Can try these steps in a blank scene:
- Load MRHead sample data.
- Go to segment Editor and click on segment geometry button, and from the Source Geometry drop down choose ‘MRHead’. Set the oversampling to 2. Do you see something like this?
- Hit OK.
- Create a blank segment, and then threshold effect with 69.75-258.00 range and hit apply.
- Go to Segmentation Geometry again, and this time choose the segmentation as your source geometry. Confirm that you are seeing:
This oversampling of 2 for MRhead should not cause any noticeable delay or lag on your computer at all. If these work out, try with your data.