# Subtracting volumes from two different scans

**URL:** <https://discourse.slicer.org/t/subtracting-volumes-from-two-different-scans/17580>\
**Category:** Support\
**Created:** [May 12, 2021, 1:16am UTC](https://discourse.slicer.org/t/subtracting-volumes-from-two-different-scans/17580 "2021-05-12T01:16:25Z")\
**Posts on this page:** 1\
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**Author:** ![JanWitowski](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/janwitowski/32/4512_2.png) [@JanWitowski](https://discourse.slicer.org/u/JanWitowski)\
**Post date:** [May 12, 2021, 1:36am UTC](https://discourse.slicer.org/t/subtracting-volumes-from-two-different-scans/17580/2 "2021-05-12T01:36:29Z")

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To create subtraction images you can use Subtract Scalar Volume module that is pre-built inside 3D Slicer. Alternatively, you can use Python and perform simple subtraction between two volumes. Relevant thread: [Scalar subtraction](https://discourse.slicer.org/t/scalar-subtraction/4401)

However, if you are calculating difference between two segmentations (bone segmented on image 1 - bone segmented on image 2), you don’t need to subtract them, just segment both and calculate their respective volumes with Segment Statistics module.

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