code: def header_str(self):
      result_str = [self.m_dict[key][1] for key in self.measures]
      result_str = "," + ",".join(result_str)
      return result_str
  
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 6 for calling the PairwiseMeasuresRegression obj's underlying member method code with example usage: obj.header_str() and returns: result_str