Inverse identification of local stiffness across ascending thoracic aortic aneurysms
Résumé
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 signicant correlation between a rupture criterion based on the ultimate stretch of the ATAA and the local membrane sti-ness of the aorta. Therefore, reconstructing regional variations of the membrane stiness across the aorta appears highly important. In this paper, we present a novel noninvasive inverse method to identify the patientspecic local membrane stiness of aortic walls based on preoperative gated CT scans. Using these scans, a structural mesh is dened across the aorta with a set of nodes attached to the same material points at dierent 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 membrane stiness, and writing the local equi-2 Solmaz Farzaneh et al. librium satised by the tensions, the local membrane stiness is nally derived at every position. The methodology is applied onto the ascending and descending aorta of three patients. Interestingly, the regional distribution of identied stiness properties appears heterogeneous across the ATAA. Averagely, the identied sti-ness is also compared with values obtained using other non-local methodologies. The results support the possible non-invasive prediction of stretch-based rupture criteria in clinical practice using local stiness reconstruction.
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