docs: def _metadata(image, datapath):
      """Function which returns metadata dict.
  
      :param image: image to get spacing from
      :param datapath: path to data
      :return: {'series_number': '', 'datadir': '', 'voxelsize_mm': ''}
      """
      metadata = {'series_number': 0, 'datadir': datapath}
      spacing = image.GetSpacing()
      metadata['voxelsize_mm'] = [
          spacing[2],
          spacing[0],
          spacing[1],
      ]
      return metadata