the attribute random_seed defined in the DTITrackerInputSpec Class has some mistake,the defination should be random_seed = traits.Int(desc="use random location in a voxel instead of the center of the voxel to seed. can also define number of seed per voxel. default is 1", argstr="-rseed %d") not random_seed = traits.Int(desc="use random location in a voxel instead of the center of the voxel to seed. can also define number of seed per voxel. default is 1", argstr="-rseed")