Finite element and photoelastic modelling of an abdominal aortic aneurysm: a comparative study.

Rupture prediction of abdominal aortic aneurysms (AAAs) remains a clinical challenge. Finite element analysis (FEA) may allow for improved identification for intervention timing, but the method needs further substantiation. In this study, experimental photoelastic method and finite element techniques were compared using an idealised AAA geometry. There was good agreement between the numerical and experimental results. At the proximal and distal end of the AAA model, the maximum differences in principle strain for an internal pressure of 120 mmHg had differences ranging from 0.03 to 10.01%. The maximum difference in principle strain for the photoelastic and the finite element model at a pressure of 120 mmHg was 0.167 and 0.158, respectively. The current research strengthens the case for using FEA as an adjunct to the current clinical practice of utilising diameter measurement for intervention timing.

Geometrical enhancements for abdominal aortic stent-grafts.

PURPOSE: To compare the function of 2 stent-graft designs for endovascular abdominal aortic aneurysm repair. METHODS: Computational fluid dynamics was used to investigate the performance of a conventional stent-graft versus one with a novel tapered configuration (equal area ratios at the inlet and bifurcation). Idealized geometries (uniplanar) were formed first for both devices. To mimic the clinical setting with pulsatile blood flow, a realistic model (multiplanar) was created for the conventional stent-graft based on computed tomography scans from 3 patients with different aortic geometries. A similar model was created for the tapered stent-graft by mimicking the deployment of the conventional stent-graft through its centerline. RESULTS: The tapered stent-graft model demonstrated reduced secondary flow vortices and wall shear stresses in the iliac limbs compared to the conventional graft in the idealized scenario. The drag forces in the idealized models were similar for both designs, though the tapered stent-graft showed a 4% reduction. Flow was split more evenly between the tapered stent-graft limbs in the realistic scenario. CONCLUSION: The novel tapered design reduced flow velocities and secondary flows due to its smooth trunk-to-limb transition, while also splitting the flow between the iliac limbs more evenly. In multiplanar models, the out-of-plane curvature was the greatest cause of skewed flow, which reduced the benefits of the tapered stent-graft.

A review of the in vivo and in vitro biomechanical behavior and performance of postoperative abdominal aortic aneurysms and implanted stent-grafts.

Endovascular repair of abdominal aortic aneurysms has generated widespread interest since the procedure was first introduced two decades ago. It is frequently performed in patients who suffer from substantial comorbidities that may render them unsuitable for traditional open surgical repair. Although this minimally invasive technique substantially reduces operative risk, recovery time, and anesthesia usage in these patients, the endovascular method has been prone to a number of failure mechanisms not encountered with the open surgical method. Based on long-term results of second- and third-generation devices that are currently becoming available, this study sought to identify the most serious failure mechanisms, which may have a starting point in the morphological changes in the aneurysm and stent-graft. To investigate the "behavior" of the aneurysm after stent-graft repair, i.e., how its length, angulation, and diameter change, we utilized state-of-the-art ex vivo methods, which researchers worldwide are now using to recreate these failure modes.