Patient specific stress and rupture analysis of ascending thoracic aneurysms

Abstract

An ascending thoracic aortic aneurysm (ATAA) is a serious medical condition which, more often than not, requires surgery. Aneurysm diameter is the primary clinical criterion for determining when surgical intervention is necessary but, biomechanical studies have suggested that the diameter criterion is insufficient. This manuscript presents a method for obtaining the patient specific wall stress distribution of the ATAA and the retrospective rupture risk for each patient. Five human ATAAs and the preoperative dynamic CT scans were obtained during elective surgeries to replace each patient's aneurysm with a synthetic graft. The material properties and rupture stress for each tissue sample were identified using bulge inflation tests. The dynamic CT scans were used to generate patient specific geometries for a finite element (FE) model of each patient's aneurysm. The material properties from the bulge inflation tests were implemented in the FE model and the wall stress distribution at four different pressures was estimated. Three different rupture risk assessments were compared: the maximum diameter, the rupture risk index, and the overpressure index. The peak wall stress values for the patients ranged from 28% to 94% of the ATAA's failure stress. The rupture risk and overpressure indices were both only weakly correlated with diameter (ρ=-0.29, both cases). In the future, we plan to conduct a large experimental and computational study that includes asymptomatic patients under surveillance, patients undergoing elective surgery, and patients who have experienced rupture or dissection to determine if the rupture risk index or maximum diameter can meaningfully differentiate between the groups.

Local mechanical properties of human ascending thoracic aneurysms

“…1 d-f) consistently revealed strain localizing in the rupture region preceding failure, confirming the observations reported in [26]. Dynamic-CT scans collected prior to surgery were used to create patient-specific finite element models for Patients 2, 4, 5, and 6 [33]. The results show that the wall tensions and strains observed at rupture exceed those expected in vivo.…”

Failure of the Porcine Ascending Aorta: Multidirectional Experiments and a Unifying Microstructural Model

“…As our community moves forward to more patient-based geometries and simulations involving realistic geometries that necessarily lead to complex stress fields, validation of models in multidimensional loading is crucial. For example, it is common [62][63][64][65][66] to report results in terms of principal stresses, which are informative but do not address the fact that a stress acting radially or in shear is more likely to lead to tissue failure than one acting circumferentially. Martin et al [65] used a potentially generalizable energy-based failure threshold, but they based the failure criterion on uniaxial circumferential tests.…”

Biaxial rupture properties of ascending thoracic aortic aneurysms

“…The experimental set-up and the bulge inflation tests performed by our group are explained in details in previous publications [27,28,34]. The aim of the present study is to review the failure properties (maximum stress, maximum stretch) obtained by the bulge inflation test and compare them with failure properties obtained by uniaxial testing.…”

“…Our group recently conducted bulge inflation tests on human ATAA tissues [26][27][28], to test media/adventitia samples as well as complete layers. Stereo-digital image correlation (SDIC) was used to obtain the strain field of the entire inflated membrane.…”