text: """
  Nodes' configurations for *epi_ref* pipelines.
  """
  import nipype.pipeline.engine as pe
  from nipype.interfaces import utility as niu
  from nipype.interfaces import mrtrix3 as mrt
  
  from dwiprep.workflows.dmri.pipelines.epi_ref.configurations import (
      INPUT_NODE_FIELDS,
      OUTPUT_NODE_FIELDS,
      DWIEXTRACT_KWARGS,
      MRMATH_KWARGS,
  )
  
  #: i/o
  INPUT_NODE = pe.Node(
      niu.IdentityInterface(fields=INPUT_NODE_FIELDS),
      name="inputnode",
  )
  OUTPUT_NODE = pe.Node(
      niu.IdentityInterface(fields=OUTPUT_NODE_FIELDS),
      name="outputnode",
  )
  
  #: Building blocks
  DWIEXTRACT_NODE = pe.Node(
      mrt.DWIExtract(**DWIEXTRACT_KWARGS), name="dwiextract"
  )
  
  MRMATH_NODE = pe.Node(
      mrt.MRMath(**MRMATH_KWARGS),
      name="mrmath",
  )
  