Normalisation to MNI space

Hi All, I realise that this has kind of been addressed in a past post but i’m still slightly confused by the best approach for my application. I basically want to output TDI maps in MNI space so that I can identify tracts with an atlas. Do I perform normalisation on the tracks (tcknormalise) and then create my TDI outputs?
Sorry if this is a repeat question, but i’ve spent awhile trawling through the past posts and am more confused now than I was before I started!

Hey Rish,

Yes, in the case of a basic TDI target, it’s preferable to transform the streamlines then calculate the TDI in template space. This intrinsically does precisely the same orientation-dependent modulation as what is captured in the Fibre change in Cross-section (FC) term in Fixel-Based Analysis (FBA). If you calculate the TDI in subject space first, then transform the resulting image, you can’t do this modulation properly, because the orientation information is gone.

The second figure in this abstract might help to demonstrate what’s going on.


Thank you for the clarification Rob!

Hi Rob,

I understand the concern why one need to normalize streamlines to template space first and then calculate TDI.

However, I think the TW-FC should have the same concern regarding to the streamlines and Jacobians. But why wouldn’t you normalize the streamlines first and then calculate TW-FC, but rather calculate TW-FC first and then normalize to template space, per Track-weighted functional connectivity (TW-FC): A tool for characterizing the structural–functional connections in the brain - ScienceDirect?



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