code: def _pair_grad_sensors_ch_names_neuromag122(ch_names):
      """Find the indices for pairing grad channels in a Neuromag 122 system.
  
      Parameters
      ----------
      ch_names : list of str
          A list of channel names.
  
      Returns
      -------
      indexes : list of int
          Indices of the grad channels, ordered in pairs.
      """
      pairs = defaultdict(list)
      for i, name in enumerate(ch_names):
          if name.startswith("MEG"):
              key = (int(name[-3:]) - 1) // 2
              pairs[key].append(i)
  
      pairs = [p for p in pairs.values() if len(p) == 2]
  
      grad_chs = sum(pairs, [])
      return grad_chs
  
imports: import logging
  from collections import defaultdict
  from itertools import combinations
  from pathlib import Path
  import numpy
  from scipy.spatial.distance import pdist, squareform
  from .._fiff.constants import FIFF
  from .._fiff.meas_info import Info
  from .._fiff.pick import _FNIRS_CH_TYPES_SPLIT, _picks_to_idx, pick_types
  from ..transforms import _cart_to_sph, _pol_to_cart
  from ..utils import _check_ch_locs, _check_fname, _check_option, _check_sphere, _clean_names, fill_doc, logger, warn
  from ..viz.topomap import plot_layout
  from .channels import _get_ch_info
label_desc: Use image node_id 14 for calling a global function with example usage: _pair_grad_sensors_ch_names_neuromag122(ch_names) and returns: grad_chs