# Whole-Heart Assessment of Turbulent Kinetic Energy in the Repaired Tetralogy of Fallot
## 4 Discussion  
This study demonstrated that TKE may impact the entire heart throughout the cardiac cycle. Patients with rTOF showed abnormal TKE changes in all chambers, providing further insight into the hemodynamic alterations of the entire heart for this patient cohort. Our main findings showed that controls exhibit higher TKEmean and TKEmax in both the LA and LV compared to patients. This may be due to defects that are mostly observed on the right side of the heart. In addition, we may observe this difference because patients with rTOF may also exhibit slower velocities in these vessels compared to controls. Hence, this may have led to lower values of TKE, as observed in this study. Furthermore, this study did observe higher values of both TKEmean and TKEmax in the RV in patients compared to controls. These results were similar to previously reported findings in energetic changes on rTOF, as compared with controls [2]. Therefore, this may suggest that patients with rTOF may have an imbalance of velocities between left- and right-sided chambers of the heart, leading to higher velocities on the right and resulting in elevated TKE values in the RV. In the current study, we derived TKE from a whole-heart 4D-flow MRI acquisition in adult patients. It is important to remark that this type of acquisition can also be performed in pediatric patients by adjusting the spatial resolution and velocity-encoding parameters [5]. In adults, a spatial resolution of 2.5-3.0 mm\({}^{3}\) is recommended; in pediatric populations, 1.5 mm\({}^{3}\) is recommended, and 0.75-1.0 mm\({}^{3}\) is recommended in neonates. The advantages of 4D-flow MRI in neonatal and pediatric populations over standard 2D phase-contrast are well-documented [31,32]. The advances in acceleration techniques reached clinically acceptable scan times, and the possibility of free-breathing protocols and the use of feed and wrap have become more practical for diminishing emotional stress [33]. However, the use of sedation and anesthesia is still clinical routine for facilitating the exam [34,35]. In both adult and pediatric patients, motion artifacts can impact the accuracy of the 4D-flow acquisition. Respiratory motion is usually well managed by using a respiratory navigator,  
Figure 5: Turbulent kinetic energy in the left ventricle and right ventricle. Mean turbulent kinetic energy (TKE) and max TKE were calculated throughout the entire cardiac cycle, including peak systole (PS), average systole (avg systole), average diastole (avg diastole), and total cardiac cycle (TCC) in the Left Ventricle (LV) and Right Ventricle (RV) for both patients and controls. Panels (**A**,**B**) show the mean TKE and the max TKE in the LV throughout the entire cardiac cycle for controls and patients. Panels (**C**,**D**) show the mean TKE and the max TKE in the RA throughout the entire cardiac cycle for controls and patients. Statistical significance between the two cohorts was only observed in the RV at PS, avg systole, and avg diastole (*: \(p<0.05\)). as we used in our study cohort. Novel free-breathing methods manage motion effects within the image acquisition framework [36, 37]. However, large motion effects cannot be effectively corrected. TKEmax was also shown to be elevated in the PA within patients compared to controls throughout the entire cardiac cycle. This may be due to the fact that PR is observed within this patient cohort [38]. This relates to how we observed elevated TKE in the RV, as previous studies demonstrated that PR significantly impacts the flow in the RV [39]. Unfortunately, not many studies evaluated TKE in patients with rTOF, but some studies demonstrated elevated KE in the RV and PA compared to controls [40]. In particular, [PERSON] et al. highlighted the potential clinical value of TKE in the development of late complications after TOF repair and the importance of follow-up [22]. TKE comes to provide additional information beyond the heart function and strain characterization that can be achieved with a standard-of-care ultrasound and MRI.