Finite element model of abdominal aortic aneurysm

摘要

Abdominal aortic aneurysm (AAA) is a pathological change in lumen (inner diameter) of aorta, with synchronous decrease of wall thickness, often in the whole part between renal arteries and aortic bifurcation. Whithout an adequate treatment the risk of aneurysm rupture increases in time so that an assessment of this risk is decisive for a surgical treatment. Stresses in AAA wall predict the risk of its rupture better than the mere maximum diameter of the aneurysm, used as a criterion for decision about its operability in clinical practice.The paper presents creation of a 3D finite element model of AAA of an individual patient, based on its unloaded (reduced) geometry reconstructed from CT-scans. In most models published till now, the geometry of CT-scans is supposed to be unloaded while, in fact, a blood pressure is always acting in the aneurysm. Recent computer tomographs enable us to record the individual scans in a defined phase of the cardiac cycle, i.e. under a known value of the blood pressure. The paper presents a relatively simple method of how to find the unloaded geometry that results in a shape corresponding to the CT scans when loaded by the original value of blood pressure. This process depends on the chosen constitutive model; isotropic hyperelas-tic constitutive behaviour of the tissues is supposed here.The rupture risk assessment is based on the ratio of maximum first principal stresses in the walls of the AAA and of the intact aorta, rather than on the absolute stress value.