Estimating the Haemodynamic Streamline Vena Contracta as the Effective Orifice Area Measured from Reconstructed Multislice Phase-contrast MR Images for Patients with Moderately Accelerated Aortic Stenosis

Figures

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  Fig. 1. Classification of the study population. AS, aortic stenosis; LF/LG AS, low-flow low-gradient severe AS; LVEF, left ventricular ejection fraction; MG, mean pressure gradient; NF/LG AS, normal-flow low-gradient severe AS; Paradoxical LF/LG AS, paradoxical low-flow low-gradient severe AS; SVI, stroke volume index; TTE-EOA, transthoracic echocardiography-derived effective orifice area; Vmax, peak aortic flow velocity.

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  Fig. 2. Correction of the aliasing and a representative case with phase-corrected aliased accelerated flow, in the accelerated AS group with a transaortic flow velocity of 5 m/sec on echocardiographic examination. (a) Phase contrast images. During systole, the exceeding VENC pixels are found to have black and white inversion, in the shape of an island around the center of the accelerated flow, in the phase images in the through-plane direction. (b) Velocity distribution curve (on a red line). Flow velocity profiles have discontinuous regions due to the phase shift caused by aliasing in the phase images, which indicates a 2D flow velocity distribution in the through-plane direction. The pixel-by-pixel pickup in these discontinuous inverted phase images and phase correction are performed. (c) 3D reconstruction of the aortic blood flow during peak systole at the level of the vena-contract. Velocity aliasing due to the blood flow velocities exceeding VENC (4 m/s) can be seen at the opposite side of the forward flow vectors (red arrow). (d) 3D reconstructions of blood flow after anti-aliasing phase correction. (e) Aliasing signals are recognized as a black areas in 2D cine PC-MRI (red arrow),…

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  Fig. 3. Visualization of blood flow and determination of the effective orifice area by 2D phase-contrast MRI. (a) The positioning of the image planes uses 10 slices parallel to the aortic valve, from 2 cm below the aortic annulus to 6 cm above the annulus in the ascending aorta. (b) Structural true FISP cine imaging and PC imaging at the same cross-sectional area with three orthogonal velocity axes: lateral, longitudinal, and vertical directions, are acquired for analysis. The 2D planes are oriented to the short axis of the aortic root to fully cover the sinus of Valsalva with 10 serial slices as described in (a). (c) Blood flow velocity patterns are visualized using iTFlow, where 3D streamline is created using data from the aforementioned 2D true FISP and cine PC MRI. Trajectory blood streamlines in the Valsalva sinus are created with 3D velocity vector visualizations in the peak systole. The convergence of the streamline, which corresponds to the vena contracta, is selected (yellow line). (d) 3D reconstruction of aortic blood flow during peak systole with colorized velocity vector maps at the selected cross-sectional area determined by the yellow line (c) as vena contracta. The red…

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  Fig. 4. Correlation between the EOA obtained from TTE and MRI in the moderately accelerated and highly accelerated AS groups. Scatter plot showing the correlation between TTE-EOAs and MRI-EOAs. Pearson’s correlation coefficient was calculated. AS, aortic stenosis; EOA, effective orifice area; MRI-EOA, MRI-derived effective orifice area; TTE, transthoracic echocardiogram; TTE-EOA, TTE-derived effective orifice area.

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  Fig. 5. Agreement between the TTE-EOA and MRI-EOA in the highly accelerated and moderately accelerated AS groups. Bland-Altman plot with mean bias and limits of agreement. The solid line shows the mean bias, and the dashed lines show ± 1.96 standard deviations. (a) Moderately accelerated AS group; (b) Highly accelerated AS group. AS, aortic stenosis; MRI-EOA, MRI-derived effective orifice area; TTE, transthoracic echocardiogram; TTE-EOA, TTE-derived effective orifice area.

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  Fig. 6. Case 1. A 76-year-old man presented with exertional dyspnea and was observed to have left main coronary artery disease (NYHA Ⅲ). He was diagnosed with paradoxical LF/LG AS (TTE-EOA of 0.36 cm2, Vmax of 3.8 m/sec, and SVI of 17.3 ml/m2) with LVEF of 84.8%. However, calcification protruding and bulging septum into the LVOT might yield an incorrectly small LVOT diameter, resulting in small TTE-EOA (a). A 2D phase-contrast MRI is performed for evaluation of the AS severity. The MRI-EOA is calculated as 0.67 cm2 (b), confirming severe AS. He underwent a surgical AVR. During the operation, a gross specimen of the aortic valve shows heavily calcified changes on all leaflets (c). In this case, MRI-EOAs may have supported the determination of surgical indication in paradoxical LF/LG AS. Case 2. A 61-year-old man was asymptomatic (NYHA I) but was diagnosed with paradoxical LF/LG AS (TTE-EOA of 0.89 cm2, Vmax of 2.8 m/sec, and SVI of 25.6 ml/m2) with preserved LVEF of 52.8% on echocardiography (d). However, the TTE-EOA may be inaccurate as it is difficult to correctly evaluate the LVOT dimensions based on anatomical properties. In 2D phase-contrast MRI, the MRI-EOA is calculated as 1.76 cm2…