Unsteady wall shear stress analysis from image-based computational fluid dynamic aneurysm models under Newtonian and Casson rheological models

The aim of this work was to determine whether or not Newtonian rheology assumption in image-based patient-specific computational fluid dynamics (CFD) cerebrovascular models harboring cerebral aneurysms may affect the hemodynamics characteristics, which have been previously associated with aneurysm progression and rupture. Ten patients with cerebral aneurysms with lobulations were considered. CFD models were reconstructed from 3DRA and 4DCTA images by means of region growing, deformable models, and an advancing front technique. Patient-specific FEM blood flow simulations were performed under Newtonian and Casson rheological models. Wall shear stress (WSS) maps were created and distributions were compared at the end diastole. Regions of lower WSS (lobulation) and higher WSS (neck) were identified. WSS changes in time were analyzed. Maximum, minimum and time-averaged values were calculated and statistically compared. WSS characterization remained unchanged. At high WSS regions, Casson rheology systematically produced higher WSS minimum, maximum and time-averaged values. However, those differences were not statistically significant. At low WSS regions, when averaging over all cases, the Casson model produced higher stresses, although in some cases the Newtonian model did. However, those differences were not significant either. There is no evidence that Newtonian model overestimates WSS. Differences are not statistically significant.Fil: Castro, Marcelo Adrian. Universidad Tecnológica Nacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Olivares, María C. Ahumada. Universidad Favaloro; ArgentinaFil: Putman, Christopher M.. Texas Neurointerventional Surgery Associates; Estados UnidosFil: Cebral, Juan R.. George Mason University; Estados Unido

Virtual endovascular treatment of intracranial aneurysms: models and uncertainty

Virtual endovascular treatment models (VETMs) have been developed with the view to aid interventional neuroradiologists and neurosurgeons to pre-operatively analyze the comparative efficacy and safety of endovascular treatments for intracranial aneurysms. Based on the current state of VETMs in aneurysm rupture risk stratification and in patient-specific prediction of treatment outcomes, we argue there is a need to go beyond personalized biomechanical flow modeling assuming deterministic parameters and error-free measurements. The mechanobiological effects associated with blood clot formation are important factors in therapeutic decision making and models of post-treatment intra-aneurysmal biology and biochemistry should be linked to the purely hemodynamic models to improve the predictive power of current VETMs. The influence of model and parameter uncertainties associated to each component of a VETM is, where feasible, quantified via a random-effects meta-analysis of the literature. This allows estimating the pooled effect size of these uncertainties on aneurysmal wall shear stress. From such meta-analyses, two main sources of uncertainty emerge where research efforts have so far been limited: (1) vascular wall distensibility, and (2) intra/intersubject systemic flow variations. In the future, we suggest that current deterministic computational simulations need to be extended with strategies for uncertainty mitigation, uncertainty exploration, and sensitivity reduction techniques. WIREs Syst Biol Med 2017, 9:e1385. doi: 10.1002/wsbm.138

Influencia de aspectos morfológicos del aneurisma cerebral en el volumen de sangrado

El volumen de sangrado que un aneurisma cerebral produce al romperse ha demostrado influir de manera muy relevante y negativa en el pronóstico delos pacientes con hemorragia subaracnoidea (HSA). Siendo así, es llamativo el escaso conocimiento existente sobre los factores determinantes de un mayor volumen de sangrado aneurismático. El objetivo principal es determinar la influencia de la morfología del aneurisma cerebral en el volumen de sangrado tras su ruptura. Material y métodos: Tras una revisión bibliográfica y publicación sobre el estado del arte actual, analizamos una cohorte prospectiva de pacientes que presentan HSA atendidos en el Hospital Universitario 12 de Octubre, desde el año 2008 al2020.Para el cálculo del volumen de sangrado se utiliza un método volumétrico semiautomático, cuya fiabilidad ha sido publicada por el grupo de trabajo previamente. Para el análisis detallado de la morfología 3D del aneurisma se utiliza un programa informático reciente (VMTKLab). En la segunda publicación, evaluamos la fiabilidad de este programa en sus mediciones para los primeros 40 pacientes estudiados. Para ello se compara con la prueba estándar de referencia para la morfología (arteriografía cerebral),respecto a 4 diámetros fundamentales del aneurisma. La tercera publicación evalúa la correlación entre 18 variables morfológicas, 2 variables topográficas, y 12 variables clínicodemográficas, con respecto al volumen de sangrado aneurismático, en 116pacientes..