Longitudinal 4D Flow MRI ‐Derived Wall Shear Stress in Patients With an Abdominal Aortic Aneurysm

BACKGROUND: 4D flow MRI-derived parameters such as wall shear stress (WSS) may improve abdominal aortic aneurysm (AAA) progression prediction. Validation of this biomarker is needed, but longitudinal data are lacking. PURPOSE: Investigate longitudinal WSS changes and associations with AAA morphology. STUDY TYPE: Prospective. SUBJECTS: Fifteen patients (mean age 68.7 ± 8.9 years; 1 female) with AAA > 30 mm in diameter. FIELD STRENGTH/SEQUENCE: 3.0 T, 4D flow MRI, 3D cine balanced steady state free precession, and Dixon. ASSESSMENT: Patients had baseline and follow-up MRI studies, separated by 6 months. A previously developed automated post-processing 4D flow MRI software was utilized to assess WSS, total lumen, and thrombus volumes. Maximum diameter in the anteroposterior (AP) and left-right (LR) directions was measured by three radiologists (with 13, 12, and 3 years of experience) based on the Dixon MRI at both time-points. Statistically significant growth was defined as an increase exceeding twice the standard error of the measurement. Baseline and follow-up 3D WSS maps were visually compared to identify potential temporal differences. STATISTICAL TESTS: The Wilcoxon signed-rank test was applied to evaluate differences in diameter, volume, and WSS measurements between baseline and follow-up. Spearman's rank correlation coefficients were calculated to assess correlations between (half-year change in) WSS values and AAA diameter and volumes. RESULTS: Maximum AAA diameter increased significantly from baseline to follow-up. Also, a significant difference was observed in maximum peak WSS between baseline and follow-up. A significant inverse correlation was observed between the change in minimum peak WSS and AAA lumen volume over follow-up. Visual assessment of WSS maps may improve 4D flow-based AAA surveillance by identifying localized changes. DATA CONCLUSION: Maximum AAA diameter increased over the study period. Changes in WSS were inversely associated with changes in AAA lumen volume over follow-up but not with maximum AAA diameter. Longer follow-up is needed to assess the potential of WSS as a biomarker for AAA progression. EVIDENCE LEVEL: Level 2. TECHNICAL EFFICACY: Level 3.