Segmentation, using paint, the bulb of paint disappears instead of remaining

To understand what’s going on and why it is happening try these steps:

  1. Download MRHead and CT Chest sample datasets
  2. Right click on MRHead and choose “segment this”
  3. Create a single segment, and paint somewhere with a paint brush.
  4. While in segment editor, switch Source Volume from MRHead to CTChest
  5. Try to paint any region using Segment_1 and notice that everything you paint immediately disappears.

That’s because segmentation geometry is determined by the physical extends of the first volume you choose (MRHead). If the second volume has different physical dimensions, existing segmentation and the volume to be segmented does not overlap in physical space, so you can’t paint/segment anything.

In this example we blatantly choose very different volumes to demonstrate what’s going on. Their names are different, their regions are different etc. it may not be that obvious all the time. After double checking that the visibility settings and editable area settings are indeed correct, you can assume you have mismatch between segment geometry and the volume you are trying to segment and that you should double check your steps about how you created the segmentation in the first place.