Overview of four-dimensional (4D)-flow scan. 4D-flow MRI involves acquiring three-directional velocity data in three-dimension (3D). These data can be then used offline to perform retrospective valve tracking to compute valvular flow. This method factors in valve motion, cardiac motion and allows direct regurgitant jet quantification as demonstrated in steps 3 and 4. 3D, three-dimensional; 4D, four-dimensional;CMR, cardiovascular magnetic resonance; FOV, field-of-view; FH, foot-head; RL, right-left; AP, anterior-posterior.