Construction of a comprehensive endovascular test bed for research and device development in mechanical thrombectomy in stroke

Safety Window for Effective Lesion Crossing in Patients With Chronic Thromboembolic Pulmonary Hypertension

Background

Balloon pulmonary angioplasty for chronic thromboembolic pulmonary hypertension (CTEPH) is limited by a lack of safe and effective tools for crossing these lesions. We aim to identify a safety window for an intraluminal crossing device in this vascular bed by studying the piercing properties of pulmonary arterial vessel walls and intraluminal CTEPH lesion specimens. As a secondary objective, we also describe the histopathologic features of CTEPH lesions.

Methods

Specimens were procured from 9 patients undergoing pulmonary endarterectomy. The specimens were subsampled and identified grossly as arterial wall or intraluminal CTEPH lesions. The force needed for tissue penetration was measured using a 0.38-mm (0.015-in) diameter probe in an ex vivo experimental model developed in our lab. Concurrent histology was also performed.

Results

The mean force needed to penetrate the arterial wall and intraluminal CTEPH lesions was 1.75 ± 0.10 N (n = 121) and 0.30 ± 0.04 N (n = 56), respectively (P < .001). Histology confirmed the presence of intimal hyperplasia with calcium and hemosiderin deposition in the arterial wall as well as an old, organized thrombus in the lumen.

Conclusions

The pulmonary arterial wall is friable and prone to perforation during instrumentation with workhorse coronary guide wires. However, the results of this study demonstrate that a much lower force is needed for the 0.38-mm (0.015-in) probe to penetrate an intraluminal CTEPH lesion compared to pulmonary arterial intima. This finding suggests the existence of a safety window for lesion-crossing devices, enabling effective balloon pulmonary angioplasty.

Evaluating the accuracy of cerebrovascular computational fluid dynamics modeling through time-resolved experimental validation

Accurate modeling of cerebral hemodynamics is crucial for better understanding the hemodynamics of stroke, for which computational fluid dynamics (CFD) modeling is a viable tool to obtain information. However, a comprehensive study on the accuracy of cerebrovascular CFD models including both transient arterial pressures and flows does not exist. This study systematically assessed the accuracy of different outlet boundary conditions (BCs) comparing CFD modeling and an in-vitro experiment. The experimental setup consisted of an anatomical cerebrovascular phantom and high-resolution flow and pressure data acquisition. The CFD model of the same cerebrovascular geometry comprised five sets of stationary and transient BCs including established techniques and a novel BC, the phase modulation approach. The experiment produced physiological hemodynamics consistent with reported clinical results for total cerebral blood flow, inlet pressure, flow distribution, and flow pulsatility indices (PI). The in-silico model instead yielded time-dependent deviations between 19-66% for flows and 6-26% for pressures. For cerebrovascular CFD modeling, it is recommended to avoid stationary outlet pressure BCs, which caused the highest deviations. The Windkessel and the phase modulation BCs provided realistic flow PI values and cerebrovascular pressures, respectively. However, this study shows that the accuracy of current cerebrovascular CFD models is limited.

In vitro models for the experimental evaluation of mechanical thrombectomy devices in acute ischemic stroke

Mechanical thrombectomy has become an important method for the treatment of acute ischemic stroke for large vessel occlusions. The current hotspots of mechanical thrombectomy are optimizing the treatment methods, improving the recanalization rate and reducing complications. The in vitro model has become a common and convenient method for mechanical thrombectomy research. This review summarizes the in vitro model in the following aspects: the preparation of clot analogues; the experimental platform; the application of the in vitro model in the testing of thrombectomy devices; and the advantages, limitations and future trends of the in vitro experimental model. This review describes the characteristics and applications of the in vitro experimental model with the hope that the in vitro experimental model will be further improved and play a more effective role in the study of mechanical thrombectomy.

Evaluation of vessel injury after simulated catheter use in an endothelialized silicone model of the intracranial arteries

PURPOSE

Neurothrombectomy catheters can disrupt or injure the vessel wall. This potential injury is often studied in animal or cadaver models, but prior work suggests that endothelialized silicone models may be an option for early in vitro assessment. The purpose of this work was to create a complex, clinically-relevant endothelialized neurovascular silicone model, and to determine the utility of the model for evaluating vessel injury due to catheter simulated use.

METHODS

Models of the ICA and MCA were fabricated out of silicone, sterilized, coated with fibronectin, placed in bioreactors, and endothelialized with HUVECs. These silicone vessels were maintained under flow for 3 and 7 days, and cellular linings were assessed. Subsequently, 24 silicone vessels were created and treated with neurovascular catheters. Vessels were accessed with a guidewire, microcatheter, and/or aspiration catheter, either once (1-pass) or three times (3-pass). Vessels were then fixed, and injury was evaluated through quantitative image analysis and a visual scoring system.

RESULTS

Complex silicone models were successfully endothelialized and maintained with consistent cell linings. The transparent silicone permitted catheter simulated use without fluoroscopy, and injury to the vessel wall was observed and successfully imaged and characterized. Vessels subjected to 3-passes exhibited more injury than 1-pass, and injury increased with the number and size of devices. These results illustrated expected trends and support use of these models for early assessment of vessel injury.

CONCLUSION

Complex silicone neurovascular models can be endothelialized and used in vitro to assess and compare injury due to the use of neurovascular catheters.

Construction and Validation of a Benchtop Model for Testing of Mechanical Thrombectomy Devices for Pulmonary Embolism

PURPOSE

This study aims to define the process of designing and manufacturing 3D printed and glass models of the pulmonary artery (PA) and utilizing them in a test bed for evaluation of devices for mechanical thrombectomy of pulmonary embolism (PE).

MATERIALS AND METHODS

Patient derived computed tomography angiography (CTA) images of the PA were digitally converted into a hollowed-out structure and translated into clear 3D printed and glass models. A test bed was created using a peristaltic pump and silicone tubing connected to the models. Human clot analogs were then prepared and injected within the models. Thrombectomy testing was done using clinically used predicates and baseline characteristics of the models were evaluated by independent interventionalists.

RESULTS

The mean sizes of the main pulmonary artery (MPA) for the 3D printed model and glass model were 30.4 mm and 29.2 mm, mimicking those of the patient's PA obtained on CTA. Heterogeneous human clot analogs were created with fibrin composition ranging from 60 to 30%. Mechanical thrombectomy was successfully attempted by independent interventionalists. Both the 3D printed, and glass model were appraised as very good for multiple attributes.

CONCLUSION

A complete test bed using 3D printed and glass models of the PA with human clot analogs was created for testing of mechanical thrombectomy devices for PE.

A Review of the Advancements in the in-vitro Modelling of Acute Ischemic Stroke and Its Treatment

In-vitro neurovascular models of large vessel occlusions (LVOs) causing acute ischemic stroke (AIS) are used extensively for pre-clinical testing of new treatment devices. They enable physicians and engineers to examine device performance and the response of the occlusion to further advance design solutions for current unmet clinical needs. These models also enable physicians to train on basic skills, to try out new devices and new procedural approaches, and for the stroke team to practice workflows together in the comfort of a controlled environment in a non-clinical setting. Removal of the occlusive clot in its entirety is the primary goal of the endovascular treatment of LVOs via mechanical thrombectomy (MT) and the medical treatment via thrombolysis. In MT, recanalization after just one pass is associated with better clinical outcomes than procedures that take multiple passes to achieve the same level of recanalization, commonly known as first pass effect (FPE). To achieve this, physicians and engineers are continually investigating new devices and treatment approaches. To distinguish between treatment devices in the pre-clinical setting, test models must also be optimized and expanded become more nuanced and to represent challenging patient cohorts that could be improved through new technology or better techniques. The aim of this paper is to provide a perspective review of the recent advancements in the in-vitro modeling of stroke and to outline how these models need to advance further in future. This review provides an overview of the various in-vitro models used for the modeling of AIS and compares the advantages and limitations of each. In-vitro models remain an extremely useful tool in the evaluation and design of treatment devices, and great strides have been made to improve replication of physiological conditions. However, further advancement is still required to represent the expanding indications for thrombectomy and thrombolysis, and the generation of new thrombectomy devices, to ensure that smaller treatment effects are captured.

Robotics in neurointerventional surgery: a systematic review of the literature

BACKGROUND

Robotically performed neurointerventional surgery has the potential to reduce occupational hazards to staff, perform intervention with greater precision, and could be a viable solution for teleoperated neurointerventional procedures.

OBJECTIVE

To determine the indication, robotic systems used, efficacy, safety, and the degree of manual assistance required for robotically performed neurointervention.

METHODS

We conducted a systematic review of the literature up to, and including, articles published on April 12, 2021. Medline, PubMed, Embase, and Cochrane register databases were searched using medical subject heading terms to identify reports of robotically performed neurointervention, including diagnostic cerebral angiography and carotid artery intervention.

RESULTS

A total of 8 articles treating 81 patients were included. Only one case report used a robotic system for intracranial intervention, the remaining indications being cerebral angiography and carotid artery intervention. Only one study performed a comparison of robotic and manual procedures. Across all studies, the technical success rate was 96% and the clinical success rate was 100%. All cases required a degree of manual assistance. No studies had clearly defined patient selection criteria, reference standards, or index tests, preventing meaningful statistical analysis.

CONCLUSIONS

Given the clinical success, it is plausible that robotically performed neurointerventional procedures will eventually benefit patients and reduce occupational hazards for staff; however, there is no high-level efficacy and safety evidence to support this assertion. Limitations of current robotic systems and the challenges that must be overcome to realize the potential for remote teleoperated neurointervention require further investigation.

Human "live cadaver" neurovascular model for proximal and distal mechanical thrombectomy in stroke

BACKGROUND

Preclinical testing platforms that accurately replicate complex human cerebral vasculature are critical to advance neurointerventional knowledge, tools, and techniques. Here, we introduced and validated a human "live cadaveric" head-and-neck neurovascular model optimized for proximal and distal vascular occlusion and recanalization techniques.

METHODS

Human cadaveric head-and-neck specimens were cannulated bilaterally in the jugular veins, carotid, and vertebral arteries. Specimens were then coupled with modular glass models of the aorta and extracranial carotid arteries, as well as radial and femoral access ports. Intracranial physiological flow was simulated using a flow-delivery system and blood-mimicking fluid. Baseline anatomy, histological, and mechanical properties of cerebral arteries were compared with those of fresh specimens. Radiopaque clot analogs were embolized to replicate proximal and distal arterial occlusions, followed by thrombectomy. Experienced interventionalists scored the model on different aspects.

RESULTS

Compared with counterpart fresh human arteries, formalin-fixed arteries showed similar mechanical properties, including maximum stretch, increased tensile strength/stiffness, and friction coefficients were also not significantly different. On histology, minimal endothelial damage was noted in arteries after 3 months of light fixation, otherwise the arterial wall maintained the structural integrity. Contrast angiographies showed no micro- or macro-vasculature obstruction. Proximal and distal occlusions created within the middle cerebral arteries were consistently obtained and successfully recanalized. Additionally, interventionists scored the model highly realistic, indicating great similarity to patients' vasculature.

CONCLUSIONS

The human "live cadaveric" neurovascular model accurately replicates the anatomy, mechanics, and hemodynamics of cerebral vasculature and allows the performance of neurointerventional procedures equivalent to those done in patients.

Brain Oxygen Optimization in Severe Traumatic Brain Injury (BOOST-3): a multicentre, randomised, blinded-endpoint, comparative effectiveness study of brain tissue oxygen and intracranial pressure monitoring versus intracranial pressure alone

INTRODUCTION

Management of traumatic brain injury (TBI) includes invasive monitoring to prevent secondary brain injuries. Intracranial pressure (ICP) monitor is the main measurement used to that intent but cerebral hypoxia can occur despite normal ICP. This study will assess whether the addition of a brain tissue oxygenation (PbtO2) monitor prevents more secondary injuries that will translate into improved functional outcome.

METHODS AND ANALYSIS

Multicentre, randomised, blinded-endpoint comparative effectiveness study enrolling 1094 patients with severe TBI monitored with both ICP and PbtO2. Patients will be randomised to medical management guided by ICP alone (treating team blinded to PbtO2 values) or both ICP and PbtO2. Management is protocolised according to international guidelines in a tiered approach fashion to maintain ICP <22 mm Hg and PbtO2 >20 mm Hg. ICP and PbtO2 will be continuously recorded for a minimum of 5 days. The primary outcome measure is the Glasgow Outcome Scale-Extended performed at 180 (±30) days by a blinded central examiner. Favourable outcome is defined according to a sliding dichotomy where the definition of favourable outcome varies according to baseline severity. Severity will be defined according to the probability of poor outcome predicted by the IMPACT core model. A large battery of secondary outcomes including granular neuropsychological and quality of life measures will be performed.

ETHICS AND DISSEMINATION

This has been approved by Advarra Ethics Committee (Pro00030585). Results will be presented at scientific meetings and published in peer-reviewed publications.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov Registry (NCT03754114).

Arterial Collapse during Thrombectomy for Stroke: Clinical Evidence and Experimental Findings in Human Brains and In Vivo Models

BACKGROUND AND PURPOSE

Aspiration thrombectomy has become a preferred approach to recanalize large-vessel occlusion in stroke with a growing trend toward using larger-bore catheters and stronger vacuum pumps. However, the mechanical response of the delicate cerebral arteries to aspiration force has not been evaluated. Here, we provide preclinical and clinical evidence of intracranial arterial collapse in aspiration thrombectomy.

MATERIALS AND METHODS

We presented a clinical case of arterial collapse with previously implanted flow diverters. We then evaluated the effect of vacuum with conventional aspiration catheters (with and without stent retrievers) in a rabbit model (n = 3) using fluoroscopy and intravascular optical coherence tomography. Then, in a validated human cadaveric brain model, we conducted 168 tests of direct aspiration thrombectomy following an experimental design modifying the catheter inner diameter (0.064 inch, 0.068 inch, and 0.070 inch), cerebral perfusion pressures (mean around 60 and 90 mm Hg), and anterior-versus-posterior circulation. Arterial wall response was recorded and graded via direct transluminal observation.

RESULTS

Arterial collapse was observed in both the patient and preclinical experimental models. In the human brain model, arterial collapse was observed in 98% of cases in the M2 and in all the cases with complete proximal flow arrest. A larger bore size of the aspiration catheter, a lower cerebral perfusion pressure, and the posterior circulation in comparison with the anterior circulation were associated with a higher probability of arterial collapse.

CONCLUSIONS

Arterial collapse does occur during aspiration thrombectomy and is more likely to happen with larger catheters, lower perfusion pressure, and smaller arteries.

Thrombus Histology as It Relates to Mechanical Thrombectomy: A Meta-Analysis and Systematic Review

BACKGROUND

Appropriate thrombus-device interaction is critical for recanalization. Histology can serve as a proxy for mechanical properties, and thus inform technique selection.

OBJECTIVE

To investigate the value of histologic characterization, we conducted a systematic review and meta-analysis on the relationship between thrombus histology and recanalization, technique, etiology, procedural efficiency, and imaging findings.

METHODS

In this meta-analysis, we identified studies published between March 2010 and March 2020 reporting findings related to the histologic composition of thrombi in large vessel occlusion stroke. Studies with at least 10 patients who underwent mechanical thrombectomy using stent retriever or aspiration were considered. Only studies in which retrieved thrombi were histologically processed were included. Patient-level data were requested when data could not be directly extracted. The primary outcome assessed was the relationship between thrombus histology and angiographic outcome.

RESULTS

A total of 22 studies encompassing 1623 patients met inclusion criteria. Clots associated with good angiographic outcome had higher red blood cell (RBC) content (mean difference [MD] 9.60%, 95% CI 3.85-15.34, P = .008). Thrombi retrieved by aspiration had less fibrin (MD -11.39, 95% CI -22.50 to -0.27, P = .046) than stent-retrieved thrombi. Fibrin/platelet-rich clots were associated with longer procedure times (MD 13.20, 95% CI 1.30-25.10, P = .037). Hyperdense artery sign was associated with higher RBC content (MD 14.17%, 95% CI 3.07-25.27, P = .027). No relationship was found between composition and etiology.

CONCLUSION

RBC-rich thrombi were associated with better recanalization outcomes and shorter procedure times, suggesting that preinterventional compositional characterization may yield important prognostic and therapeutic guidance.

A Thrombectomy Model Based on Ex Vivo Whole Human Brains

BACKGROUND AND PURPOSE

The persistent challenges in thrombectomy for large-vessel occlusion, such as suboptimal complete recanalization and first-pass effect imply an insufficient understanding of the artery-clot-device interaction. In this study, we present a thrombectomy model using fresh human brains, which can capture the artery-clot-device interaction through concurrent transmural and angiographic visualizations.

MATERIALS AND METHODS

Fresh nonfrozen whole adult human brains were collected and connected to a customized pump system tuned to deliver saline flow at a physiologic flow rate and pressure. Angiography was performed to verify the flow in the anterior-posterior and vertebrobasilar circulations and collaterals. Large-vessel occlusion was simulated by embolizing a radiopaque clot analog. Thrombectomy was tested, and the artery-clot-device interactions were recorded by transmural and angiographic videos.

RESULTS

Baseline cerebral angiography revealed excellent penetration of contrast in the anterior-posterior and vertebrobasilar circulations without notable arterial cutoffs and with robust collaterals. Small branches (<0.5 mm) and perforating arteries were consistently opacified with good patency. Three device passes were performed to achieve recanalization, with failure modes including elongation, fragmentation, and distal embolization.

CONCLUSIONS

This model enables concurrent transmural and angiographic analysis of artery-clot-device interaction in a human brain and provides critical insights into the action mechanism and failure modes of current and upcoming thrombectomy devices.

Preclinical testing platforms for mechanical thrombectomy in stroke: a review on phantoms, in-vivo animal, and cadaveric models

Preclinical testing platforms have been instrumental in the research and development of thrombectomy devices. However, there is no single model which fully captures the complexity of cerebrovascular anatomy, physiology, and the dynamic artery-clot-device interaction. This article provides a critical review of phantoms, in-vivo animal, and human cadaveric models used for thrombectomy testing and provides insights into the strengths and limitations of each platform. Articles published in the past 10 years that reported thrombectomy testing platforms were identified. Characteristics of each test platform, such as intracranial anatomy, artery tortuosity, vessel friction, flow conditions, device-vessel interaction, and visualization, were captured and benchmarked against human cerebral vessels involved in large-vessel occlusion stroke. Thrombectomy phantoms have been constructed from silicone, direct 3D-printed polymers, and glass. These phantoms represent oversimplified patient-specific cerebrovascular geometry but enable adequate visualization of devices and clots under appropriate flow conditions. They do not realistically mimic the artery-clot interaction. For the animal models, arteries from swine, canines, and rabbits have been reported. These models can reasonably replicate the artery-clot-device interaction and have the unique value of evaluating the safety of thrombectomy devices. However, the vasculature geometries are substantially less complex and flow conditions are different from human cerebral arteries. Cadaveric models are the most accurate vascular representations but with limited access and challenges in reproducibility of testing conditions. Multiple test platforms should be likely used for comprehensive evaluation of thrombectomy devices. Interpretation of the testing results should take into consideration platform-specific limitations.

Failure modes and effects analysis of mechanical thrombectomy for stroke discovered in human brains

OBJECTIVE

Despite advancement of thrombectomy technologies for large-vessel occlusion (LVO) stroke and increased user experience, complete recanalization rates linger around 50%, and one-third of patients who have undergone successful recanalization still experience poor neurological outcomes. To enhance the understanding of the biomechanics and failure modes, the authors conducted an experimental analysis of the interaction of emboli/artery/devices in the first human brain test platform for LVO stroke described to date.

METHODS

In 12 fresh human brains, 105 LVOs were recreated by embolizing engineered emboli analogs and recanalization was attempted using aspiration catheters and/or stent retrievers. The complex mechanical interaction between diverse emboli (elastic, stiff, and fragment prone), arteries (anterior and posterior circulation), and thrombectomy devices were observed, analyzed, and categorized. The authors systematically evaluated the recanalization process through failure modes and effects analysis, and they identified where and how thrombectomy devices fail and the impact of device failure.

RESULTS

The first-pass effect (34%), successful (71%), and complete (60%) recanalization rates in this model were consistent with those in the literature. Failure mode analysis of 184 passes with thrombectomy devices revealed the following. 1) Devices loaded the emboli with tensile forces leading to elongation and intravascular fragmentation. 2) In the presence of anterograde flow, small fragments embolize to the microcirculation and large fragments result in recurrent vessel occlusion. 3) Multiple passes are required due to recurrent (15%) and residual (73%) occlusions, or both (12%). 4) Residual emboli remained in small branching and perforating arteries in cases of alleged complete recanalization (28%). 5) Vacuum caused arterial collapse at physiological pressures (27%). 6) Device withdrawal caused arterial traction (41%), and severe traction provoked avulsion of perforating and small branching arteries.

CONCLUSIONS

Biomechanically superior thrombectomy technologies should prevent unrestrained tensional load on emboli, minimize intraluminal embolus fragmentation and release, improve device/embolus integration, recanalize small branching and perforating arteries, prevent arterial collapse, and minimize traction.

Novel Human Acute Ischemic Stroke Blood Clot Analogs for In Vitro Thrombectomy Testing

BACKGROUND AND PURPOSE

Previous studies have successfully created blood clot analogs for in vitro endovascular device testing using animal blood of various species. Blood components vary greatly among species; therefore, creating clot analogs from human blood is likely a more accurate representation of thrombi formed in the human vasculature.

MATERIALS AND METHODS

Following approval from the Mayo Clinic institutional review board, human whole-blood and platelet donations were obtained from the blood transfusion service. Twelve clot analogs were created by combining different ratios of red blood cells + buffy coat, plasma, and platelets. Thrombin and calcium chloride were added to stimulate coagulation. Clot composition was assessed using histologic and immunohistochemical staining. To assess the similarities of mechanical properties to patient clots, 3 types of clot analogs (soft, elastic, and stiff) were selected for in vitro thrombectomy testing.

RESULTS

The range of histopathologic compositions produced is representative of clots removed during thrombectomy procedures. The red blood cell composition ranged from 8.9% to 91.4%, and fibrin composition ranged from 3.1% to 53.4%. Platelets (CD42b) and von Willebrand Factor ranged from 0.5% to 47.1% and 1.0% to 63.4%, respectively. The soft clots had the highest first-pass effect and successful revascularization rates followed by the elastic and stiff clots. Distal embolization events were observed when clot ingestion could not be achieved, requiring device pullback. The incidence rate of distal embolization was the highest for the stiff clots due to the weak clot/device integration.

CONCLUSIONS

Red blood cell-rich, fibrin-rich, and platelet-rich clot analogs that mimic clots retrieved from patients with acute ischemic stroke were created in vitro. Differing retrieval outcomes were confirmed using in vitro thrombectomy testing in a subset of clots.

Vascular tortuosity in endovascular mechanical thrombectomy

Endovascular mechanical thrombectomy effectively removes occlusive thrombi from the arterial lumen; however, there is little literature supporting the relevance of vascular geometry on surgical outcomes. Critical vessel characteristics including the degree of angulation and tortuosity influence the ability to advance stent retriever devices toward the site of occlusion. Therefore, it is crucial to evaluate the impact of carotid artery catheter pathway accessibility on the thrombectomy outcomes in acute ischemic stroke (AIS) patients. Traditional imaging modalities generate incomplete pictures of the vascular tortuosity and are prone to clinical judgment errors. Recent three-dimensional computed tomography angiography image analysis techniques circumvent these limitations to calculate accurate tortuosity and angulation measurements. These novel images facilitate classifying common anatomical variant patients into groups that may be treated with specially designed catheter devices. Importantly, this image analysis method reveals significant angulation in the common carotid artery and extracranial internal carotid artery that correlates with delays in reaching the occlusion site. Increased age, which is associated with increased risk of stroke, also increases the incidence of severe tortuosity. The semi-automated measurements technique also demonstrate that full 360° arterial loops are present in nearly 3% of catheter pathways and that the overall degree of angulation differs bilaterally. In this review, we examine the utility of this novel image analysis procedure and evaluate the recent literature relevant to neuroendovascular thrombectomy in AIS patients. Three literature databases – PubMed, Embase, and Web of Science were queried for original articles investigating both preclinical and clinical thrombectomy applications.

Trends in Academic Spine Neurosurgeon Productivity as Measured by the Relative Citation Ratio

BACKGROUND

Publication metrics such as the author-level h-index are often used to evaluate and compare research productivity in academia. The h-index, however, is not a field-normalized statistic and has been criticized as inappropriate for comparison of authors from different fields. For example, fields such as internal medicine have a larger audience and thus afford publications a higher likelihood of increased citations compared with a perhaps equally impactful paper in a smaller field such as neurosurgery. The National Institutes of Health (NIH) has developed a new field-normalized article-level metric called the relative citation ratio (RCR) that can be used to more accurately compare author productivity between fields. Spine represents a distinct subset of neurosurgery with a designated fellowship and distinct differences in the RCR metrics. The authors look to analyze the unique results found in the academic spine neurosurgeon RCR values compared with all academic neurosurgeons.

PURPOSE

The assessment of academic physicians should use field-independent publication metrics to measure the improvement of grant outcomes, promotion, and continued evaluation of research productivity. Here, we provide an analysis of RCR indices for 358 academic spine neurosurgeons in the United States, including the mean RCR of each author's total publications and the weighted RCR, which is the sum of all publication-level RCR values of an author. We further assess the impact of gender, career duration, academic rank, and Ph.D. acquisition on the RCR scores of U.S. academic spine neurosurgeons.

METHODS

The mean RCR is the total citations per year of a publication divided by average citations per year received by NIH-funded papers in the same field. A value of 1 is the normal NIH-funded standard. iCite database searches were performed for all physician faculty members affiliated with accredited neurological surgery programs who have subspecialized in spine as of November 1, 2019. Gender, career duration, academic rank, additional degrees, total publications, mean RCR, and weighted RCR were collected for each individual. RCR and weighted RCR were compared between variables to assess patterns of analysis.

RESULTS

A total of 358 fellowship-trained academic spine neurosurgeons from 125 institutions were included in the analysis. Exceptional research productivity was noted, with a median RCR of 1.38 (interquartile range = 0.94-1.95) and a weighted median RCR of 25.28 (interquartile range = 6.87-79.93). Overall, gender and academic rank were associated with increased mean RCR and weighted RCR values. Career duration and Ph.D. acquisition were not. All subgroups analyzed had an RCR value above 1.0, with professor-level faculty or department chair having the highest mean and weighted RCR values overall.

CONCLUSIONS

Current academic spine neurosurgeons have high median RCR values relative to the NIH standard RCR value of 1.0. Relative to the field of neurological surgery overall, RCR values for the spine subspecialty are comparable. These data offer a more accurate means for self-evaluation of academic neurosurgeons as well as evaluation of faculty by institutional and departmental leaders.

Feasibility of a customizable training environment for neurointerventional skills assessment

OBJECTIVE

To meet increasing demands to train neuroendovascular techniques, we developed a dedicated simulator applying individualized three-dimensional intracranial aneurysm models ('HANNES'; Hamburg Anatomic Neurointerventional Endovascular Simulator). We hypothesized that HANNES provides a realistic and reproducible training environment to practice coil embolization and to exemplify disparities between neurointerventionalists, thus objectively benchmarking operators at different levels of experience.

METHODS

Six physicians with different degrees of neurointerventional procedural experience were recruited into a standardized training protocol comprising catheterization of two internal carotid artery (ICA) aneurysms and one basilar tip aneurysm, followed by introduction of one framing coil into each aneurysm and finally complete coil embolization of one determined ICA aneurysm. The level of difficulty increased with every aneurysm. Fluoroscopy was recorded and assessed for procedural characteristics and adverse events.

RESULTS

Physicians were divided into inexperienced and experienced operators, depending on their experience with microcatheter handling. Mean overall catheterization times increased with difficulty of the aneurysm model. Inexperienced operators showed longer catheterization times (median; IQR: 47; 30-84s) than experienced operators (21; 13-58s, p = 0.011) and became significantly faster during the course of the attempts (rho = -0.493, p = 0.009) than the experienced physicians (rho = -0.318, p = 0.106). Number of dangerous maneuvers throughout all attempts was significantly higher for inexperienced operators (median; IQR: 1.0; 0.0-1.5) as compared to experienced operators (0.0; 0.0-1.0, p = 0.014).

CONCLUSION

HANNES represents a modular neurointerventional training environment for practicing aneurysm coil embolization in vitro. Objective procedural metrics correlate with operator experience, suggesting that the system could be useful for assessing operator proficiency.

Standardized Fabrication Method of Human-Derived Emboli with Histologic and Mechanical Quantification for Stroke Research

BACKGROUND

As access to patient emboli is limited, embolus analogs (EAs) have become critical to the research of large vessel occlusion (LVO) stroke and the development of thrombectomy technology. To date, techniques for fabricating standardized human blood-derived EAs are limited in the variety of compositions, and the mechanical properties relevant to thrombectomy are not quantified.

METHODS

EAs were made by mixing human banked red blood cells (RBCs), plasma, and platelet concentrate in 10 different volumetric percentage combinations to mimic the broad range of patient emboli causing LVO strokes. The samples underwent histologic analysis and tensile testing to mimic the pulling action of thrombectomy devices, and were compared to patient emboli.

RESULTS

EAs had histologic compositions of 0-96% RBCs, 0.78%-92% fibrin, and 2.1%-22% platelets, which can be correlated with the ingredients using a regression model. At fracture, EAs elongated from 81% to 136%, and the ultimate tensile stress ranged from 16 to 949 kPa. These EAs' histologic compositions and tensile properties showed great similarity to those of emboli retrieved from LVO stroke patients, indicating the validity of such EA fabrication methods. EAs with lower RBC and higher fibrin contents are more extensible and can withstand higher tensile stress.

CONCLUSIONS

EAs fabricated and tested using the proposed new methods provide a platform for stroke research and pre-clinical development of thrombectomy devices.