[Simnibs-discuss] tDCS electrode is being simulated as skin

[Oula Puonti]

Hi Gülce,

I would consider this a segmentation error. You might want to try the
new segmentation method (charm) included in simnibs version 4. In my
experience it does a bit better job on ignoring the electrodes in the
type of MRI data you have.

The other option is that you edit the skin masks, which are inside the
MASK_prep folder, manually and then re-run the surface and volume
masking steps.

The manual editing process was made easier in the new version, see
here: 

https://simnibs.github.io/simnibs/build/html/tutorial/advanced/fix_headmodel.html

so you might want to consider using SimNIBS4 in any case.

Best,
Oula


On Tue, 2023-01-17 at 15:50 +0100, Gülce Lale wrote:
> Dear SimNIBS Team,
> We conduct post-hoc modelling for each subject using T1 and T2 images
> acquired while the participant was in the scanner with the tDCS
> electrodes attached. Here SimNIBS headreco images the 2mm layer of
> electrode paste and includes in in the head mesh but segments it as
> skin (see attached images).
> According to SimNIBS skin conductance is 0.465 s/m and the electrode
> material conductivity is 29.4 s/m. One would expect the Ten20
> Electrode paste which is applied with a 2mm thickness between the
> electrode and skin to have a different measure. However, since it is
> being considered and modelled as skin this could results in
> deviations in the electric field modelling.
> How do we account/solve this?
> Could we model the electrodes 2mm below the head surface, knowing
> that the outer 2mm thickness of the skin are actually due to the
> paste? Thus, modelling the electrodes on the “actual” skin outer
> layer (and not on top of the paste). SimNIBS then allows us to
> specify past + electrode thickness. Where we assume SimNIBS
> calculates a different conductivity measure for both.
> Is there an alternative solution to best account for the change of
> conductance?
> Thank you for your help in advance.
> Best wishes,
> Gülce 
> 
> Gülce Lale
> MSc Neurosciences
> 
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