# Segmenting only within a ROI

**URL:** <https://discourse.slicer.org/t/segmenting-only-within-a-roi/46129>\
**Category:** Support\
**Tags:** segmentation\
**Created:** [February 12, 2026, 7:05am UTC](https://discourse.slicer.org/t/segmenting-only-within-a-roi/46129 "2026-02-12T07:05:17Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![jamie.miller.phd](https://avatars.discourse-cdn.com/v4/letter/j/c57346/32.png) [@jamie.miller.phd](https://discourse.slicer.org/u/jamie.miller.phd)\
**Post date:** [February 12, 2026, 7:05am UTC](https://discourse.slicer.org/t/segmenting-only-within-a-roi/46129/1 "2026-02-12T07:05:17Z")

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Hi team, I am a novice user of 3D Slicer and trying to upskill. I have MRI images of the upper airway and I am trying to segment out only the airways (nasal and oral cavities). I have been using the threshold masking to some success, however the threshold of the air I am segmenting is the same as the image background and other areas of the head I do not wish to segment. I want to use a different threshold for the nasal airways than the oral airway. I thought it might be handy to create a ROI around the nasal airways and restrict my segmentation to that but I haven’t figured out how to segment only within the ROI i have made. Any help greatly appreciated