[FieldTrip] different gradiometer-units from fiff-file

Murphy, Kelly (Research Student) murphyk5 at aston.ac.uk
Wed Mar 8 18:49:55 CET 2017

Hi Michael,

You could try using ft_read_data as per usual, then convert the units to the desired ones after.  For example:

"grad = ft_read_sens(MEG_data);  %get fiducial coordinates under grad.chan
sens = ft_convert_units('mm', grad);"

From: fieldtrip-bounces at science.ru.nl [fieldtrip-bounces at science.ru.nl] on behalf of Michael Scholz [scho at med.ovgu.de]
Sent: 08 March 2017 16:52
To: fieldtrip at science.ru.nl
Subject: [FieldTrip] different gradiometer-units from fiff-file

Dear community,

My name is Michael Scholz and I am working in Magdeburg (Germany)
in the Department of Neurology.
We just started using our Elekta Neuromag Triux System.
I was going to use fieldtrip to create some simulation data to
test Elekta software. Therefore I read data from a fiff-file acquired
by the Elekta-MEG-system including 102 magnetometer-data and 2x102
gradiometer data.
Reading fiff-files with ft_read_data creates output with magnetometer-data
in Tesla (T) and gradiometer-data in T/m  just as in the fiff-file.
Reading the same fiff-file by ft_read_sens creates a structure with
header-info including T/cm-unit-info for the gradiometer-sensors.
This was not expected and was misleading; if one doesn?t recognize
these different units for the gradiometers and combines data based
on ft_read_sens-output and ft_read_data-output, the result is unusable,
since scaling of magnetometer-data and gradiometer-data won?t match.

How can I prevent ft_read_sens from reading gradiometer in different
units as given in the source-fiff-file?


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