I am recently working with a time series of volumes. First, I obtained a sequence (Sequence module) of volumes and then registered them using the SequenceRegistration module obtaining the corresponding Transforms and displacement fields. I would like to obtain the time-averaged transformation. Is there a way in Slicer or also in Python to perform the time average operation over the sequence of transformations?

Also, can I apply mathematical operations (such as invention or composition) to these transforms?
Thanks a lot!

You can write a small Python code snippet that iterates through the sequence for each time point it exports the transform into a displacement field vector volume, and you copy the voxels of the volume into a numpy array. In the end you can concatenate the arrays and use numpy to compute statistics along any axis (e.g., compute mean along time axis).

Thanks for the suggestion! Once the time-averaged displacement field is loaded back in Slcier, how can I apply it on a Volume? Can I convert a Displacement Field into a Transform?
P.S. is there any example of a snippet code like the one you mentioned?

You can load a displacement field image file (e.g., in a nrrd file) as a transform. Or you can manually create a grid transform and set the displacement image into it.

I converted all the Transform nodes into Displacement Fields with:
displacement_field_volume =slicer.modules.transforms.logic().CreateDisplacementVolumeFromTransform(transformNode, referenceVolumeNode, False)

Then I tried to extract the corresponding array in this way:
displacement_field_volume_node = slicer.util.getNode(displacement_field_volume.GetID())
array_displacement_field = slicer.util.arrayFromVolume(displacement_field_volume_node)

But slicer gives the error:
File “/opt/Slicer-4.11.20210226-linux-amd64/bin/Python/slicer/util.py”, line 1443, in arrayFromVolume
narray = vtk.util.numpy_support.vtk_to_numpy(vimage.GetPointData().GetScalars()).reshape(nshape)
ValueError: cannot reshape array of size 1720320 into shape (28,160,128)

It seems that the arrayFromVolume tries to reshape all the 3 channels of the displacement fields together, do you know how to solve this?