Ultrasound strain mapping of the non-aneurysmal abdominal aorta for detecting age-related aortic stiffening

Fig. 1. Ultrasound strain mapping workflow. This six-step workflow was adapted from previously described ultrasound-based strain mapping methods [18]. (A) B-mode ultrasound of the abdominal aorta in transverse scan plane. (B) Acquisition of a 10-s cineloop during breath hold. (C) Manual segmentation by placement of 15-20 tracking points at the interface between the vessel wall and lumen. (D) Automatic tracking of the vessel wall displacement within an automatically generated region of interest. (E) Generation of a strain map, based on deformation of the vessel wall during the cardiac cycle. The different colours illustrate different zones of strain in the vascular wall (blue = positive strain, red = negative strain, and green = no strain). (F) Final strain pattern extracted by centring a circle on the aortic centre. Each degree on this circle represents the radially averaged strain values. The circumferential axis in the polar plot is degrees around the vessel wall (0○-360○), and the radial axis is strain in percentage. (For interpretation of the references to colour in this figure legend, the reader is referred to the Web version of this article.)

Fig. 2. Inter-operator acquisition reproducibility of ultrasound-derived aortic strain features. Extended Bland-Altman analysis of inter-operator agreement for (A) antero-posterior aortic diameter, (B) mean strain, and (C) strain heterogeneity index. For each participant, the standard deviation across the three operators was calculated and used as the measure of variability, allowing agreement to be assessed across more than two raters. Limits of agreement were ±1.5 mm for aortic diameter, ±1.64 percentage points for mean strain, and ±0.18 for the heterogeneity index.

Fig. 3. Age-related differences in ultrasound-derived aortic strain features and strain patterns. (A) Boxplot of mean strain according to age group; (B) boxplot of strain heterogeneity index according to age group; (C) polar plot of mean circumferential strain patterns according to age group; and (D) polar plot of mean circumferential strain patterns according to sex assigned at birth. Mean strain summarises deformation across the full aortic circumference, whereas the strain heterogeneity index describes the spatial variation in deformation around the vessel wall. In the polar plots, the circumferential axis ranges from 0° to 360° around the aortic wall, and the radial axis represents strain (%).