C4. Doing measurements

MEG skills - C4. Doing MEG Measurements

Checklist MEG preparation



1. Prepare Magnetic Shielded Room (MSR)


Check availability and functioning of stimulus and response equipment

Check dewar position,

Check experimental paradigm

Check that the stimuli and responses are as expected

Check arrival of triggers in MEG recording

Prepare subject prepping

Label electrodes for EOG (2), ECG (2) and any other (i.e. EMG) electrodes. Have some additional ready in case you have to redo them.

Electrode gel

Tape for attaching electrodes on skin (transparent tape)

Tape for securing electrodes (yellow tape)

Set up HPI chair. Attach the big receiver on the back of the chair. The wire has to go down.




2. Prepare MEG system


Prepare system

Check quality of channels. If necessary heat and reset using Squiddler.

Select or create project

Check or select acquisition parameters

Check or create online averaging parameters

Select or create subject




3. Prepare subject


Explain preparation procedure

Explain experiment

Let subject read and sign informed consent.

Remove metal objects, change clothing



4. Attach electrodes


Rub skin with alcohol pads where the electrodes and HPI coils will be attached (see figure below). Don't overdo it as the skin can be very sensitive and fragile.

Use tissues to gently wipe-off excess alcohol.

hEOG: Attach an electrode on the outside of the subject's left eye (hEOG left) and on the outside of the subject's right eye (hEOG right). Make sure that the electrodes are in line with the eyes.

vEOG: Attach an electrode above subject's right eye (vEOG up) and below the subject's right eye (vEOG down). Make sure that the electrodes are in line with the eyes.

ECG: Attach an electrode on the left collarbone (ECG left) and on the right collarbone (ECG right).

GND: Attach an electrode on the back of the subject's neck (GND).

REF: Attach an electrode on the subject's right cheekbone (REF).




Figure 1. Standard locations of EOG and ECG electrodes














5. Check impedance of electrodes


Take the SIGGI impedance meter.

Turn it on with the middle white button.

Press middle white button again to enter impedance check menu.

On the side of the SIGGI attach GND to N

On the side of the SIGGI attach REF to -

On the side of the SIGGI attach the electrode of interest on +

Cycle through all your electrodes and make sure the impedance is below 10kOhm.




6. Attach HPI coils


Attach HPI coils with tape on the forehead below the hairline and behind the ears (where there is exposed skin) according the Figure 2 bove. The coils should be covered by the MEG helmet, so place them as high on the head as possible.

Tape the red coil to the shoulder. This one will not be used.

Attach the small receiver firmly on the forehead using tape or glasses.


Click here for more details on HPI placement.


Figure 2. Standard locations of HPI coils

















7. Digitize head-coordinate system


Turn on the Isotrack system (button on the back).

Select digitization on the acquisition panel.

Click Coordinate frame alignment

The order in which the fiducial points are digitized does not matter.

Remove the cap of the pen. Do not drop it as the point is very sensitive!

Rest the tip of the pen gently on the nasion or pre-auricular points (see green crosses in Figure 1) and press the button on the pen. Repeat for all fiducial points.

As a sanity-check see if the measured location of the pre-auricular points are in alignment.

If necessary, redo measurement by clicking Coordinate frame alignment again and repeating procedure.



8. Digitize HPI coils


Click HPI coils

The order in which the HPI coils are digitized does not matter.

Rest the tip of the pen gently on little hole in the middle of the coils and press the button on the pen. Repeat for all coils.

Stop the digitization after the fourth coil by holding the pen away from the receivers and clicking once. You should hear two beeps.

If necessary, redo measurement by clicking HPI coils again and repeating procedure.



9. Digitize headshape


Click Pen in the bottom right.

Gently stroke the point of the pen over several (especially bony) shapes of the head: eyebrows, nose, and along the skull, while pressing the button of the pen.

Stop when ready by holding the pen away from the receivers and clicking once. You should hear two beep



Click here for details on remote digitalization


Click here for a script to assess accuracy of HPI-digitalization.





10. Prepare the subject in the MSR


At all times make sure the subject knows what is going to happen. Make him/her comfortable in expressing his/her opinions.


Before moving the subject, secure any cables to the body (i.e.: shoulder) of the subjects using tape.

When the subject is seated, connected the cables of the sensors from the picture on the gantry to the corresponding electrodes on the subject.

Attach HPI coils (red plug) into the red plug at the left panel of the gantry.

Lift subject into helmet until the top of the head touches the top of the (inside of) the helmet.

Make subject comfortable with cushions and/or by raising the leg rests of the chair.

Close door of MSR (from the outside).

Check communication using intercom. Put the subject at ease.

Check that the subjects knows what to do.



11. Start recording


Instruct subject to remain still and relaxed, and announce the start of the experiment.

Start acquisition by pressing GO!

Tick record raw data

Tick record averaged data

Start experiment



12. Finishing recording session


When the paradigm has run, press Stop

Tell the subject that the experiment is over but to remain seated, and that you will be there shortly.

If averages were recorded as well, the first file that will be saved will be the averaged data and the second file will be the raw data.

Adhere to the standard file-naming scheme:

ProjectID_SubjectID.fif'*

If different tasks or conditions are recorded separately, use: ProjecID_SubjectID_TaskID.fif or ProjectID_SubjectID_ConditionID.fif.

Do not change the default path (ProjectName/MEG/SubjectID).

Disconnect electrode cables and HPI coils.

Move subject to chair outside of the MSR and gently remove all electrodes. Make sure to remove tape from HPI coils directly.

Instruct subjects to dressing room.