# Impact of Respiratory Gating on Hemodynamic Parameters from 4D Flow MRI
## 3 Results  
Figure 1 shows a representative case of the hemodynamic parameters in the aorta that was obtained from respiratory and non-respiratory gated 4D flow MRI data. By visual inspection, the images look similar. Nevertheless, differences can be observed in the WSS, viscous dissipation, energy loss, and kinetic energy. Table 2 shows the mean and CV obtained for each hemodynamic parameter at each section of the aorta. The mean of the hemodynamic parameters was similar in section I, but it showed differences in the other sections. Further, the CV values were greater in the 4D flow data acquired without respiratory self-gating compared to the self-gated data. The CV values were greater in section I. \begin{table}
\begin{tabular}{l c} \hline \hline \multicolumn{1}{c}{**Parameter**} \\ \hline Field of view, mm & \(236\times 226\times 134\) \\ Voxel size, mm & \(2.34\times 2.34\times 2.5\) \\ Cardiac phases & \(25\) \\ VENC, cm/s & \(250\) \\ Echo time, ms & \(2.66\) \\ Repetition time, ms & \(4.78\)–\(4.80\) \\ Flip angle & \(5^{\circ}\) \\ \hline  & Self-Gated & Non-Gated \\ \hline Temporal resolution, ms & \(37.62\pm 4.43\) & \(36.11\pm 4.18\) \\ Heart rate, bpm & \(66.33\pm 7.62\) & \(67.93\pm 8.03\) \\ Acquisition time, min & \(15.00\pm 2.86\) & \(12.33\pm 0.37\) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: The MRI acquisition parameters. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**Section I**} & \multicolumn{2}{c}{**Section II**} \\ \hline \multirow{2}{*}{**Hemodynamic Parameter**} & **Self-Gated** & **Non-Gated** & **Self-Gated** & **Non-Gated** \\  & **Mean (CV)** & **Mean (CV)** & **Mean (CV)** & **Mean (CV)** \\ \hline Velocity (m/s) & 0.686 (0.197) & 0.652 (0.251) & 0.571 (0.159) & 0.527 (0.204) \\ WSS (N/m\({}^{2}\)) & 1.320 (0.186) & 1.265 (0.245) & 1.165 (0.138) & 1.092 (0.209) \\ WSSA (N/m\({}^{2}\)) & 1.308 (0.187) & 1.252 (0.242) & 1.157 (0.135) & 1.084 (0.208) \\ WSSC (N/m\({}^{2}\)) & 0.121 (0.343) & 0.122 (0.505) & 0.101 (0.333) & 0.094 (0.302) \\ Vorticity (1/s) & 45.549 (0.310) & 45.838 (0.330) & 42.008 (0.345) & 39.730 (0.370) \\ Viscous Dissipation (1/s\({}^{2}\)) & 4.569 (0.394) & 4.826 (0.590) & 3.047 (0.377) & 2.611 (0.370) \\ Kinetic Energy (\(\mu\)J) & 0.258 (0.404) & 0.271 (0.601) & 0.172 (0.386) & 0.147 (0.384) \\ Energy Loss (\(\mu\)W) & 4.303 (0.392) & 4.002 (0.479) & 2.976 (0.324) & 2.572 (0.401) \\ \hline \multicolumn{4}{c}{**Section III**} & \multicolumn{2}{c}{**Section IV**} \\ \hline \multirow{2}{*}{**Hemodynamic Parameter**} & **Self-Gated** & **Non-Gated** & **Self-Gated** & **Non-Gated** \\  & **Mean (CV)** & **Mean (CV)** & **Mean (CV)** & **Mean (CV)** \\ \hline Velocity (m/s) & 0.558 (0.205) & 0.501 (0.318) & 0.528 (0.277) & 0.445 (0.375) \\ WSS (N/m\({}^{2}\)) & 1.230 (0.198) & 1.099 (0.318) & 1.224 (0.268) & 1.027 (0.384) \\ WSSA (N/m\({}^{2}\)) & 1.228 (0.198) & 1.096 (0.319) & 1.222 (0.268) & 1.024 (0.385) \\ WSSC (N/m\({}^{2}\)) & 0.048 (0.314) & 0.049 (0.316) & 0.047 (0.254) & 0.051 (0.330) \\ Vorticity (1/s) & 35.541 (0.258) & 32.558 (0.306) & 41.900 (0.312) & 34.369 (0.287) \\ Viscous Dissipation (1/s\({}^{2}\)) & 1.999 (0.471) & 1.753 (0.580) & 2.394 (0.643) & 1.803 (0.545) \\ Kinetic Energy (\(\mu\)J) & 0.112 (0.477) & 0.097 (0.588) & 0.132 (0.637) & 0.099 (0.553) \\ Energy Loss (\(\mu\)W) & 2.995 (0.410) & 2.523 (0.579) & 2.873 (0.510) & 2.184 (0.642) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The hemodynamic parameter means and the coefficient of variation (CV) of the mean values at each section of the vessel for the self-gated and non-gated data, which were measured at a representative peak systolic cardiac phase. Figure 1: The hemodynamic parameters obtained from 4D flow MRI, both with and without self-gating. In this figure, we show visual representations of the hemodynamic parameters for one volunteer, which were measured at a representative peak systolic cardiac phase. Table 3 shows the results obtained from the statistical analysis.