- The dewar should be tilted at the mark for seated recording.
- If it is an auditory experiment, ask the particpant to insert the eartips before raising the chair.
- Bring the dewar forward until it is directly above and centred over the participant’s head. Ask the participant to rest the back of their head inside the helmet and reposition until it is comfortable for the participant to lean their head in the scanner.
- Push the cage back as far as possible before the participant’s head is raised inside the helmet. Then, slowly raise the chair until the participant can feel the top of the helmet lightly touching the crown of their head. (see Section 4.5, in Chapter 4 MSR - Magnetically Shielded Room). Ask the participant to breathe deeply and “slouch” down in the chair to simulate relaxation during the course of the experiment.
- Once the participant has relaxed, slowly raise the chair again
until the participant can feel that the top of their head is near
to/touching the top of the helmet helmet. If it is a visual
experiment, the participant's head should be as close to the top of
the sensor helmet as possible without blocking their view of the
screen.
![[Caution]](images/html-admon/caution.jpg)
Caution Care should be taken when adjusting the chair height while a participant is seated under the helmet. Always adjust the chair very slowly in small increments when their head is well inside the helmet. - Move the projector screen to the appropriate distance from the participant’s face. Check that the participant can see the stimuli properly on the screen.
- Give the response device to the participant and show them how to hold it comfortably (a cushion may be placed on the lap).
- Remove the Polhemus head rest.
- Ask the participant to sit up.
- If it is an auditory experiment, ask them to put the ear tips connected to the Etymotic tubes. Participants should compress the ear tips with their fingers until the sponge becomes slim enough to be inserted into the ear canal. Once the ear tip is inside the ear canal, the participant should hold it in place for a few seconds until the sponge has expanded sufficiently to provide a snug fit.
- Whilst the participant is inserting the ear tips, tilt the dewar to the mark on the dewar arm designated for the supine procedure.
- Move the RC cage as far back as possible.
- When the dewar is tilted at the correct angle, bring it forward until it is almost touching the top of the bed.
- Raise/lower the bed to roughly the same height as the dewar helmet.
- Place a foam pad inside the dewar helmet where the participant’s head will rest.
- Ask the participant to move their head into the helmet. This will require guidance.
- Place the etymotic tubes so that they are lying on the participant’s body and over the foot of the bed. Ensure that the weight of the tubes is not pulling them across the body or over the side of the bed. Allow the participant plenty of slack in the length of the etymotic tubes whilst they try to get themselves into position.
- Instruct the participant to move down the bed so that they have enough room to lie down but not hit their head on the helmet. Then he/she should wriggle back up the bed and get their head as far as possible inside the helmet. This procedure can be difficult so give the participant as much help as possible. Hold the dewar steady with the handles until the participant is in the correct position.
- Make sure that the ear tips do not come out of the participant’s ears. You may want to use tape to hold the ear tips in place.
- If the supine screen is required, place it in position, verifying that the stimuli are visible to the participant.
Some patients will require special attention. Under these circumstances the experimenter who booked the MEG session is ultimately responsible for the welfare of the patient. The experimenter should remain in MEG for the duration of the experiment.
In case of an emergency, the operator should explain to the patient how to get out of the helmet and get off the bed without assistance. To evacuate patients quickly, sheets can be placed under the patient.