4D Flow MRI-Based Quantification of Tricuspid Regurgitation: A Possible Approach to Improve Measurement Repeatability

To address limitations in tricuspid regurgitation (TR) quantification by magnetic resonance imaging (MRI) or transthoracic echocardiography (TTE), a new method is proposed to directly quantify TR volume (TR_V) using 4D Flow MRI with retrospective tricuspid valve (TV) annular tracking.

Thirty patients with TR were prospectively enrolled. TR_V was quantified using four MRI-based methods: (i) indirect, (ii) direct (2D phase-contrast), (iii) 4D Flow with a static TV plane, and (iv) 4D Flow with dynamic annular tracking. Reproducibility and agreement were assessed in terms of TR grading against standard MRI- and TTE-based methods.

The dynamic 4D Flow method correlated strongly with all other MRI methods (r = 0.77-0.81, p < 0.0001) but consistently yielded higher TR_V values. Compared with the indirect method, it showed a Bland-Altman bias of 16 mL (limits of agreement: -19 to 51 mL), along with the highest agreement (intraclass correlation coefficient of 0.88). Agreement in TR severity grading was poor across methods (kappa ≤ 0.07), with dynamic 4D Flow classifying more cases as moderate or severe. Agreement with TTE was slight (kappa = 0.17, p = 0.27) with concordant TR grading in 50% of patients. Inter-observer reproducibility was excellent (r = 0.99, bias = 0.7 mL, kappa = 0.80).

4D Flow with dynamic TV tracking offers a reproducible and potentially more sensitive method for TR_V quantification than conventional MRI techniques. Despite limited alignment with TTE, this technique may help overcome key imaging limitations and improve TR clinical evaluation, especially in complex cases.