Comparison of Four-Dimensional Flow Parameters for Quantification of Flow Eccentricity in the Ascending Aorta

Purpose: To compare quantitative parameters for assessing the degree of eccentric systolic blood flow in the ascending thoracic aorta (AsAo). Materials and Methods: Forty-one patients were studied with three-dimensional (3D), cine phase-contract MRI (4D Flow). Analysis was performed at peak systole for a cross-sectional plane in the AsAo just distal to the sinotubular junction. AsAo flow was graded as normal, mildly, or markedly eccentric based on qualitative visual assessment. For quantitative analysis, flow jet angle and normalized flow displacement from the vessel center were calculated. Results: Patients with normal AsAo systolic flow (n = 25) had an average flow jet angle of 13.7 degrees and flow displacement 0.04. These parameters were significantly elevated for patients with mild eccentric systolic flow (n = 6): 24.6 degrees (P = 0.012) and 0.12 (P = 0.001), respectively. However, for patients with marked eccentric flow (n = 10), only flow displacement was significantly elevated compared with the mild eccentric group (0.18; P = 0.04); flow angle was 25.7 degrees. Conclusion: Flow displacement is a more reliable quantitative parameter for measuring eccentric AsAo systolic flow than flow jet angle, and should be evaluated in studies investigating the role of eccentric flow in the promotion of aortic pathology.