Rationale and clinical applications of 4D flow cardiovascular magnetic resonance in assessment of valvular heart disease: a comprehensive review

Fig. 1. 4D Flow CMR visualisation and quantification of valvular flow by retrospective valve tracking. Step 1. Identification of valve plane from cines acquired in 2 orthogonal planes. Step 2. Valve plane is tracked in all phases in the first view and cross-checked with the second view. Arrow allows confirmation of flow in the correct direction. Step 3. Visualisation of flow enables accurate quantification of flow in phase-contrast images

Fig. 2. 4D Flow CMR assessment of mitral regurgitation. a Shows four-dimensional mitral regurgitation flow streamline. b Demonstrates mitral forward flow visualised by 4D Flow CMR and c quantification of mitral forward flow by phase-contrast image obtained from 4D Flow CMR. d Shows aortic forward flow and e quantification of aortic forward flow by phase-contrast image obtained by 4D Flow CMR

Fig. 3. Invasive and 4D Flow CMR assessment of moderate mitral stenosis. a Demonstrates invasive assessment of mitral stenosis with simultaneous recording of pulmonary artery wedge pressure and left ventricular pressure. The mean pressure gradient by this method was 6 mmHg. b–d CMR left ventricular outflow tract (LVOT) view, 4-chamber view and vertical long axis view, demonstrating reduced opening and thickening of the mitral valve leaflets and left atrial dilatation. e demonstrates quantification of peak velocity in the red areas of peak velocity zone on f–h. f–h In-plane velocities are superimposed on the above images, demonstrating increased forward flow velocity through the mitral valve

Fig. 4. TTE and 4D Flow CMR assessment of moderate aortic regurgitation. a 4-chamber colour Doppler transthoracic echo (TTE) demonstrating aortic regurgitation jet and b TTE continuous wave Doppler demonstrating pressure half time consistent with moderate aortic regurgitation. c is a four-dimensional flow streamline visualisation of aortic regurgitation in left ventricular diastole. d is pathline visualization of flow reversal in the early diastole in the descending aorta. e is a reformatted c at aortic valve level flow quantification. f is the reformatted plane at the descending aorta level flow quantification

Fig. 5. 4D Flow CMR assessment of severe aortic stenosis. a is a sagittal LVOT view and b coronal LVOT view demonstrating restrictive aortic valve opening with dephasing artefact demonstrating higher velocities through a narrow orifice. c and d further demonstrate increased velocity by superimposing in-plane velocity overlay onto the sagittal and coronal LVOT view. e shows four-dimensional flow streamline tracing through the aortic valve. f is a reformatted phase-contrast plane through the aortic valve demonstrating quantification of aortic valve forward flow and peak velocity. g is a zoomed in images of e demonstrating where the peak velocity through the aortic valve is (red ball). h Shows streamline visualisation of aortic regurgitation into the outflow tract

Fig. 6. 4D Flow CMR assessment of tricuspid regurgitation. a shows 4D flow streamline of tricuspid regurgitation. b demonstrates tricuspid forward flow visualised by 4D Flow CMR and c quantification of tricuspid forward flow by phase-contrast image obtained by 4D Flow CMR. d Shows pulmonary forward flow and e quantification of pulmonary forward flow by phase-contrast image obtained by 4D Flow CMR

Fig. 7. Phase Contrast CMR and 4D Flow CMR assessment of pulmonary regurgitation post tetralogy of Fallot repair. a and b Show sagittal and coronal right ventricular outflow tract views used for planning of pulmonary through-plane flow. Red line demarcates the analysis plane. c and d Show quantifications of pulmonary flow by PCMR revealing significant regurgitant flow. e Shows significant pulmonary regurgitation by 4D Flow CMR. f Demonstrates quantification of pulmonary regurgitant flow by 4D Flow CMR