Simultaneous measurements of 3D wall shear stress and pulse wave velocity in the murine aortic arch

Figures

• 

  Fig. 1. a An Illustration of the reconstruction process for the WSS- and PWV evaluation. For WSS calculation, the 4D-PC data was reconstructed at high spatial and low temporal resolution (HS/LT-res. reconstruction, see top panels). The aortic lumen was labeled with semi-automatic segmentation. Using the flow and label data, velocity gradients were calculated. For PWV calculation, the 4D-PC data was reconstructed at low spatial and high temporal resolution (LS/HT-res. reconstruction, see bottom panels). The segmentation data obtained from the HS/LT-res. reconstruction was temporally interpolated. Using the interpolated label and flow data, through plane flow was determined at multiple locations. b For the LS/HT-res. reconstruction (PWV), only the inner k-space points with kr < 85/FOV were used (red points, shown in 2D for better illustration). The HS/LT-res. reconstruction uses all available k-space frequencies (red and blue points)

• 

  Fig. 2. a Sliding window selection of cardiac phases for the HS/LT-resolution reconstruction (illustrated for only 3 frames and unscaled for a better clarity). The selection window width of the average heart cycle was W = 1/20 and the distance between each window Δ = 1/20. b Sliding window selection of cardiac phases for the LS/HT- resolution reconstruction. Overlapping selection windows with a width of W = 1/33 and a distance of Δ = 1/200 of the average cardiac cycle were used. The lighter shadings at the left and right edges of the selection windows mark the overlapping areas (not at scale)

• 

  Fig. 3. a Illustration of the transit time pulse wave velocity (PWV) measurement. Through-plane flow was determined at various positions along the aortic arch (for illustration only 8 planes are shown; in the experiment approx. 50 slices were used). b For each location (here shown for one plane in the ascending and descending aorta), the time point of the systolic upstroke was identified as the intersection of a line fitted to the pre-systolic data points and a line fitted to the upstroke of the early systolic pulse. c The distances Δx of each plane (relative to the proximal ascending aorta) were plotted against the time points of the systolic upstroke Δt (relative to the time point of the first plane). PWV was calculated from the slope of a line fitted to this plot

• 

  Fig. 4. Stability of self-navigation, undersampling and temporal blurring. a Cardiac periods TRR for wildtype and ApoE−/− mice. A slight significance was observed between both groups (*, p = 0.01). b No significant differences could be observed in the total number N of detected heartbeats. c Yield for both groups, showing no significant differences. d Undersampling factors for the high spatial/low atemporat (HS/LT) and low spatial/high temporal (LS/HT) reconstructions in both animal groups (Wildtype: (HS/LT vs. LS/HT, *, p = 0.03. ApoE−/−: HS/LT vs. LS/HT, **, p < 0.01). e Temporal blurring for the HS/LT and LS/HT reconstructions in both animal groups (HS/LT: Wildtype vs. ApoE-/- *, p < 0.04. Wildtype: HS/LT vs. LS/HT, ****, p < 0.0001. ApoE−/−: HS/LT vs. LS/HT, **, p < 0.01). f Peak flow values for the HS/LT and LS/HT reconstructions in both animal groups (HS/LT: Wildtype vs. ApoE−/−, *, p = 0.02. ApoE−/−: HS/LT vs. LS/HT, *, p = 0.05)

• 

  Fig. 5. Correlation plots of cardiac periods with different parameters. a No dependency of the yield on the heart rate was observed (p = 0.56). b No correlation was observed between undersampling and heart rates (HS/LT: p = 0.47, LS/HT: p = 0.52). c A correlation was observed between the temporal blurring and the heart rate (HS/LT: p < 0.0001, LS/HT: p < 0.001) due to the relation of the width of the selection window with the cardiac periods. d In both reconstructions, no significant correlation between the cardiac periods and peak flow values was observed (HS/LT: p = 0.09, LS/HT: p = 0.53)

• 

  Fig. 6. a Through-plane flow in the ascending aorta of an ApoE−/− mouse, determined with the HS/LT-resolution (blue) and LS/HT-resolution (red) reconstruction. b Peak flow profile of the same plane (HS/LT and LS/HT reconstruction)

• 

  Fig. 7. Time-dependent median WSS values for different temporal resolutions. a WSS values with 20 frames. b WSS values with 30 frames. c WSS values with 40 frames. d WSS values with 50 and 60 (e) frames. In d and e, severe undersampling factors are noticeable. f Boxplots of the WSS distribution over the cardiac cycle for all reconstructions. A slight increase of peak WSS values compared to the 20 frames reconstruction when using higher frame rates and smaller selection windows is observable

• 

  Fig. 8. Time-dependent median WSS values for different temporal resolutions with overlapping selection windows. a WSS values with 20 frames. b WSS values with 60 overlapping (OV) frames. c WSS values with 200 overlapping (OV) frames. d Boxplots of the WSS distribution over the cardiac cycle for all reconstructions. The reconstruction with the highest frame rate (200 frames, W = 1/33) features a slightly larger peak WSS

• 

  Fig. 9. a Scheme of the aortic arch with the chosen regions: ascending (A), top region (T) and descending (D). White ring: Scheme of the inner, outer, anterior and posterior radius of the aorta. b + c Bulls-Eye plots for the temporal averaged WSS values (magnitude) for b: Wildtype and c: ApoE−/− mice. Inner ring: Ascending aorta (A). Middle ring: top region (T). Outer ring: descending aorta (D). Scale: N/m2

• 

  Fig. 10. Pulse wave velocities for wildtype and ApoE−/− mice. Data are presented as mean ± SD. Statistically significant differences are observable in ApoE−/− mice compared to the wild type group (***, p < 0.001)