# Comparison of Manual versus Semi-Automatic Segmentations of the Stenotic Carotid Artery Bifurcation
## 3 Results
### Effect of Differences of Segmentation on Flow Analysis  
The overview of the results obtained from the CFD simulations can be seen in Figures 5 and 6. Velocity profiles were extracted at three locations and time-averaged WSS (TawSS) was calculated by cycle-averaging the last cycle of the simulation.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**ADDV vs.**} & \multicolumn{2}{c|}{**Group I.**} & \multicolumn{2}{c|}{**Group II.**} & \multicolumn{2}{c}{**Group III.**} \\  & & **Individual** & **Collective** & **Separate** \\ \hline \multirow{2}{*}{**Calcification**} & Corr. Coefficient & 0.59 & 0.19 & 0.71 \\ \cline{2-5}  & \(p\) & \(<\)0.001 & \(<\)0.0001 & \(<\)0.001 \\ \hline \multirow{2}{*}{**Calcification**} & Corr. Coefficient & 0.44 & \(-\)0.20 & 0.57 \\ \cline{2-5}  & \(p\) & \(<\)0.05 & \(<\)0.001 & \(<\)0.01 \\ \hline \multirow{2}{*}{**Calcification**} & Corr. Coefficient & 0.61 & 0.46 & 0.82 \\ \cline{2-5}  & \(p\) & \(<\)0.01 & \(<\)0.001 & \(<\)0.001 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Pearson correlation coefficients and \(p\) values calculated between ADDV (average diameter difference normalized by the voxel length) and calcification metrics in each group.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & \(\mathbf{D_{min\ AVG}}\) & \(\mathbf{D_{min\ AVG}}\) & \(\mathbf{Relative}\) & \(\mathbf{Relative}\) & \multirow{2}{*}{**Correlation**} & \(p\) \\  & **VascuCap** & **Slicer** & **Difference** & **Std** & & & \\ \hline  & **[mm]** & **[mm]** & **[\%]** & **[\%]** & **[–]** & **[–]** \\ \hline Group I. & 1.950 & 2.636 & 35.16 & \(\mp\)38.75 & 0.138 & \(<\)0.01 \\ \hline Group IL. & 1.815 & 2.178 & 19.99 & \(\mp\)27.92 & 0.680 & \(<\)0.05 \\ \hline Group III. & 1.883 & 2.067 & 9.80 & \(\mp\)36.47 & 0.084 & \(<\)0.25 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Results of the comparison of group averaged \(\mathrm{D_{min}}\) values between the two segmentation methods.  
The vicinity of the stenosis and the three locations can be seen on the left of Figure 6 for cases 010 and 042. At the systolic time instant, the velocity profile at the most stenotic location looks similar for both cases with small to negligible absolute differences. On the other hand, in the diastolic phase, qualitative differences are present as the shape of the profile varies. Other locations for both cases show similarities in the systolic phase that the velocity profiles look similar. However, major differences can occur in the diastolic phase, such as at the location P3 in Case 010 and locations P2 and P3 in Case 042.  
Figure 6 demonstrates that the TaWSS field near the stenosis globally looks similar, yet clear qualitative differences can be visualized between the semi-automatic and manual segmentation results, even in this cycle-averaged representation. Quantitatively, for the maximum TAWSS, 30% difference was measured for Case 010 (ADDV = 1.73), while for Case 042 (ADDV = 0.64) this difference can drop to 4%. Further evaluation was performed by mapping of the TaWSS distribution to a parametrized rectangular space [27] (illustrated as flattening in the middle panel of Figure 6). This space is suitable for comparisons, thus values on two lines were extracted which is essentially the comparison of two circumferences at different altitudes from the bifurcation. Both of them show that at the stenosis (Line 2), the values--obtained from the geometry created by  
Figure 5: Results of the CFD simulations for Case 010 (**a**) and Case 042 (**b**). Velocity profiles extracted in the systolic and diastolic time instants are colored orange and blue, respectively. Dashed and continuous lines correspond to the VascuCap (semi-automatic) and Slicer (manual) geometries. The profiles are plotted along the non-dimensional diameter length. CFD: Computational fluid dynamics.  
manual segmentation--considerably underestimate those obtained by the semi-automatic segmentation.