Comparison of 4D flow and 2D velocity-encoded phase contrast MRI sequences for the evaluation of aortic hemodynamics

Abstract

The purpose of this study was to compare aortic flow and velocity quantification using 4D flow MRI and 2D CINE phase-contrast (PC)-MRI with either one-directional (2D-1dir) or three-directional (2D-3dir) velocity encoding. 15 healthy volunteers (51 ± 19 years) underwent MRI including (1) breath-holding 2D-1dir and (2) free breathing 2D-3dir PC-MRI in planes orthogonal to the ascending (AA) and descending (DA) aorta, as well as (3) free breathing 4D flow MRI with full thoracic aorta coverage. Flow quantification included the co-registration of the 2D PC acquisition planes with 4D flow MRI data, AA and DA segmentation, and calculation of AA and DA peak systolic velocity, peak flow and net flow volume for all sequences. Additionally, the 2D-3dir velocity taking into account the through-plane component only was used to obtain results analogous to a free breathing 2D-1dir acquisition. Good agreement was found between 4D flow and 2D-3dir peak velocity (differences = -3 to 6 %), peak flow (-7 %) and net volume (-14 to -9 %). In contrast, breath-holding 2D-1dir measurements exhibited indices significantly lower than free breathing 2D-3dir and 2D-1dir (differences = -35 to -7 %, p < 0.05). Finally, high correlations (r ≥ 0.97) were obtained for indices estimated with or without eddy current correction, with the lowest correlation observed for net volume. 4D flow and 2D-3dir aortic hemodynamic indices were in concordance. However, differences between respiration state and 2D-1dir and 2D-3dir measurements indicate that reference values should be established according to the PC-MRI sequence, especially for the widely used net flow (e.g. stroke volume in the AA).

Keywords: 4D flow MRI; Aortic hemodynamics; MRI; Phase-contrast.

Fig. 1

Analysis workflow of 2D one-directional (2D-1dir), three-directional (2D-3dir) and 4D flow phase-contrast (PC) MRI data: preprocessing (a), coregistration of the 2D slice location on 4D flow data (b), as well as 2D segmentation of ascending (AA) and descending (DA) aortic borders (c), used for the estimation of peak through-plane velocity (peak Vz_max), peak velocity magnitude (peak Vmag_max), peak flow (peak Q) and net flow volume (Q_net)

Fig. 2

Examples of velocity profiles obtained in the AA (a) and DA (b) using 2D-1dir (top row), 2D-3dir (middle row) PC-MRI and 4D flow (bottom row) data throughout the systolic period in a healthy volunteer

Fig. 3

Group-averaged maximal through-plane velocity Vz_max (left), maximal velocity magnitude Vmag_max (middle) and flow rate Q (right) throughout the cardiac cycle as estimated in the AA (a) and DA (b), using 2D-1dir (dashed blue lines), 2D-3dir (dotted grey lines) PC-MRI and 4D flow (solid red lines) data. Standard deviations over the whole group are represented as bars for each cardiac phase. *Indicates p < 0.05 for comparison across the three sequences

Fig. 4

Bland–Altman diagrams for comparison between 2D-1dir and 2D-3dir PC-MRI peak systolic maximal through-plane velocity (peak Vz_max), peak systolic maximal velocity magnitude (peak Vmag_max), peak systolic flow (peak Q) and net flow volume (Q_net), in the AA (a) and DA (b). Solid red line indicates mean bias while dashed red lines indicate limits of agreement. Mean values of the relative difference in percentage of the averaged value are provided

Fig. 5

Bland–Altman diagrams for comparison between 2D-3dir PC-MRI and 4D flow peak through-plane velocity (peak Vz_max), peak velocity magnitude (peak Vmag_max), peak flow (peak Q) and net flow volume (Q_net), in the AA (a) and DA (b). Solid red line indicates mean bias while dashed red lines indicate limits of agreement. Mean values of the relative difference in percentage of the averaged value are provided

Fig. 6

Linear regressions for comparison between peak through-plane velocity (peak Vz_max), peak velocity magnitude (peak Vmag_max), peak flow (peak Q) and net flow volume (Q_net), in the AA (a) and DA (b) estimated with and without performing eddy current correction (ECC), while pooling the three PC-MRI sequences. Slopes and Pearson correlation coefficients (r) are provided