4D Flow versus Conventional 2D MRI for Measuring Pulmonary Flow after Tetralogy of Fallot Repair

Abstract

After tetralogy of Fallot (TOF) repair, pulmonary regurgitation and right ventricular function must be monitored. Conventional (2D) cardiac magnetic resonance (CMR) is currently the clinical reference method for measuring pulmonary regurgitation. However, 4D CMR has been reported to provide a more comprehensive flow analysis than 2D CMR. We aimed to compare 4D CMR to 2D CMR for assessing pulmonary regurgitation and flow, as well as aortic flow, in children and adults after surgical repair of TOF. Retrospective analysis of patients with repaired TOF admitted for cardiac MRI with 4D flow acquisition from 2016 to 2018. Linear regression was used to assess correlations and Bland-Altman analyses were performed. The 60 included patients had a mean age of 18.2 ± 10.4 years (range, 2-54 years). Significant correlations between the two techniques were found for pulmonary regurgitant fraction (R 2 = 0.6642, P < 0.0001), net pulmonary flow (R 2 = 0.6782, P < 0.0001), forward pulmonary flow (R 2 = 0.6185, P < 0.0001), backward pulmonary flow (R 2 = 0.8192, P < 0.0001), and aortic valve flow (R 2 = 0.6494, P < 0.0001). The Bland-Altman analysis showed no significant bias, narrow limits of agreement, and few scattered points. The correlation between pulmonary and aortic flow was better with 4D CMR than with 2D CMR (R 2 = 0.8564, P < 0.0001 versus R 2 = 0.4393, P < 0,0001, respectively). Interobserver reliability was good. These results establish the feasibility and reliability of 4D CMR for assessing pulmonary flow in a large paediatric and adult population with repaired TOF. 4D CMR may be more reliable than 2D MRI for pulmonary flow assessment after TOF repair.