DWI metrics for demyelination

Dear mrtrix3’s experts,

I would like to characterize demyelination based on DWI imaging. I know that RD is a DTI metric to assess demyelination but I wonder whether fixel analysis would be of interest in this case?

Best,
Matthieu

Hi,

It may be sensitive but not specific. Your question is too big to answer here, I’d strongly recommend having a look at these papers and references therein:


https://onlinelibrary.wiley.com/doi/full/10.1002/mrm.21965
https://onlinelibrary.wiley.com/doi/full/10.1002/mrm.27101

I might be biased… but yes I’d recommend using FBA over tensor-based analysis but neither method is specific to specific myelin properties.

Cheers,
Max

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Hi,

Thanks for this detailed answer !

Why do you say that it might be biased to use FBA over tensor-based analysis in this case?

Best,
Matthieu

was a somewhat tongue in cheek comment in that my pointing you towards our recommended pipeline could be influenced by some degree of brainwashing and/or emotional investment of working with people who developed these techniques. You’re coming to a Mercedes showroom and asking whether to get a Trabant or one of their 4x4s to cross the desert. That being said, if your data supports FBA and you want to investigate fibre-specific group-differences, FBA is currently your best way to get meaningful measures about fibre density and morphology.

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Hi,

Thank you for this objective explanation, I understand.

I saw that for FBA it is recommended to have high b-values (>2000s/mm2). What would you advice me with multi-shell b-values of 1000 (32 dir) and 2000s/mm2 (32 dir)?

Best,
Matthieu

32 directions in the outer shell are at the lower end but I think should be sufficient. I’d suggest you try it out (read on here).

The interpretation of fibre density in FBA hinges on a few assumptions, in particular, the ability to suppress extracellular signal, a maximum b-value of b=2000s/mm2 gets you pretty far into that regime.

More detailed discussions are in Dave’s papers:

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Thank you for the references, I will read these papers.

So you advice me to use the 32 b=2000s/mm2 for FBA analysis. Wouldn’t it be possible to gain in using both shells b=1000s/mm2 and b=2000s/mm2 for CSD as suggested here?: [http://userdocs.mrtrix.org/en/latest/constrained_spherical_deconvolution/multi_shell_multi_tissue_csd.html]

Yes, use all shells and the MSMT CSD FBA pipeline.