open-discussion > MNI coordinates for electrodes
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Jul 17, 2014 10:07 AM | Frank Oltmanns
MNI coordinates for electrodes
Hello,
given a preop-mri and a postop-ct, already registered (ct to mri), and a *.mgrid file all in individual space, I now like to know the coordinates of the electrodes in MNI space.
Do I have to register the preop-mri to MNI_T1_1mm and apply the resulting *.grd to the *.mgrid in the Grid Transformation Control? Is there any need to use the Data Tree Manager, because I'm not very familiar with this module?
About two years ago there was a similar question, but maybe someone can give a more detailed explanation.
Thank you
Frank
given a preop-mri and a postop-ct, already registered (ct to mri), and a *.mgrid file all in individual space, I now like to know the coordinates of the electrodes in MNI space.
Do I have to register the preop-mri to MNI_T1_1mm and apply the resulting *.grd to the *.mgrid in the Grid Transformation Control? Is there any need to use the Data Tree Manager, because I'm not very familiar with this module?
About two years ago there was a similar question, but maybe someone can give a more detailed explanation.
Thank you
Frank
Jul 17, 2014 03:07 PM | Xenophon Papademetris
MNI coordinates
for electrodes
Frank,
You need to invert the .grd file and apply this to the mgrid file (you can put the transformations in the electrode editor tool directly so you don't need the grid). The basic rule is that to move the mgrid files to the MNI brain you will need to use the inverse transformations that you use for the images (images move backwards, surfaces move forwards).
So you will need to combine
1. The inverse mapping from MNI to MRI
2. The inverse matrix from MRI to CT (assuming that you use a linear map for this)
Put these in the right places in Electrode Control/Grid Transform Grid. This has specific labels but basically put the inverse of MRI to CT in the top (Postop CT->Post op MRI) and the inverse of MNI to MRI in the (postop MR -> PreopMRI) and leave the last box empty (identity).
Good luck,
Xenios
You need to invert the .grd file and apply this to the mgrid file (you can put the transformations in the electrode editor tool directly so you don't need the grid). The basic rule is that to move the mgrid files to the MNI brain you will need to use the inverse transformations that you use for the images (images move backwards, surfaces move forwards).
So you will need to combine
1. The inverse mapping from MNI to MRI
2. The inverse matrix from MRI to CT (assuming that you use a linear map for this)
Put these in the right places in Electrode Control/Grid Transform Grid. This has specific labels but basically put the inverse of MRI to CT in the top (Postop CT->Post op MRI) and the inverse of MNI to MRI in the (postop MR -> PreopMRI) and leave the last box empty (identity).
Good luck,
Xenios