Implement Tissue Segmentation (FSL-FAST)

[nx10]

Segment brain into CSF, GM, WM using FSL FAST.

• Create src/rbc/core/anatomical/segmentation.py
• Run FSL FAST: img_type=1, segments=True, probability_maps=True
• Threshold at 0.95 for CSF, WM, GM
• Integrate into workflows/anatomical.py
• Unit tests for thresholding
• Integration test (~2-3 min, mark as slow)

Outputs: label-{CSF,GM,WM}_mask, label-{CSF,GM,WM}_probseg

Reference: Step 4: Tissue Segmentation

[kaitj]

I would actually rename the skull_stripping.py to segmentation.py since it is in theory a "segmentation" of the brain. But that is a small thing.

[nx10]

Not sure I'm following - it does say segmentation.py already?

[kaitj]

Sorry - was more of a mental note for myself. The current brain extraction sits in skull_stripping.py in the anatomical draft PR