Cardiac MR elastography using reduced‐FOV, single‐shot, spin‐echo EPI

Figures

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  Figure 1. (a) The timing diagram for the ECG‐gated, SE‐EPI, cardiac MRE pulse sequence with 2D RF excitation, (b) the custom‐designed 2D RF excitation pulse, and (c) its simulated excitation profile showing the location of water (blue) and lipid (yellow) signals. Only the water signal is refocused by the subsequent slice‐selective 180 ° pulse in the SE‐EPI pulse sequence (dashed line).

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  Figure 2. Representative comparison between the full‐FOV (top row) and the reduced‐FOV (rFOV) technique (bottom row) showing magnitude images (a,d), the corresponding log‐scaled images (b,e) to highlight the ghosting, and stiffness maps (c,f). Yellow arrows indicate the ghosting that was significantly reduced when using the rFOV technique. The red contours show the LV endocardium and epicardium ROIs that were manually traced on the magnitude images and copied onto the stiffness maps.

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  Figure 3. Example curl wave field images from the same subject as shown in Figure 2. (a,e) x, (b,f) y, and (c,g) z components of the curl field from the full‐FOV (top row) and the rFOV (bottom row) scans. The ghosting (white arrows) in the full‐FOV scans overlapped the LV wall (white contours) and contaminated the waves. The masked OSS‐SNR maps (d,h) showed increased wave quality in the LV wall in the rFOV images.

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  Figure 4. A representative case comparing the ghosting level in the myocardium (red and white contours) between the full‐FOV (top row) and rFOV techniques (bottom row) including magnitude images (a,d), the corresponding log‐scaled images (b,e) to highlight the ghosting, and the stiffness maps (c,f). The full‐FOV scan exhibits an artefactual hotspot in the stiffness map (arrow in c) arising from the severe ghosting. In contrast, the rFOV technique substantially reduced the ghosting, hence resulting in a more homogenous stiffness map of the myocardium.

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  Figure 5. The qualitative evaluation with pooled histograms of each of the 6 image characteristics as shown in the titles. Fisher's combined probability test was performed on the scores from the 2 readers (blue and yellow). The score −2 indicates a strong preference for the full‐FOV images and +2 a strong preference for the rFOV images. The significance results of the right‐tailed tests are included with each histogram.

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  Figure 6. Boxplots of the quantitative comparisons between the (a) OSS‐SNR and (b) stiffness of the full‐FOV and rFOV acquisitions. The box represents data from the 25th to 75th percentiles; the red line represents the median value; and dashed lines extend from the box to the 10th and 90th percentiles. The right‐sided Wilcoxon, sign‐rank test was performed on the OSS‐SNR data, and the 2‐sided test was performed on the stiffness data. The dashed lines link the data points from the same volunteer.