Eduardo Bravo

Comparison between computational fluid dynamics, fluid–structure interaction and computational structural dynamics predictions of flow-induced wall mechanics in an anatomically realistic cerebral aneurysm model

Haemodynamically induced stress plays an important role in the progression and rupture of cerebral aneurysms. The current work describes computational fluid dynamics (CFD), fluid–structure interaction (FSI) and computational structural dynamics (CSD) simulations in an anatomically realistic model of a carotid artery with two saccular cerebral aneurysms in the ophthalmic region. The model was obtained from three-dimensional (3D) rotational angiographic imaging data. CFD and FSI were studied under a physiologically representative waveform of inflow. The arterial wall was assumed elastic or hyperelastic, as a 3D solid or as a shell depending on the type of modelling used. The flow was assumed to be laminar, non-Newtonian and incompressible. The CFD, FSI and CSD models were solved with the finite elements package ADINA. Predictions of velocity field and wall shear stress (WSS) on the aneurysms made using CFD and FSI were compared. The CSD model of the aneurysms using complete geometry was compared with isolated aneurysm models. Additionally, the effects of hypertensive pressure on CSD aneurysm models are also reported. The vortex structure, WSS, effective stress, strain and displacement of the aneurysm walls showed differences, depending on the type of modelling used.

Fluid Structural Analysis of Human Cerebral Aneurysm Using Their Own Wall Mechanical Properties

Computational Structural Dynamics (CSD) simulations, Computational Fluid Dynamics (CFD) simulation, and Fluid Structure Interaction (FSI) simulations were carried out in an anatomically realistic model of a saccular cerebral aneurysm with the objective of quantifying the effects of type of simulation on principal fluid and solid mechanics results. Eight CSD simulations, one CFD simulation, and four FSI simulations were made. The results allowed the study of the influence of the type of material elements in the solid, the aneurisms wall thickness, and the type of simulation on the modeling of a human cerebral aneurysm. The simulations use their own wall mechanical properties of the aneurysm. The more complex simulation was the FSI simulation completely coupled with hyperelastic Mooney-Rivlin material, normal internal pressure, and normal variable thickness. The FSI simulation coupled in one direction using hyperelastic Mooney-Rivlin material, normal internal pressure, and normal variable thickness is the one that presents the most similar results with respect to the more complex FSI simulation, requiring one-fourth of the calculation time.

Numerical investigation of the hemodynamics in anatomically realistic lateral cerebral aneurysms

Hemodynamically induced stress plays an important role in the progression and rupture of cerebral aneurysms. The current work describes computational fluid dynamics (CFD) simulations in anatomically realistic models of cerebral aneurysms. Twenty lateral aneurysms models were investigated. The models were obtained from three-dimensional rotational angiographic imaging data and CFD were studied under the same physiologically representative waveform of inflow. The flow was assumed to be laminar, non-Newtonian, and incompressible. The CFD models were solved with the finite elements package ADINA. Predictions of velocity field and wall shear stress (WSS) on the aneurysms were compared for the different cases. Linear correlations between the WSS on the aneurysm fundus at peak systole for lateral aneurysms with an area index were found.

Endovascular treatment of aneurysm arising from fenestration of the supraclinoid internal carotid artery--two case reports.

We report two cases of aneurysm located in a fenestration of the supraclinoid internal carotid artery, an extremely rare anatomical variant, and describe the feasibility of endovascular treatment using two different strategies applicable for each case. Each presented aneurysm had a particular location on the fenestration, which led to different endovascular approaches. In one case, the aneurysm arose from the proximal junction of fenestration, involving both of its limbs. For this aneurysm, the treatment strategy adopted aimed to achieve a selective exclusion. In the second case, two aneurysms arose from the minor limb of the fenestration, which could be entirely excluded, considering the absence of perforating arteries arising from that carotid segment. To our knowledge, these two cases are the first ICA fenestration aneurysms treated exclusively by endovascular approach, showing two treatment strategies using coils in association to two different endovascular devices (stent/TrisPan(®)).

Unusual origin of the left ophthalmic artery from the basilar trunk

The formation of the ophthalmic artery (OA) is a complex process with two different proposed embryological steps for its development. Several anatomical variants have been described. We present a very unusual origin of the ophthalmic artery from the basilar trunk, in a 45-year-old male with a history of pontine hemorrhagic stroke. MRI and CTA showed evidence of previous hemorrhage in the pons and several intracranial arterial dysplastic dilatations. DSA confirmed several fusiform dilatations of the basilar trunk. In the left ICA, no ophthalmic artery was seen arising from the carotid siphon. The left ophthalmic artery arises from the basilar trunk and runs lateral to the cavernous sinus through the middle cranial fossa, entering the left orbit at the superior orbital fissure. The patient was treated conservatively. Two main theories for this anomaly are known, one from Lasjaunias and the other from Paget. To our knowledge, this basilar origin of the OA has only been described three times in the literature. For its origin, we propose a partial persistence of the trigeminal artery together with a dominance of the dorsal ophthalmic artery.

MECHANICAL TEST OF HUMAN CEREBRAL ANEURYSM SPECIMENS OBTAINED FROM SURGICAL CLIPPING

The walls of the blood vessels involved with cerebral aneurysms present different mechanical properties, when compared with those of normal artery. Consequently the models which may describe then predict an aneurysm rupture need as input their mechanical properties. This paper describes the experimental determination of the mechanical properties of the tissues of the blood vessels affected with a cerebral aneurysm. In particular, we determine and discuss the critical elongation and the rupture strength. The affected tissues were obtained from surgical clipping and extraction; six specimens were tested. The mechanical tests were performed in a tensile device. The experimental data was fitted numerically with a Mooney–Rivlin hyper elastic model. The model was compared with previous published data.

Middle cerebral artery occlusion with moyamoya-like vessels and aneurysms. A report of two cases.

We describe two cases of aneurysmal rupture in moyamoya-like vessels in middle cerebral artery occlusion. This phenomenon was previously described in severe steno-occlusive disease and accounts for the hemorrhagic presentation. To our knowledge, these are the second and third clinical cases published in modern neuroradiological literature.

SENSITIVITY ANALYSIS OF COMPUTATIONAL STRUCTURAL DYNAMICS IN A CEREBRAL ANEURYSM MODEL TO WALL THICKNESS AND MODEL

Intracranial saccular aneurysms tend to be thin walled and stiffer compared with a normal artery. The current work describes computational structural dynamics (CSD) in an anatomically realistic model of a cerebral aneurysm located in the ophthalmic region, using different wall thickness, model data for the artery and aneurysm, and geometry size. The model was obtained from three-dimensional rotational angiography image data. The wall was assumed three-dimensional hyperelastic solid with different thickness in the artery and in the aneurysm regions. The effects of carotid siphon length are reported. The CSD was solved with the finite elements package ADINA. The predictions of stress and strain on the aneurysm wall were compared.

Análisis de Sensibilidad en Simulaciones Fluido Dinámicas de Aneurismas Cerebrales Incluyendo Interacción Fluido Estructura

Se presenta un estudio sobre sensibilidad de los resultados de simulacion fluido dinamica (CFD) en modelos de aneurismas cerebrales, incluyendo la interaccion entre la pared arterial y el fluido (FSI). Con 83 modelos reconstruidos de aneurismas cerebrales se hizo un estudio geometrico y se selecciono un caso para estudiar la fluido dinamica en detalle. Se vario el numero de sifones carotideos usados para la simulacion CFD. Se realizaron cinco simulaciones FSI variando el modulo de elasticidad arterial y el espesor arterial, y se reporto el efecto de la hipertension arterial en los resultados. Las simulaciones FSI mostraron que el efecto mas relevante en el incremento del estado de esfuerzos en la aneurisma es la hipertension arterial, con esfuerzos maximos cercanos a 900 kPa. Se concluye que las simulaciones FSI se deben usar para determinar simultaneamente el estado de esfuerzos de la pared y la fluido dinamica dentro de aneurismas.

A mechanical study of patient-specific cerebral aneurysm models: a correlation between stress and geometrical index

Solid mechanics plays an important role in the progression and rupture of cerebral aneurysms. The hypothesis is that the mechanism that control aneurysm enlargement is the wall remodeling under the effect of time dependent arterial pressure. The mechanism of rupture could be based on plastic deformation under a fatigue-like mechanism. The current work describes the solid dynamics in 30 patient-specific models of cerebral aneurysms. An area based index shows significant difference between unruptured and ruptured aneurysms. The effective wall stress showed large variation depending on aneurysm size and form. A correlation between the maximal effective stress with the geometrical index was found.