MZvyagintsev at UKAACHEN.DE
Wed Oct 4 12:38:00 CEST 2006
Dear Robert / other fieldtrippers,
I have a question regarding MEG realign procedure. I actually found it
very useful and trying to learn how to deal with it.
I am using 4 D Neuroimaging mashine (BTi), and, therefore, I had to
change the routine a bit - at least change settings, concerning the
sensors name. In my particular case I got the message 'mean distance
towards template gradiometers is 25.45 mm'. (I actually attached a
picture regarding sensors' position's difference derived from Matlab,
but probably it is not so easy to recognize what is what on this picture
- points are sensors and different colors - positions in different
sessions, the view is from front).
And later in this routine I use the approach based on calculation of
brain surface from headshape. As a headshape we use here points from
bridge (of nose) to nape (of the neck).
I get 644 dipoles from it 'prunedinv' subfunction gives me 'pruning 49
out of 148 singular values' (so, we use 148 channels mashine). After
calculation of realign matrix and applying it for 'realigning trial' the
residual variance (RV) which I get for one trial is arround 30%. I have
a feelling that it is rather to much, or might be it's normal, becouse
difference between sensors is rather big one.
Because in case 'mean distance towards template gradiometers' was 6.48
mm - residual variances were arround 5-6%.
6.48 mm 5-6%
25.45 mm ~30%.
My question is - is such RV difference correspondent to the difference
distance I have and how many points should be like a 'control value' for
Thank you in advance,
Mikhail Zvyagintsev MD, BSc
Klinik für Psychiatrie & Psychotherapie
tel +49-0241-80 85580
FAX +49-0241-80 82401
MZvyagintsev at UKAachen.de
-------------- next part --------------
A non-text attachment was scrubbed...
Name: session 1 and 3 positions.tif
Size: 706680 bytes
Desc: not available
More information about the fieldtrip