# Deformable Registration Grid DICOM import

**URL:** <https://discourse.slicer.org/t/deformable-registration-grid-dicom-import/4095>\
**Category:** Support\
**Tags:** registration, dicom\
**Created:** [September 13, 2018, 2:48am UTC](https://discourse.slicer.org/t/deformable-registration-grid-dicom-import/4095 "2018-09-13T02:48:21Z")\
**Posts on this page:** 2\
**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:** [September 13, 2018, 2:48am UTC](https://discourse.slicer.org/t/deformable-registration-grid-dicom-import/4095/1 "2018-09-13T02:48:21Z")

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Hi there,

I am trying to get my head around how Slicer reads TPS exported Displacement fields and calculates its **Grid Orientation** values.

For example, I have exported an arbitrary displacement field from my TPS and have the following values for **Grid orientation** ,

![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/e/a/ea968d775fe02af53b88e2d89acace7a9353a1a7.png)

However, when I look at the DICOM metadata regarding the same displacement field I get the following,

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/4/a/4ac33ad4448ab3679afe8763fd862b728f3919d5.png)

I assume the **FrameOfReferenceTransformationMatrix** DICOM tag has something to do with the previously mentioned **Grid orientation** but they seem to be inverted compared to one another.

All of this is important because I want to accumulate dose by applying the inverse displacement field to a dose distribution. I am wondering if I need to rotate/tilt my dose distribution before applying the inverse displacement field.

Any help would be greatly appreciated!

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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:** [September 13, 2018, 4:57am UTC](https://discourse.slicer.org/t/deformable-registration-grid-dicom-import/4095/2 "2018-09-13T04:57:38Z")

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DICOM uses LPS coordinate system, while Slicer internally uses RAS. When the displacement field is imported from DICOM, the position and orientation is converted accordingly. See details [here](https://github.com/SlicerRt/SlicerRT/blob/988f0746d0a5e9fef8d1872585ad78656bf90cca/DicomSroImport/Logic/vtkSlicerDicomSroReader.cxx#L158-L251).