Comparison of existing aneurysm models and their path forward

The two most important aneurysm types are cerebral aneurysms (CA) and abdominal aortic aneurysms (AAA), accounting together for over 80\% of all fatal aneurysm incidences. To minimise aneurysm related deaths, clinicians require various tools to accurately estimate its rupture risk. For both aneurysm types, the current state-of-the-art tools to evaluate rupture risk are identified and evaluated in terms of clinical applicability. We perform a comprehensive literature review, using the Web of Science database. Identified records (3127) are clustered by modelling approach and aneurysm location in a meta-analysis to quantify scientific relevance and to extract modelling patterns and further assessed according to PRISMA guidelines (179 full text screens). Beside general differences and similarities of CA and AAA, we identify and systematically evaluate four major modelling approaches on aneurysm rupture risk: finite element analysis and computational fluid dynamics as deterministic approaches and machine learning and assessment-tools and dimensionless parameters as stochastic approaches. The latter score highest in the evaluation for their potential as clinical applications for rupture prediction, due to readiness level and user friendliness. Deterministic approaches are less likely to be applied in a clinical environment because of their high model complexity. Because deterministic approaches consider underlying mechanism for aneurysm rupture, they have improved capability to account for unusual patient-specific characteristics, compared to stochastic approaches. We show that an increased interdisciplinary exchange between specialists can boost comprehension of this disease to design tools for a clinical environment. By combining deterministic and stochastic models, advantages of both approaches can improve accessibility for clinicians and prediction quality for rupture risk.Comment: 46 pages, 5 figure

On the major role played by the curvature of intracranial aneurysms walls in determining their mechanical response, local hemodynamics, and rupture likelihood

The properties of intracranial aneurysms (IAs) walls are known to be driven by the underlying hemodynamics adjacent to the IA sac. Different pathways exist explaining the connections between hemodynamics and local tissue properties. The emergence of such theories is essential if one wishes to compute the mechanical response of a patient-specific IA wall and predict its rupture. Apart from the hemodynamics and tissue properties, one could assume that the mechanical response also depends on the local morphology, more specifically, the wall curvature, with larger values at highly-curved wall portions. Nonetheless, this contradicts observations of IA rupture sites more often found at the dome, where the curvature is lower. This seeming contradiction indicates a complex interaction between local hemodynamics, wall morphology, and mechanical response, which warrants further investigation. This was the main goal of this work. We accomplished this by analysing the stress and stretch fields in different regions of the wall for a sample of IAs, which have been classified based on particular local hemodynamics and local curvature. Pulsatile numerical simulations were performed using the one-way fluid-solid interaction strategy implemented in OpenFOAM (solids4foam toolbox). We found that the variable best correlated with regions of high stress and stretch was the wall curvature. Additionally, our data suggest a connection between the local curvature and local hemodynamics, indicating that the curvature is a property that could be used to assess both mechanical response and hemodynamic conditions, and, moreover, to suggest new metrics based on the curvature to predict the likelihood of rupture.Comment: Preprint submitted to Acta Biomaterialia, with 27 pages and 11 figure

Endovascular treatment of middle cerebral artery aneurysms : single-centre results

Purpose: The middle cerebral artery (MCA) is the second most common location of intracerebral aneurysms. Traditionally, they are treated by microsurgical clipping, but with the development of new techniques and devices endovascular embolisation is gaining more importance. The aim of this study was to summarise six years of experience of our department in endovascular treatment of MCA aneurysms. Material and methods: Forty patients with 41 MCA aneurysms treated in a single centre were included in this study. Data on patients' comorbidities, aneurysm morphology, and treatment course were collected, with special emphasis on complications. Results: There were no statistically significant differences in terms of aneurysm morphology between males and females and between ruptured and unruptured aneurysms. None of the diseases analysed in the current study were linked with significantly increased risk of SAH. Unruptured aneurysms were significantly more frequently treated by stent-assisted coiling (30.4% vs. 5.6%, p = 0.0388) than were ruptured aneurysms, while ruptured aneurysms were treated more frequently by coiling alone (77.8% vs. 34.8%, p = 0.0062). After an initial course of treatment 63.4% (n = 26) of patients had class I in Raymond-Roy occlusion classification, 22% (n = 9) had class II, and 14.6% (n = 6) had class III. Complications of the procedure were observed in 17.5% (n = 7) of patients: 22.2% (n = 4) with ruptured and 13.6% (n = 3) with unruptured aneurysms. Conclusions: Endovascular treatment of MCA aneurysms is feasible, and our results are convergent with other studies. Ruptured MCA aneurysms may be treated endovascularly with similar effects as unruptured MCA aneurysms. The complication rate of such treatment is low

Decomposition of Velocity Field Along a Centerline Curve Using Frenet-Frames: Application to Arterial Blood Flow Simulations

This paper presents a novel method for the evaluation of three-dimensional blood-flow simulations based, on the decomposition of the velocity field into localized coordinate systems along the vessels centerline. The method is based on the computation of accurate centerlines with the Vascular Modeling Toolkit (VMTK) library, to calculate the localized Frenet-frames along the centerline and the morphological features, namely the curvature and torsion. Using the Frenet-frame unit vectors, the velocity field can be decomposed into axial, circumferential and radial components and visualized in a diagram along the centerline. This paper includes case studies with four idealized geometries resembling the carotid siphon and two patient-specific cases to demonstrate the capability of the method and the connection between morphology and flow. The proposed evaluation method presented in this paper can be easily extended to other derived quantities of the velocity fields, such as the wall shear stress field. Furthermore, it can be used in other fields of engineering with tubular cross-sections with complex torsion and curvature distribution