code: def _anisotropic_DTD():
      """Return a distribution of six fully anisotropic diffusion tensors whose
      directions are uniformly distributed around the surface of a sphere.
      """
      evals = np.array([1, 0, 0])
      phi = (1 + np.sqrt(5)) / 2
      directions = np.array(
          [
              [0, 1, phi],
              [0, 1, -phi],
              [1, phi, 0],
              [1, -phi, 0],
              [phi, 0, 1],
              [phi, 0, -1],
          ]
      ) / np.linalg.norm([0, 1, phi])
      DTD = np.zeros((6, 3, 3))
      for i in range(6):
          R = vec2vec_rotmat(np.array([1, 0, 0]), directions[i])
          DTD[i] = np.matmul(R, np.matmul(np.eye(3) * evals, R.T))
      return DTD
  
imports: import numpy
  import numpy.testing
  import dipy.reconst.qti
  from dipy.core.gradients import gradient_table
  from dipy.sims.voxel import vec2vec_rotmat
  from dipy.core.sphere import disperse_charges, HemiSphere
  from dipy.reconst.dti import fractional_anisotropy
  from dipy.testing.decorators import set_random_number_generator
  from dipy.utils.optpkg import optional_package
label_desc: Use image node_id 8 for calling a global function with example usage: _anisotropic_DTD() and returns: DTD