Reproducibility of Deriving Parameters of AAA Rupture Risk from Patient-specific 3D Finite Element Models

Purpose: To assess the reproducibility of estimating biomechanical parameters of abdominal aortic aneurysms (AAA) based on finite element (FE) computations derived from a commercially available, semiautomatic vascular analyzer that reconstructs computed tomographic angiography (CTA) data into FE models.

Methods: The CTA data from 10 consecutive male patients (mean age 74 years, range 63-87) with a fusiform infrarenal AAA >5 cm in diameter were used for this study, along with the CTA scans from 4 individuals without aortic disease. Three different observers used semiautomatic reconstruction software to create deformable contour models from axial CT scans. These 3-dimensional FE models captured the aortic wall and thrombus tissue using isotropic finite strain constitutive modeling. Geometric (maximum diameter and volume measurements based on an anatomical centerline) and biomechanical determinants [aneurysm peak wall stress (PWS) and the peak wall rupture risk (PWRR) index] were then calculated from the FE models. The determinations were made 5 times for each anonymized dataset presented for analysis in random order (5-fold measurements for 14 datasets produced 210 measurements from the 3 observers). Inter- and intraobserver variability were assessed by calculating the coefficient of variation of these repeated measures. The methodological variations were expressed with the intraclass correlation coefficient (ICC) and Bland-Altman plots.

Results: The median segmentation time was < 1 hour (mean 39.2 minutes, range 25-48) for datasets from the AAA patients; for the healthy individuals, segmentation times were considerably shorter (median 8.7 minutes, range 4-15). Intraobserver reproducibility was high, as represented by a CV <3% for the diameter measurement and < 5.5% for volume, PWS, and the PWRR index. The ICC was 0.97 (range 0.95-0.98) for diameter and 0.98 (range 0.97-0.99) for volume; for PWS and the PWRR index, the ICCs were equal at 0.98 (range 0.97-0.99).

Conclusion: The reproducibility of volume and maximum diameter measurements in infrarenal AAAs with FE analysis is high. With the model used in this semiautomatic reconstruction software, wall stress analysis can be achieved with high agreement among observers and in serial measurements by a single observer.