Hello, I am working on lesion segmentation and need to extract a clean 2-mm peri-lesional bone shell for texture/fractal analysis.
The problem is: when I click “Add” to create a new segment (e.g. Segment_2), Slicer still keeps modifying Segment_1 only. Even if I manually select Segment_2 and apply “Margin” (2 mm) or “Logical Operators → SUBTRACT”, Slicer always changes Segment_1 — and Segment_2 does not update at all.
What I have tried:
• Set Application Settings → Segmentations → “Default overwrite mode” = Allow overlap
• Manually selected the segment (Segment_2) before applying Margin
• Confirmed I am in the Segment Editor, not Segmentations
• Tried both 2D slice views and 3D view
• Restarted Slicer
Still, every operation affects only Segment_1.
My goal:
I want to duplicate the original lesion as Segment_2, expand it by exactly +2 mm (Margin effect), then subtract the original lesion (Segment_1) to isolate only the hollow peri-lesional shell.
What could still be forcing Slicer to always keep Segment_1 active, even after adding and selecting a new segment?
Is there any UI or masking setting I might still be missing?
If needed, I can provide a quick screen recording. Thank you in advance.