DTI measurements: spherical and linear

Dear all,
after tractography I used my vtk files to extract measurements using Slicer. In the resulting table there are two columns with numbers that I cannot really identify. They are called “spherical” and “linear”. Is this synonymous for radial and axial diffusivity or something else?
I would really appreciate your help and thank you in advance.
Best wishes

Those measures are described in this paper: Processing and visualization for diffusion tensor MRI - ScienceDirect