Hi, I also have a little problem with applying bipolar montage to SEEG. As we know, the contacts of SEEG which are out of the brain should be excluded. When doing bipolar, what's the right thing to do? I'm not sure about the two methods:
- We just excluded all the contacts that are out of the brain, and then do bipolar, which may cause this situation: The original contacts are A1, A2, A3, A4, and A5. Ley's say we exclude A2 and A3, then after bipolar, we have A1-A4, A4-A5.
- We firstly do bipolar, so we have A1-A2, A2-A3, A3-A4, A4-A5. Then we see the location of A1-A2 the same as A1(or the mean coordinates of A1+A2, as I saw in the fieldtrip). Follow this rule, we should drop A2-A3, A3-A4.
The original contacts are A1, A2, A3, A4, and A5. Ley's say we exclude A2 and A3, then after bipolar, we have A1-A4, A4-A5.
How can you have A1 and A4 "inside the brain" and A2 and A3 "outside the brain"?
Do you mean inside and outside the gray matter? If you want to remove A2 and A3 because they are in the white matter, instead you can probably keep them to compute your bipolar montages, but then simply avoid to process "A2-A3" (mark it as a bad channel).
then after bipolar, we have A1-A4
I don't think you should use this measure A1-A4 for anything.
How did you get this? Did Brainstorm compute something like this on its own?
Then we see the location of A1-A2 the same as A1(or the mean coordinates of A1+A2, as I saw in the fieldtrip).
Brainstorm should use the mid-point between the contacts as well:
I don't think there is a unique solution to your question, ask 10 neurologists and you might get 10 different answers.
Sorry, when I say out of the brain, I mean not in the gray matter, and A2 and A3 are out of the brain is just an example, my bad. Anyway, I couldn't agree more with your solution. I am going to do bipolar using all the channels, and drop some of them based on the location of the new bipolar channels.
I would not exclude contact because they are not in the gray matter as they can still record some neural signal because of passive signal spread.
Check if A2 and A3 are both fully outside the gray matter, but it seems unlikely. Here, I mean not only their centroid/center of mass but also the nearest voxels of their centroid. As the electrode is generally bigger than the voxel that is affiliated with in the MRI.