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Hello,

I produced an m3z warp file with mri_gradunwarp.

Now I need to 0 out all displacement in the z direction, while keeping 
everything else the same since I need to combine multiple warps from images 
with different geometries.


I see two strategies:

(1) working directly on the m3z file
I could not get mri_convert or mris_calc to do the trick. I thought I nailed it 
by manually editing the m3z file in freeview, but freeview saves the results in 
mgz format :-( Is there anything else I missed?

(2) converting to mgz or nii timeseries, manupulate those and convert back to 
m3z
mri_convert produced a nii file that freeview could not read and a single-frame 
mgz file that looks like some mishmash of the original 3-frame m3z.


Any idea on how I can acheive my goal?


A word on why would I want to do this silly thing. I have single-slice EPI and 
fov-matched higher-inplane-resolution single-slice GRE images. They have 
different within-slice gradient-non-linearity-related distortions. I want to 
undistort the GRE image then distort it to the EPI space. I need to zero out 
through-plane distortions to avoid displacing signal outside the imaging grid. 
Ignoring through-plane distortions should not be a problem for overlaying my 
GRE and EPI since, unlike within-plane distorsions, through-plane distortions 
are matched.


Thanks a lot for the help and
Have a very good day!
Sebastien
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