What is the best way to concatenate 2 rsfMRI volumes within the same session?

I would like to construct a functional connectome from 2 rsfMRI volumes. So i’m wondering if i should

  1. concatenate both raw volumes and preprocess the concatenated volume as per normal (i.e. via fmriprep)?
  2. preprocess both volumes separately, concatenate the denoised timeseries data from both volumes and then extract the connectivity matrix from the concatenated timeseries data
  3. preprocess and extract the connectivity matrix separately for both volumes, then compute the average of these matrices

I think I would do 3, because it gives you a clearer picture of the amount of variability around the final connectivity estimate.
Bertrand Thirion