def extract_nodif_volume(outdir, dwi, bval):
"""
Parameters
----------
outdir: Str, path to directory where to write "b0.nii.gz"
dwi: Str, path to DW data in which at least one volume was acquired
with bvalue=0.
bval: Str, path to .bval file associated to the DW data.
Return
------
nodif_volume: Str, path to a/the volume for which bvalue is 0.
<unit>
<input name="outdir" type="Directory" />
<input name="dwi" type="File" />
<input name="bval" type="File" />
<output name="nodif_volume" type="File" />
</unit>
"""
# Get index of the first volume acquired with bvalue=0
b0_index = select_first_b0(bval)
# Extract volume to a temporary Nifti
nodif_volume = os.path.join(outdir, "nodif.nii.gz")
extract_image(dwi, index=b0_index, out_file=nodif_volume)
return nodif_volume
