# isotropic expansion

**URL:** <https://discourse.slicer.org/t/isotropic-expansion/39492>\
**Category:** Support\
**Tags:** segmentation, extensions-manager, segmentations, segment-editor, extension-manager\
**Created:** [October 2, 2024, 12:29pm UTC](https://discourse.slicer.org/t/isotropic-expansion/39492 "2024-10-02T12:29:22Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Farah\_BH](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/farah_bh/32/78099_2.png) [@Farah\_BH](https://discourse.slicer.org/u/Farah_BH)\
**Post date:** [October 2, 2024, 12:29pm UTC](https://discourse.slicer.org/t/isotropic-expansion/39492/1 "2024-10-02T12:29:22Z")

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Hello, I’m trying to expand isotropically a ROI using grow/shrink. The problem is my voxel size is anisotropic [0.9,0.9,2.5] and I want to do a 2 mm expansion which is not possible using slicer segment editor (as shown in the image) . Also I want understand how this growing of ROIs work in 3D Slicer  
 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/4/8/48951b717280585ae86f33fc1eac9267df83543e.png)

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**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [October 2, 2024, 12:34pm UTC](https://discourse.slicer.org/t/isotropic-expansion/39492/2 "2024-10-02T12:34:14Z")

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You can [decrease the spacing of the segmentation](https://slicer.readthedocs.io/en/latest/user_guide/modules/segmenteditor.html#segmentation-is-not-accurate-enough) if your current spacing is comparable or larger than the desired margin. Setting a 0.9mm isotropic spacing could make sense (that would allow exactly 1.8mm expansion), but if you want exact 2.0mm growth then you have to resample to something like 1.0mm or 0.5mm.