4D flow cardiovascular magnetic resonance (4D Flow CMR) enable time-varying and multidirectional comprehensive retrospective flow quantification in patients after repaired tetralogy of Fallot (TOF). This imaging modality must, however, prove its relevance compared to conventional CMR.

4D flow and 2D flow MRI were acquired using a clinical 1.5T MRI scanner (GE; GE Healthcare, Milwaukee, WI, USA). The 4D flow data were acquired in 18 patients after repair of TOF and in 5 healthy controls during free breathing using retrospectively ECG-gated and navigator-gated three-dimensional, three-directional phase contrast MRI (spatial resolution∼1.4mm, temporal resolution=33ms). Data analysis included the evaluation of haemodynamics in the aorta, the pulmonary trunk (TP), quantitative measurements of flow velocity, right ventricular volumes both by conventional 2D CMR and 4D Flow.

Eighteen patients with TOF underwent 2D CMR and 4D Flow CMR (mean age 31±13 years, mean size 168±13cm, mean weight 56.2±13.4kg). Among them 12 patients had complete evaluation including flow and ventricular volumes. The mean systolic ejection volume was 109±44mL; the mean right ventricle systolic function was 55±12%. The mean end-diastolic right ventricle volume was respectively 185±66mL by 2D CMR, and 200±68mL using 4D Flow. The mean pulmonary regurgitation fraction was respectively 39±18% by 2D CMR, and 32±18% using 4D Flow. Pulmonary regurgitation fraction was almost interchangeable according to the Pearson's coefficient (r²=0.9, P<0.001) and the Bland–Altman analysis (COV 87%; 95% limits of agreement [−4.5; 2.8]). There was a good agreement about end-diastolic right ventricle volume (r²=0.3, P=0.02) and as shown in the Bland–Altman analysis (COV 61%; 95% limits of agreement [−46; 15]).

Based on our experience, 4D Flow imaging can be clinically helpful especially in TOF, compared to 2D CMR. Despite some biases, our results shows good accuracy compared to conventional 2D CMR. Further studies are needed to validate our first conclusions.