Modélisation de la compliance de l'aorte dans le cas de pathologies de type anévrisme

Abstract : The Abdominal Aorta Aneurysm (AAA) is a pathology that is defined by a localized and permanent dilation of the artery and which involves over 8.8% of the seniors. Currently, when a patient has a dilatation of the aorta leading to a surgery because of the rupture risk, the therapeutic decision is made depending on the diameter of the aneurysm. To determine this diameter, it is usually conducted an examination by medical imaging (ultrasound, CT, MRI...). However, it notes that the diagnosis can’t be satisfied with a single dimensional measurement face to induced risks: first of all, when the diameter exceed a certain growth, the risk of rupture can reach 50% but more than 5% of surgical procedures may cause the patient's death. Other metrics such as compliance of the artery can be used for the decision for surgery. Compliance corresponds to a precise definition by cardiologists: this is a quantity that characterizes the deformability, describing the ability of aorta to distend under the influence of blood pressure. From our point of view, this concept is insufficient because, generally, in the case of an aneurysm, rupture is highly localized because of the complexity of the shape. It is therefore necessary to extend its definition in a quantity not localized at a section or a specific location but to the whole wall. Diagnostics methods will be more reliable if they can determine localized compliance. From a mechanical standpoint, determining compliance is thus transformed into the measurement of localized parietal elasticity of aorta. The elasticity is not a directly measurable parameter. Therefore, the problem comes down to determining the local strain of the aortic wall in the hemodynamic condition. Solving this problem is complex. Indeed, the mechanical stresses are dependent on the flow of blood, the artery surrounding organs, the material properties of the artery and the geometry of the aneurysm which are specific to each patient. At present, many numerical and experimental works is done but few studies have well correlated medical imaging techniques for the diagnostic aid. It is in this context that are my thesis in collaboration both with the Dijon University Hospital where were performed all experiments using MRI and GMedTech laboratory GMIT (Galway- Mayo Institute of Technology) in Ireland who provided the replicas and their expertise in the cardiovascular area. This work, conducted on various form of phantoms in Vitro, are intended, first to build a metrological methodology to help doctors understand and validate MRI measurements using other devices measurement, on the other hand, to improve the methods of diagnosing the abdominal aortic aneurysm. The principle of this work is to develop experimental modeling in vitro in a metrology framework and correlate the results from different measurement techniques and numerical modeling throughout a cycle reproducing the hemodynamic conditions. To consider the problem as a whole, not only the evolution of deformation representing the elasticity of the aorta should be studied, but also the evolution of soliciting flow. Therefore, in this thesis, several devices such as stereovision, Particle image velocimetry (PIV), MRI kinetic sequence but also the flow 2D and 4D were employed. Various numerical models were established to not only correlate the results with those obtained experimentally, therefore, to improve the credibility of our study, but also to be part of the aid protocol to the diagnosis that we have proposed. In the end, all the results from different experimental and numerical models have led to propose a validated and feasible diagnosis protocol based on MRI sequences. The application of this protocol on a realistic AAA complex phantom showed its feasibility. We can therefore say that the feasibility of the proposed protocol is demonstrated and that based on MRI (…).
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Yufei Wang. Modélisation de la compliance de l'aorte dans le cas de pathologies de type anévrisme. Mécanique [physics.med-ph]. Université de Bourgogne, 2015. Français. ⟨NNT : 2015DIJOS038⟩. ⟨tel-01271049⟩

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