docstr: This function returns the dice score coefficient between a reference
  and segmentation images
  
  :return: dice score
docstr_tok: ["This","function","returns","the","dice","score","coefficient","between","a","reference","and","segmentation","images",":","return",":","dice","score"]
code: def dice_score(self):
      """
      This function returns the dice score coefficient between a reference
      and segmentation images
  
      :return: dice score
      """
      return 2 * self.tp() / np.sum(self.ref + self.seg)
  
imports: from __future__ import absolute_import, print_function
  import numpy
  from scipy import ndimage
  from niftynet.utilities.util_common import MorphologyOps, CacheFunctionOutput
label_desc: Use image node_id 25 for calling the PairwiseMeasures obj's underlying member method code with example usage: obj.dice_score() and returns: unknown