code: def S0_hat(self):
      return self.model_S0
  
imports: import numpy
  import scipy.optimize
  from dipy.core.gradients import check_multi_b, unique_bvals_magnitude, round_bvals
  from dipy.reconst.base import ReconstModel
  from dipy.reconst.dti import MIN_POSITIVE_SIGNAL
  from dipy.core.ndindex import ndindex
  from dipy.core.onetime import auto_attr
label_desc: Use image node_id 3 for calling the MeanDiffusionKurtosisFit obj's underlying member method code with example usage: obj.S0_hat() and returns: self