How to create new segmentation from growing margins

Support
1

Operating system: MacOS Monterey 12.2.1
Sliver version: 5.0.2

Hello. I am currently using 3D slicer for cardiac CT analysis. I’ve been currently struggling with trying to create a new segmentation for periatrial fat.
At this moment I have segmented the left atrium with the paint tool and filled between slices to gain a model of the left atrium, then I applied the margin tool to grow the segment with the editable intensity range with the hounsfield units for fat to select the periatrial fat.
However, I would like to create a separate segmentation for the periatrial fat (as in the image below), without including the left atrial segment. How can I “exclude” the left atrium from the periatrial fat segmentation?

segmentation example
segmentation example801×731 101 KB

2

You can either prevent going inside left atrium during segmentation by masking (Editable area → Outside al segments), or subtract one segment from the other using “Logical operators” effect.

3

Thank you! That is a much better (and simpler) solution than what I was trying to do :smile: