[Neuroimaging] nipy.algorithms.registration.histogram_registration fails for registering CT image to MRI

[Carina Forster]

Hello neuroimaging community,

I want to align a CT image with a T1 MPRAGE to eventually mark ECoG
electrodes on the T1.
I aligned the T1 to acpc and used freesurfer for surface reconstruction.
My next step would be to align the CT image with FSL output orig.mgz.

My CT has the follwing dimensions:

512 x 512 x 734, image orientation: LAS

My MRI:

256x256x256, image orientation: RAS

It worked for a few images but not for all.
nipy tells me the coregistration worked, however I noticed that the
normalized mutual information is 0.2 for the images that are correctly
aligned and about 2.0 for the ones where coregistration didn't work.
My understanding is that NMI shoudl be between 0 and 1, so I think there is
something wrong.

If anyone has any idea what might go wrong, I am forever grateful.

Have a great monday,

Carina
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