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Background: Vortex formation time (VFT) had been considered a useful marker for assessing diastolic performance. the VFT assessment of diastolic function using four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has not been used in repair of tetralogy of Fallot (rTOF) patient. The aims of this study were as follows: (I) establish reference ranges for VFT measurements in healthy children and adolescents using 4D flow CMR imaging; and (II) analyze VFT parameters to assess diastole dysfunction in rTOF patients group., Methods: We acquired the CMR data was of 62 healthy participants (aged 6-18 years; male: 40, female: 22) and 20 patients with rTOF (aged 10-13 years; male: 15, female: 5) using 4D flow and cine sequence in routine chamber view. The VFT was calculated based on comparison of different algorithms from cine measurements (VFT volume ) and 4D flow measurements (VFT blood ). Then, VFT measurements were compared to subject peak filling rate (PFR), age, and cardiac mass using simple linear regression and multiple regression analyses. Data were also categorized according to age for VFT and cardiac functional assessment comparisons between 3 age groups (Group 1: 6-9 years; Group 2: 10-13 years; Group 3: 14-18 years). The correlation of VFT and cardiac function parameters were analyzed in the rTOF group., Results: Normal mean value of VFT volume and VFT blood were 4.25±0.92 and 3.77±1.11 in healthy children participants. The VFT volume was correlated with VFT blood (r=0.61, P<0.001). There was a moderately significant correlation between VFT volume and PFR (r=0.46, P<0.001) and between VFT blood and PFR (r=0.47, P<0.001), age (r=0.41, P=0.002) and left ventricular (LV) mass (r=0.48, P<0.001). Multiple regression analyses demonstrated that VFT volume was independently associated with PFR (T=2.239; P<0.05) and VFT blood (T=4.361; P<0.001). There was a significant difference in VFT volume between healthy controls and rTOF patients (5.44±1.93 vs. 4.27±0.88, P=0.018)., Conclusions: The VFT measurements showed that the LV that had appropriate space to form the optimal vortex ring in normal children and adolescents aged 6-18 years old. The VFT volume could potentially be helpful in improving our understanding of LV diastolic dysfunction in rTOF patients., Competing Interests: Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-22-67/coif). All authors report technical assistance from Gaston Vogel and Qiuchen Wang (Pie Medical Imaging Corporation Netherlands), and statistical assistance from Tingfan Wu (GE Healthcare). The authors have no other conflicts of interest to declare., (2022 Translational Pediatrics. All rights reserved.)