## 3 Results
### The 3D Thresholding Error  
Verification results of the optically scanned dry skull are presented in Table 5. The results verified that the standard STL surface, generated by GOM ATOS (Professional 2016, GOM GmbH, Braunschweig, Germany) software, contained an appropriate mesh size. The results reached steady state values from 3 rd to 6 th iterations. The results of the standard STL mesh size are within 0.166 % of the mean distance and 1.094 % of the standard deviation for the final iteration. The thresholding error, including relatively negligible CT imaging error, of the verified standard mesh size is shown in Figure 4. The legend contains a range of the distance deviations. The red color code depicts the segmented surface above the optically scanned surface, the green color code denotes the segmented surface with no deviations, and the blue color code represents the segmented surface below the optically scanned surface. In addition, the legend contains a histogram to graphically represent the frequency of the deviations. In this case, the histogram shows asymmetric deviations that skew to the left (negatively skewed). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Sensitivity Analysis of the SD Skull**} \\ \hline \multirow{2}{*}{**Iteration**} & \multicolumn{2}{c}{**Optically Scanned Dry Skull Mesh (STL) Properties**} & \multicolumn{2}{c}{**Mean Distance**} & \multicolumn{2}{c}{**Standard**} & \multicolumn{2}{c}{**Difference [\%]**} \\ \cline{2-7}  & \multicolumn{1}{c}{**Max. Edge Length [mm]**} & \multicolumn{1}{c}{**Number of Triangles [-]**} & \multicolumn{1}{c}{**Number of Points [-]**} & \multicolumn{1}{c}{**Deviation [mm]**} & \multicolumn{1}{c}{**Deviation**} & \multicolumn{1}{c}{**Mean**} & \multicolumn{1}{c}{**Standard**} \\ \hline Standard & - & 988577 & 502772 & 0.602 & 0.914 & - & - \\ \hline
1 & 1 & 1147107 & 582037 & 0.620 & 0.891 & 2.990 \% & 2.516 \% \\ \hline
2 & 0.5 & 1915921 & 966444 & 0.621 & 0.863 & 3.156 \% & 5.580 \% \\ \hline
3 & 0.1 & 2940303 & 1478635 & 0.602 & 0.907 & 0.000 \% & 0.766 \% \\ \hline
4 & 0.05 & 8809479 & 4413223 & 0.602 & 0.905 & 0.000 \% & 0.985 \% \\ \hline
5 & 0.01 & 26428255 & 13222611 & 0.601 & 0.906 & \(-\)0.166 \% & 0.875 \% \\ \hline
6 & 0.005 & 79284523 & 39650745 & 0.603 & 0.904 & 0.166 \% & 1.094 \% \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The mesh sensitivity analysis of the SD skull surface with respect to the segmented SD head surface. Figure 3: The quality assurance Phantom for examining the MSCT imaging error. The thresholding error of the SD head for all protocols and thresholding values is shown in Figure 5. The vertical axis shows the mean distance between the segmented SD head as a function of the CT protocols and Hounsfield units compared to the optically scanned dry skull. The horizontal axis depicts four CT protocols. The legend contains a shade plot of the thresholding values. The error bars represent a standard deviation. A maximum allowable distance of 4 mm ensured that all the data points were within the computational range of the surface comparison. The mean distance represents a central arithmetic average of all points of the surface comparison. The standard deviation evaluates the spread of the mean distance. According to the results shown in Figure 5, as the thresholding value increases, the mean distance decreases and the standard deviation increases. Estimating the optimal CT protocol and thresholding  
Figure 4: The thresholding error of the segmented SD head on the dry skull with the verified mesh size. Figure 5: The thresholding error of the segmented SD head as a function of the CT Protocols and Hounsfield units with respect to the optically scanned dry skull (blue). value based on these relationships alone was deemed trivial. To this end, Table 6 lists the additional parameters of the surface comparison results. The area of valid distance is the reference surface area that is used for the comparison. The integrated distance is the inscribed volume of the surface comparison.