Liisa Helle

Liisa Helle




MaxFilter your data

This lectures will give you an overview to data preprocessing using MaxFilter.


The learning goals are: understanding artefacts and intereferences in MEG data, signals space separation (SSS), temporal extension of SSS, internal active shielding (IAS), and finally set some guidelines for MaxFilter software methodology. For each part, you will have a theoretical background presentation, and a practical demonstration with examples using real MEG data.


Lecture 1:Introduction and Learning Outcomes

Learning goal number 1: understanding artefacts in MEG data is important because magnetic fields arising from the brain have extremely low amplitude, typically much lower than the ones arising from the artefacts. So they are likely to interfere in our conclusions, if not controlled. They can came from any metallic object in the body, and also from external noise such as traffic. This includes artefacts produced by the MEG machine itself.


The demo video offers an example of real MEG data measured from a healthy subject. It shows artefacts in gradiometers and magnetometers and you are able to see the big variation caused by external magnetic fields to the signals of interest.

Lecture 2: Artefacts in MEG data

Lecture 3: Artefacts demo

MaxFilter softaware by Elekta Neuromag is an MEG preprocessing toolbox for suppresion of close-by and external artefacts, as well as head movement compensation. It reads and writes *.fif format, includes graphical user interface and also command lines for scripting the analysis.


The demo video offers an overview of how to access MaxFilter software and manual, as well as how to use the command line window.

Lecture 4: Introduction to MaxFilter

Lecture 5: Introduction to MaxFilter demo

Interferences suppresion in MEG can be devided into hardware shielding or software shielding. Regarding hardware shielding, when the magnetically shielded room (MSR) is not sufficient to suppress external interferences, also active shielding can be used. All the sensors should be measuring only magnetic fields all times. Once accomplished, software shielding can be aplied to data to reduce residual interference.

Lecture 6: Interference and Suppression