[FieldTrip] MNI Coordinates in Virtual-Sensor-Analysis

[Yildirim, Devram]

Hi Jan-Mathijs,

thank you very much for your help. It was indeed in ALS coordinates and like said the coordinates seem to be fine. I'm very happy you could confirm my method and the results seem to make sense.

Best wishes,
Devran


Am 30.08.2021 um 11:47 schrieb Schoffelen, J.M. (Jan Mathijs) via fieldtrip <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>>:

Hi Devran,



On 26 Aug 2021, at 00:00, Yildirim, Devram via fieldtrip <fieldtrip at science.ru.nl<mailto:fieldtrip at science.ru.nl>> wrote:

Dear fieldtripers,

I have a question about the use of MNI Coordinates from a literature for my virtual sensor analysis.

I followed all the steps from the tutorial, i.e. creating the mni-alligned sourcemodel. I did this so I could easily use mni coordinates for my virtual sensor analysis and in the end do a group analysis.

My question is now how do I use this coordinates from the literature for my analysis? Do I use it for each individual or do I use it on the template?


For example:

I found coordinates for the left IFG from a Meta-Analysis ( -56 8 8) in mm.
My idea was that I first use the template and search for the nearest grid point, e.g in this case it was grid point 21289 (-5.75 1 1) in cm.
Then I use this grid point for each individual in the grid.pos field of the virtual sensor analysis.

I am not sure if this is a possible way because of multiple reasons:

1: I can’t do this for the exact coordinate because there is no grid point for that. Is this still a valid grid point?

Given the overall spatial resolution of source reconstruction I would say that this is still a valid grid point.

2: The coordinates from the individual are pretty far apart from the template (e.g. (-0.4 50 46.2)), is this normal? I checked if I used the correct template and also made sure that I used the mni-alligned sourcemodel with mni coordinates.

Did you check the metric units and coordinate system of the reported coordinate? If it’s in mm, and based on an ALS coordinate system, rather than an RAS coordinate system, then it looks fine to me. If you want to learn more about coordinate systems, please check out this reference page: https://www.fieldtriptoolbox.org/faq/how_are_the_different_head_and_mri_coordinate_systems_defined/

Best wishes,
Jan-Mathijs



I searched a long time for a solution but couldn’t really be sure if I’m doing things right so far.

I would really appreciate any help and feedback.

Kind regards,
Devran




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