Inverse identification of local stiffness across ascending thoracic aortic aneurysms

Abstract

Aortic dissection is the most common catastrophe of the thoracic aorta, with a very high rate of mortality. Type A dissection is often associated with an ascending thoracic aortic aneurysm (ATAA). However, it is widely acknowledged that the risk of type A dissection cannot be reliably predicted simply by measuring the ATAA diameter and there is a pressing need for more reliable risk predictors. It was previously shown that there is a significant correlation between a rupture criterion based on the ultimate stretch of the ATAA and the local extensional stiffness of the aorta. Therefore, reconstructing regional variations of the extensional stiffness across the aorta appears highly important. In this paper, we present a novel noninvasive inverse method to identify the patient-specific local extensional stiffness of aortic walls based on preoperative gated CT scans. Using these scans, a structural mesh is defined across the aorta with a set of nodes attached to the same material points at different time steps throughout the cardiac cycle. For each node, time variations of the position are analyzed using Fourier series, permitting the reconstruction of the local strain distribution (fundamental term). Relating these strains to tensions with the extensional stiffness, and writing the local equilibrium satisfied by the tensions, the local extensional stiffness is finally derived at every position. The methodology is applied onto the ascending and descending aorta of three patients. Interestingly, the regional distribution of identified stiffness properties appears heterogeneous across the ATAA. Averagely, the identified stiffness is also compared with values obtained using other nonlocal methodologies. The results support the possible noninvasive prediction of stretch-based rupture criteria in clinical practice using local stiffness reconstruction.

Arterial Stiffness: Different Metrics, Different Meanings

“…Finally, although well suited for nearly cylindrical samples, standard distension-extension tests are not sufficient for more complex arterial geometries, particularly those manifesting in disease. Fortunately, new methods are emerging that enable local material properties to be inferred using full-field strain measurements and inverse methods for material characterization [44,45].…”

Relationship Between Ascending Thoracic Aortic Aneurysms Hemodynamics and Biomechanical Properties

“…The second limitation concerns our rupture risk criterion which was established in vitro and not in vivo. To address this limitation, we are developing a new method enabling the non-invasive characterization of local biomechanical properties of the aorta based on medical imaging analysis [7,23,24]. Moreover, our numerical model used to calculate the hemodynamic descriptors (WSS and TAWSS) relies on a number of assumptions.…”

“…Advanced insight in imaging techniques have enabled acquiring detailed anatomical images and in vivo hemodynamic information in large arteries. High Relationship between ascending thoracic aortic aneurysms hemodynamics and biomechanical properties F. Condemi, PhD, S. Campisi, MD, M. Viallon, PhD, P. Croisille, PhD, MD, and S. Avril*, PhD T resolution dynamic CT imaging, for example, has been employed to build finite element models (FEM) and to obtain information about the biomechanical properties of the wall tissue [6,7]. However, although this useful noninvasive technique provides important information on aTAA mechanics, it does not provide functional insight on aTAA hemodynamics.…”

Computational prediction of hemodynamical and biomechanical alterations induced by aneurysm dilatation in patient‐specific ascending thoracic aortas

“…However, rupture/dissection occurs for aneurysms with a diameter smaller than 5.5 cm, with an incidence of 5% to 10% . Hence the large diameter criterion is found to be insufficient in predicting the risk of rupture and the necessity for surgical intervention . Biomechanical factors such as peak wall stress are found to be more reliable in predicting the risk of rupture than the size of aorta diameter .…”