How to plot Current density at the surface of the spinal cord and roots after running a Electro Ohmic Quasi-stat simulation.

[Seifeldin_E]

I am trying to run scTS using Sim4Life science version, but I do not know how to calculate the current and how to plot the current density at the surface of the spinal cord and roots, as shown in this figure from "Novel Noninvasive Spinal Neuromodulation Strategy Facilitates Recovery of Stepping after Motor Complete Paraplegia.".