[FieldTrip] MEG gradiometer leadfield units (HINDRIKS, RIKKERT)

[Marc Lalancette]

Hi Rikkert,

I ran into the same question some time ago and eventually figured it out.  Assuming the code has not changed, it depends on the units you use and I had to use a correction factor when using lengths in cm.  See this thread for details:
http://mailman.science.ru.nl/pipermail/fieldtrip/2014-September/008438.html

By the way, there were open issues regarding units back then, you can search fieldtrip's Bugzilla to check the current status.

Cheers,

Marc Lalancette
Lab Research Project Manager, Research MEG lab
Department of Diagnostic Imaging, Program in Neurosciences and Mental Health
The Hospital for Sick Children, 555 University Avenue, Room S742, Toronto, ON, M5G 1X8
416-813-7654 x201535



-----Original Message-----
Date: Wed, 26 Aug 2015 12:42:49 +0200
From: "HINDRIKS, RIKKERT" <rikkert.hindriks at upf.edu>
To: fieldtrip at science.ru.nl
Subject: [FieldTrip] MEG gradiometer leadfield units
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        <CADFLVFyRef3kSxKVbocHFPisj51UBgJSyV4q1SLSXnBW_XxTMg at mail.gmail.com>
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Hi all,

I constructed a single-sphere leadfield in Fieldtrip for the CTF 275 MEG system, but am unsure about the units:

If I assume that dipole moments are expressed in pAm and sensor signals in T, then a dipole moment of 10 nAm gives sensor signals in the range 10-100 fT, which is what one expects.

Can anyone confirm the units I assumed for this leadfield?

Thanks a lot,
Rikkert Hindriks

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