Correlation of 4D ultrasound strain analysis with CTA wall stress simulations in abdominal aortic aneurysms

Objective Biomechanical modelling of infrarenal aortic aneurysms seeks to predict ruptures in advance, thereby reducing aneurysm-related deaths. As individual methods focusing on strain and stress analysis lack adequate discretisation power, this study aims to explore multifactorial characterisation for progressive aneurysmal degeneration. The study’s objective is to compare stress and strain-related parameters in infrarenal aortic aneurysms. Methods Twenty-two patients with abdominal aortic aneurysm (AAA) (mean maximum diameter 53.2 ± 7.2 mm) were included in the exploratory study, examined by computed tomography angiography (CTA) and 3D real-time speckle tracking ultrasound (4D-US). The conformity of aneurysm anatomy in 4D-US and CTA was determined with the mean point-to-point distance (MPPD). CTA was employed for each AAA to characterise stress-related indices using the semi-automated A4-clinics RE software. Five segmentations from one 4D-US examination were fused into one averaged model for strain analysis using MATLAB and the Abaqus solver. Results The mean MPPD between the adjacent points of the 4D-US and CTA-derived geometry was 1.8 ± 0.4 mm. The interclass correlation coefficients for all raters and all measurements for the maximum AAA diameter in 2D, 4D ultrasound and CTA indicate moderate to good reliability (ICC1 0.69 with 95% CI 0.49, 0.84, P < .001). The peak wall stress (PWS) correlates fairly with the maximum AAA diameter in 2D-US (r = 0.54, P < .01) and 4D-US (r = 0.53, P < .05) and moderately strongly with the maximum exterior AAA diameter (r = 0.63, P < .01). The peak wall rupture risk index (PPRI) shows a strong correlation with the PWS (ρ > 0.9, P < .001) and is influenced by anatomical parameters with equal strength. Isolated observation of the intraluminal thrombus does not provide significant information in the determination of PWS. The maximum AAA diameter in 2D-US shows a fair negative correlation with the mean circumferential, longitudinal and in-plane shear strain (ρ = – 0.46, r = – 0.45, ρ = – 0.47, P < .05 for all). The circumferential strain ratio as an indicator of wall motion heterogeneity increases with the aneurysm diameter (r = 0.47, P < .05). The direct comparison of wall strain and wall stress indices shows no quantitative correlation. Conclusions The strain and stress analyses provide independent biomechanical information of AAA. At the current stage of development, the two methods are considered complementary and may optimise a more patient-specific rupture risk prediction in the future.