Reproducibility and interobserver variability of systolic blood flow velocity and 3D wall shear stress derived from 4D flow MRI in the healthy aorta

Abstract

Purpose To investigate the reproducibility and inter-observer variability of 3D aortic velocity vector fields and wall shear stress (WSS) averaged over five systolic timeframes derived from non-contrast 4D-flow-MRI. Methods Fourteen controls underwent test-retest 4D-flow-MRI examinations separated by 16±3 days (resolution=3.0–3.6×2.3–2.6×2.5–2.7mm3; TE/TR/FA=2.5ms/4.9ms/7°; Venc=150cm/s). Two observers was segmented the aorta, and WSS was calculated for both series of scans and both segmentations. Test-retest and inter-observer velocity and WSS vectors were compared on a voxel-by-voxel basis in the aorta and on a regional basis by subdividing the aortas in six segments. Results Test-retest: voxel-by-voxel Bland-Altman analysis revealed small differences (−0.03/−0.02 m/s/Pa), limits of agreement of 0.25 m/s/0.29 Pa and coefficients of variation (CV) of 20% for velocity/WSS. Voxel-by-voxel orthogonal regression analysis showed moderate agreement (Slope: 1.14/1.16, Intraclass Correlation Coefficient (ICC): 0.76/0.67 for velocity/WSS). The regional analysis revealed a CV of 9%/8% and ICC of 0.9/0.9 for velocity/WSS. Inter-observer: voxel-by-voxel difference for WSS was 0, LOA: 0.17/0.19 Pa, CV: 12/13%, slope: 1.01/1.09, ICC: 0.87/0.85 for test/retest. The CV/ICC for WSS in the regional analysis was 4%/1.0 for test and 3%/1.0 for retest. Conclusions Systolic velocity and WSS derived from 4D flow MRI are reproducible between consecutive visits, with low inter-observer variability in healthy volunteers.

Aortic Valve Stenosis Alters Expression of Regional Aortic Wall Shear Stress: New Insights From a 4‐Dimensional Flow Magnetic Resonance Imaging Study of 571 Subjects

“…An additional challenge associated with WSS determination is aortic root motion. As a result, we used a recently described method, which does not require a time‐resolved segmentation and has been found robust in the computation of WSS from a systolic phase‐contrast magnetic resonance angiography geometry and the associated systolic velocity field 14. However, regions of slow and recirculating flow can be difficult to capture with the phase‐contrast magnetic resonance angiography approach.…”

“…Furthermore, advances in imaging have enabled the robust use of 4‐dimensional (4D) flow magnetic resonance imaging (MRI), a technique which is capable of measuring 3‐dimensional (3D) blood velocity and WSS in the entire volume of the thoracic aorta 14. For example, a recent 4D flow MRI study in BAV patients demonstrated strong relationships between elevated aortic WSS and locations of regional aortopathy, as determined by aortic wall tissue histopathology (protein expression and tissue architecture) 8.…”

Altered aortic 3D hemodynamics and geometry in pediatric Marfan syndrome patients

“…1c) using a previously described algorithm, which was shown to provide good reproducibility [25, 26]. Briefly, WSS vector was estimated for each wall point on the aortic surface based on the 3D velocity spatial gradient perpendicular to the vessel wall.…”

Transcatheter aortic valve replacement alters ascending aortic blood flow and wall shear stress patterns: A 4D flow MRI comparison with age-matched, elderly controls

“…Previous studies have reported alterations in aortic WSS distribution and flow eccentricity after both TAVR and SAVR [11]. However, no studies have been conducted comparing TAVR with age-and gender-matched controls, despite described age-related changes in aortic blood flow haemodynamics among healthy individuals [11][12][13].…”