Dear Martin,
>. To fix it for now I will try to obtain the correct fiducial
> coordinates by aligning the electrode locations from the file with a
> structural MRI of the subject wearing the electrode cap.
You can actually do that in SPM. Load your problematic sfp file and
then go to the 3D source reconstruction window and use the 'MRI'
button (first make sure that your structural is roughly aligned to SPM
template). Then when you press the 'Coregister' button you will be
asked to select the fiducials out of the full list of all the points
in the file. You can then pick 3 or more electrodes that you can find
on the structural and use those as fiducials clicking on the
corresponding points in your structural.
If you want to do source reconstruction, this will work well. For 2D
projection the code you have will not use this coregistration, but I
recently changed this and it'll be available in the next update. If
you are interested in this specific application, let me know and I'll
send you some updated functions.
Best,
Vladimir
On Sat, Jun 13, 2009 at 2:26 PM, Martin Luessi<[log in to unmask]> wrote:
> Vladimir,
>
> Yes you are right, using the code you posted it is pretty obvious that
> there is a problem with the file. I will need to investigate why this
> happened, I was confident that we did the location acquisition
> correctly. To fix it for now I will try to obtain the correct fiducial
> coordinates by aligning the electrode locations from the file with a
> structural MRI of the subject wearing the electrode cap.
>
> Thanks a lot,
>
> Martin
>
> On Fri, Jun 12, 2009 at 4:43 PM, Vladimir
> Litvak<[log in to unmask]> wrote:
>> Dear Martin,
>>
>> If you execute the code below, you'll get a 3D plot of your channel
>> locations from the original file and by examining it you'll be able to
>> see that indeed the fiducials do not seem to be make sense with
>> respect to your channel labels. This is indeed a problem in your
>> Neuroscan file. For 10-20 labels SPM provides default locations so you
>> don't have to load an sfp file unless you have individually measured
>> locations that you want to use.
>>
>> Best,
>>
>> Vladimir
>>
>> ---
>> L = importdata('locations.DAT');
>> figure;plot3(L.data(:, 2), L.data(:, 3), L.data(:, 4), '.r')
>> axis equal
>> text(L.data(:, 2), L.data(:, 3), L.data(:, 4), L.textdata)
>>
>>
>> On Fri, Jun 12, 2009 at 10:24 PM, Martin
>> Luessi<[log in to unmask]> wrote:
>>> Hi,
>>>
>>> I'm trying to convert a neuroscan .DAT file with electrode locations
>>> so that I can read it in SPM8. The file was obtained by digitizing the
>>> electrode locations of a subject using a polhemus digitizer with
>>> neuroscan software. The .DAT file contains 5 columns. The first one
>>> contains the channel label, the second one the channel type (I assume)
>>> and the rest xyz coordinates. From the coordinates of the fiducials,
>>> it appears that x points towards the back of the head, y towards the
>>> right ear, and z upwards. I converted the file into a *.sfp file
>>> having three columns, i.e, "Label x y z". When I import this file into
>>> SPM8 (via EEG->Prepare), the electrode locations are incorrect, the
>>> locations of the electrodes seem to be rotated 90 degrees clockwise,
>>> i.e. FPZ is close to the "RIGHT" fiducial, see the attached
>>> screenshot. I'm not sure if I make a mistake when doing the
>>> coregistration, if neuroscan uses some non-obvious system for the
>>> coordinates, or if we did something wrong when registering the
>>> electrode locations. I did the corgistration using the fiducials "nas
>>> = NAISON", "lpa = LEFT", and "rpa = RIGHT".
>>>
>>> I attached the neuroscan file and a screenshot, any help is greatly appreciated.
>>>
>>> Martin
>>>
>>
>
>
>
> --
>
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