[Simnibs-discuss] Coil position _question modified

[Mana Biabani]

Hi again!

I apologise for the additional email. I would like to modify my question below regarding the coil position. 

Would appreciate if you could ignore my previous email and help me with the points below:

> I am using SimNIBS to simulate TMS-induced e-field and had two questions :
> 
> 1- Is there any method to measure the exact distance between the coil and scalp surface? The 4mm default distance is not appropriate for my experiment; as the participants have EEG cap on and also there is a foam between the coil and the cap. Also, I’d like to account for the differences in the hair volume, etc.  I was thinking to measure the minimum euclidean distance between the coil centre and the scalp coordinates but as far as I understood the coil centre is actually a scalp position. So, it shouldn’t work.
> 
> 2- My second question was about the coil orientation (in a more accurate way than choosing a reference electrode …). I am using Brainsight to get the information about the coil position, but not sure which outputs represent coil angels around different axes. I guess I can use [m0n0 m0n1 m0n2;  m1n0 m1n1 m1n2; m2n0 m2n1 m2n2 ] from Brainsight to make the transformation matrix, is that correct? If so, could you please let me know how I should modify them to be compatible with the coil axes in SimNIBS. 
> 

Kind regards,
Mana



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MANA BIABANI
Research Fellow

Turner Institute for Brain and Mental Health
Monash University
18 Innovation Walk
Clayton VIC 3800
Australia

E: mana.biabanimoghadam at monash.edu <mailto:mana.biabanimoghadam at monash.edu>




> On 21 Jan 2021, at 4:19 pm, Mana Biabani <mana.biabanimoghadam at monash.edu> wrote:
> 
> Hi, 
> 
> I am using SimNIBS to simulate TMS-induced e-field and had two questions :
> 
> 1- Is there any method to measure the exact distance between the coil and scalp surface? The 4mm default distance is not appropriate for my experiment; as the participants have EEG cap on and also there is a foam between the coil and the cap. Also, I’d like to account for the differences in the amount of hair, etc.  I was thinking to measure the minimum euclidean distance between the coil centre and the scalp but as far as I understood the coil centre coordinates are actually scalp positions. So, it shouldn’t work.
> 
> 2- My second question was about coil angle. I am using the angles that Brainsight provides to make the transformation matrix as below :
> 
> [ m0n0	-m0n1	m0n2 	coil.center(1)
>  m1n0	-m1n1	m1n2	coil.center(2)
>  m2n0	-m2n1	m2n2	coil.center(3)] . 
> 
> Could you please confirm if this matrix is correct.  My understanding is that I need to inverse the y axis in Brainsight and it does not need any transformations (like MNI to subject space). Is that correct?
> 
> Greatly appreciate your help in advance!
> 
> Kind Regards,
> Mana
> 
> 
> ---
> MANA BIABANI
> Research Fellow
> 
> Turner Institute for Brain and Mental Health
> Monash University
> 18 Innovation Walk
> Clayton VIC 3800
> Australia
> 
> E: mana.biabanimoghadam at monash.edu <mailto:mana.biabanimoghadam at monash.edu>
> 
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