Abstract
Purpose
To evaluate the reproducibility of important biomarkers like wall shear stress (WSS) and pulse wave velocity (PWV) across two 4D flow MRI imaging protocols with different coverages: aorta-targeted 4D flow MRI (AT4D) and whole-heart 4D flow (WH4D) protocols.
Methods
Thirty-eight control subjects (43.2 ± 10.1 years old; 6 males) and ten patients (45.7 ± 8.9 years old; 22 males) with bicuspid aortic valve (BAV) were included. Each subject underwent AT4D and WH4D scans. PWV and absolute WSS were assessed for each patient across both protocols and compared using Bland-Altman analysis. Areas of elevated WSS were assessed for BAV patients across different WSS thresholds that define WSS to be elevated compared to a normal population average. A sensitivity analysis was conducted to determine the best WSS threshold at which WH4D-derived areas most closely resemble AT4D-derived areas. Inter-rater reproducibility was evaluated in twenty-four subjects.
Results
AT4D and WH4D PWV and WSS estimates demonstrated good agreement (PWV: -0.12 ± 1.84 m/s, p = 0.4; Median WSS: 0.06 ± 0.13 Pa, p < 0.01; Maximum WSS: 0.04 ± 0.27 Pa, p = 0.07). PWV correlated with age across protocols (AT4D: r = 0.68, p < 0.01; WH4D: r = 0.72, p < 0.01). Sensitivity analysis identified a WSS threshold where WH4D-derived areas of elevated WSS most closely resembled AT4D-derived areas. Inter-rater assessment resulted in a small mean difference percentage of < 3%.
Data conclusion:
PWV and WSS demonstrated good agreement across protocols. The WSS threshold should be adjusted for WH4D estimates to optimally match AT4D-derived output. Reproducibility analysis showed good test-retest agreement. This study demonstrates the reproducibility of certain hemodynamic parameters across two 4D flow MRI protocol.