Computation of Wall Stress in Abdominal Aortic Aneurysms

An abdominal aortic aneurysm (AAA) is a permanent and irreversible dilation of the lower region of the aorta. It is a symptomless condition that, if left untreated, can expand to the point of rupture. Mechanically-speaking, rupture of an artery occurs when the local wall stress exceeds the local wall strength. It is therefore desirable to be able to estimate the patient-specific AAA wall stress non-invasively, quickly and reliably.
The stress in the AAA wall is induced by the blood pressure. Many authors have proposed to use the finite element method to compute the wall stress, based on the recorded blood pressure and AAA geometry extracted from medical images. One fact disregarded by most proposed methods is that the geometry extracted from images is not the “stress-free” un-deformed geometry, but the deformed geometry under the influence of blood pressure. Therefore we consider that an inverse solution method is more appropriate, with the wall stress being computed based on the deformed geometry and the measured blood pressure. We show that in this approach material properties have very little influence on the computed stresses, and develop a simplified method for AAA wall stress computation applicable in the clinic.