Dear Brainstorm Team,
We would like to compute the head model to do source analyses on our EEG data.
When we select "Compute head model" in the functional tab, we get the following error: No valid sensor types to estimate a head model
When examining the channel file, we have noted that the channel type is set to EEG for all 76 channels, but there is also a 77th channel of EDF type. Additionally, the "Loc" column does not have any coordinates (all zeros). Please see the attached screenshot for reference.
We tried right-clicking on the channel file > Add EEG positions > Import from file to load our 76.elp channel file exported from BESA Research, but once selected and imported, nothing in the display or channel file changes/updates.
Please advise.
Thank you very much,
Manda
I should mention, as well, that we are using a 64 channel BioSemi cap with 12 facial electrodes (76 in total).
Thank you very much,
Manda
When we select "Compute head model" in the functional tab, we get the following error: No valid sensor types to estimate a head model
A valid sensor for estimating the forward model should have the type "EEG" and correct 3D positions.
right-clicking on the channel file > Add EEG positions > Import from file to load our 76.elp channel file exported from BESA Research
This is the correct thing to do.
This procedure matches the channels described in the channel with the electrode position in your .elp file using the channel names. The labels must be strictly identical in two two lists, other wise the matching fail. As your channels are all named with and extra "E" (eg. "EF4"), the electrodes defined in the .elp file must include this extra "E" as well. If it is not the case, you can edit the .elp text file and add them manually.
Also make sure you use the correct ".elp" file format in the import window (try them all).
After importing your positions, you will most likely need to adjust them on the head surface. Right-click on the channel file > MRI registration > Edit > Rotate/translate/resize and project on the head surface (read the tooltips of the buttons for help)
PS: Is this a common BioSemi cap?
If so, I could add it to the Brainstorm distribution, together with the other template BioSemi caps, to help other users.
Please do this registration on the ICBM152 template head surface, then send me the channel_*.mat file (upload it somewhere and post the download link here): I will add it to the Brainstorm distribution.
Thanks
Dear Francois,
Thank you. The .elp file only contains two coordinates (Azimuth (theta) and Latitude (phi)). I am not sure if it is possible to get 3D coordinates with the 12 facial electrodes included.
The cap is a common one (64 channel), however, I am not sure about the facial electrodes. I tried applying the BioSemi 64 10-10 channel file, but the facial electrodes were not carried through.
I understand that the Name column should be edited (additional E), but I am not sure how to edit the .elp location column if there are only 2 coordinates.
Also, is the 77th row in the channel file (titled "annotations") problematic for compatibility? This row was created when I read in my EDF files.
Thank you,
Manda
Thank you. The .elp file only contains two coordinates (Azimuth (theta) and Latitude (phi)). I am not sure if it is possible to get 3 D coordinates with the 12 facial electrodes included.
No, it is not possible. These are not realistic 3D coordinates, but spherical coordinates, for the types of disc/sphere display you can have in EEGLAB or BESA. You can't use this elp file for source estimation.
The cap is a common one (64 channel), however, I am not sure about the facial electrodes. I tried applying the BioSemi 64 10-10 channel file, but the facial electrodes were not carried through.
You can use the BioSemi 10-10 positions if they seem to work for you, and then add the missing positions:
- Start by creating an empty folder
- Set the 10-10 cap as the channel file
- Right-click on the channel file > MRI registration
- Add the missing facial electrodes (put them where it seems right to you)
- Right-click on the modified template channel file > File > Export to file > Select file format "EEG: ASCII: Name, XYZ"
- Right-click on the channel file of your dataset > Add EEG positions > Load from file, select the file you just created
Also, is the 77th row in the channel file (titled "annotations") problematic for compatibility? This row was created when I read in my EDF files.
This is the channel containing the EDF+ event timestamps, which were read and converted to Brainstorm structures when you linked the file to the database. Just ignore it.
Thank you very much for your help.
For your records/Brainstorm distribution and for future users, we used the following file for the coordinates (76) and then co-registered according to the co-registration tutorial:
76channels.sfp (3.2 KB)
Thank you for sharing this file.
It would be best to make this cap directly available in the Brainstorm distribution.
Could you do this co-registration work based on the template ICBM152, then send me the resulting channel...mat file? Right-click on the channel file in your Brainstorm database > File > Show in file explorer, upload the .mat file somewhere and post the download link here.
What is the commercial name of this cap?
(so I can reference it correctly in the software)
Thanks
Francois
