Fixel base analysis on HCP

Hello,I am using the preprocessed HCP_S1200 dataset to do the fixel based analysis, whcih including eddy current distortion correction. Should I do the Denoising and unringing, Motion and distortion correction from the userdocs where descrbing FBA analysis?

Welcome @refrain!

Given the HCP minimally-preprocessed data have already undergone motion / susceptibility / eddy current correction, which involves interpolation of image data to produce that result, the denoising and Gibbs ringing correction algorithms are not applicable to those data. There would additionally be no benefit (or potentially even detriment) to re-running the aforementioned corrections on data where such distortions have already been estimated and corrected.

There can still be a B1 bias field in the HCP DWI data. Such a field is not considered problematic for many alternative diffusion models that use the b=0 intensity as a reference, but for FBA it can be deleterious. Whether there is any benefit in performing the dwibiascorrect step, as opposed to deferring to the mtnormalise step, for these particular data, I don’t actually know / can’t recall right now. So most likely you would commence processing at the response function estimation step.