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.".

[bryn]

Hi @Seifeldin_E

I assume you’re referring to the second row, where the field is shown on the surface of the spinal cord and peripheral nerves.

Here’s the simplest way to achieve this:

• In the Field Sensor, select Current Density.
• Add a Masking Filter:
• Set selection to None (deselect everything).
• Type Nerve in the search filter and activate all nerve structures.
• Search for the spinal cord and activate it as well.
• Add a Surface Viewer — this will extract the surface at the masked regions.

How it works:

• The masking filter replaces all unselected field values with NaN (not-a-number).
• The surface viewer detects NaN values and extracts the surface surrounding the masked voxels.

Alternative method (less robust):

• Drag a TriangleMesh entity (e.g., Spinal_cord) to the Analysis tab.
• Select Current Density and the spinal cord mesh (now in Analysis, apply the Model to Grid filter).
• Add the Interpolation filter.
• Add a Surface Viewer

Be aware: if the field changes abruptly near the surface, this method may interpolate the field on the "wrong" side of the surface. That’s why the masking approach is usually more reliable and easier to use.