Explore the Two-Phase Approach for the instance segmentation

[valosekj]

We are now thinking about training a single model segmenting both cervical and lumbar rootlets. As the training of such a model might be problematic (due to the number of classes: cervical + lumbar rootlets), we could explore the Two-Phase Approach as done in SPINEPS. First, we would do binary segmentation of the rootlets, followed by instance segmentation (i.e., labeling of C2, C3, ..., L1, L2, ...). Alternatively, the first step could include two classes (aka groups: cervical and lumbar rootlets).