Objective: Knowledge of aortic shape changes throughout the cardiac cycle can offer improved understanding of vascular pathophysiology and may have crucial impact on stentgraft design and EVAR durability. To understand underlying mechanisms of dynamic changes in aortic aneurysm (neck) morphology, the undiseased aorta has to be studied first. Objective is to visualize and characterize dynamic aortic shape changes in young healthy volunteers.
Materials and methods: Fifteen healthy volunteers (7 male, median age 24 year, range 18-28) were scanned using ECG-gated balanced gradient-echo MRI, with 16 reconstructed cardiac phases. Transverse scans were made perpendicular to the aorta: (A) above the aortic bifurcation, (B) infrarenal, (C) juxtarenal, (D) suprarenal and (E) above the celiac trunk. After aortic lumen segmentation, radial changes during the cardiac cycle were measured, from the center of mass, over 360 degrees, and plotted. An ellipse was fitted over the distention plots, yielding the direction (AP:0 degrees, Right: -90 degrees, Left: 90 degrees ) and magnitude of radius change over the major and minor axis.
Results: Asymmetric distention was observed, with a variable rate per patient and level. Radius changes decreased from the proximal to distal aorta. Radius changes over the major axis ranged from 14% to 41%. At level A mean change in radius over the minor versus major axis was 1.4+/-0.2mm (17%) versus 1.6+/-0.2mm (20%), respectively. At B 1.7+/-0.4mm (22%) versus 2.0+/-0.4mm (25%), at C 1.7+/-0.4mm (22%) versus 2.2+/-0.4mm (27%) at D 2.0+/-0.4mm (25%) versus 2.4+/-0.5mm (30%) and at E 2.2+/-0.3mm (27%) versus 2.6+/-0.3mm (32%). Mean orientation of the major axis was (A) 0.8+/-23.3 degrees , (B) 1.8+/-31.3 degrees , (C) 14.0+/-15.5 degrees , (D) -28.8+/-48.0 degrees and (E) 18.4+/-22.2 degrees.
Conclusions: Aortic pulsatile distention in young healthy volunteers is asymmetric, with up to 41% radius change in the descending aorta. This study offers a frame of reference for dynamic imaging studies in patients with aortic pathology and provides a valuable non-invasive tool for future research into aortic distention, development and localization of vascular pathology.