Reproducibility of Flow and Wall Shear Stress Analysis Using Flow-Sensitive Four-Dimensional MRI

Purpose: To systematically investigate the scan-rescan reproducibility and observer variability of flow-sensitive four-dimensional (4D) MRI in the aorta for the assessment of blood flow and global and segmental wall shear stress. Materials and Methods: ECG and respiration-synchronized flow-sensitive 4D MRI data (spatio-temporal resolution = 1.7 x 2.0 x 2.2 mm(3)/40.8 ms) were acquired in 12 healthy volunteers. To analyze scan-rescan variability, flow-sensitive 4D MRI was repeated in 10 volunteers during a second visit. Data analysis included calculation of time-resolved and total flow, peak systolic velocity, and regional and global wall shear stress (WSS) in up to 24 analysis planes distributed along the aorta. Results: Scan-rescan, inter-observer, and intra-observer agreement was excellent for the calculation of total flow and peak systolic velocity (mean differences <5% of the average flow parameter). Global WSS demonstrated moderate agreement and increased variability regarding wall shear stress (scan-rescan, inter-observer, and intra-observer agreement; mean differences <10% of the average WSS parameters). The segmental distribution of wall shear stress in the thoracic aorta could reliably be reproduced (r > 0.87; P < 0.001) for different observers and examinations. Conclusion: Flow-sensitive 4D MRI-based analysis of aortic blood flow can be performed with good reproducibility. Robustness of global and regional WSS quantification was limited, but spatio-temporal WSS distributions could reliably be replicated.