Three-dimensional characterization of sex differences in abdominal aortic aneurysm progression via vascular deformation mapping

Fig. 1. Mean three-dimensional abdominal aortic aneurysm shapes and corresponding growth maps for males (a) and females (b) by statistical shape modeling. Growth is displayed using a colorized scale (Green = 0 cm/year, Red = 0.2 cm/year). Note: one female growth map was excluded because it included severe deviation in growth and was deemed an outlier.

Fig. 2. Three-dimensional display of differences in baseline AAA size by aortic region between males and females overlying a sample aorta. Blue denotes a higher value in males. Pink displays a higher value in females. Grey denotes no difference.

Fig. 3. Three-dimensional display of differences in growth rate by aortic region between males and females overlying a sample aorta. Blue denotes a higher value in males. Pink displays a higher value in females. Grey denotes no difference.

Fig. 4. Schematic overview of the steps in vascular deformation mapping (VDM) analysis. First, computed tomography angiography (CTA) scans at two time points (baseline and follow-up) undergo segmentation (blue box). Second, a multi-step registration of the two CTAs is performed including a rigid registration step to approximately align the two scans, followed by a highly regularized deformable registration with rigidity penalty to implicitly align the aortic centerlines (“centerline rigid”), and finally a b-spline deformable registration to align the outer wall of the aortas (red box). Lastly, a mesh of the abdominal aorta is created from the baseline CT mask and 3D deformation/growth metrics from the final deformable registration are plotted on the aortic surface. Growth is quantified as the degree of aortic expansion in the direction perpendicular (normal) to the aortic wall and normalized to interval to yield a growth rate in millimeters per year (black box) and displayed using a colorized scale (Green = 0 cm/year, Red = 0.5 cm/year).

Fig. 5. Aortic regions used for quantitative analysis. Each aorta (derived from VDM) was split into longitudinal zones and lateral zones. Longitudinal zones were defined by setting a value of 1 at the iliac bifurcation and then increasing by a value of 1 for every 5% along the centerline toward the renal arteries (range 1 to 19). Two longitudinal regions were then defined: 1) AAA (1 to 14), 2) aneurysm neck (15 to 19). Lateral zones were defined as 1 for points normal to the plane of the iliac bifurcation and then by an increase of 1 for every 30 degrees circumferentially (range 1 to 12). Four lateral regions were then defined: 1) anterior (1,2,12), 2) right lateral (3,4,5) posterior (6,7,8), and 4) left lateral (9,10,11). Using two longitudinal and four lateral regions, aortic growth can be compared across 8 segments.