Intracranial Volume and DTI / NODDI Metrics

Hi everyone,

I have read that metrics such as FA tend to covary with brain volume. Related to this, I have two questions:

  1. Given the non-specificity of FA, is there a good intuition for why FA and brain volume would covary?
  2. Are there any global biasses in other DTI / NODDI metrics that would motivate regressing out brain volume for other DWI measures?

Best,
Steven

Can you describe what do you mean by “brain volume”?

Total intracranial volume as indexed by FreeSurfer eTIV, for example.

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Hmm, I think I don’t know enough to answer this then. I am a bit surprised similar to you that FA covaries with brain volume. I cannot think of a straightforward reason about why this should be the case.