Error message creating a volume source grid

Hi Brainstorm,

Brainstorm gave me an error message I did not understand, and I don't know if I did something wrong.

Some background: I am doing an analysis on MEG data. I used the default anatomy for my subjects and warped the anatomy for each of them. I want to look at the cortex surface as well as the deeper structures, so I decided to create both a surface model and a volume model separately.

To be able to average my volume models across recordings in the future, I had to create a 'New group analysis' and a 'Source grid' before doing the head model and source estimation steps, according to the tutorial (and it was not needed for the surface models). When I wanted to create the Source Grid, Brainstorm gave the following error in a pop-up screen:

'Surfaces or MEG/EEG recordings have already been imported for subject "@default_subject".
Editing the MRI orientation or the position of the NAS/LPA/RPA anatomical fiducials might break the coregistration between the different files, you might have to import everything again. THERE IS NO UNDO BUTTON - MAKE A BACKUP FIRST.
Are you sure you want to edit the MRI volume now?
yes no (<-- choices to click on)'

As I was not sure, I clicked 'no'. This opened a second pop-up message, as well as an MRI view (3 directions).

The message was:
'You have imported a standard anatomy, with standard fiducials positions (ears, nasion), but during the acquisition of your recordings, you may have used different positions. If you do not fix this now, the source localisations might be very unprecise.
Please check and fix now the following points:

  • NAS (Nasion)
  • LPA (Left pre-auricular)
  • RPA (Right pre-auricular)'

As we used the same positions during acquisition of recordings, I did not want to edit anything. Next to that, I could not find any marked fiducials in the opened MRI view. I closed everything and decided to reach out for advice to a colleague that might have dealt with this before.

When we tried to create the source grid again, the error did NOT appear again and I was able to create the grid. So, I wonder:

  • Do you know why I got the error?
  • Why did the error only appear once? Does this mean I did change something in the MRI viewer, even though I did not mean to?

I continued with my volume source estimation and all sources seem to be fit well onto the brain. Does this mean there is no issue in the end?

Thank you in advance for helping me,

1 Like

This is not an error message, but a warning. When creating a Group analysis subject, it is set to use the default anatomy, so this message indicates the user that any change in the anatomy that is being imported into the database (which is the "default anatomy" and belongs to the @default_subject") will affect the imported the registration with its surfaces. You can safely indicate No, as you do not intent to edit the fiducials in the default anatomy.

It shows the default anatomy, which was imported for the Group analysis subject. The pop-up message informs the user to verify that the fiducial points in the MRI are the same as the fiducial points used in the recordings, as these are the ones used for the registration.

Once you click click on No, the positions fiducials have been validated. So it does not ask again.

No, nothing changed in the fault anatomy.

In the MRI viewer, right-click > Figure > Edit fiducials
(if you modify by accident, just click on Cancel or close the figure, to avoid saving changes)

Thanks a lot! It's good to know that the warning was resolved by clicking 'No'.