## 3 Results
### Assessment of Intensity Variability and Segmentation Performance
#### 3.2.1 Comparison Between Bias Field Correction Methods  
To assess if there were statistically significant differences between RBVs when employing different BFC methods (SPM-BFC and N4 ITK), the Wilcoxon signed-rank test was applied to the volumes obtained with each BE method (Table 3).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Brain Tissue**} & \multirow{2}{*}{**Bias Field Correction**} & \multicolumn{5}{c}{**Brain Extraction Method**} \\ \cline{3-6}  & & **Manual** & **BET2** & **SWS** & **HD-BET** & **SynthStrip** \\ \hline \multirow{4}{*}{Cerebellum} & SPM-BFC & 27.0 \(\pm\) 3.5 & 27.1 \(\pm\) 3.4 & 25.8 \(\pm\) 3.5 & 26.8 \(\pm\) 3.3 & 26.8 \(\pm\) 3.4 \\  & & 26.9 & 27.0 & 25.2 & 26.5 & 26.5 \\ \cline{2-6}  & \multirow{2}{*}{N4 ITK} & 26.9 \(\pm\) 3.4 & 27.1 \(\pm\) 3.3 & 25.8 \(\pm\) 3.5 & 26.8 \(\pm\) 3.2 & 26.8 \(\pm\) 3.3 \\  & & 26.2 & 26.8 & 25.4 & 26.4 & 26.5 \\ \hline \multirow{4}{*}{Brainstem} & SPM-BFC & 6.5 \(\pm\) 0.8 & 6.4 \(\pm\) 0.7 & 6.5 \(\pm\) 0.7 & 6.3 \(\pm\) 0.7 & 6.4 \(\pm\) 0.7 \\  & & 6.3 & 6.3 & 6.5 & 6.1 & 6.2 \\ \cline{2-6}  & \multirow{2}{*}{N4 ITK} & 6.4 \(\pm\) 0.7 & 6.3 \(\pm\) 0.7 & 6.4 \(\pm\) 0.7 & 6.2 \(\pm\) 0.7 & 6.3 \(\pm\) 0.7 \\  & & 6.3 & 6.2 & 6.3 & 6.1 & 6.1 \\ \hline \end{tabular}
\end{table}
Table 2: _Cont._  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Brain Tissue** & **Brain Extraction Method** & **Z** & **_p_** \\ \hline \multirow{4}{*}{Critical Grey Matter} & Manual & \(-\)3.703 & \textless{}0.001 * \\ \cline{2-5}  & BET2 & \(-\)3.329 & \textless{}0.001 * \\ \cline{2-5}  & SWS & \(-\)3.524 & \textless{}0.001 * \\ \cline{2-5}  & HD-BET & \(-\)3.053 & 0.002 * \\ \cline{2-5}  & SynthStrip & \(-\)3.052 & 0.002 * \\ \hline \multirow{4}{*}{White Matter} & Manual & \(-\)3.739 & \textless{}0.001 * \\ \cline{2-5}  & BET2 & \(-\)1.844 & 0.065 \\ \cline{2-5}  & SWS & \(-\)3.634 & \textless{}0.001 * \\ \cline{2-5}  & HD-BET & \(-\)3.287 & 0.001 * \\ \cline{2-5}  & SynthStrip & \(-\)2.348 & 0.019 * \\ \hline \multirow{4}{*}{Cerebral Spinal Fluid} & Manual & \(-\)3.268 & \textless{}0.001 * \\ \cline{2-5}  & BET2 & \(-\)2.975 & 0.003 * \\ \cline{2-5}  & SWS & \(-\)2.018 & 0.044 * \\ \cline{2-5}  & HD-BET & \(-\)2.439 & 0.015 * \\ \cline{2-5}  & SynthStrip & \(-\)2.868 & 0.004 * \\ \hline \multirow{4}{*}{Deep Nuclear Grey Matter} & Manual & \(-\)1.575 & 0.115 \\ \cline{2-5}  & BET2 & \(-\)2.208 & 0.027 * \\ \cline{1-1} \cline{2-5}  & SWS & \(-\)1.947 & 0.052 \\ \cline{1-1} \cline{2-5}  & HD-BET & \(-\)1.596 & 0.110 \\ \cline{1-1} \cline{2-5}  & SynthStrip & \(-\)1.656 & 0.098 \\ \hline \end{tabular}
\end{table}
Table 3: Wilcoxon signed-rank test statistics (_Z_ and _p_-value (_p_)) for evaluating the differences regarding regional segmentation volumes when using two BFC methods (SPM-BFC and N4 ITK) for each of the five BE methods (Manual, BET2, SWS, HD-BET, and SynthStrip).  
Table 3 showed that the use of different BFC methods results in statistically significant changes in RBVs, for several BE methods: CGM (all); WM (all, except BET2 with \(p\) = 0.065); CSF (all); DNGM (BET2, \(p\) = 0.027); Hip (BET2, \(p\) = 0.019); Amy (Manual, \(p\) = 0.013; BET2, \(p\) = 0.035); CB (none); and BS (all).