Accuracy of four-dimensional (4D) flow magnetic resonance imaging (MRI) in quantifying aortic regurgitation: a comparison with two- dimensional (2D) MRI and echocardiography

Abstract Background Aortic regurgitation (AR) is a common valvular disorder that may occur as an isolated lesion or alongside congenital heart disease (CHD). While transthoracic echocardiography (TTE) remains the primary imaging modality for diagnosing and grading AR, cardiovascular magnetic resonance (CMR) is increasingly used for its high accuracy in quantifying ventricular volumes and function. Traditional CMR relies on Two-Dimensional (2D) phase-contrast (PC) sequences with flow assessment limited to predefined planes. In hcontrast, Four-Dimensional (4D) flow CMR offers comprehensive volumetric coverage, enabling retrospective blood flow analysis at any location. This prospective study of 44 subjects (29 with AR and 15 healthy controls) aims to evaluate the diagnostic performance of 4D flow CMR in assessing aortic valve AR and to compare its performance with 2D-PC MRI and TTE. Results In AR patients, left ventricular parameters were significantly increased. Aortic regurgitant fraction (RF) values did not differ significantly between 2 and 4D flow MRI measured at levels of aortic valve and pulmonary artery. RF at aortic valve level was significantly lower than at supra-valvular levels. The highest concordance between 4D flow MRI and TTE for AR grading occurred at the pulmonary artery level. Conclusion 4D flow MRI provides reliable estimation of AR, with measurement of aortic RF at the pulmonary artery level showing the strongest agreement with echocardiographic grading, while measurement at aortic valve level tends to underestimate severity. These findings support pulmonary artery level assessment as the preferred site for accurate AR evaluation.