Patient-Specific AAA Wall Stress Analysis: 99-Percentile Versus Peak Stress

Objective: Biomechanically, rupture of an Abdominal Aortic Aneurysm (AAA) occurs when the stress acting on the watt due to the blood pressure, exceeds the strength of the wall. Peak wall stress estimations, based on CT reconstruction, may be prone to observer variation. This study focuses on the robustness and reproducibility of AAA watt stress assessment and the relation with geometrical features of the AAA. Methods: The AAAs of twenty patients were reconstructed by three operators. Both the peak and 99-percentile stress were used for intra- and inter-operator variability using the intraclass correlation coefficient (ICC). A regression analysis was performed to relate the stress parameters with the maximum diameter. Outliers were analyzed by their geometrical characteristics. Results: The intra-operator ICC was 0.73-0.79 for the peak stress and 0.94 for the 99-percentile stress. The inter-operator ICC was 0.71 for the peak stress and 0.95 for the 99-percentile stress. A significant linear relation with the diameter was found only for the 99-percentile stress. Conclusions: The 99-percentile stress is more reproducible than peak watt stress. A significant relation between watt stress and diameter was found. Other geometrical features had no statistical relation with high stress. (C) 2008 European Society for Vascular Surgery. Published by Elsevier Ltd. All rights reserved.