Yes that is the reason we didn’t use apply_topup.  I’m not sure why we used 
more iterations.  Perhaps Jesper changed the config at some point or knows why.

Matt.

From: 
<hcp-users-boun...@humanconnectome.org<mailto:hcp-users-boun...@humanconnectome.org>>
 on behalf of "Kastman, Erik" 
<kast...@fas.harvard.edu<mailto:kast...@fas.harvard.edu>>
Date: Monday, October 1, 2018 at 10:46 AM
To: "hcp-users@humanconnectome.org<mailto:hcp-users@humanconnectome.org>" 
<hcp-users@humanconnectome.org<mailto:hcp-users@humanconnectome.org>>
Subject: [HCP-Users] SE Fieldmap - apply_topup HCP replacement

Hi HCP,

In the fMRI Volume processing, we noticed that although the spin-echo fieldmaps 
are calculated using topup, there are a set of custom applywarp commands to 
generate distortion-corrected final-space fieldmaps instead of applywarp: (e.g. 
the DistortionCorrection script 
DistortionCorrectionAndEPIToT1wReg_FLIRTBBRAndFreeSurferBBRbased.sh<https://github.com/Washington-University/HCPpipelines/blob/0a27221d0c44e45db6bdc5a8f38f05c3f32adbdb/fMRIVolume/scripts/DistortionCorrectionAndEPIToT1wReg_FLIRTBBRAndFreeSurferBBRbased.sh#L328>
 called from the 
GenericFMRIVolume.sh<https://github.com/Washington-University/HCPpipelines/blob/0a27221d0c44e45db6bdc5a8f38f05c3f32adbdb/fMRIVolume/GenericfMRIVolumeProcessingPipeline.sh#L377>).

It seems like the warps are used instead of apply_topup to 1) do 1-step 
resampling, 2) handle modulation (Least Squares Restoration _or_ jacobian) and 
3) bring along the sbref. I just wanted to check that I understood the 
reasoning and that I’m not I’m not missing something obvious.

The reason this came up is because we acquired HCP-style se-based fieldmaps for 
another study and want to be sure that we’re applying them in a consistent way.

Finally, we also noticed that the topup config file used in HCP is 
nearly-identical with the standard FSL-distributed topup config, except that 
the final set of iterations was increased from 20 to 50. Do you recommend this 
change for all data, or was it something specific that you saw in the HCP 
fieldmaps?

Thanks for any advice,

Erik


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