# Comparison of CT and USG 3D images

**URL:** <https://discourse.slicer.org/t/comparison-of-ct-and-usg-3d-images/13361>\
**Category:** Support\
**Tags:** segmentation\
**Created:** [September 7, 2020, 6:51am UTC](https://discourse.slicer.org/t/comparison-of-ct-and-usg-3d-images/13361 "2020-09-07T06:51:01Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![emipaw](https://avatars.discourse-cdn.com/v4/letter/e/ed8c4c/32.png) [@emipaw](https://discourse.slicer.org/u/emipaw)\
**Post date:** [September 7, 2020, 6:51am UTC](https://discourse.slicer.org/t/comparison-of-ct-and-usg-3d-images/13361/1 "2020-09-07T06:51:01Z")

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Hi!  
I have data from CT and from USG 3D. The patient has a liver tumor. I am trying to compare tumor volume in both modalities. For CT I know that the computed volume is reliable but I am not sure what about USG 3D. Should I scale it somehow?

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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:** [September 8, 2020, 3:31am UTC](https://discourse.slicer.org/t/comparison-of-ct-and-usg-3d-images/13361/2 "2020-09-08T03:31:47Z")

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If the 3D ultrasound imaging system is calibrated then it should provide correct physical dimensions. Most ultrasound systems assume a certain speed of sound in tissue, which may differ from the actual speed, but this should not cause more than a few percent error.