# Displacement vector from a deformable reg; WARNING inverse innaccuate

**URL:** <https://discourse.slicer.org/t/displacement-vector-from-a-deformable-reg-warning-inverse-innaccuate/5569>\
**Category:** Support\
**Tags:** transforms\
**Created:** [January 29, 2019, 9:05pm UTC](https://discourse.slicer.org/t/displacement-vector-from-a-deformable-reg-warning-inverse-innaccuate/5569 "2019-01-29T21:05:35Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Lowey](https://avatars.discourse-cdn.com/v4/letter/l/e36b37/32.png) [@Lowey](https://discourse.slicer.org/u/Lowey)\
**Post date:** [January 29, 2019, 9:05pm UTC](https://discourse.slicer.org/t/displacement-vector-from-a-deformable-reg-warning-inverse-innaccuate/5569/1 "2019-01-29T21:05:35Z")

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Slicer 4.8.1  
Windows 10

Hi there,

I am doing research regarding deforming dose distributions and have questions about the warning you can receive regarding inverse displacement vectors.

The warning is - Warning: inverse is inaccurate! (see attached image)!

 ![Alpha_29_inverse_inaccurate](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/9/0/909f93efc33feb3a9dc02908c4b14f89d6e6860d.png)

I am curious (i.e., the mathematics behind) how slicer determines that the inverse is inaccurate? Or, is this warning encoded in the DICOM metadata somewhere?

Many thanks  
Nick

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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:** [January 30, 2019, 12:48am UTC](https://discourse.slicer.org/t/displacement-vector-from-a-deformable-reg-warning-inverse-innaccuate/5569/2 "2019-01-30T00:48:46Z")

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The warning is displayed when the forward and inverse transform at the mouse pointer position is not consistent: applying forward then the inverse transform result in non-zero translation.

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**Author:** ![Lowey](https://avatars.discourse-cdn.com/v4/letter/l/e36b37/32.png) [@Lowey](https://discourse.slicer.org/u/Lowey)\
**Post date:** [January 30, 2019, 1:34am UTC](https://discourse.slicer.org/t/displacement-vector-from-a-deformable-reg-warning-inverse-innaccuate/5569/3 "2019-01-30T01:34:14Z")

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Great - makes sense now of course! Thank you!

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**Author:** ![Lowey](https://avatars.discourse-cdn.com/v4/letter/l/e36b37/32.png) [@Lowey](https://discourse.slicer.org/u/Lowey)\
**Post date:** [January 30, 2019, 3:54am UTC](https://discourse.slicer.org/t/displacement-vector-from-a-deformable-reg-warning-inverse-innaccuate/5569/4 "2019-01-30T03:54:00Z")

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Sorry one more question, is there a method with Slicer to export deformable spatial registrations to DICOM? I can’t seem to export these files, even if they are grouped in a patient (see attached)

Many thanks!

 ![exportDR](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/6/6/66b700c91e18b7d8ee58a1b2607ed9f662f7ccd5.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:** [January 31, 2019, 12:23am UTC](https://discourse.slicer.org/t/displacement-vector-from-a-deformable-reg-warning-inverse-innaccuate/5569/5 "2019-01-31T00:23:55Z")

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You need to install SlicerRT extension to be able to save the displacement field as a DICOM spatial registration object.