Four-Dimensional Flow MRI-Derived Hemodynamics in Abdominal Aortic Aneurysms: Reproducibility and Associations With Diameter, Intraluminal Thrombus Volume, and Vorticity.

Background: Maximum diameter measurements are used to assess the rupture risk of abdominal aortic aneurysms (AAAs); however, these are not precise enough to predict all ruptures. Four-dimensional (4D) flow MRI-derived parameters provide additional information by visualizing hemodynamics in AAAs but merit further investigation before they are clinically applicable.

Purpose: To assess the reproducibility of 4D flow MRI-derived hemodynamics, to investigate possible correlations with lumen and maximum diameter, and to explore potential relationships with vorticity and aneurysm growth.

Study Type: Prospective single-arm study.

Population: A total of 22 (71.5 ± 6.1 years, 20 male) asymptomatic AAA patients with a maximum diameter of at least 30 mm.

Field Strength/sequence: A 3.0 T/Free-breathing 4D flow MRI phase-contrast acquisition with retrospective ECG-gating.

Assessment: Patients underwent two consecutive 4D flow MRI scans 1-week apart. Aortic volumes were segmented from time-averaged phase contrast magnetic resonance angiographies. Reproducibility was assessed by voxelwise analysis after registration. Mean flow velocity, mean wall shear stress (WSS), mean lumen diameter, and qualitative vorticity scores were assessed. In addition, Dixon MRI and retrospective surveillance data were used to study maximum diameter (including thrombus), intraluminal thrombus volume (ILT), and growth rate.

Statistical Tests: For reproducibility assessment, Bland-Altman analyses, Pearson correlation, Spearman's correlation, and orthogonal regression were conducted. Potential correlations between hemodynamics and vorticity scores were assessed using linear regression. P < 0.05 was considered statistically significant.

Results: Test-retest median Pearson correlation coefficients for flow velocity and WSS were 0.85 (IQR = 0.08) m/sec and 0.82 (IQR = 0.10) Pa, respectively. Mean WSS significantly correlated with mean flow velocity (R = 0.75) and inversely correlated with mean lumen diameter (R = -0.73). No significant associations were found between 4D flow MRI-derived hemodynamic parameters and maximum diameter (flow velocity: P = 0.98, WSS: P = 0.22).

Data Conclusion: A 4D flow MRI is robust for assessing the hemodynamics within AAAs. No correlations were found between hemodynamic parameters and maximum diameter, ILT volume and growth rate.

Level Of Evidence: 2 TECHNICAL EFFICACY: Stage 2.