[Eeglablist] Co-registration procedure DIPFIT

[Katy Ericson]

Dear all,
I'm
new to the EEGLAB, this seems to be a nice software. Anyway i have some
trouble, if one can call it a trouble at all. I need to find the
locations of equivalent dipoles for my ICA components. My recordings
are done on EGI 128 channel system and then the exact locations of the
sensors are modeled with Photogrametry procedure. As i understand, in
order to get more or less correct locations of dipoles, i have to do a
co-registration procedure (my net does not correspond exactly to any of
10-5 or 10-10 systems and sensor locations are "scanned" for every
patient).
I was trying to do the co-registration using a standard
standard-10-5-cap385.elp file as the template file and spherical model.
This analysis takes quite a long time, when one has to pair all 128
channels to template locations, because my system has channels numbered
as E1 till E128 and Cz as a reference. It may be unreasonable use of
time to sit for several hours trying to co-register electrodes to the
standard template. On the other hand there was a study, which
calculated correspondences of E1:E128 channel names to the 10-5 names.
Which may really speed up the process, but the pairing may be done with
a greater distances between electrodes.
It would be a great help from you, if some one could answer my questions:
1. How big can the errors be, if i use no co-registration and file with the scanned locations.
2.
Is there a way to speed up the process or some other solution of
co-registration and dipole fitting in my case (i should mention though,
if it concerns accuracy, we would rather take a longer processing time,
rather than do the work inaccurately).
3. We have a possibility to
export location file from EGI in spherical and in Cartesian
coordinates, will there be a difference in accuracy and time consume
during co-registration procedure between files in these 2 coordinate
systems.
4.
When one does the co-registration, the locations of electrodes are
changed (custom locations are aligned with predefined ones), how does
this affect the accuracy of dipole fitting. 
Thank a lot for your answers and the great mailing lists:)
Cheers!
Katy


      
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