## 3 Results
### Local Evaluation of Ventricle Segmentations  
Figure 3A demonstrates that the nnU-Net model generally showed a low median difference and a low range in the differences between the GT and across most of the ventricle structure, indicating overall acceptance of the DL-generated segmentations. However, in the left and right temporal horns of the lateral ventricles, a low median difference paired with a high range suggests substantial interobserver variability in the differences between GT and nnU-Net segmentation. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & MODEL & DSC [index] & HD95 [mm] & Surface DSC [index] & APL [mm] & Volume GT [cm\({}^{3}\)] & Volume Segmentation [cm\({}^{3}\)] \\ \cline{2-7}  & nnU-Net & 0.93 (0.86–0.95) & 0.9 (0.7–2.5) & 0.97 (0.90–0.98) & 876 (407–1298) & 26.0 (9.1–52.8) & 25.0 (92.7–56.9) \\ \cline{2-7}  & SynthSeg & 0.85 (0.67–0.91) & 2.2 (1.7–4.8) & 0.84 (0.70–0.89) & 2809 (2311–3622) & 26.0 (9.1–52.8) & 24.1 (8.8 –60.3) \\ \hline  & nnU-Net & 0.84 (0.69–0.89) & 2.1 (1.6–5.8) & 0.75 (0.63–0.84) & 3653 (2612–5667) & 29.7 (15.3–56.9) & 22.9 (10.0–48.5) \\ \cline{2-7}  & SynthSeg & 0.83 (0.63–0.89) & 2.9 (2.2–7.6) & 0.73 (0.55–0.78) & 4562 (3373–5280) & 29.7 (15.3–56.9) & 25.0 (9.8–56.0) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Segmentation results from the nnU-Net and SynthSeg models on the internal and external test set reported as median (range). Figure 3B displays that for the SynthSeg model on the internal test set, a low median difference with a low range was observed, further indicating general acceptance of the  
Figure 3: Differences in median values and the 10–90 percentile range displayed on the reference shape of the ventricles. Positive differences indicate an outward deviation of the automated segmentation compared to the GT. The 10–90 percentile range illustrates the variability of the differences between the automated segmentations and the GT across a patient population. (**A**) nnU-Net results from the internal test set; (**B**) SynthSeg results from the internal test set; (**C**) nnU-Net results from the external test set; (**D**) SynthSeg results from the external test set. automated segmentations. However, a region of low median difference with a high range is apparent in the middle of the left and right temporal horns of the lateral ventricles, as well as in the occipital horn of the lateral ventricles, which again points to relatively high interobserver variability in the differences between the GT and the SynthSeg contours. An example of an internal test set patient where both the nnU-Net and the SynthSeg model failed to segment the central region of the left and right temporal horn of the lateral ventricles is displayed in Figure 4A. Figure 3C displays that the nnU-Net model showed a high median difference and a wide range in the central region of the left and right temporal horns of the lateral ventricles, suggesting that the model frequently failed to accurately segment this region on the external test set. Additionally, the occipital horns of the lateral ventricle and the inferior region of the third ventricle exhibited a low median difference with a high range, suggesting substantial interobserver variability in the differences between GT and nnU-Net segmentation for this anatomical region. Figure 3D displays that on the external test set, where the SynthSeg model has a low median and high range in the central region of the left and right temporal horns of the lateral ventricles, as well as in the caudal part of the third ventricle and the cerebral aqueduct. The low median and high range suggest substantial interobserver variability in the differences between GT and SynthSeg segmentations for these anatomical regions. In addition, Figure 3D displays a high median difference and a wide range in the occipital horn of the lateral ventricles, suggesting that the SynthSeg model often failed in segmenting this region accurately.