Importing captrak files

[bakerdon]

@Raymundo.Cassani

Yes, the alignment between the MRI (default or individual's) and the electrode positions from the bvct file is done with the positions for Naison, LPA and RPA. For subjects using their individual anatomy, you may want to use the option in the channel file right-click menu MRI registration > Refine using head points. This will try to find the best fit between the head points (electrode positions) and the subject anatomy.

Is it best practice to refine the CapTrak positions using head points, and when do I know that I need to do this? I thought we said above that we should not have to refine CapTrak data using head points, as the NAS/LPA/RPA are defined for CapTrak during the data collection.
Also, if the CapTrak positions are accurate relative to the NAS/LPA/RPA from the data collection, how is refining with head points different than projecting to the scalp surface?

@Raymundo.Cassani

• For subject with default anatomy:
  Just Add EEG positions > ICBM152 > BrainProducts > BrainProducts ActiCap 97
• For subjects with individual'a anatomy
  Perform MNI normalization
  Then you can add the positions from the default anatomy (as above), the locations in the individual's anatomy will be done using the MNI normalization

Does converting the MRI to MNI space for some of our patients (but not all, such as in the case of those with MRI and CapTrak data) affect computations or their results later? I feel that if we were to convert some of the MRIs to MNI space, but not all, there may introduce some bias.

@Raymundo.Cassani

Both methods should lead to very similar results.
As a test, you could try with a subject with CapTrak sensor digitization. Test the both methods and compare them against the ground-of-truth location (from CapTrak)

Thanks for this. I will test.