Regurgitant volume (Rvol) measured using the indirect method (left), four-dimensional (4D) flow MRI in combination with valve tracking (middle), and 4D flow MRI in combination with flow tracking (right), divided into classes of severity on the basis of semiquantitative echocardiographic findings. Black horizontal lines represent Rvol means per severity class. Dashed red lines indicate cutoff values for mild mitral valve (MV) regurgitation (Rvol <30 mL), moderate MV regurgitation (Rvol 30–59 mL), and severe MV regurgitation (Rvol >60 mL) used in quantitative echocardiography. Adoption of these cutoff values would cause most moderate and severe MV regurgitation cases to be reclassified to a lower class. Inset contingency tables provide comparison of MRI-based severity classification resulting from cutoff values of 30 and 60 mL with echocardiography-based classification. Neither flow tracking nor valve tracking or the indirect method enable a sharp distinction among the severity groups.