Non-enhanced MRI flow evaluation using 4D versus 2D phase-contrast in repaired Tetralogy of Fallot adults.

Objectives: To describe the reliability of quantitative MRI analysis of flows using 4D-PC (Phase Contrast) compared to 2D-PC flow, without contrast agents.

Materials and methods: The study was conducted at one centre in a retrospective manner from 2021 to 2023. Eligible patients were adults with repaired Tetralogy of Fallot (rToF) whose follow-up MRI protocol included 4D-PC and 2D-PC, without contrast agent. Assessment involved quantitative measurement of aortic and pulmonary flows on both 4D and 2D. Student's T was used for comparisons of means and Lin's concordance correlation coefficient agreement (CCC). A 2nd observer was hired.

Results: Twenty-six patients were included (50% men, median age of 27 [20; 34]). Scanning mean time was 13 min for 4D and 47 min for non-4D part. Systematic underestimation in pulmonary regurgitation fraction (-10 ± 15%, p = 0.02) and backward volume (-13 ± 18 mL, p = 0.02) was found. Agreement on regurgitant fraction was strong for pulmonary (CCC = 0.75 [0.58-0.86], p < 0.001) and aortic (CCC = 0.91 [0.81-0.95], p < 0.001). Inter-observer showed overall strong results.

Conclusion: Non-enhanced 4D-PC flow MRI seems to be a reliable method of quantitative flow in rToF patients, but it may underestimate pulmonary regurgitation.

Key points: Question 4D-MRI stands out as an innovative tool for evaluating flows in adults with repaired Tetralogy of Fallot during follow-up. Findings 4D phase-contrast imaging without the use of contrast agents exhibits robust results and high reproducibility. Clinical relevance 4D-MR is presented as an accurate and versatile tool of cardiac exploration that could improve patient comfort. Minimizing brain gadolinium exposure and reducing scanning time are key objectives of non-enhanced 4D-MR.