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Background: Aortic flow parameters can be quantified using 4D flow MRI. However, data are sparse on how different methods of analysis influence these parameters and how these parameters evolve during systole., Purpose: To assess multiphase segmentations and multiphase quantification of flow-related parameters in aortic 4D flow MRI., Study Type: Prospective., Population: 40 healthy volunteers (50% male, 28.9 ± 5.0 years) and 10 patients with thoracic aortic aneurysm (80% male, 54 ± 8 years)., Field Strength/sequence: 4D flow MRI with a velocity encoded turbo field echo sequence at 3 T., Assessment: Phase-specific segmentations were obtained for the aortic root and the ascending aorta. The whole aorta was segmented in peak systole. In all aortic segments, time to peak (TTP; for flow velocity, vorticity, helicity, kinetic energy, and viscous energy loss) and peak and time-averaged values (for velocity and vorticity) were calculated., Statistical Tests: Static vs. phase-specific models were assessed using Bland-Altman plots. Other analyses were performed using phase-specific segmentations for aortic root and ascending aorta. TTP for all parameters was compared to TTP of flow rate using paired t-tests. Time-averaged and peak values were assessed using Pearson correlation coefficient. P < 0.05 was considered statistically significant., Results: In the combined group, velocity in static vs. phase-specific segmentations differed by 0.8 cm/sec for the aortic root, and 0.1 cm/sec (P = 0.214) for the ascending aorta. Vorticity differed by 167 sec -1  mL -1 (P = 0.468) for the aortic root, and by 59 sec -1  mL -1 (P = 0.481) for the ascending aorta. Vorticity, helicity, and energy loss in the ascending aorta, aortic arch, and descending aorta peaked significantly later than flow rate. Time-averaged velocity and vorticity values correlated significantly in all segments., Data Conclusion: Static 4D flow MRI segmentation yields comparable results as multiphase segmentation for flow-related parameters, eliminating the need for time-consuming multiple segmentations. However, multiphase quantification is necessary for assessing peak values of aortic flow-related parameters., Level of Evidence: 2 TECHNICAL EFFICACY STAGE: 3., (© 2023 The Authors. Journal of Magnetic Resonance Imaging published by Wiley Periodicals LLC on behalf of International Society for Magnetic Resonance in Medicine.)

Background: Hemodynamic aorta parameters can be derived from 4D flow MRI, but this requires lumen segmentation. In both commercially available and research 4D flow MRI software tools, lumen segmentation is mostly (semi-)automatically performed and subsequently manually improved by an observer. Since the segmentation variability, together with 4D flow MRI data and image processing algorithms, will contribute to the reproducibility of patient-specific flow properties, the observer's lumen segmentation reproducibility and repeatability needs to be assessed., Purpose: To determine the interexamination, interobserver reproducibility, and intraobserver repeatability of aortic lumen segmentation on 4D flow MRI., Study Type: Prospective and retrospective., Population: A healthy volunteer cohort of 10 subjects who underwent 4D flow MRI twice. Also, a clinical cohort of six subjects who underwent 4D flow MRI once., Field Strength/sequence: 3T; time-resolved three-directional and 3D velocity-encoded sequence (4D flow MRI)., Assessment: The thoracic aorta was segmented on the 4D flow MRI in five systolic phases. By positioning six planes perpendicular to a segmentation's centerline, the aorta was divided into five segments. The volume, surface area, centerline length, maximal diameter, and curvature radius were determined for each segment., Statistical Tests: To assess the reproducibility, the coefficient of variation (COV), Pearson correlation coefficient (r), and intraclass correlation coefficient (ICC) were calculated., Results: The interexamination and interobserver reproducibility and intraobserver repeatability were comparable for each parameter. For both cohorts there was very good reproducibility and repeatability for volume, surface area, and centerline length (COV = 10-32%, r = 0.54-0.95 and ICC = 0.65-0.99), excellent reproducibility and repeatability for maximal diameter (COV = 3-11%, r = 0.94-0.99, ICC = 0.94-0.99), and good reproducibility and repeatability for curvature radius (COV = 25-62%, r = 0.73-0.95, ICC = 0.84-0.97)., Data Conclusion: This study demonstrated no major reproducibility and repeatability limitations for 4D flow MRI aortic lumen segmentation., Level of Evidence: 3 TECHNICAL EFFICACY STAGE: 2., (© 2020 The Authors. Journal of Magnetic Resonance Imaging published by Wiley Periodicals LLC. on behalf of International Society for Magnetic Resonance in Medicine.)