In Vivo Three-Dimensional MR Wall Shear Stress Estimation in Ascending Aortic Dilatation

Purpose: To estimate surface-based wall shear stress (WSS) and evaluate flow patterns in ascending aortic dilatation (AscAD) using a high-resolution, time-resolved, three-dimensional (3D), three-directional velocity encoded, radially undersampled phase contrast MR sequence (4D PC-MRI). Materials and Methods: 4D PC-MRI was performed in 11 patients with AscAD (46.3 +/- 22.0 years) and 10 healthy volunteers (32.9 +/- 13.4 years) after written informed consent and institutional review board approval. Following manual vessel wall segmentation of the ascending aorta (MATLAB, The Mathworks, Natick, MA), a 3D surface was created using spline interpolation. Spatial WSS variation based on surface division in 12 segments and temporal variation were evaluated in AscAD and normal aortas. Visual analysis of flow patterns was performed based on streamlines and particle traces using En Sight (v9.0, CEI, Apex, NC). Results: AscAD was associated with significantly increased diastolic WSS, decreased systolic to diastolic WSS ratio, and delayed onset of peak WSS (all P < 0.001). Temporally averaged WSS was increased and peak systolic WSS was decreased. The maximum WSS in AscAD was on the anterior wall of the ascending aorta. Vortical flow with highest velocities along the anterior wall and Increased helical flow during diastole were observed in AscAD compared with controls. Conclusion: Changes in WSS in the ascending aorta of AscAD correspond to observed alterations in flow patterns compared to controls.