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.