# I need help subtracting 2 DICOMs and getting a volume (mm3) as result   

**URL:** <https://discourse.slicer.org/t/i-need-help-subtracting-2-dicoms-and-getting-a-volume-mm3-as-result/30245>\
**Category:** Support\
**Created:** [June 26, 2023, 8:51pm UTC](https://discourse.slicer.org/t/i-need-help-subtracting-2-dicoms-and-getting-a-volume-mm3-as-result/30245 "2023-06-26T20:51:18Z")\
**Posts on this page:** 6\
**Page:** 1

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**Author:** ![Manita](https://avatars.discourse-cdn.com/v4/letter/m/5fc32e/32.png) [@Manita](https://discourse.slicer.org/u/Manita)\
**Post date:** [June 26, 2023, 8:51pm UTC](https://discourse.slicer.org/t/i-need-help-subtracting-2-dicoms-and-getting-a-volume-mm3-as-result/30245/1 "2023-06-26T20:51:18Z")

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Hi, I need help. I’m new here.

I have 2 DICOM from the same patient. One before the intervention and one after. I can see there’s a difference, but I would like to get the volumetric difference between the two files.  
I would appreciate a step by step, since I’m pretty new.

Thanks!

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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:** [June 27, 2023, 2:41am UTC](https://discourse.slicer.org/t/i-need-help-subtracting-2-dicoms-and-getting-a-volume-mm3-as-result/30245/2 "2023-06-27T02:41:40Z")

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Is it for assessing fat resorption for breast reconstruction?  
What imaging modality did you use?

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**Author:** ![Manita](https://avatars.discourse-cdn.com/v4/letter/m/5fc32e/32.png) [@Manita](https://discourse.slicer.org/u/Manita)\
**Post date:** [June 27, 2023, 12:19pm UTC](https://discourse.slicer.org/t/i-need-help-subtracting-2-dicoms-and-getting-a-volume-mm3-as-result/30245/3 "2023-06-27T12:19:43Z")

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Thanks for answering.

I want to calculate the hard tissue/bone gain or loss of the procedure, comparing two DICOMs of the same patient taken at different times. I can visually see the difference of both surfaces, but I would like to calculate the volume of such difference

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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:** [June 27, 2023, 2:05pm UTC](https://discourse.slicer.org/t/i-need-help-subtracting-2-dicoms-and-getting-a-volume-mm3-as-result/30245/4 "2023-06-27T14:05:19Z")

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You can measure volume difference of bone and tissue by the following steps:

- [Register the images.](https://slicer.readthedocs.io/en/latest/user_guide/registration.html)
- Segment the same region in both images using [Segment Editor](https://slicer.readthedocs.io/en/latest/user_guide/modules/segmenteditor.html). Enable overlap in Masking settings.
- Use Erase effect or Logical operators effect to remove regions that are farther away from the region of interest. Use the same region for all segments.
- Use [Segment Statistics](https://slicer.readthedocs.io/en/latest/user_guide/modules/segmentstatistics.html) module to get volume of each segment

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<div class="post-metadata">

**Author:** ![Manita](https://avatars.discourse-cdn.com/v4/letter/m/5fc32e/32.png) [@Manita](https://discourse.slicer.org/u/Manita)\
**Post date:** [June 28, 2023, 12:44am UTC](https://discourse.slicer.org/t/i-need-help-subtracting-2-dicoms-and-getting-a-volume-mm3-as-result/30245/5 "2023-06-28T00:44:25Z")

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Thank you for answering.

I’m just unable to grasp how to use this.

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<div class="post-metadata">

**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:** [June 28, 2023, 2:40am UTC](https://discourse.slicer.org/t/i-need-help-subtracting-2-dicoms-and-getting-a-volume-mm3-as-result/30245/6 "2023-06-28T02:40:45Z")

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You can start with learning how to segment the bone using Segment Editor. [This page](https://slicer.readthedocs.io/en/latest/user_guide/image_segmentation.html) is a good starting point. There are also lots of tutorials on youtube.