Evaluation of a modular in vitro neurovascular procedure simulation for intracranial aneurysm embolization

Brain Arteriovenous Malformation In Vitro Model for Transvenous Embolization Using 3D Printing and Real Patient Data

BACKGROUND AND PURPOSE

Transvenous embolization has emerged as a novel technique for treating selected brain AVMs with high reported occlusion rates. However, it requires anatomic and technical skills to be successful and to ensure patient safety. Therefore, training and testing are essential for preparing clinicians to perform these procedures. Our aim was to develop and test a novel, patient-specific brain AVM in vitro model for transvenous embolization by using 3D printing technology.

MATERIALS AND METHODS

We developed a brain AVM in vitro model based on real patient data by using stereolithography resin 3D printing. We created a closed pulsed circuit with flow passing from the arterial side to the venous side, and we tested the effect of mean arterial pressure on retrograde nidal filling with contrast injections. Transvenous embolization simulations were conducted for each of the 12 identical models divided into 2 groups (2×6). This involved the use of an ethylene-vinyl alcohol liquid embolic agent injected through microcatheters either without or with a coil in the vein (groups 1 and 2, respectively).

RESULTS

Retrograde contrast advance to nidus was directly related to lower mean arterial pressure. Transvenous embolization tests with a liquid embolic agent adequately reproduced the usual embolization plug and push technique. We found no differences between the 2 group conditions, and additional venous coil neither increased nidus penetration nor reduced injection time in the model (57.6 versus 61.2% nidus occlusion rate, respectively).

CONCLUSIONS

We were able to develop and test a functional in vitro brain AVM model for transvenous embolization by using 3D printing to emulate its conditions and characteristics. Better contrast penetration was achieved with less mean arterial pressure, and no embolization advantage was found by adding coil to the vein in this model.

First experience with Walrus balloon guide catheter in a whole-body flow model

PURPOSE

Flow arrest using a balloon guide catheter (BGC) in mechanical thrombectomy (MT) due to large vessel occlusion has been associated with better outcomes. Known limitations of currently commercially available BGCs are incompatibility with large bore aspiration catheters (AC) and lack of distal flexibility. Walrus presents variable stiffness and compatibility with large bore AC. The goal of this study is to describe the first experience with Walrus in a realistic stroke simulation model.

METHODS

A full-length modular vascular model under physiological conditions was used. 8F+-Walrus inner-diameter (ID) 0.087in 95 cm combined with 6F-Sofia AC ID 0.070in 131 cm and an 8F-Flowgate2 BGC ID 0.084in 95 cm with a 5F-Sofia AC ID 0.055in 125 cm were used to perform aspiration MT. User surveys, access to target and occlusion site, technique, time of delivery, anatomical change, and catheter kick-back were assessed.

RESULTS

Seven neuroradiologists with average of 10 years-experience in MT performed primary aspiration using the above-mentioned combinations in three different anatomies (N = 41). All operators would likely (29%) or very likely (71%) use again Walrus in combination with large bore AC and the majority (86%) found its navigability easier than with other BGCs. Time to reach final BGC position and catheter kick-back did not differ significantly among anatomies or catheter combinations (p > 0.05). However, Walrus was more likely to reach ICA petrous segment (p < 0.05) and intracranial occlusion with AC (p < 0.01).

CONCLUSION

The Walrus combined with large bore AC presented significantly better distal access and navigability for primary aspiration in an in vitro stroke model.

Medical 3D Printing Using Desktop Inverted Vat Photopolymerization: Background, Clinical Applications, and Challenges

Medical 3D printing is a complex, highly interdisciplinary, and revolutionary technology that is positively transforming the care of patients. The technology is being increasingly adopted at the Point of Care (PoC) as a consequence of the strong value offered to medical practitioners. One of the key technologies within the medical 3D printing portfolio enabling this transition is desktop inverted Vat Photopolymerization (VP) owing to its accessibility, high quality, and versatility of materials. Several reports in the peer-reviewed literature have detailed the medical impact of 3D printing technologies as a whole. This review focuses on the multitude of clinical applications of desktop inverted VP 3D printing which have grown substantially in the last decade. The principles, advantages, and challenges of this technology are reviewed from a medical standpoint. This review serves as a primer for the continually growing exciting applications of desktop-inverted VP 3D printing in healthcare.

Endovascular treatment simulations using a novel in vitro brain arteriovenous malformation model based on three-dimensional printing millifluidic technology

BACKGROUND

Brain arteriovenous malformations (bAVM) are complex vascular diseases. Several models have been used to simulate endovascular treatments; thus in vitro models have not been widely employed because it has been difficult to recreate realistic phantoms of this disease.

OBJECTIVE

To describe the development and evaluate the preliminary experience of a novel bAVM in vitro model for endovascular embolization using millifluidic three-dimensional (3D) printing technology.

METHODS

We designed a bAVM phantom starting from simple to more complex designs, composed of a nidus, feeding arteries and draining vein. We recreate the design by using millifluidic technology with stereolithography 3D printing. Structural and functional tests were performed using angiographic images and computer flow dynamics. Treatment simulations with ethylene vinyl alcohol were tested using two different microcatheter position techniques. A Likert-scale questionnaire was applied to perform a qualitative evaluation of the model.

RESULTS

We developed a realistic model of a bAVM with hollow channels. The structural evaluation showed a high precision of the 3D printing process. Embolization tests with the liquid agent gave similar sensations and material behaviour as in vivo cases. There were no significant differences between microcatheter position techniques, thus we observed a trend for better nidus filling with a deeper in-nidus position technique.

CONCLUSIONS

We were able to create and test a novel bAVM in vitro model with stereolithography 3D printing in resin. It showed a high capacity for simulating endovascular embolization characteristics, with an excellent user experience. It could be potentially used for training and testing of bAVM embolizations.

Irregular pulsation of aneurysmal wall is associated with symptomatic and ruptured intracranial aneurysms

BACKGROUND

Irregular pulsation of aneurysmal wall detected by four-dimensional CT angiography (4D-CTA) has been described as a novel imaging feature of aneurysm vulnerability. Our study aimed to investigate whether irregular pulsation is associated with symptomatic and ruptured intracranial aneurysms (IAs).

METHODS

This retrospective study included consecutive patients with IAs who underwent 4D-CTA from January 2018 to July 2021. IAs were categorized as asymptomatic, symptomatic or ruptured. The presence of irregular pulsation (defined as a temporary focal protuberance ≥1 mm on more than three successive frames) was identified on 4D-CTA movies. Univariate and multivariate analyses were used to identify the parameters associated with aneurysm symptomatic or ruptured status.

RESULTS

Overall, 305 patients with 328 aneurysms (37 ruptured, 60 symptomatic, 231 asymptomatic) were included. Ruptured and symptomatic IAs were significantly larger in size compared with asymptomatic IAs (median (IQR) 6.5 (5.1-8.3) mm, 7.0 (5.5-9.7) mm vs 4.7 (3.8-6.3) mm, p=0.001 and p<0.001, respectively) and had more irregular pulsations (70.3%, 78.3% vs 28.1%, p<0.05). Irregular pulsation (OR 5.03, 95% CI 2.83 to 8.92; p<0.001) was independently associated with aneurysm symptomatic/ruptured status in the whole population. With unruptured IAs, both irregular pulsation (OR 6.31, 95% CI 3.02 to 13.20; p<0.001) and size (OR 1.17, 95% CI 1.03 to 1.32; p=0.015) were independently associated with the symptoms. The combination of irregular pulsation and size increased the accuracy over size alone in identifying symptomatic aneurysms (AUC 0.81 vs 0.77, p=0.007) in unruptured IAs.

CONCLUSION

In a large cohort of patients with IAs detected by 4D-CTA, the presence of irregular pulsation was independently associated with aneurysm symptomatic and ruptured status.

Novel synthetic clot analogs for in-vitro stroke modelling

Purpose

The increased demand for training of mechanical thrombectomy in ischemic stroke and development of new recanalization devices urges the creation of new simulation models both for training and device assessment. Clots properties have shown to play a role in procedural planning and thrombectomy device effectiveness. In this study, we analyzed the characteristics and applicability of completely synthetic, animal-free clots in the setting of an in-vitro model of mechanical thrombectomy for training and device assessment.

Methods

Synthetic clots based on agarose (n = 12) and silicone (n = 11) were evaluated in an in-vitro neurointervention simulation of mechanical thrombectomy with clot extraction devices. Calcified clots of mixed nature were simulated with addition of 3D printed structures. 9 clots were excluded due to insufficient vessel occlusion and failure to integrate with clot extraction device. Synthetic thrombi were characterized and compared using a categorical score-system on vessel occlusion, elasticity, fragmentation, adherence and device integration.

Results

Both agarose-based and silicone-based clots demonstrated relevant flow arrest and a good integration with the clot extraction device. Silicone-based clots scored higher on adherence to the vessel wall and elasticity.

Conclusion

Selected synthetic clots can successfully be implemented in an in-vitro training environment of mechanical thrombectomy. The clots’ different properties might serve to mimic fibrin-rich and red blood cell-rich human thrombi.

Systematic Review on Endovascular Access to Intracranial Arteries for Mechanical Thrombectomy in Acute Ischemic Stroke

PURPOSE

In acute ischemic stroke for large vessel occlusions, delayed or failed access to intracranial occlusions has a negative impact on procedural and clinical outcomes. The aim of this review is to identify and quantify access failures and challenges in mechanical thrombectomy.

METHODS

A systematic literature review of PubMed and Scopus databases from January 2014 to October 2020 was performed. Articles reporting consecutive patients were used to calculate a crude failure rate of femoral and alternative accesses.

RESULTS

A total of 50 articles met the inclusion criteria, totalling 12,838 interventions. Failure to access the occlusion through transfemoral access occurred in 4.4% of patients, most commonly due to challenging supra-aortic vessel anatomy, decreasing to 3.6% when all alternative access routes were attempted. Failed access from alternative routes (direct carotid, radial and brachial approaches) attempted first-line or after failed femoral attempt were reported in 7.3% of patients. The occurrence rate of potentially challenging features (anatomical, diseases or others) ranged from 4.7% to 47.4%, primarily impacting the access time, procedure time, recanalization and clinical outcomes.

CONCLUSION

Failure to access the occlusion is a significant contributor to failed recanalization, regardless of access routes. Challenging, but eventually successful access is also a relevant factor in procedural and clinical outcomes; however challenging access requires a universal definition to enable quantification, so that methods for procedural optimization can be critically assessed.

Application of 3D Printing in Preoperative Planning

Preoperative planning is critical for success in the surgical suite. Current techniques for surgical planning are limited; clinicians often rely on prior experience and medical imaging to guide the decision-making process. Furthermore, two-dimensional (2D) presentations of anatomical structures may not accurately portray their three-dimensional (3D) complexity, often leaving physicians ill-equipped for the procedure. Although 3D postprocessed images are an improvement on traditional 2D image sets, they are often inadequate for surgical simulation. Medical 3D printing is a rapidly expanding field and could provide an innovative solution to current constraints of preoperative planning. As 3D printing becomes more prevalent in medical settings, it is important that clinicians develop an understanding of the technologies, as well as its uses. Here, we review the fundamentals of 3D printing and key aspects of its workflow. The many applications of 3D printing for preoperative planning are discussed, along with their challenges.

Irregular pulsation of intracranial unruptured aneurysm detected by four-dimensional CT angiography is associated with increased estimated rupture risk and conventional risk factors

BACKGROUND

Intracranial aneurysms (IAs) are common in the population and current imaging-based rupture risk assessment needs to be refined. We aimed to use four-dimensional CT angiography (4D-CTA) to investigate the associations of irregular pulsation of IAs with conventional risk factors and the estimated rupture risk.

METHODS

One hundred and five patients with 117 asymptomatic IAs underwent 4D-CTA. Geometric and morphologic parameters were measured and the presence of irregular pulsation (defined as a temporary focal protuberance ≥1 mm on more than three successive frames) was identified on 4D-CTA movies. One- and 5 year aneurysm rupture risk were estimated using UCAS and PHASES calculators. Univariate and multivariate analyses were performed to investigate the conventional risk factors associated with irregular pulsation.

RESULTS

Irregular pulsation was observed in 41.0% (48/117) of IAs. Aneurysm size (OR=1.380, 95% CI 1.165 to 1.634), irregular shape (OR=3.737, 95% CI 1.108 to 12.608), and internal carotid artery location (OR=0.151, 95% CI 0.056 to 0.403) were independently associated with irregular pulsation (P<0.05). Aneurysms with irregular pulsation had more than a 6-fold higher estimated rupture risk (1- and 5-year risk [95% CI], 1.56% [0.42%-3.91%], and 2.40% [1.30%-4.30%], respectively) than aneurysms without irregular pulsation (0.23% [0.14%-0.78%] and 0.40% [0.40%-1.30%], respectively) (P<0.001).

CONCLUSIONS

IAs with irregular pulsation are associated with larger size, irregular-shape, and non-ICA origin, and have more than a 6-fold higher estimated 1- and 5-year rupture risk than aneurysms without irregular pulsation. Irregular pulsation should be validated in future longitudinal studies to determine its predictive value for aneurysm growth and rupture.

Design of Personalized Devices—The Tradeoff between Individual Value and Personalization Workload

Personalized medical devices adapted to the anatomy of the individual promise greater treatment success for patients, thus increasing the individual value of the product. In order to cater to individual adaptations, however, medical device companies need to be able to handle a wide range of internal processes and components. These are here referred to collectively as the personalization workload. Consequently, support is required in order to evaluate how best to target product personalization. Since the approaches presented in the literature are not able to sufficiently meet this demand, this paper introduces a new method that can be used to define an appropriate variety level for a product family taking into account standardized, variant, and personalized attributes. The new method enables the identification and evaluation of personalizable attributes within an existing product family. The method is based on established steps and tools from the field of variant-oriented product design, and is applied using a flow diverter—an implant for the treatment of aneurysm diseases—as an example product. The personalization relevance and adaptation workload for the product characteristics that constitute the differentiating product properties were analyzed and compared in order to determine a tradeoff between customer value and personalization workload. This will consequently help companies to employ targeted, deliberate personalization when designing their product families by enabling them to factor variety-induced complexity and customer value into their thinking at an early stage, thus allowing them to critically evaluate a personalization project.

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.

The novel Tenzing 7 delivery catheter designed to deliver intermediate catheters to the face of embolus without crossing: clinical performance predicted in anatomically challenging model

Background

In large vessel occlusionstroke, navigation of aspiration catheters (AC) can be impeded by vessel tortuosity and the ophthalmic artery origin. A novel tapered delivery catheter was designed to facilitate delivery without disturbing the embolus. We assessed AC deliverability in vitro and validated the observations in a first-in-human experience.

Methods

In a vascular model with three challenging craniocervical scenarios, two commercial AC were advanced from the carotid to the middle cerebral artery by four neurointerventionalists. Catheter deliverability with standard microwire and microcatheter (MC) combinations and the Tenzing 7 (T7) Delivery Catheter (Route 92 Medical, San Mateo, CA) were compared. Operators rated aspects of catheter deliverability on a 5-point scale. Results were compared with device delivery patterns at a neurovascular center before and after clinical introduction of T7.

Results

In vitro, success rate and speed were higher with T7 (96%; mean 30±10 s) than with MC (65%; 72±47 s, p<0.001 each), with fewer interactions with the occlusion site (T7: 54% vs MC: 77%, p=0.004). T7 received superior ratings regarding carotid artery deflection (T7: 2, IQR1-3 vs MC: 3, IQR2-3, p<0.001), guide catheter pushback (T7: 2, IQR1-3 vs MC: 3, IQR3-3, p<0.001) and ophthalmic artery passage (T7: 1.5, IQR1-2 vs MC: 4, IQR3-5, p<0.001). Before introduction of T7 at a single center, delivery of AC to a large vessel occlusion without crossing was achieved in 15/123 cases (12%). With T7, this rate was 28/31 patients (90.3%).

Conclusion

Compared with microcatheter and microwire combinations, T7 improves aspiration catheter delivery in vitro, minimizing the need to cross the occlusion. Initial clinical experience appears to validate the model’s observations.

Biomodex patient-specific brain aneurysm models: the value of simulation for first in-human experiences using new devices and robotics

Background

With the recent advent of advanced technologies in the field, treatment of neurovascular diseases using endovascular techniques is rapidly evolving. Here we describe our experience with pre-surgical simulation using the Biomodex EVIAS patient-specific 3D-printed models to plan aneurysm treatment using endovascular robotics and novel flow diverter devices.

Methods

Pre-procedural rehearsals with 3D-printed patient-specific models of eight cases harboring brain aneurysms were performed before the first in-human experiences. To assess the reliability of the experimental model, the characteristics of the aneurysms were compared between the patient and 3D models. The rehearsals were used to define the patient treatment plan, including technique, device sizing, and operative working projections.

Results

The study included eight patients with their respective EVIAS 3D aneurysm models. Pre-operative simulation was performed for the first in-human robotic-assisted neurovascular interventions (n=2) and new generation flow-diverter stents (n=6). Aneurysms were located in both the anterior (n=5) and posterior (n=3) circulation and were on average 11.0±6.5 mm in size. We found reliable reproduction of the aneurysm features and similar dimensions of the parent vessel anatomy between the 3D models and patient anatomy. Information learned from pre-surgical in vitro simulation are described in detail, including an improved patient treatment plan, which contributed to successful first in-world procedures with no intraprocedural complications.

Conclusions

Pre-procedural rehearsal using patient-specific 3D models provides precise procedure planning, which can potentially lead to greater operator confidence, decreased radiation dose and improvements in patient safety, particularly in first in-human experiences.