# Rescale voxel values of CBCT to MDCT HU

**URL:** <https://discourse.slicer.org/t/rescale-voxel-values-of-cbct-to-mdct-hu/12876>\
**Category:** Support\
**Created:** [August 6, 2020, 2:48pm UTC](https://discourse.slicer.org/t/rescale-voxel-values-of-cbct-to-mdct-hu/12876 "2020-08-06T14:48:03Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![ahmad\_abbas](https://avatars.discourse-cdn.com/v4/letter/a/bc79bd/32.png) [@ahmad\_abbas](https://discourse.slicer.org/u/ahmad_abbas)\
**Post date:** [August 6, 2020, 2:48pm UTC](https://discourse.slicer.org/t/rescale-voxel-values-of-cbct-to-mdct-hu/12876/1 "2020-08-06T14:48:03Z")

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I have a CBCT and MDCT of the same specimen and I want to “convert” the grey values in CBCT accordingly the ones in MDCT and consequently be able to measure “HU” values in the CBCT volume?

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**Author:** ![ahmad\_abbas](https://avatars.discourse-cdn.com/v4/letter/a/bc79bd/32.png) [@ahmad\_abbas](https://discourse.slicer.org/u/ahmad_abbas)\
**Post date:** [August 6, 2020, 2:07pm UTC](https://discourse.slicer.org/t/rescale-voxel-values-of-cbct-to-mdct-hu/12876/2 "2020-08-06T14:07:16Z")

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I have a CBCT and MDCT of the same specimen and I want to “convert” the grey values in CBCT accordingly the ones in MDCT and consequently be able to measure “HU” values in the CBCT volume?

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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:** [August 6, 2020, 4:07pm UTC](https://discourse.slicer.org/t/rescale-voxel-values-of-cbct-to-mdct-hu/12876/3 "2020-08-06T16:07:02Z")

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If you know the correspondence between original values and HU then applying that transformation to voxel intensities should be trivial. If you need don’t know it then you need to do a few measurements.

These topics should help:

> [@From CT to qCT?](https://discourse.slicer.org/t/from-ct-to-qct/11782):
>
> Dear all Is there an extension that allows to extract segment statistics for known CT calibration parameters? I would like to extract bone density values instead of HU. Thanks

> [@Bone Mineral Density (BMD) measurement method](https://discourse.slicer.org/t/bone-mineral-density-bmd-measurement-method/11010):
>
> I have been told a method of calculating BMD from micro CT data using a proprietary software and i am wondering about the accuracy of the method and replicating it with the 3D Slicer. The way it was done in the software was, we use 3 phantoms of know density, water and 0.25 and 0.75 and the mean hounsfield values was water 0 = -575.936 0.25 = 1142.4 0.75 = 3267.8 so the equation was X =(y+11.708)/4381.1 so i try to do this the same with the 3D Slicer,

Note that for many operations, such as visualization, registration, segmentation, a calibrated CT is useful, but not essential. What is your application? What would you like to achieve overall?

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<div class="post-metadata">

**Author:** ![ahmad\_abbas](https://avatars.discourse-cdn.com/v4/letter/a/bc79bd/32.png) [@ahmad\_abbas](https://discourse.slicer.org/u/ahmad_abbas)\
**Post date:** [August 6, 2020, 7:23pm UTC](https://discourse.slicer.org/t/rescale-voxel-values-of-cbct-to-mdct-hu/12876/4 "2020-08-06T19:23:40Z")

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i need the HU units for the treatment planning system and monte carlo simulation

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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:** [August 7, 2020, 3:15am UTC](https://discourse.slicer.org/t/rescale-voxel-values-of-cbct-to-mdct-hu/12876/5 "2020-08-07T03:15:15Z")

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For radiation therapy treatment planning you indeed need voxels in HU, so you need to calibrate the intensity as described in the topics linked above.