[FieldTrip] Omission in ft_compute_leadfield for MEG and OpenMEEG headmodel

Knipscheer, B. B.Knipscheer at umcutrecht.nl
Tue Jan 12 15:34:39 CET 2021


Dear all,
There seems to be an omission in the ft_compute_leadfield script causing some problems down the line. Can someone check if my observations are correct?
In the most recent version of ft_compute_leadfield, when calculating the leadfields for MEG using a headmodel based on OpenMEEG, this is done for the MEG coils and not the sensors.
There seems to be a few lines missing. These lines are:
  if isfield(sens, 'tra')
    % construct the channels from a linear combination of all magnetometer coils
    lf = sens.tra * lf;
  end
These lines are present in the code for other headmodel types and convert lf per coil to lf per sensor.
These missing lines subsequently causes the leadfield matrix to be modified in ft_sourceanalysis. Since the number of labels is less than the number of coils, the leadfield matrix is truncated, losing a certain amount of leadfields.

My suggestion is to include the aforementioned lines in ft_compute_leadfield. Please let me know what you think!

Kind regards,

Bram Knipscheer


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