The present prospective study was designed to evaluate the accuracy of quantitative assessment of mitral regurgitant fraction (MRF) by echocardiography and cardiac magnetic resonance imaging (cMRI) in the modern era using as reference method the blinded multiparametric integrative assessment of mitral regurgitation (MR) severity. 2-Dimensional (2D) and 3-dimensional (3D) MRF by echocardiography (2D echo MRF and 3D echo MRF) were obtained by measuring the difference in left ventricular (LV) total stroke volume (obtained from either 2D or 3D acquisition) and aortic forward stroke volume normalized to LV total stroke volume. MRF was calculated by cMRI using either (1) (LV stroke volume - systolic aortic outflow volume by phase contrast)/LV stroke volume (cMRI MRF [volumetric]) or (2) (mitral inflow volume - systolic aortic outflow volume)/mitral inflow volume (cMRI MRF [phase contrast]). Six patients had 1 + MR, 6 patients had 2 + MR, 12 patients had 3 + MR, and 10 had 4 + MR. A significant correlation was observed between MR grading and 2D echo MRF (r = 0.60, p <0.0001) and 3D echo MRF (r = 0.79, p <0.0001), cMRI MRF (volumetric) (r = 0.87, p <0.0001), and cMRI MRF (phase contrast r = 0.72, p <0.001). The accuracy of MRF for the diagnosis of MR ≥3+ or 4+ was the highest with cMRI MRF (volumetric) (area under the receiver-operating characteristic curve [AUC] = 0.98), followed by 3D echo MRF (AUC = 0.96), 2D echo MRF (AUC = 0.90), and cMRI MRF (phase contrast; AUC = 0.83). In conclusion, MRF by cMRI (volumetric method) and 3D echo MRF had the highest diagnostic value to detect significant MR, whereas the diagnostic value of 2D echo MRF and cMRI MRF (phase contrast) was lower. Hence, the present study suggests that both cMRI (volumetric method) and 3D echo represent best approaches for calculating MRF.
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