class_docstr: Collect all tf.Tensor object, to be evaluated by tf.Session.run()
  These objects are grouped into::
  
      NETWORK_OUTPUT: to be decoded by an aggregator
      CONSOLE: to be printed on command line
      TF_SUMMARIES: to be added to tensorboard visualisation
docstr: add a variable to be decoded in application.interpret_output
docstr_tok: ["add","a","variable","to","be","decoded","in","application.interpret_output"]
code: def _add_to_network_output(
      self, var, name, average_over_devices=False
  ):
      """
      add a variable to be decoded in application.interpret_output
      """
      self._add_to_dict(
          self.output_vars, var, name, average_over_devices
      )
  
imports: from __future__ import absolute_import, print_function
  import tensorflow
  from tensorflow.contrib.framework import list_variables
  from niftynet.io.misc_io import image3_axial, image3_coronal, image3_sagittal, resolve_checkpoint
  from niftynet.utilities import util_common
  from niftynet.utilities.restore_initializer import restore_initializer
label_desc: Use image node_id 6 for calling the OutputsCollector obj's underlying member method code with example usage: obj._add_to_network_output(var, name, average_over_devices) without return types