Hello,
I am trying to apply the detect head motion steps for my MEG data acquired using CTF.
This MEG data was acquired simultaneously with SEEG so we did not have head points on the scalp but just around the glasses and nose and mastoids.
What is strange is that patient did not have much space left inside helmet to move but I see about 180mm of motion during most time points of the recording (see top figure). Secondly, after I apply the adjust the reference head position, the after correction is really off (see bottom figure).
Please let me know if you have any suggestions for fixing this issue.
Thank you
Rasheda
@Marc.Lalancette do you have any suggestions for this head localization in MEG ?
Hello
Check the raw head coil data first. Possibly there was mislocalization of at least one coil, which you would see by having much higher fit error, and greater variations in the coordinates. The fit error and coordinate data appear as separate categories of channels when you right click on the data file. Depending on whether the continuous head localization was not working properly the entire time or not, you could possibly reuse some segments to adjust the position, but it doesn’t look promising from what you shared. You’ll probably have to fully rely on the initial position. You hopefully could still use the good coils to at least identify when there was real movement, although it will not be possible to localize the head with only 2 out of the 3 coils.
Let me know if that’s not the issue, and we can try to see what else might be the problem. We can also look at it together if you want. Just email me.
Finally, note that this CHL issue, which is specific to the CTF software v6.1, can be seen during recording. At the bottom of the screen, it would show much larger fit error and possibly erratic large motion. The head coil channels would also show this motion, if they are displayed during acquisition. When this occurs, it is possible to either reposition the head a little and restart which is likely to fix the problem, or we can also switch to v6.2. Don’t hesitate to reach out to me if/when any issue arises.
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