[Eeglablist] Co-registration procedure DIPFIT

[Katy Ericson]

Hi Kelly,
thanks a lot for your reply. I think i understand what you mean (sorry if i don't ;) ). As i understood ,this is a standard way, when you have a 10-10 or 10-5 marking of your electrodes, which corresponds to the standard 10-5 marking of the file, given in DIPFIT. The problem in my case was, that i have a custom system with E1-E129 electrode marking, which does not correspond to the DIPFIT file. In this case wrap function does not recognize those locations and, from my point of view, there are two options:
1. Do a co-regestarationmanually, which takes tons of time
2. Find a .loc file with custom electrodes from EGI in spherical format, that will represent my 129 electrodes with the names E1-E129, and set it as a template file. In this case the wrap function will be able to recognize location names and will do wrapping automatically. I'm not sure that this will work in EEGLAB, right now looking for an appropriate file to do try this out. 
Best regards,
Katy





________________________________
From: Kelly.Kaneswaran <kelly.kaneswaran at ul.ie>
To: Katy Ericson <katy.ericson at yahoo.com>
Sent: Mon, February 15, 2010 3:34:02 PM
Subject: RE: [Eeglablist] Co-registration procedure DIPFIT

  
Katy,
 
I had similar problem before, follow the turorial it explains a way of doing it that speeds it up. First you should have a channel location file with all the locations in an acceptable format .sph .loc etc. from the locate dipole using dipfit menu , choose head and model settings , leave the default settings and choose manual co registration. then a spherical model pops up , choose warp montage , the list shows the models fudicials and you can select corresponding electrode locations that your model has exact. then press ok , the montage is warped to fit the model and press ok it will generate the tailrach co-ordinates.
 
i could be way off so apologies if I mis-understood what you were trying to do 
 
Kelly
 
From:eeglablist-bounces at sccn.ucsd.edu [mailto:eeglablist-bounces at sccn.ucsd.edu] On Behalf Of Katy Ericson
Sent: 11 February 2010 18:20
To: EEGLAB
Subject: [Eeglablist] Co-registration procedure DIPFIT
 
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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