Organizing data for dwipreproc


#1

hello
what is the directory order/file organization before doing dwipreproc?

I have blip up and down data with corresponding bvals and bvecs.

Thanks
A


#2

Hi @ameoded1,

I’m aware that the documentation for dwipreproc really needs examples with images… I just haven’t gotten around to it yet.

In your case the best approach is:

  1. Convert each of the two series independently to .mif using the -fslgrad option to import the gradient tables into the image headers.

  2. Concatenate the two series using mrcat. This will additionally automatically concatenate the two gradient tables.

  3. Provide this image as the input to dwipreproc, either using:

  • -rpe_all to specify that the second half of volumes have precisely the opposite phase encoding to the first but the same gradient directions, as well as -pe_dir to provide the phase encoding direction of the first half of volumes;

  • -rpe_header if the image headers contain the requisite phase encoding information (only if the data are from Siemens and you can convert directly from DICOM).

In either case dwipreproc will automatically extract the b=0 volumes from the input data and provide these to topup, so you don’t need to use the -se_epi option.

Rob


#3

ok
im my case
blip up folder: blip_up.miff, bvecs, bvals
blip_dn folder: blip_dn.mif, bvecs, bvals

do I need to rename bvecs and bvals differently? do you save all files in one new folder and concatenate ?

Thanks

A


#4

You only need the .mif files – no need for the bvecs/bvals, as long as they’ve been included in the header of the corresponding .mif files. I recommend you go through how we handle DW gradients, you’ll probably find most of your questions answered there.


#5

ok thanks

can we go back to .nii after dwipreproc?? can I convert to nifiti my files to be able to work with other programs?

Than you


#6

yes you can convert back to nifti, this will imply than every mrtrix command that need to read the gradient information will be call with the -grad or -fslgrad option. One of the advantage of the .mif format is that the gradient information is stored in the header.
for intance with mrcat with .mif file you do not need to concatenate yourself the bvec and bvals file …


#7

Just to add to that:

To convert to NIfTI and output the corresponding bvecs/bvals at the same time, use the -export_grad_fsl option on the relevant commands.