[FieldTrip] MEG magnetometer leadfields

Cristiano Micheli michelic72 at gmail.com
Thu Aug 24 13:11:27 CEST 2017

Dear Rikkert,
as far as I know the CTF toolbox is incorporated in the /external directory
of FieldTrip and can help you a big deal.
If, for example, you recorded or have access to original CTF recordings you
can use the readin functions (ft_read_header) to read your datasets.
After read-in,you will find that one of the header fields is called 'grad'
andin  there you have the information of all coils positions.
See also this for further reading:

One of the grad sub-fields is called 'tra' and contains the magnetometers
(columns) to gradiometer (rows) weights matrix.
If you take care to define a new 'tra' matrix which weights 1 for each
magnetometer then you reach your goal.
You'll probably need to look into *grad.coilpos *and retain only a subset
of your magnetometers positions (either the nearest or the furthest set
from the head center)*, *and take care to keep consistency with the indexes
in grad.tra too


On Thu, Aug 24, 2017 at 11:58 AM, HINDRIKS, RIKKERT <
rikkert.hindriks at upf.edu> wrote:

> Dear all,
> I'm generating simulated data for leadfield matrices for the CTF 275 axial
> gradiometer system and I would like to compare different the results with
> those obtained from data simulated using a magnetometer configuration.
> It is possible to generate equivalent magnetometer leadfield matrices?
> (Equivalent in the sense of having the same number of coils at the same
> positions).
> Thanks and kind regards,
> Rikkert
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