Dear helpful people,
I get negative radial diffusivity values, and I do not understand why.
I am calculating radial diffusivity from the L2 and L3 images as follows:
- I merge L2 and L3 for each subject: fslmerge -t dti_L23 dti_L2 dti_L3
- then I calculate their mean: fslmaths dti_L23 -Tmean Radial_D
The resulting images, Radial_D contain lots of negative values, as if they
are standardised across the image.
Since the original L2 and L3 images only contain positive values, I don't
understand how their mean can have negative values. I don't know exactly
what fslmaths -Tmean does but until now I assumed it just calculated the
mean of images over "time". Of course I could simply do fslmaths -add first
and then fslmaths -div 2, but now I would like to know why my approach does
not work.
Best,
Emma
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