[Simnibs-discuss] Nexstim TMS simulation

[Axel Thielscher]

Hi Alessandra,

we don't have coil models for Nextim coils. If the company is willing to 
share detailed information about the coil geometry, we can likely help 
you to get a reasonable model, though.

Regarding the coil position coordinates: Please use headreco, not 
mri2mesh to create the head model, because headreco doesn't change the 
header information of the T1 image. In addition, read the same T1 image 
into the neuronavigation system. If this still results in different 
positions for the coil center, then the Nexstim system interally changes 
the coordinate system of the image. In that case, we would need 
information from Nexstim on their internal coordinate system to be able 
to resolve that issue.

Best regards,

Axel


On 08-06-2022 01:52, Alessandra Dallavecchia wrote:
> Dear all,
>
> I have been working on trying to do some e-field simulations for our 
> TMS-EEG data, but have been running into a couple of issues.
>
> We use a Nexstim system (NBT 2.2), so my first question would be if 
> there was a reasonable approximation for a coil configuration file 
> that I could use, or how I might be able to create one specific to the 
> Nexstim figure-8 coil.
>
> My second question is in regards to the coil position coordinates. 
> Nexstim outputs three coordinates for coil location, direction, and 
> normal in mm. However, I've noticed that these coordinates are wildly 
> different from those that SimNIBS gives me when I manually place a 
> point on the GUI as close to the center of the coil. Both are in mm 
> and are in subject space. I know that their coordinates line up with 
> FreeSurfer as I do source modeling for my EEG data, and I've tried a 
> number of permutations (e.g., switching x/y/z axes), but nothing seems 
> to get me close in SimNIBS to this actual coil position when I use the 
> Nexstim output coords.
>
> *Left Parietal Stimulation Site from the Nexstim Neuronavigation*
> Coil direction.png
>
> *Similar Coil Position in the SimNIBS GUI:*
>
> Coil Pos SimNIBS.png
>
> Thank you,
>
> /--/
> *Alessandra DallaVecchia, M.A.*
> PhD candidate, Cognitive Neuroscience
> UCLA Department of Psychology
> She/her
>
> /If this email finds you outside of your normal business hours, please 
> do not feel obligated to reply and feel free to respond when you're 
> next working or in front of a computer./
>
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-- 
Dr. Axel Thielscher
Professor of Neurophysics and Neuroimaging
Danish Research Center for Magnetic Resonance
Copenhagen University Hospital Hvidovre
DK-2650 Hvidovre, Denmark
www.drcmr.dk
&
Department of Health Technology
Technical University of Denmark
DK-2800 Kgs. Lyngby
http://www.healthtech.dtu.dk/
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