Three-dimensional analysis of segmental wall shear stress in the aorta by flow-sensitive four-dimensional-MRI

Purpose: To assess the distribution and regional differences of flow and vessel wall parameters such as wall shear stress (WSS) and oscillatory shear index (OSI) in the entire thoracic aorta. Materials and Methods: Thirty-one healthy volunteers (mean age = 23.7 ± 3.3 years) were examined by flow-sensitive four-dimensional (4D)-MRI at 3T. For eight retrospectively positioned 2D analysis planes distributed along the thoracic aorta, flow parameters and vectorial WSS and OSI were assessed in 12 segments along the vascular circumference. Results: Mean absolute time-averaged WSS ranged between 0.25 ± 0.04 N/m² and 0.33 ± 0.07 N/m² and incorporated a substantial circumferential component (-0.05 ± 0.04 to 0.07 ± 0.02 N/m²). For each analysis plane, a segment with lowest absolute WSS and highest OSI was identified which differed significantly from mean values within the plane (P < 0.05). The distribution of atherogenic low WSS and high OSI closely resembled typical locations of atherosclerotic lesions at the inner aortic curvature and supraaortic branches. Conclusion: The normal distribution of vectorial WSS and OSI in the entire thoracic aorta derived from flow-sensitive 4D-MRI data provides a reference constituting an important perquisite for the examination of patients with aortic disease. Marked regional differences in absolute WSS and OSI may help explaining why atherosclerotic lesions predominantly develop and progress at specific locations in the aorta.