Comparison of different methods for the estimation of aortic pulse wave velocity from 4D flow cardiovascular magnetic resonance

Figures

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  Fig. 1. Aortic pulsed wave velocity (PWV) estimation from 4D flow CMR. a Shared pre-processing step for all aortic PWV (aoPWV) strategies: aortic 3D segmentation, positioning of cross-sectional planes perpendicular to the aortic centreline between the distal descending aorta (1st plane) and proximal ascending aorta (25th plane), extraction of the corresponding 25 mean velocity curves, as well as Di distances between the 1st and the ith planes along the centreline. Of note, mean velocity curves were interpolated with a 1-ms time step using a spline function. b For strategy 1 (S1), aoPWV was defined as the ratio of the distance (D25) between the most distal (#1) and most proximal (#25) planes to the transit time (TT25) estimated from the corresponding normalized velocity waveforms. Transit time estimation methods are described in Fig. 2. c For strategy 2 (S2), intermediate distances (Di) and transit times (TTi) were estimated as in S1 between plane 1 and each successive plane (#i), until the proximal ascending aortic plane is reached. Such process provides the plot at the bottom, which was then linearly fitted (L: TTi = a*Di + b). aoPWV was equal to reciprocal of the slope (a). d For…

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  Fig. 2. Transit time estimation from 4D flow CMR normalized time-resolved velocity curves. a Transit time (TT) is defined as the time shift needed to maximise the overlap between two normalized aortic velocity curves x(t) and y(t) extracted from two distinct planes positioned along the aortic centreline as illustrated in Fig. 1. Three TT estimation methods are used. b Cross-correlation transit-time (TTc): a time shift (ti), comprised between 0 and the systolic duration is applied to x(t) while maximizing its overlap with y(t) in terms of systolic upslope. Such overlap was iteratively defined by the cross-correlation Cor(ti) between the shifted curve x(t + ti) and y(t) systolic upslopes. TTc was set to the time shift maximizing the cross-correlation function Cor(ti). c Wavelet transform transit-time (TTw): 4th order Gaussian wavelet transform was applied on the normalized mean velocity curves x(t) and y(t) resulting in the provided modulus and phase of the cross-spectrum. TTw is then defined as the sum of such phase weighted by its modulus (see equation), while considering only the systolic upslope. d Fourier transform transit-time (TTf): time shift is modelled by the group delay…

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  Fig. 3. Associations between 4D flow CMR aortic PWV and carotid-femoral (Cf) PWV. Linear regressions (solid lines) and confidence intervals (shaded blue area) are displayed. Linear regression equations are provided. S1, S2 and S3: Strategies 1, 2 and 3. TTc, TTw and TTf: transit times estimated using cross-correlation, wavelets and Fourier transforms, respectively. Correlation coefficients (R) are provided along with their levels of significance, which were indicated by *** for p < 0.001, ** for p < 0.01, * for p < 0.05

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  Fig. 4. Bland-Altman analysis between S2-TTw and the remaining 4D flow CMR-derived aortic PWV. Mean bias (solid lines), limits of agreements (shaded light blue region and dotted lines) and confidence intervals (shaded green region) are showed. Intra-class correlation coefficients (ICC) are provided above each plot. S1, S2 and S3: Strategies 1, 2 and 3, respectively. TTc, TTw and TTf: transit times estimated using cross-correlation, wavelets and Fourier transforms, respectively