code: def head_to_mni(
      pos, subject, mri_head_t, subjects_dir=None, verbose=None
  ):
      """Convert pos from head coordinate system to MNI ones.
  
      Parameters
      ----------
      pos : array, shape (n_pos, 3)
          The coordinates (in m) in head coordinate system.
      %(subject)s
      mri_head_t : instance of Transform
          MRI<->Head coordinate transformation.
      %(subjects_dir)s
      %(verbose)s
  
      Returns
      -------
      coordinates : array, shape (n_pos, 3)
          The MNI coordinates (in mm) of pos.
  
      Notes
      -----
      This function requires either nibabel.
      """
      subjects_dir = get_subjects_dir(subjects_dir, raise_error=True)
  
      # before we go from head to MRI (surface RAS)
      head_mni_t = combine_transforms(
          _ensure_trans(mri_head_t, "head", "mri"),
          read_talxfm(subject, subjects_dir),
          "head",
          "mni_tal",
      )
      return apply_trans(head_mni_t, pos) * 1000.0
  
imports: import os.path
  from gzip import GzipFile
  from pathlib import Path
  import numpy
  from ._fiff.constants import FIFF
  from ._fiff.meas_info import read_fiducials
  from .surface import _read_mri_surface, read_surface
  from .transforms import Transform, _ensure_trans, apply_trans, combine_transforms, invert_transform, read_ras_mni_t
  from .utils import _check_fname, _check_option, _import_nibabel, _validate_type, get_subjects_dir, logger, verbose
label_desc: Use image node_id 11 for calling a global function with example usage: head_to_mni(pos, subject, mri_head_t, subjects_dir, verbose) and returns: unknown