A Finite Element Analysis Rupture Index (FEARI) as an Additional Tool for Abdominal Aortic Aneurysm Rupture Prediction

Abstract

Currently, abdominal aortic aneurysms (AAAs), which are a permanent dilation of the aorta, are treated surgically when the maximum transverse diameter surpasses 5.5cm. AAA rupture occurs when the locally acting wall stress exceeds the locally acting wall strength. There is a need to review the current diameter-based criterion, and so it may be clinically useful to develop an additional tool to aid the surgical decision-making process. A Finite Element Analysis Rupture Index (FEARI) was developed.Ten patient-specific AAAs were reconstructed, and the corresponding wall stress computed. Previous experimental work on determination of ultimate tensile strengths (UTS) from AAA tissue samples was implemented in this study. By combining peak wall stress along with average regional UTS, a new approach to the estimation of patient-specific rupture risk has been developed.Ten cases were studied, all of which were awaiting or had previously undergone surgical AAA repair. A detailed examination of these ten cases utilising the FEARI analysis suggested that there was a possibility that some of the AAAs may have been less prone to rupture than previously considered.It is proposed that FEARI, used alongside other rupture risk factors, may improve the current surgical decision-making process. The use of FEARI as an additional tool for rupture prediction may provide a useful adjunct to the diameter-based approach in surgical decision-making.

New Approaches to Abdominal Aortic Aneurysm Rupture Risk Assessment

“…Similar observations have been reported throughout numeric studies in the literature, which have shown that inflection points exhibit higher wall stresses than the maximum diameter regions. 6,11,12 Each experimental model was imaged using CT before testing to generate accurate numeric reconstructions for validation purposes using previously reported 3D reconstruction techniques and the commercially available software Mimics (Materialise). 16,23,36 Rupture occurred at the location of numerically predicted peak wall stress in 80% of cases and at high, but not peak, stress regions in 10% of cases.…”

“…Some interesting rupture risk parameters have recently emerged as alternatives to AAA size. AAA wall stress, 7,8 vessel asymmetry, 11 finite element analysis rupture index (FEARI), 12 rupture potential index (RPI), 9 severity parameter (SP), 10 growth of intraluminal thrombus, 18 and a method of determining AAA growth and rupture based on mathematical models 19,20 have all been proposed as useful adjuncts to AAA size, yet all require extensive validation before they can be clinically accepted. Several of these newer approaches to rupture risk rely on biomechanics and numeric models to quantify the threat.…”

“…In particular, finite element analysis (FEA) has been extensively used to determine the distribution of wall stress in the aneurysm and has revealed some interesting correlations with both AAA asymmetry 11 and AAA geometry. 21 Overall AAA wall stress has been shown to be independent of maximum diameter, [5][6][7][8][9][10][11][12][13][14][15][16] hence the general understanding that more than size alone should be considered in rupture risk evaluation. This article reviews some of the more recent advances in both numeric and experimental engineering methodologies used to investigate the possible rupture risk of patient-specific AAAs.…”

Investigation of material modeling in fluid–structure interaction analysis of an idealized three-layered abdominal aorta: aneurysm initiation and fully developed aneurysms

“…The AAA arises in the infrarenal aorta with a diameter greater than 3 cm and can be up to 9 cm in length [1,2]. Most of the studies on aneurysms have focused on already existing realistic or idealized aneurysms [33][34][35][36][37][38][39][40][41][42][43] with the aim of defining a relevant rupture criterion [4,7,10,19,20,24]. The ratio of the vessel stress to vessel strength is regarded as an alternative tool to conventional diameter criteria, which may be insufficient in small aneurysms.…”

Prediction of deformations during endovascular aortic aneurysm repair using finite element simulation

“…Otherwise several works attempted to implement Finite Element Methods (FEM) based simulation in the context of endovascular procedures. They were intended to deal with issues related to the understanding and the anticipation of aneurysm rupture risk, of strain, migration and endoleaks at the stent, in their pre-computed implementation [6][7][8] or to deal with catheterization simulation issues in their interactive / real time implementation 9,10 . With the extension of EVAR to more complex cases, in particular to the use of a fenestrated endograft in certain patients, the quantification of vascular deformations will become an important aspect in the planning and sizing of such devices.…”