MEG Data Acquisition Checklist

Click on the checklists to mark your progress through data collection.

Prepare Control Room & MSR

Prepare MEG system

Login to the Console, start MEG Acquisition program (megacq).
Load latest Tuning file, check quality of channels.
"Heat Sensor", "Reset Channels" as necessary.
- See this flowchart Noisy Channels, or for a more detailed process see this walkthrough To fix noisy channels.
Exit Tuner and return to megacq. Adjust Settings
- Select Project, or create new.
- Input pseudonymised participant details from Participant Logging Computer (PLC).
- Adjust Acquisition parameters or load settings...
  File -> Load settings .
- Create or adjutst stimulus generation, on-line averaging (as necessary).

Prepare participant

Offer bathroom break.
Explain preparation procedure.
Explain experiment.
Have participant read and sign ethics consent and screening questionaire.
Have participant remove metal objects, and do a comprehensive check with both metal detectors. Participant to change into scrubs if necessary (show participant to Changing Room and show scrubs sizes that are available).

We are trying to reduce our laundry bill so only use scrubs if necessary e.g. metal in clothing.

Attach electrodes

Reusable and disposable electrodes available for use as required.

Clean hands with provided Alcohol Gel Sanitizer.
Ask participant to sit in Digitisation Chair.

When ready to attach a reusable electrode:

Carefully attach a sticky disc to the electrode, centering the hole over the grey Ag/AgCl. Remove the paper protective cover, exposing the disc adhesive.
Using a gel-filled syringe and blunt needle, place a drop of gel in the electrode center and place the electrode on the prepared site.
Do not pull on the cable when applying it or when attached. Apply Micropore tape as necessary to help secure it in place.

If using the NeuroTab disposable electrodes.

Remove the transparent backing from the electrode and place the electrode on the prepared site.
To ensure good contact, apply pressure to the center of the electrode and move to the edges.
Do not pull on the cable when applying it or when attached. Apply Micropore tape as necessary to help secure it in place.

For either electrode type:

Where necessary, remove makeup with the provided Micellar water and cotton pads.
Rub skin with alcohol wipes where the electrodes and HPI coils will be attached (see Figure 1 below).

Don't overdo it as the skin can become sensitive.

Some Operators also like to then abrade the skin with NuPrep paste.
- Using one of our small stainless steel bowls, squeeze out some NuPrep and rub it onto the skin using a cotton bud.
- Use tissues to gently wipe-off excess NuPrep as it is non-conducting (some Operators then like to re-rub the skin with an alcohol wipe).
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).
vEOG: Attach an electrode above subject's right eye (vEOG up) and below the subject's right eye (vEOG down).

In both cases, make sure that the electrodes are in line with the eyes - horizonally & vertically.

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

Note

REF may not be required for the bipolar EOG, ECG, but use as necessary if channels are noisy.
For EMG, site REF electrode where required/as per your paradigm.
Use Micropore tape over the electrodes to help hold them in place.

Our Electrode input on the gantry is to the right of the subject, so we use the right eye for vEOG.

Check impedance of electrodes

Use the SIGGI II impedance meter

Press the white button, labelled Enter/Esc, on the jog-shuttle to turn on.
Press the white button again to enter Impedance Meter menu.
On the top side of the SIGGI ("Single-Ch-In") plug GND electrode into "N".
On the top side of the SIGGI plug REF electrode into "-".
On the top side of the SIGGI plug the electrode of interest into "+".

If measuring EEG cap impedance, use the provided adapter.

Cycle through all electrodes, and make sure the impedance is <10kOhm.
Quit Impedance Meter by selecting Return symbol and press Enter/Esc.
Select Power off via the jog-shuttle and press Enter/Esc.

Attach HPI coils

Why do we attach HPI coils?

Our HPI coils are energised at different frequencies (now 25Hz separation) compared to the default
(HPI Coil Placement and Frequencies)

If necessary test the HPI coils first, for continuity, uisng our HPI Coil Tester
With many thanks to Gary Chandler & David Hayes (MRC-CBU).
Attach HPI coils with either Tegaderm tape, Blenderm tape, or Micropore tape, on the forehead below the hairline, and behind the ears (where there is exposed skin) as shown in Figure 2 below.

Note

If using Micropore, a good trick is then to mark the center of the tape-covered HPI coil with a pencil to aid digitisation/locate the stylus tip correctly.
The coils must be covered by the MEG helmet/sensor array, so place them as high on the head as possible.
The coils behind the ears as high up as possible, without being in the hair.
The coils on the forehead well separated, but not in the hair.
The coils should not be directly under the Internal Active Shielding (IAS) reference channels, i.e. they should not be in the middle of the forehead, on the inion or near peri-auricular points.
The most precise HPI information is obtained when the coils are as far apart as possible but still within the sensor helmet.
Try avoiding situations where coils form a nearly perfect square.

If using only 4 coils, tape the 5th (YELLOW) coil to the shoulder.
This one will not be used or digitised.

Note

If desired, The 5th coil can be placed in the upper parietal region, preferably somewhat off midline.
Do not place the fifth coil directly on vertex as it may interfere with the Internal Active Shielding (IAS) if turned on.
Avoid the locations of the zero detectors when placing the HPI coils in order to prevent this problem. Refer to the IAS User’s Manual section found in the User's Manual for zero detector locations (middle shelf, right-hand white cupboard in Control Room).

Place the Polhemus goggles carefully on your participant, or attach the small receiver firmly on the forehead using tape. Make sure the coils do not come unstuck.

Figure 2: Standard locations of HPI coils

Please don’t rush the HPI coil attachment!

The better the coils are attached, the less likely they will move during digitisation and when the participant is sitting in the gantry chair.
- Less likely to produce a non-Acceptance when performing the megacq HPI check.

Digitise head-coordinate system

Make sure that the goggles don't move when making the digitisation.

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

Turn on the Polhemus system (switch on the back right of the unit).
Place the Transmitter cube in the grey bracket on the back of the Digitisation chair, with the cable pointing down.
Place the Polhemus goggles on your Participant.
Click Change next to HPI: not digitized! in the Acquisition control Settings panel.
Click Coordinate frame alignment in the Head shape digitization window.
Remove the black rubber tip cover from the stylus. Do not drop the stylus as the point is easily damaged!
- Rest the tip of the stylus gently on the first fiducial point, e.g. nasion or a peri-auricular point (see green crosses in Figure 2 above), and press the stylus button.
- Repeat this procedure for the other two fiducial points. You should hear two beeps after the 3rd point, signfying completion.
If time allows, as a sanity-check, to make sure the measured location of the fiducial points are in still in alignment...
- Click Coordinate frame alignment again, and select Check from the pop-up window.
- Digitise all three fiducial points (cardinal landmarks) again by pressing the stylus button after each beep. You should hear two beeps after the 3rd point, signifying completion.
- To abort digitise a point 75cm from the head origin/receiver, by pressing the stylus button at that distance.
- Deviations from the first digitisation will appear in another pop-up window after you have digitised all three fiducial points/landmarks.
- Deviations < 5mm are considered to be "OK", no redo required.
If necessary (values > 5mm), redo measurement by clicking Coordinate frame alignment again and selecting Redo.

Digitise HPI coils

The coils must not move relative to the head during the measurement!

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

Click HPI coils in the Head shape digitization window.
- Rest the tip of the stylus gently in the little hole in the centre of a coil and press the stylus button.
- Repeat this procedure for the other three coils, as shown in Figure 2 above.
Stop the digitisation after the 4th coil (if only using four coils) by digitising a point 30cm from the head origin.
- Hold the stylus that distance away from the receiver on the Polhemus goggles, and press the stylus buttton once. You should hear two beeps.
- If you were digitising all five HPI coils, you should hear two beeps after the 5th coil, signifying completion.
If time allows, as a sanity-check, to make sure the measured locations of the HPI coils are in alignment.
- Click HPI coils again, and select Check from the pop-up window.
- Digitise all four (or five) HPI coils again by pressing the stylus button after each beep.
- To abort, digitise a point 30cm from the head origin/receiver, by pressing the stylus button at that distance.
- Deviations from the first digitisation will appear in another pop-up window after you have digitised all four (or five) HPI coils.
- Deviations < 5mm are considered to be "OK", no redo required.
If necessary (values > 5mm), redo measurement by clicking HPI coils again and selecting Redo.

Digitise head shape

Leave the Polhemus goggles in place on your participant, then ...
Click Pen in the bottom right (Additional Data) window.
- Gently stroke the tip of the stylus (usually with the black rubber tip cover in place) over several (especially bony) shapes of the head ...
  eyebrows, around the eyes, nose, and along the scalp,
  ...to capture the head shape, while pressing the button of the stylus.
- At least 200 extra points would be the minimum number to digitise.
Ideally select the cardinal landmark locations again as the last 3 points you collect.
Stop when ready by digitising a point 30cm from the head origin.
- Hold the stylus that distance away from the receiver on the Polhemus glasses and click the stylus button once. You should hear two beeps.

Prepare the participant in the MSR

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

If using the EyeLink 1000 Plus

See the [EyeLink Operations Guide] for more detailed usage.

NOTE: STIM PC will need to be powered up to allow network communication to the EyeLink PC
(both APC Back-UPS 1400s will need to be powered).

Switch on 6-way bar plug on table alongside EyeLink Host PC (to power EyeLink camera (on desk), Host PC, and monitor).
EyeLink Batteries: Use a fully charged battery where possible.
- Press the TEST button to check the power level (batteries #1 and #2).
- Power on, and press the TEST button (new batteries #3 and #4).

"A battery with 2-3 hours left should be fine for a short experiment. Do not risk using it for a 2-hour experiment"(SR Research).

Put any used battery on charge as required.
- Make sure battery is switched OFF when charging.
- #1 and #2: AC Adapter Orange LED will extinguish when battery is charged.
- #3 and #4: AC Adapter Red LED will change to Yellow when battery is charged, eventually Green.
- Unplug battery once fully charged, switch off AC Adapter (at Mains socket).
- DO NOT leave a battery on charge overnight, or unsupervised!
  - Leave a strip of Micropore on battery to signify charging required the following day.
Swap to a new battery between Acquisition sessions. Put the used battery on charge.
Take a battery into the MSR. Place in front left corner (as viewed from gantry chair).
Arrange power cable around the edge of the MSR, avoiding any loops. Attach power cable to battery and to FO Camera Head/IR Illuminator. Switch on battery.

NOTE: If you don’t power the Camera Head/IR Illuminator first, the Host PC will complain when "EyeLink” starts up (ticking sound).

Place FO Camera Head/IR Illuminator on small table. Position table as required, use provided table risers as necessary.
Turn on EyeLink 1000 Plus Host PC and monitor.
- Select "EyeLink" with the mouse, or just wait.
Set up EyeLink FO Camera Head/IR Illuminator as per usual...
- Adjust Camera Head position, remove lens cap, adjust focus/thresholds etc.

NOTE: You can view the EyeLink IR lamp via the MSR camera monitor on the wall in the Control Room - helps in checking lamp alignment on the participant.

Start recording

Instruct participant to remain still and relaxed, and announce the start of the experiment.
Start Acquisition by pressing "GO!".
Tick Record raw.
Tick Average (if required).
Start experiment on Stim PC.

Finishing recording session

When the experiment has finished, press Stop.
Inform participant that the experiment is over, to remain seated, and that you will be in there shortly.
If Average was ticked, the first file saved will be the averaged data and the second file will be the raw data.
Name your files as per your usual file-naming scheme.
Do not change the default path (ProjectName/SubjectID/Date).
Enter MSR, disconnect electrode cables and HPI coils. As a help, ask participant to hold cabling.
Lower chair by using foot pedal, and pull chair out from under the gantry.
Help participant up out of the chair (if required), and escort them back to the Digitisation chair. When seated, gently remove all electrodes and tape. If used, remove the Tegaderm tape from the HPI coils as soon as convenient - see [Tidying Up] page.

MEG Data Acquisition Checklist

Prepare Control Room & MSR

Prepare MEG system

Prepare participant

Attach electrodes

Check impedance of electrodes

Attach HPI coils

Digitise head-coordinate system

Digitise HPI coils

Digitise head shape

Prepare the participant in the MSR

If using the EyeLink 1000 Plus

Start recording

Finishing recording session

Tidying Up