[FieldTrip] combining magnetometers and planad gradiometers for analysis

Elena Orekhova Elena.Orekhova at neuro.gu.se
Thu Jun 2 18:22:03 CEST 2011


Dear Michael,

I have tried to multiply the leadfield by -1 as you suggested:

for i = 1 : size (grid.leadfield, 2)
    grid.leadfield{i}(3:3:306, :) = -1*grid.leadfield{i}(3:3:306, :);
end

This had no effect on the 'lcmv' output. I attached the pictures for ‘GRA only, ’MAG only’ and ‘GRA + MAG’

In this experiment I measured evoked field in response to  the unilateral (left) click.
The source is expected to be in the right superior temporal cortex.  This is the case  for  ‘GRA only' and ’MAG only’ datasets. The combined sensors give meaningless result.

Elena

________________________________
From: fieldtrip-bounces at donders.ru.nl [fieldtrip-bounces at donders.ru.nl] on behalf of Michael Wibral [michael.wibral at web.de]
Sent: Wednesday, June 01, 2011 4:04 PM
To: Email discussion list for the FieldTrip project
Subject: Re: [FieldTrip] combining magnetometers and planad gradiometers for analysis

Dear Elena,

could you give the following a try: invert (*-1) the leadfileds for one of the two sensor types. Let me know what happens.
I would also be interested in taking a look at the results - maybe you could sent images off-list: Michael.Wibral <at> web.de.

Michael



________________________________
Von: "Elena Orekhova" <Elena.Orekhova at neuro.gu.se>
Gesendet: Jun 1, 2011 12:23:29 PM
An: "fieldtrip at donders.ru.nl" <fieldtrip at donders.ru.nl>
Betreff: [FieldTrip] combining magnetometers and planad gradiometers for analysis

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Dear  fieldtrippers,
This message is mainly for Neuromag users.

When I do  'lcmv' beamforming analysis separately on planar gradiometers or magnetometers, I get quite meaningful results.
If I combine the two types of sensors without weighting, the result is meaningless.
Apparently, the algorithm does not take care of different scales and units of the GRA and MAG measurements.  Does anybody know how to deal with this problem?


Elena




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