Valvular imaging in the era of feature‐tracking: A slice‐following cardiac MR sequence to measure mitral flow

Figures

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  Figure 1. Workflow to obtain slice‐following phase contrast. 1) Obtain 4‐chamber cine. 2) Export the 4‐chamber cine offline and perform feature‐tracking of the mitral valve insertion points using Segment software. 3–4) While the offline analysis is being performed, continue scanning short‐axis cine stack and aortic flow. 5) Import the tracked displacements into the phase contrast slice‐following sequence. 6) Run the slice‐following sequence. The required time between the acquisition of the 4‐chamber cine and the slice‐following sequence was 5–10 minutes during which other sequences can be acquired.

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  Figure 2. Illustration of the mitral valve image planes and the resulting data. Yellow lines represent the planned slice locations in the 4‐chamber long‐axis. Regions of interest for flow analysis along the mitral valvular borders are marked in blue in the phase contrast images, which are shown at end diastole. Mean forward and backward flow curves of all healthy subjects at their corresponding slice positions are shown as solid and dashed blue lines, respectively. Motion correction and background phase offset error correction was performed in all flow curves. a: Slice‐following phase contrast images were planned at the location of the mitral valve in the 4‐chamber long‐axis at end diastole. b: Conventional static phase contrast images were planned at the valve location in end systole.

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  Figure 3. Phantom setup to confirm slice‐following. Cone geometry was 7 cm in height, top diameter was 12 cm, and bottom diameter was 3 cm. A 5‐mm thick horizontal bar was located midway at the height 3.5 cm, where the cone diameter was 7.5 cm. The center of the cone in both height and width was marked with an elevated cross on top of the bar. a: 3D rendering of the phantom cone from above. b: 3D rendering of the phantom cut through in the long‐axis direction. c: Long‐axis magnetic resonance image of the phantom. d: Short‐axis magnetic resonance image of the phantom at the middle of the cone. White line illustrates the radius in the depicted slice. e: Theoretical and measured cone radius in two phantom experiments, demonstrating accurate slice‐following.

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  Figure 4. Illustration of quantitative flow. a: Mitral stroke volume was defined as the total volume of the forward flow during diastole. Mitral regurgitant volume was defined as the backward systolic flow. b: Aortic stroke volume was defined as the total volume of the net flow over the whole cardiac cycle. c: Diastolic parameters E and A were defined as the maximum mitral blood flow velocity at early diastole and atrial contraction, respectively.

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  Figure 5. Example of mitral valve images acquired with valvular slice‐following phase contrast and corresponding flow profiles from motion‐corrected slice‐following (blue) and static images (green). a: Healthy subject acquired at 3T. White arrows points at the open mitral leaflets. b: Patient with double orifice mitral valve and mitral regurgitation imaged at 1.5T. White arrows points at the double orifice during diastole. A pronounced mitral regurgitation can be seen in the slice‐following backward flow profile, but is not distinguishable from the left ventricular outflow measured in the static net flow profile.

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  Figure 6. Comparison of SV in healthy subjects, showing scatterplots (left) and Bland–Altman analysis (right). Blue open circles show motion‐corrected static PC data and black closed circles shows motion‐corrected slice‐following data. a: Mitral SV with static and slice‐following PC vs. aortic SV. b: Mitral SV with static and slice‐following PC vs. planimetric SV.