4D Flow Yields Similar Clinical Results Compared To 2D Phase Contrast for Decision Making Regarding Pulmonary Valve Replacement in Repaired Tetralogy of Fallot

2D phase contrast (PC) CMR is critical for monitoring pulmonary regurgitant fraction (PRF) in patients with a history of repaired tetralogy of Fallot (rTOF) and guides decisions about pulmonary valve replacement (PVR). However, newer techniques such as 3D time-resolved phase contrast (4D flow) MRI are gaining momentum due to the added clinical value beyond conventional flow metrics. While agreement between 2D PC CMR and 4D flow is well-established, the real-world implications for clinical decision-making have not been fully studied and are thus the primary aim of this study. All patients with rTOF who underwent standard CMR plus retrospectively gated 4D flow between February 2021 – June 2023 were identified. Clinical information was collected from the electronic medical record (EMR). 2D cine steady-state free procession (SSFP), PC data, and 4D flow imaging data were analyzed using standard post-processing analysis. Clinical decisions (“intervention vs. no intervention”) were determined using a standardized algorithm, and inter-rater agreement was assessed using the intra-class coefficient (ICC) and the coefficient. 33 patients were included. PRF correlated strongly between 2D PC and 4D flow ( r  = 0.87, r _s = 0.89) and between 4D flow and volumetric SSFP analysis ( r  = 0.81, r _s = 0.79). The mean absolute difference between 2D and 4D PRF was − 3.76% (95% CI [-6.91, -0.60]) with an ICC of 0.83. Inter-rater agreement for the decision was moderate ( =0.58) using only PRF calculated only using 2D PC and 4D flow, and was strong ( =0.76) when using PRF calculated by 2D PC and 4D flow with volumetric PRF. Though clinical indications for PVR in rTOF vary, 4D flow generates accurate measurements of PRF and yields similar clinical decisions about intervention in rTOF. Future studies exploring ventricular volume assessment by 4D flow could potentially eliminate the need for cine SSFP acquisitions and lead to a shorter, more comprehensive CMR exam for TOF patients.