04022019 1549290446

Mechanical analysis of aortic aneurysms using 3D ultrasound: towards patient-specific risk assessment - Emiel van Disseldorp

An abdominal aortic aneurysm (AAA) is a progressive, irreversible dilatation of the aorta with a maximum diameter of 3 cm or larger. Most AAAs are asymptomatic until rupture, which result in a life-threatening hemorrhage in 80% of all cases. Therefore, according to current clinical guidelines, surgery is recommended when the risk of rupture outweighs the risk of intervention. Large population-based studies have suggested to intervene when the maximum diameter reaches 5.5 cm, or when it grows more than 1 cm/year. Unfortunately, these thresholds do not always apply for the individual patient, since 2 – 10% of all AAAs rupture before these thresholds are reached, whereas approximately 25% of all large, but stable AAAs are currently exposed to (yet) unnecessary surgical risks due to overtreatment. Hence, a personalized approach is required. From a biomechanical perspective, AAA wall mechanics (wall stresses, strains) and tissue properties will play an important role in growth and rupture, and may be able to distinguish between stable and more susceptible aneurysms. Model-based wall stress analysis has been introduced and successfully performed in the last two decades using finite element analysis (FEA). The method revealed that ruptured and symptomatic aneurysms have an increased peak wall stress compared to non-ruptured AAAs, indicating that peak wall stress might be a relevant criterion for patient-specific risk stratification. Despite promising results, wall stress analysis has not yet been clinically accepted. The main drawback is the use of Computed Tomography (CT) imaging for geometry assessment which suffers from exposure to radiation and nephrotoxic contrast agents, rendering the current method unsuitable for prospective, clinical validation studies. Recently, time-resolved 3D ultrasound (4D US) had been clinically introduced, which provides multiple 3D US volumes over the cardiac cycle. AAA geometry assessment based on 4D US might be a good alternative for wall stress analysis, due to its non-invasive and harmless character. In addition, using the temporal information in the 4D US data, the arterial stiffness could be assessed simultaneously. Therefore, the aim of this thesis was to develop and verify a biomechanical model to predict the mechanical behavior of the patient-specific AAA wall using non-invasive, 4D ultrasound imaging.

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