Investigation of Aortic Wall Thickness, Stiffness and Flow Reversal in Patients With Cryptogenic Stroke: A 4D Flow MRI Study

Abstract

Background: Stroke etiology is undetermined in approximately one-sixth to one-third of patients. The presence of aortic flow reversal and plaques in the descending aorta (DAo) has been identified as a potential retrograde embolic mechanism.

Purpose: To assess the relationships between aortic stiffness, wall thickness, and flow reversal in patients with cryptogenic stroke and healthy controls.

Study type: Prospective.

Population: Twenty one patients with cryptogenic stroke and proven DAo plaques (69 ± 9 years, 43% female), 18 age-matched controls (age: 65 ± 8 years, 61% female), and 14 younger controls (36 ± 9 years, 57% female).

Field strength/sequence: 1.5T; 4D flow MRI and 3D dark blood T₁ -weighted turbo spin echo MRI of the aorta.

Assessment: Noncontrast aortic 4D flow MRI to measure 3D flow dynamics and 3D dark blood aortic wall MRI to assess wall thickness. 4D flow MRI analysis included automated quantification of aortic stiffness by pulse wave velocity (PWV) and voxelwise mapping of the flow reversal fraction (FRF).

Statistical tests: Analysis of variance (ANOVA) or Kruskal-Wallis tests, Student's unpaired t-tests or Wilcoxon rank-sum tests, regression analysis.

Results: Aortic PWV and FRF were statistically higher in patients (8.9 ± 1.7 m/s, 18.4 ± 7.7%) than younger controls (5.3 ± 0.8 m/s, P < 0.0167; 8.5 ± 2.9%, P < 0.0167), but not age-matched controls (8.2 ± 1.6 m/s, P = 0.22; 15.6 ± 5.8%, P = 0.22). Maximum aortic wall thickness was higher in patients (3.1 ± 0.7 mm) than younger controls (2.2 ± 0.2 mm, P < 0.0167) and age-matched controls (2.7 ± 0.5 mm) (P < 0.0167). For all subjects, positive relationships were found between PWV and age (R² = 0.71, P < 0.05), aortic wall thickness (R² = 0.20, P < 0.05), and FRF (R² = 0.47, P < 0.05). Patients demonstrated relationships between PWV and FRF in the ascending aorta (R² = 0.32, P < 0.05) and arch (R² = 0.24, P < 0.05).

Data conclusion: This study showed the utility of 4D flow MRI for evaluating aortic PWV and voxelwise flow reversal. Positive relationships between aortic PWV, wall thickness, and flow reversal support the hypothesis that aortic stiffness is involved in this retrograde embolic mechanism.

Level of evidence: 2 TECHNICAL EFFICACY STAGE: 1.

Keywords: 4D flow MRI; aortic stiffness; cryptogenic stroke; flow reversal mapping; pulse wave velocity; retrograde embolic mechanism.