# 4D-Flow MRI Characterization of Pulmonary Flow in Repaired Tetralogy of Fallot
## 3 Results  
Subject baseline characteristics are reported in Table 3. The total population (_n_ = 37) included 20 controls and 17 rTOF patients. Baseline age was higher in controls as compared with patients (38 \(\pm\) 13 year vs. 29 \(\pm\) 13 year, \(p\) = 0.022). PA diameter was larger in rTOF patients as compared with controls (34 \(\pm\) 4 mm vs. 24 \(\pm\) 4 mm, \(p\) < 0.001). As showed in Table 3, LVEF was similar in both groups (60 \(\pm\) 4% vs. 62 \(\pm\) 4%, \(p\) = 0.353), but indexed LV volumes were lower in patients as compared with controls: LVEDVi (77 \(\pm\) 46 mL/m\({}^{2}\) vs. 111 \(\pm\) 46 mL/m\({}^{2}\), \(p\) = 0.006) and LVESVi (31 \(\pm\) 19 mL/m\({}^{2}\) vs. 42 \(\pm\) 19 mL/m\({}^{2}\), \(p\) = 0.044). Figure 2: Post-processing of 4D-flow. First, 4D-flow velocity field (Vi, Vi, Vk) was corrected (Panel (**A**)). Followed by data correction, the pulmonary artery was segmented for regional analysis. Several analysis planes were placed at specific landmarks for blood hemodynamic assessment: right ventricular outflow tract (RVOT), pulmonary valve, main pulmonary artery (MPA), pre-bifurcation, right pulmonary artery (RPA), and left pulmonary artery (LPA). Panel (**B**,**C**) shows a sample of wall shear stress at peak systole. Pressure drop used the RVOT plane as reference location (Panel (**D**)). Energy loss used a centerline to guide a top and a bottom plane (grey lines) to define the volume of interest, (Panel (**E**)). Panel (**F**) illustrates a sample of ventricular flow analysis distribution components. RVEF was significantly reduced in rTOF patients (46 \(\pm\) 3% vs. 54 \(\pm\) 3%, \(p\) < 0.001), whereas RV volumes were higher in rTOF patients (\(p\) < 0.05). However, rTOF patients did not have severe RV dilation (RV/LV volume ratio \(\geq\) 2.30). An example comparing velocity and flow patterns between a control and an rTOF patient is shown in Figure 3. Homogeneous velocity mapping and laminar flow are observed in the healthy control, Figure 3A. Anatomic differences in the rTOF patient can be observed in the MPA producing flow acceleration and unbalanced flow distribution in the RPA and LPA, shown in Figure 3B. The descending aorta also showed flow acceleration due to the development of aortic coarctation. Similarly, pathlines showed helical flow in both MPA and bifurcation, shown in Figure 3B. Figure 4 shows the 4D-flow assessment of total volume, peak velocity, and regurgitant fraction at the RVOT, pulmonary valve, MPA, RPA, and LPA. Total volume at the pulmonary valve was significantly elevated in the controls than in the rTOF (54 \(\pm\) 18% vs. 74 \(\pm\) 18%, \(p\) = 0.001, Figure 5A). In contrast, peak velocity and regurgitant fraction were significantly higher at all plane locations for the rTOF patients in comparison with the controls (\(p\) < 0.001, Figure 5B,C). Figure 4: \(Cont\). Figure 3: Comparison of velocity and flow patterns between a control and a patient with repaired Tetralogy of Fallow. Panel (**A**) shows homogeneous flow distribution in the velocity mapping (left) and laminar flow in the pulmonary artery and in the aorta (right). Panel (**B**) shows evidence of anatomic anomalies in the main pulmonary artery and aortic arch. These anomalies produced flow acceleration, as pointed by the light grey arrow in the pulmonary artery and the orange arrow in the aorta. Helical flow was also observed along the pulmonary artery, as pointed out by the dark grey arrows. A comparison of WSS plane measurements between a control and a patient with rTOF is illustrated in Figure 6. Figure 7 presents the results of the WSS evaluation in all planes along the PA. Patients with rTOF showed an elevated maximum WSS at the pulmonary valve, MPA, and pre-bifurcation (\(p\leq 0.05\)). Average WSS was consistently elevated along the PA at all plane locations (\(p\leq 0.05\)). In line with maximum WSS, pulmonary valve, MPA, and pre-bifurcation showed greater differences with controls (\(p\leq 0.001\)).