availability of this clinically relevant benchmark model presents a potential standardized approach for neurovascular device testing.

Novel Oxygen Carrier Slows Infarct Growth in Large Vessel Occlusion Dog Model Based on Magnetic Resonance Imaging Analysis

BACKGROUND

Tissue hypoxia plays a critical role in the events leading to cell death in ischemic stroke. Despite promising results in preclinical and small clinical pilot studies, inhaled oxygen supplementation has not translated to improved outcomes in large clinical trials. Moreover, clinical observations suggest that indiscriminate oxygen supplementation can adversely affect outcome, highlighting the need to develop novel approaches to selectively deliver oxygen to affected regions. This study tested the hypothesis that intravenous delivery of a novel oxygen carrier (Omniox-Ischemic Stroke [OMX-IS]), which selectively releases oxygen into severely ischemic tissue, could delay infarct progression in an established canine thromboembolic large vessel occlusion stroke model that replicates key dynamics of human infarct evolution.

METHODS

After endovascular placement of an autologous clot into the middle cerebral artery, animals received OMX-IS treatment or placebo 45 to 60 minutes after stroke onset. Perfusion-weighted magnetic resonance imaging was performed to define infarct progression dynamics to stratify animals into fast versus slow stroke evolvers. Serial diffusion-weighted magnetic resonance imaging was performed for up to 5 hours to quantify infarct evolution. Histology was performed postmortem to confirm final infarct size.

RESULTS

In fast evolvers, OMX-IS therapy substantially slowed infarct progression (by ≈1 hour, P<0.0001) and reduced the final normalized infarct volume as compared to controls (0.99 versus 0.88, control versus OMX-IS drug, P<0.0001). Among slow evolvers, OMX-IS treatment delayed infarct progression by approximately 45 minutes; however, this did not reach statistical significance (P=0.09). The final normalized infarct volume also did not show a significant difference (0.93 versus 0.95, OMX-IS drug versus control, P=0.34). Postmortem histologically determined infarct volumes showed excellent concordance with the magnetic resonance imaging defined ischemic lesion volume (bias: 1.33% [95% CI, -15% to 18%).

CONCLUSIONS

Intravenous delivery of a novel oxygen carrier is a promising approach to delay infarct progression after ischemic stroke, especially in treating patients with large vessel occlusion stroke who cannot undergo definitive reperfusion therapy within a timely fashion.

Transvascular in vivo microscopy of the subarachnoid space

BACKGROUND

The micro-architectonics of the subarachnoid space (SAS) remain partially understood and largely ignored, likely the result of the inability to image these structures in vivo. We explored transvascular imaging with high-frequency optical coherence tomography (HF-OCT) to interrogate the SAS.

METHODS

In vivo HF-OCT was performed in 10 dogs in both the posterior and anterior cerebral circulations. The conduit vessels used were the basilar, anterior spinal, and middle and anterior cerebral arteries through which the perivascular SAS was imaged. The HF-OCT imaging probe was introduced via a microcatheter and images were acquired using a contrast injection (3.5 mL/s) for blood clearance. Segmentation and three-dimensional rendering of HF-OCT images were performed to study the different configurations and porosity of the subarachnoid trabeculae (SAT) as a function of location.

RESULTS

Of 13 acquisitions, three were excluded due to suboptimal image quality. Analysis of 15 locations from seven animals was performed showing six distinct configurations of arachnoid structures in the posterior circulation and middle cerebral artery, ranging from minimal presence of SAT to dense networks and membranes. Different locations showed predilection for specific arachnoid morphologies. At the basilar bifurcation, a thick, fenestrated membrane had a unique morphology. SAT average thickness was 100 µm and did not vary significantly based on location. Similarly, the porosity of the SAT averaged 91% and showed low variability.

CONCLUSION

We have demonstrated the feasibility to image the structures of the SAS with transvascular HF-OCT. Future studies are planned to further map the SAT to increase our understanding of their function and possible impact on neurovascular pathologies.

Biophysical targeting of high-risk cerebral aneurysms

Localized delivery of diagnostic/therapeutic agents to cerebral aneurysms, lesions in brain arteries, may offer a new treatment paradigm. Since aneurysm rupture leading to subarachnoid hemorrhage is a devastating medical emergency with high mortality, the ability to noninvasively diagnose high-risk aneurysms is of paramount importance. Moreover, treatment of unruptured aneurysms with invasive surgery or minimally invasive neurointerventional surgery poses relatively high risk and there is presently no medical treatment of aneurysms. Here, leveraging the endogenous biophysical properties of brain aneurysms, we develop particulate carriers designed to localize in aneurysm low-shear flows as well as to adhere to a diseased vessel wall, a known characteristic of high-risk aneurysms. We first show, in an in vitro model, flow guided targeting to aneurysms using micron-sized (2 μm) particles, that exhibited enhanced targeting (>7 folds) to the aneurysm cavity while smaller nanoparticles (200 nm) showed no preferable accumulation. We then functionalize the microparticles with glycoprotein VI (GPVI), the main platelet receptor for collagen under low-medium shear, and study their targeting in an in vitro reconstructed patient-specific aneurysm that contained a disrupted endothelium at the cavity. Results in this model showed that GPVI microparticles localize at the injured aneurysm an order of magnitude (>9 folds) more than control particles. Finally, effective targeting to aneurysm sites was also demonstrated in an in vivo rabbit aneurysm model with a disrupted endothelium. Altogether, the presented biophysical strategy for targeted delivery may offer new treatment opportunities for cerebral aneurysms.

Comparative route of administration studies using therapeutic siRNAs show widespread gene modulation in Dorset sheep

siRNAs comprise a class of drugs that can be programmed to silence any target gene. Chemical engineering efforts resulted in development of divalent siRNAs (di-siRNAs), which support robust and long-term efficacy in rodent and nonhuman primate brains upon direct cerebrospinal fluid (CSF) administration. Oligonucleotide distribution in the CNS is nonuniform, limiting clinical applications. The contribution of CSF infusion placement and dosing regimen on relative accumulation, specifically in the context of large animals, is not well characterized. To our knowledge, we report the first systemic, comparative study investigating the effects of 3 routes of administration — intrastriatal (i.s.), i.c.v., and intrathecal catheter to the cisterna magna (ITC) — and 2 dosing regimens — single and repetitive via an implanted reservoir device — on di-siRNA distribution and accumulation in the CNS of Dorset sheep. CSF injections (i.c.v. and ITC) resulted in similar distribution and accumulation across brain regions. Repeated dosing increased homogeneity, with greater relative deep brain accumulation. Conversely, i.s. administration supported region-specific delivery. These results suggest that dosing regimen, not CSF infusion placement, may equalize siRNA accumulation and efficacy throughout the brain. These findings inform the planning and execution of preclinical and clinical studies using siRNA therapeutics in the CNS.

Real-time MR tracking of AAV gene therapy with βgal-responsive MR probe in a murine model of GM1-gangliosidosis

Transformative results of adeno-associated virus (AAV) gene therapy in patients with spinal muscular atrophy and Leber's congenital amaurosis led to approval of the first two AAV products in the United States to treat these diseases. These extraordinary results led to a dramatic increase in the number and type of AAV gene-therapy programs. However, the field lacks non-invasive means to assess levels and duration of therapeutic protein function in patients. Here, we describe a new magnetic resonance imaging (MRI) technology for real-time reporting of gene-therapy products in the living animal in the form of an MRI probe that is activated in the presence of therapeutic protein expression. For the first time, we show reliable tracking of enzyme expression after a now in-human clinical trial AAV gene therapy (ClinicalTrials.gov: NTC03952637) encoding lysosomal acid beta-galactosidase (βgal) using a self-immolative βgal-responsive MRI probe. MRI enhancement in AAV-treated enzyme-deficient mice (GLB-1^-/-) correlates with βgal activity in central nervous system and peripheral organs after intracranial or intravenous AAV gene therapy, respectively. With >1,800 gene therapies in phase I/II clinical trials (ClinicalTrials.gov), development of a non-invasive method to track gene expression over time in patients is crucial to the future of the gene-therapy field.

High-resolution image-guided WEB aneurysm embolization by high-frequency optical coherence tomography

BACKGROUND

High-frequency optical coherence tomography (HF-OCT) is an intra-vascular imaging technique capable of assessing device-vessel interactions at spatial resolution approaching 10 µm. We tested the hypothesis that adequately deployed Woven EndoBridge (WEB) devices as visualized by HF-OCT lead to higher aneurysm occlusion rates.

METHODS

In a leporine model, elastase-induced aneurysms (n=24) were treated with the WEB device. HF-OCT and digital subtraction angiography (DSA) were performed following WEB deployment and repeated at 4, 8, and 12 weeks. Protrusion (0-present, 1-absent) and malapposition (0-malapposed, 1-neck apposition >50%) were binary coded. A device was considered 'adequately deployed' by HF-OCT and DSA if apposed and non-protruding. Aneurysm healing on DSA was reported using the 4-point WEB occlusion score: A or B grades were considered positive outcome. Neointimal coverage was quantified on HF-OCT images at 12 weeks and compared with scanning electron microscopy (SEM).

RESULTS

Adequate deployment on HF-OCT correlated with positive outcome (P=0.007), but no statistically significant relationship was found between good outcome and adequate deployment on DSA (P=0.289). Absence of protrusion on HF-OCT correlated with a positive outcome (P=0.006); however, malapposition alone had no significant relationship (P=0.19). HF-OCT showed a strong correlation with SEM for the assessment of areas of neointimal tissue (R²=0.96; P<0.001). More neointimal coverage of 78%±32% was found on 'adequate deployment' cases versus 31%±24% for the 'inadequate deployment' cases (P=0.001).

CONCLUSION

HF-OCT visualizes features that can determine adequate device deployment to prognosticate early aneurysm occlusion following WEB implantation and can be used to longitudinally monitor aneurysm healing progression.

Biomechanics and hemodynamics of stent-retrievers

In 2015, multiple randomized clinical trials showed an unparalleled treatment benefit of stent-retriever thrombectomy as compared to standard medical therapy for the treatment of a large artery occlusion causing acute ischemic stroke. A short time later, the HERMES collaborators presented the patient-level pooled analysis of five randomized clinical trials, establishing class 1, level of evidence A for stent-retriever thrombectomy, in combination with intravenous thrombolysis when indicated to treat ischemic stroke. In the years following, evidence continues to mount for expanded use of this therapy for a broader category of patients. The enabling technology that changed the tide to support endovascular treatment of acute ischemic stroke is the stent-retriever. This review summarizes the history of intra-arterial treatment of stroke, introduces the biomechanics of embolus extraction with stent-retrievers, describes technical aspects of the intervention, provides a description of hemodynamic implications of stent-retriever embolectomy, and proposes future directions for a more comprehensive, multi-modal endovascular approach for the treatment of acute ischemic stroke.

Longitudinal Monitoring of Flow-Diverting Stent Tissue Coverage After Implant in a Bifurcation Model Using Neurovascular High-Frequency Optical Coherence Tomography

BACKGROUND

Tissue growth over covered branches is a leading cause of delayed thrombotic complications after flow-diverter stenting (FDS). Due to insufficient resolution, no imaging modality is clinically available to monitor this phenomenon.

OBJECTIVE

To evaluate high-frequency optical coherence tomography (HF-OCT), a novel intravascular imaging modality designed for the cerebrovascular anatomy with a resolution approaching 10 microns, to monitor tissue growth over FDS in an arterial bifurcation model.

METHODS

FDS were deployed in a rabbit model (n = 6), covering the aortic bifurcation. The animals were divided in different groups, receiving dual antiplatelet therapy (DAPT) (n = 4), aspirin only (n = 1), and no treatment (n = 1). HF-OCT data were obtained in vivo at 3 different time points in each animal. For each cross-sectional image, metal and tissue coverage of the jailed ostium was quantified. Scanning electron microscopy images of harvested arteries were subsequently obtained.

RESULTS

Good quality HF-OCT data sets were successfully acquired at implant and follow-up. A median value of 41 (range 21-55) cross-sectional images were analyzed per ostium for each time point. Between 0 and 30 d after implant, HF-OCT analysis showed a significantly higher ostium coverage when DAPT was not given. After 30 d, similar growth rates were found in the DAPT and in the aspirin group. At 60 d, a coverage of 90% was reached in all groups.

CONCLUSION

HF-OCT enables an accurate visualization of tissue growth over time on FDS struts. The use of FDS in bifurcation locations may induce a drastic reduction of the jailed-branch ostium area.

Efficacy of beveled tip aspiration catheter in mechanical thrombectomy for acute ischemic stroke

Background

Direct aspiration thrombectomy techniques use large bore aspiration catheters for mechanical thrombectomy. Several aspiration catheters are now available. We report a bench top exploration of a novel beveled tip catheter and our experience in treating large vessel occlusions (LVOs) using next-generation aspiration catheters.

Methods

A retrospective analysis from a prospectively maintained database comparing the bevel shaped tip aspiration catheter versus non-beveled tip catheters was performed. Patient demographics, periprocedural metrics, and discharge and 90-day modified Rankin Scale (mRS) scores were collected. Patients were divided into two groups based on which aspiration catheter was used.

Results

Our data showed no significant difference in age, gender, IV tissue plasminogen activator administration, admission NIH Stroke Scale score, baseline mRS, or LVO location between the beveled tip and flat tip groups. With the beveled tip, Thrombolysis in Cerebral Infarction (TICI) 2C or better recanalization was more frequent overall (93.2% vs 74.2%, p=0.017), stent retriever usage was lower (9.1% vs 29%, p=0.024), and patients had lower mRS on discharge (median 3 vs 4, p<0.001) and at 90 days (median 2 vs 4, p=0.008).

Conclusion

Patients who underwent mechanical thrombectomy with the beveled tip catheter had a higher proportion of TICI 2C or better and had a significantly lower mRS score on discharge and at 90 days.

In situ decellularization of a large animal saccular aneurysm model: sustained inflammation and active aneurysm wall remodeling

OBJECTIVE

To investigate in situ decellularization of a large animal model of saccular aneurysm as a strategy for achieving aneurysmal growth and lasting inflammation.

METHODS

18 New Zealand White rabbits were randomized 2:1 to receive endoluminal sodium dodecyl sulfate infusion (SDS, 1% solution, 45 min) following elastase or elastase-only treatment (control). All aneurysms were measured by digital subtraction angiography every 2 weeks. Every 2 weeks, three of the rabbits (two elastase + SDS, one control) underwent MRI, followed by contrast injection with myeloperoxidase (MPO)-sensing contrast agent. MRI was repeated 3 hours after contrast injection and the enhancement ratio (ER) was calculated. Following MRI, aneurysms were explanted and subjected to immunohistopathology.

RESULTS

During follow-up MRI, the average ER for SDS-treated animals was 1.63±0.20, compared with 1.01±0.06 for controls (p<0.001). The width of SDS-treated aneurysms increased significantly in comparison with the elastase aneurysms (47% vs 20%, p<0.001). Image analysis of thin sections showed infiltration of MPO-positive cells in decellularized aneurysms and surroundings through the 12-week observation period while control tissue had 5-6 times fewer cells present 2 weeks after aneurysm creation. Immunohistochemistry demonstrated the presence of MPO-positive cells surrounding decellularized lesions at early time points. MPO-positive cells were found in the adventitia and in the thrombi adherent to the aneurysm wall at later time points.

CONCLUSIONS

In situ decellularization of a large animal model of saccular aneurysms reproduces features of unstable aneurysms, such as chronic inflammation (up to 12 weeks) and active aneurysm wall remodeling, leading to continued growth over 8 weeks.

A neurovascular high-frequency optical coherence tomography system enables in situ cerebrovascular volumetric microscopy

Intravascular imaging has emerged as a valuable tool for the treatment of coronary and peripheral artery disease; however, no solution is available for safe and reliable use in the tortuous vascular anatomy of the brain. Endovascular treatment of stroke is delivered under image guidance with insufficient resolution to adequately assess underlying arterial pathology and therapeutic devices. High-resolution imaging, enabling surgeons to visualize cerebral arteries' microstructure and micron-level features of neurovascular devices, would have a profound impact in the research, diagnosis, and treatment of cerebrovascular diseases. Here, we present a neurovascular high-frequency optical coherence tomography (HF-OCT) system, including an imaging console and an endoscopic probe designed to rapidly acquire volumetric microscopy data at a resolution approaching 10 microns in tortuous cerebrovascular anatomies. Using a combination of in vitro, ex vivo, and in vivo models, the feasibility of HF-OCT for cerebrovascular imaging was demonstrated.

Acute Thrombus Burden on Coated Flow Diverters Assessed by High Frequency Optical Coherence Tomography

PURPOSE

The implantation of flow diverters requires administration of dual anti-platelet therapy, posing the potential for complications. The p48MW HPC (phenox, Bochüm, Germany) hydrophilic-coated flow diverting stent is designed to be anti-thrombotic, thus opening the potential for single anti-platelet therapy. We deploy a novel intravascular high-resolution imaging technique, high-frequency optical coherence tomography (HF-OCT), to study in an animal model the acute thrombus formation on coated p48MW devices versus uncoated control devices.

METHODS

Three pigs were implanted with 4 flow diverters each, two test hydrophilic-coated devices, and two control uncoated devices (p48MW). Each pig was treated with a different anti-platelet regime: no anti-platelet therapy, aspirin only, aspirin and clopidogrel. Twenty minutes after the flow diverter was implanted, an HF-OCT data set was acquired. Acute clot formed on the flow diverter at each covered side branch was measured from the HF-OCT slices. Factors considered to be important were the device type (pHPC versus bare metal), aspirin, clopidogrel, and vessel location. A linear model was constructed from the significant factors.

RESULTS

Both coating (p < 0.001) and aspirin (p = 0.003) were significantly related to reduction in clot burden, leading to an approximate 100-fold and 50-fold reduction in clot, respectively.

CONCLUSIONS

This study shows the power of HF-OCT not only in the detection of clot but also the quantification of clot burden. In an animal model, the pHPC-coated p48MW significantly reduced acute thrombus formation over jailed side branches as compared to the bare metal p48MW that was nearly eliminated when combined with aspirin administration.

Abstract WP1: High-Frequency Optical Coherence Tomography for Cerebrovascular Disease

Introduction: Optical coherence tomography (OCT) has played an important role in the diagnosis and treatment guidance in coronary artery disease. However, existing OCT systems are not suitable for routine neurovascular applications due to the size and tortuosity of the arteries.

Hypothesis: We seek to demonstrate a prototype high-frequency OCT (HF-OCT) capable of high-resolution imaging in simulated cerebrovascular anatomy.

Methods: A low-profile HF-OCT system was constructed with an image resolution approaching 10μm. Using an in vitro, patient-specific model of the circle of Willis with circulating porcine blood, we characterized the delivery of the device and ability to image in a tortuous path. Also, human cadaver intracranial atherosclerosis plaques were imaged with HF-OCT and assessed by an expert imager. Finally, neurovascular devices were implanted in 8 pigs (Fig 1) and HF-OCT imaging was compared with gold-standard DSA and CT.

Results: In the phantom, optimal blood clearance was achieved through an intermediate catheter (5 Fr Navien) with infusion of contrast at 5 ml/s in the internal carotid and basilar artery, and 3 ml/sec in the MCA. The in vivo study demonstrated that both malapposition of devices or thrombus formation along the device surface could be reliably diagnosed among 3 reviewers (Fleiss’s kappa of 0.87 and 0.9, respectively). This agreement was superior to DSA and CT. Imaging in tortuous swine brachial showed in all cases imaging free of artifacts, uniform illumination and ability to visualize vessel wall layers. Plaque types including ‘lipid pools’, fibrotic, and calcific tissue from cadaver specimens of ICAD could be adequately depicted by HF-OCT.

Conclusion: In vitro, in vivo and ex vivo characterization of a novel HF-OCT device has shown it is capable of imaging in the tortuous intracranial vascular anatomy. This technology has to potential to aid in the diagnosis of cerebrovascular disease and guide optimal endovascular treatment.

A Safe and Reliable Technique for CNS Delivery of AAV Vectors in the Cisterna Magna

Global gene delivery to the CNS has therapeutic importance for the treatment of neurological disorders that affect the entire CNS. Due to direct contact with the CNS, cerebrospinal fluid (CSF) is an attractive route for CNS gene delivery. A safe and effective route to achieve global gene distribution in the CNS is needed, and administration of genes through the cisterna magna (CM) via a suboccipital puncture results in broad distribution in the brain and spinal cord. However, translation of this technique to clinical practice is challenging due to the risk of serious and potentially fatal complications in patients. Herein, we report development of a gene therapy delivery method to the CM through adaptation of an intravascular microcatheter, which can be safely navigated intrathecally under fluoroscopic guidance. We examined the safety, reproducibility, and distribution/transduction of this method in sheep using a self-complementary adeno-associated virus 9 (scAAV9)-GFP vector. This technique was used to treat two Tay-Sachs disease patients (30 months old and 7 months old) with AAV gene therapy. No adverse effects were observed during infusion or post-treatment. This delivery technique is a safe and minimally invasive alternative to direct infusion into the CM, achieving broad distribution of AAV gene transfer to the CNS.

High frequency optical coherence tomography assessment of homogenous neck coverage by intrasaccular devices predicts successful aneurysm occlusion

BACKGROUND

High frequency optical coherence tomography (HF-OCT) is a novel intravascular imaging technology developed for use in the cerebral vasculature. We hypothesize that HF-OCT characterization of intrasaccular device neck coverage can prognosticate exclusion of the aneurysm from the circulation.

METHODS

Bifurcation and sidewall aneurysms were made in six dogs. Seven aneurysms were treated with next generation intrasaccular devices (NGID) and four with traditional platinum coils. HF-OCT was performed to interrogate gaps in the neck coverage, coil herniation, or acute thrombus formation. Animals were re-imaged at 7, 30, 90, and 180 days following aneurysm embolization. An automated image processing method segmented the devices at the neck of the aneurysm and quantified neck coverage. The largest coverage gap was used to predict aneurysm occlusion at 180 days.

RESULTS

No difference was found in occlusion rates between the coil and NGID groups (P=0.45). Successful segmentation of the NGID construct was achieved in all cases. A coverage gap >1 mm2 was found to predict failed aneurysm occlusion (P=0.047). This threshold was able to predict all cases of failed occlusion. The average number of devices needed to treat the aneurysm was lower in the NGID group (1.9 vs 6.75, P=0.009). HF-OCT showed strong agreement with scanning electron microscopy (bias 0.0024 mm2 (95% CI -0.0279, 0.0327)).

CONCLUSIONS

HF-OCT enables precise and accurate measurement of coverage gaps at the neck of aneurysms treated with intrasaccular devices in vivo. We provide in vivo evidence that uniform aneurysm neck coverage by intrasaccular devices is critical for aneurysm occlusion.

Infarct Evolution in a Large Animal Model of Middle Cerebral Artery Occlusion

Mechanical thrombectomy for the treatment of ischemic stroke shows high rates of recanalization; however, some patients still have a poor clinical outcome. A proposed reason for this relates to the fact that the ischemic infarct growth differs significantly between patients. While some patients demonstrate rapid evolution of their infarct core (fast evolvers), others have substantial potentially salvageable penumbral tissue even hours after initial vessel occlusion (slow evolvers). We show that the dog middle cerebral artery occlusion model recapitulates this key aspect of human stroke rendering it a highly desirable model to develop novel multimodal treatments to improve clinical outcomes. Moreover, this model is well suited to develop novel image analysis techniques that allow for improved lesion evolution prediction; we provide proof-of-concept that MRI perfusion-based time-to-peak maps can be utilized to predict the rate of infarct growth as validated by apparent diffusion coefficient-derived lesion maps allowing reliable classification of dogs into fast versus slow evolvers enabling more robust study design for interventional research.

Focal cooling of brain parenchyma in a transient large vessel occlusion model: proof-of-concept

INTRODUCTION

The neuroprotective benefit of therapeutic hypothermia (TH) has been demonstrated, but systemic side effects and time required to achieve effective TH in acute ischemic stroke (AIS) care limits clinical use. We investigate rapid and localized cooling using a novel insulated catheter in an ischemia-reperfusion model.

METHODS

In phase I (n=4), cold saline was delivered to the canine internal carotid artery via an insulated catheter. Temperature was measured using intracerebral thermocouples. The coolant flow rate was varied to meet a target temperature of 31-32°C in the hemisphere infused. In phase II (n=8), a temporary middle cerebral artery occlusion was created. Five dogs underwent localized TH at the optimal flow rate from phase I, and the remaining animals were untreated controls. Cooling was initiated 5 min before recanalization and continued for an additional 20 min following 45 min of occlusion duration. The outcome was infarct volume and neurological function.

RESULTS

Ipsilateral tissue cooling rates were 2.2±2.5°C/min at a flow rate of 20-40 mL/min with an observed minimum of 23.8°C. Tissue cooling was localized to the ipsilateral side of the infusion with little impact on temperatures of the core or contralateral hemisphere of the brain. In phase II, animals tolerated TH with minimal systemic impact. Infarct volume in treated animals was 0.2±0.2 cm³, which was smaller than in sham animals (3.8±1.0 cm³) as well as six untreated historical control animals (4.0±2.8 cm³) (p=0.013).

CONCLUSIONS

Proof-of-concept data show that localised brain TH can be quickly and safely achieved through a novel insulated catheter. The small infarct volumes suggest potential benefit for this approach.

A canine model of mechanical thrombectomy in stroke

Purpose

To develop a preclinical model of stroke with a large vessel occlusion treated with mechanical thrombectomy.

Materials and methods

An ischemic stroke model was created in dogs by the introduction of an autologous clot into the middle cerebral artery (MCA). A microcatheter was navigated to the clot and a stent retriever thrombectomy was performed with the goal to achieve Thrombolysis in Cerebral Ischemia (TICI) 2b/3 reperfusion. Perfusion and diffusion MRI was acquired after clot placement and following thrombectomy to monitor the progression of restricted diffusion as well as changes in ischemia as a result of mechanical thrombectomy. Post-mortem histology was done to confirm MCA territory infarct volume.

Results

Initial MCA occlusion with TICI 0 flow was documented in all six hound-cross dogs entered into the study. TICI 2b/3 revascularization was achieved with one thrombectomy pass in four of six animals (67%). Intra-procedural events including clot autolysis leading to spontaneous revascularization (n=1) and unresolved vasospasm (n=1) accounted for thrombectomy failure. In one case, iatrogenic trauma during microcatheter navigation resulted in a direct arteriovenous fistula at the level of the cavernous carotid. Analysis of MRI indicated that a volume of tissue from the initial perfusion deficit was spared with reperfusion following thrombectomy, and there was also a volume of tissue that infarcted between MRI and ultimate recanalization.

Conclusion

We describe a large animal stroke model in which mechanical thrombectomy can be performed. This model may facilitate, in a preclinical setting, optimization of complex multimodal stroke treatment paradigms for clinical translation.

Complete clot ingestion with cyclical ADAPT increases first-pass recanalization and reduces distal embolization

BACKGROUND

Evidence is mounting that first-pass complete recanalization during mechanical thrombectomy is associated with better clinical outcomes in patients presenting with an emergent large vessel occlusion. We hypothesize that aspiration achieving complete clot ingestion results in higher first-pass successful recanalization with quantitative reduction in distal emboli.

METHODS

A patient-specific cerebrovascular replica was connected to a flow loop. Occlusion of the middle cerebral artery was achieved with clot analogs. Independent variables were the diameter of the aspiration catheter (0.054-0.088in) and aspiration pattern (static versus cyclical). Outcome measures were the first-pass rates of complete clot ingestion, the extent of recanalization, and the particle-size distribution of distal emboli.

RESULTS

All aspiration catheters were successfully navigated to the occlusion. Complete clot ingestion during aspiration thrombectomy resulted in first-pass complete recanalization in every experiment, only achieved in 21% of experiments with partial ingestion (P<0.0001). Aspiration through the large bore 0.088in device resulted in the highest rates of complete clot ingestion (90%). Cyclical aspiration (18-29 inHg, 0.5 Hz) significantly increased the rate of complete clot ingestion (OR21 [1.6, 266]; P=0.04). In all experiments, complete clot ingestion resulted in fewer and smaller distal emboli.

CONCLUSIONS

Complete clot ingestion results in fewer distal emboli and the highest rates of first-pass complete recanalization. The rate of complete ingestion during aspiration thrombectomy is a function of both the inner diameter of the aspiration catheter and use of cyclical aspiration.

The occurrence of neointimal hyperplasia after flow-diverter implantation is associated with cardiovascular risks factors and the stent design

Background

Neo-intimal hyperplasia (NIH) is frequently observed after flow-diverter stent (FDS) implantation. Although mostly asymptomatic, this vascular response can sometimes lead to delayed ischemic strokes. This study intended to evaluate the factors potentially influencing the rates of NIH following FDS treatment.

Material and Methods

All aneurysm treatments performed with a Pipeline embolization device (PED) or a SILK stent from May 2011 to May 2015 were collected in a prospectively maintained database. Patient demographics, clinical, and angiographic outcomes including both digital subtraction angiography and C-arm cone-beam CT were registered. Two blind reviewers rated the presence of NIH on a binary scale (present/absent).

Results

From 148 patients, 63 datasets were available for analysis. Inter-reader agreement was excellent (Kappa=0.88). NIH was positively correlated with smoking, dyslipidemia, and high blood pressure, but not with aneurysm characteristics. At early follow-up (<12 months), NIH was more frequently associated with the use of the SILK stent (68%) rather than the PED (38%): P<0.02. At long-term follow-up, the NIH rate in the total population dropped from 55% to 26% with no more significant difference between the two stents. The complete occlusion rate as seen in early follow-up was higher in the SILK group with 76% vs 65% but without statistical significance (P=0.4).

Conclusion

NIH is a dual-vessel reaction after FDS implant. When planning a treatment in locations at risk of ischemic complications if severe NIH would occur, then the stent design should be considered. However, minimal NIH might also be needed as it is involved in aneurysm healing. Before treatment patients should be recommended best medical management of their cardiovascular risks factors to prevent an excessive NIH reaction.

Microcatheter navigation through the clot: does size matter?

BACKGROUND

Despite high recanalization rates achieved with endovascular treatment of acute ischemic strokes, around 50% of eligible patients will not achieve a good outcome. Parameters that may determine patient outcomes include: time from puncture to recanalization, the collateral status, the anesthesia regimen, blood pressure management, and distal emboli. Characterization of distal emboli generated during mechanical thrombectomy has been performed in previous studies.

OBJECTIVE

To further investigate the risk of distal embolization associated with microcatheter navigation across the clot.

METHODS

A contrast-enhanced clot analog was used in an in vitro model that mimicked a middle cerebral artery occlusion within a complete circle of Willis vascular replica. The clot was crossed with one of the following microcatheters: Pro18, XT-27 or 3MAX. The emboli generated during the procedure were collected and measured.

RESULTS

The use of Pro18 and XT-27 resulted in a significant reduction of visible particles (size ≥500 µm) as compared with the 3MAX catheter (P<0.003). For the size range between 8 and 200 µm, there was a trend for Pro18 to generate fewer particles (-18%) than XT-27 but without statistical significance (P>0.05). In comparison with previously published data, acquired under the same conditions, it was found that the clot crossing maneuver accounts approximately for 12% of the total number of small emboli (<200 µm) induced during a stent retriever-mediated mechanical thrombectomy procedure via a balloon guide catheter.

CONCLUSIONS

The clot crossing maneuver has a significant effect on the total number of small particles induced during mechanical thrombectomy. Smaller microcatheter sizes should be favored when possible.

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.

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.

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.

Development of a high resolution MRI intracranial atherosclerosis imaging phantom

BACKGROUND AND PURPOSE

Currently, there is neither a standard protocol for vessel wall MR imaging of intracranial atherosclerotic disease (ICAD) nor a gold standard phantom to compare MR sequences. In this study, a plaque phantom is developed and characterized that provides a platform for establishing a uniform imaging approach for ICAD.

MATERIALS AND METHODS

A patient specific injection mold was 3D printed to construct a geometrically accurate ICAD phantom. Polyvinyl alcohol hydrogel was infused into the core shell mold to form the stenotic artery. The ICAD phantom incorporated materials mimicking a stenotic vessel and plaque components, including fibrous cap and lipid core. Two phantoms were scanned using high resolution cone beam CT and compared with four different 3 T MRI systems across eight different sites over a period of 18 months. Inter-phantom variability was assessed by lumen dimensions and contrast to noise ratio (CNR).

RESULTS

Quantitative evaluation of the minimum lumen radius in the stenosis showed that the radius was on average 0.80 mm (95% CI 0.77 to 0.82 mm) in model 1 and 0.77 mm (95% CI 0.74 to 0.81 mm) in model 2. The highest CNRs were observed for comparisons between lipid and vessel wall. To evaluate manufacturing reproducibility, the CNR variability between the two models had an average absolute difference of 4.31 (95% CI 3.82 to 5.78). Variation in CNR between the images from the same scanner separated by 7 months was 2.5-6.2, showing reproducible phantom durability.

CONCLUSIONS

A plaque phantom composed of a stenotic vessel wall and plaque components was successfully constructed for multicenter high resolution MRI standardization.

Abstract TP261: Clot Integration Factor for in-vitro Quantification of Stent-retriever Configuration Using Cone-beam CT

Objective: Mechanical thrombectomy using stent-retriever technology provides acute ischemic stroke patients with beneficial treatment of emergent large vessel occlusion. Still, the disparity between recanalization rates and clinical outcomes calls for enhanced device designs and treatment strategies with better reperfusion efficiency. Intuitively, sufficient device integration with the embolus is pursued to maximize chances of first-pass success, thereby limiting clot fragmentation and intimal trauma during extensive clot manipulation. Our aim was to develop an imaging-based measure of device integration in reproducible phantom experiments that could help identifying differences in aspects of thrombectomy procedures that may be related to angiographic and clinical outcomes.

Methods: Deployment variations of the Trevo(TM) ProVue/XP retriever were tested in an in-vitro model system that mimicked a MCA-occlusion with a silicone vascular replica and two visible clot models (soft elastic, and hard inelastic) with 8 trials/group. High-resolution cone-beam CT imaging was performed prior to retriever retraction. An image processing pipeline was devised that used level-set segmentation, path-tracing, and Steiner circumellipse fitting to extract and determine the interior volumes of the clot and the three visible wires. Clot Integration Factor (CIF) was calculated as the ratio of the volume of clot-device intersection to the clot volume.

Results: Example of the device, its wires, and the clot: Average clot volumes were 90.4±12.2mm3. CIF was significantly different for two deployment variations when the device engaged a hard clot (difference between means, 95%CI=[0.003,0.187], p=0.043), but not a soft clot model (95%CI=[-0.152,0.263], p=0.567).

Conclusion: In-vitro imaging-based quantification of clot integration can detect differences in deployment configuration relative to a clot, which may support procedural and design improvements.

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.

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.

Porcine brachial artery tortuosity for in vivo evaluation of neuroendovascular devices

We report a novel model of arterial tortuosity in the porcine brachial artery for testing of endovascular devices in the flexed forelimb position. This provides an ideal vascular territory for an in vivo assessment of guidewires, microcatheters, and endovascular implants because it closely mimics the challenging curvature at the carotid siphon.

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.

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 = V(A)/V(CM), 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.

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 psychosocial impact of food allergy and food hypersensitivity in children, adolescents and their families: a review

Food allergy affects 6% of children but there is no cure, and strict avoidance of index allergens along with immediate access to rescue medication is the current best management. With specialist care, morbidity from food allergy in children is generally low, and mortality is very rare. However, there is strong evidence that food allergy and food hypersensitivity has an impact on psychological distress and on the quality of life (QoL) of children and adolescents, as well as their families. Until recently, the measurement of QoL in allergic children has proved difficult because of the lack of investigative tools available. New instruments for assessing QoL in food allergic children have recently been developed and validated, which should provide further insights into the problems these children encounter and will enable us to measure the effects of interventions in patients. This review examines the published impact of food allergy on affected children, adolescents and their families. It considers influences such as gender, age, disease severity, co-existing allergies and external influences, and examines how these may impact on allergy-related QoL and psychological distress including anxiety and depression. Implications of the impact are considered alongside avenues for future research.

Impact of peanut allergy on quality of life, stress and anxiety in the family

BACKGROUND

Peanut allergy (PA) is known to impact on quality of life (QoL) of the sufferer, but little research has focused on all family members. We therefore sought to establish the impact of PA on QoL and reported anxiety of children with clinically confirmed PA, their parents and older siblings.

METHODS

Forty-six families, who had a child with PA, completed QoL (PedsQL or WHOQOL-BREF), anxiety (SCAS or STAI) and perceived stress (PSS) scales. PA children completed a PA specific QoL questionnaire (Pediatr Allergy Immunol 2003;14:378). Parents and sibling also completed QoL proxy questionnaires for the PA child (PedsQL, Pediatr Allergy Immunol 2003;14:378).

RESULTS

Mothers rated their own psychological (P < 0.01) and physical (P < 0.05) QoL significantly worse than fathers rated theirs, and had higher scores than fathers for anxiety (P < 0.05) and stress (P < 0.001). Children with PA had significantly poorer physical health-related QoL (P < 0.05), QoL within school (P < 0.01) and general QoL (P < 0.05) than their siblings did, and greater separation anxiety (P < 0.05). The majority of differences were between girls with PA and female siblings. Mothers felt that there was a greater impact on QoL for their PA child, compared with that reported by siblings, fathers or the PA children themselves (P < 0.01).

CONCLUSIONS

Mothers report that they have significantly poorer QoL and suffer more anxiety and stress than fathers do; this inter-parental difference may be an important feature of family stress caused by PA. Siblings have a similar view of how QoL affects the PA child as the PA child does, while mothers may possibly overestimate this impact.

Does severity of low-dose, double-blind, placebo-controlled food challenges reflect severity of allergic reactions to peanut in the community?

BACKGROUND

The severity of allergic reactions to food appears to be affected by many interacting factors. It is uncertain whether challenge-based reactions reflect the severity of past reactions or can predict future risk.

OBJECTIVE

To explore the relationship of a subject's clinical history of past reactions to the severity of reaction elicited by a low-dose, double-blind, placebo-controlled food challenge (DBPCFC) with peanut.

METHOD

Cross-sectional questionnaire assessment of community-based allergic reactions and low-dose DBPCFC in self-selected peanut-allergic subjects. Reaction severity was assessed using a novel scoring system, taking account of the dose of allergen ingested.

RESULTS

Forty subjects (15 males, 23 children, 23 asthmatics by history) were studied. Only the most recent community reaction predicted the severity of reaction in the DBPCFC, but even this association was weak (r=0.37, P=0.03). Peanut-specific IgE (PsIgE) and skin prick test (SPT) weal size were not associated with community score but PsIgE level correlated well with the challenge score (r=0.6, P=0.001). Asthma did not affect the eliciting dose or challenge score directly but the association of PsIgE and challenge score was stronger in those without asthma (r=0.72, P=0.001) than in those with asthma (r=0.48, P=0.02).

CONCLUSIONS

The scoring system developed appears to improve the sensitivity of assessment of reactions induced by DBPCFC. This is the first prospective study showing an association between PsIgE levels and clinical reactivity in DBPCFC, an effect that is more pronounced in non-asthmatics. This finding has important implications for the clinical care of subjects with food allergy. There is a poor correlation between the severity of reported reactions in the community and the severity of reaction elicited during low-dose DBPCFC with peanut.

Presentation of allergen in different food preparations affects the nature of the allergic reaction - a case series

BACKGROUND

Characterization of fatal and non-fatal reactions to food indicates that the majority of reactions are due to the ingestion of prepared foods rather than the non-processed allergen. In an ongoing study that used a double-blind placebo-controlled food challenge to investigate peanut allergy and clinical symptoms, the observed reaction severity in four of the first six subjects was greater than anticipated. We hypothesized that this was due to differences in the composition of the challenge vehicle.

OBJECTIVE

The aim was to investigate whether the severity of observed challenge reactions would be repeated on re-challenge with a lower fat challenge vehicle.

METHODS

Peanut-allergic subjects were re-challenged with a lower fat recipe after reacting more severely than was anticipated to an initial peanut challenge. Similar challenge vehicle recipes were used, the only difference being the lower fat content (22.9% compared with 31.5%). The peanut content of the two recipes was analysed using RAST inhibition studies and ELISA tests.

RESULTS

Three of four subjects reacted to much smaller doses of peanut protein on re-challenge (mean dose equivalence - 23 times less peanut) with the lower fat recipe. RAST inhibition showed that neither recipe altered epitope recognition. The higher fat recipe required twice as much peanut to cause 50% inhibition. ELISA detected far lower levels of peanut in the higher fat recipe (220 000 parts per million (p.p.m.)) than in the lower fat recipe (990 000 p.p.m.).

CONCLUSION

The fat content of a challenge vehicle has a profound effect on the reaction experienced after allergen ingestion. This is another factor to be considered in assessing the risk of certain foods to food-allergic consumers and adds another dimension to clinical, research and regulatory practice.

Similarities in body image in sisters: the role of sociocultural internalization and social comparison

The sociocultural theory of body image disturbance states that Western women experience pressure from sources such as parents, peers, and the media to maintain thinness. Social comparison theory emphasises the role of comparing one's appearance to others. Body image disturbance; awareness and Internalization of sociocultural messages regarding thinness; and sibling social comparisons were examined in 41 closest-in-age sisters through self-report questionnaires. Sisters showed similar levels of body image disturbance and sociocultural awareness and internalization. Sibling comparisons were negative for younger sisters but neutral or positive for older sisters. Sociocultural internalization predicted body dissatisfaction in both sisters, and body size distortion in younger sisters. Negative sibling comparisons during teenage years predicted body size distortion and body dissatisfaction in younger sisters, and preference for thinness in older sisters.