MEG Users //
Information for MEG Users
As an investigator working with MEG, you will be responsible for some of the parts of a scan, depending on the specific protocol. It is important that you become familiar with procedures related to the MEG. All imaging and behavioral data collected at MRN is stored on MRN's network servers. As part of study initiation, each investigator should receive a UserID and password to the data network. In addition, you will also be given access to MEG specific procedures and documentation and you will be added to the MEG Users email which will allow you to receive important information about the MEG and connect with other users. To request access, please contact firstname.lastname@example.org.
What is an MEG scan?
An MEG scan is a study of the magnetic activity in a participant's brain. The participant sits in a chair or lies on a table so that his/her head is in the MEG helmet which holds MEG sensors. The participant does some certain set of tasks that the researcher is interested in, such as listening to sounds, watching a visual task, and/or responding by pressing a button. This all takes place in a Magnetically Shielded Room (MSR), because the size of the brain's magnetic activity is much, much smaller than the ambient magnetic noise in the environment, and this noise has to be blocked out to be able to detect the brain's magnetic activity. The signals measured by the MEG sensors are sent to a computer outside the MSR. Outside, a Research Associate (RA) runs the tasks that are sent inside the MSR for the participant to do, and an MEG Tech runs the Acquisition program to acquire MEG data. Later, the data is analyzed and compiled with MRI images by the researcher's lab to determine what magnetic activity happened where in the brain during certain tasks. There are six parts to a scan: preparation, digitizing, after digitization prep, setting up participant in the scanner, running tasks / data collection, and clean-up.
Preparation: Either the investigator or MEG Technician will prep the participant, depending on the specifics of the study protocol and billing arrangements. Prep consists of:
- Making sure that the participant's head will fit in the helmet (if their head is large enough to be in question)
- Demetalling: removing metal that can cause artifacts in the data
- Placing HPI coils: these track where the participant's head is in the helmet during the scan so that movement can be compensated for in data analysis
- Placing bi-polar and single electrodes: these measure eye movement and heart beat (both of these can cause artifacts in data -- recording them can help remove the artifacts); also used as references and ground
- Placing EEG cap (if used): this records EEG signals during the MEG scan
- Testing electrodes: making sure that the impedance is low enough to get a good signal
Digitizing: Once the participant is prepped, someone (usually the MEG Tech, occasionally the RA) digitizes the subject's head. Digitizing is a process that allows the scanner to track where the measured activity occurs in the brain. It makes a map of the outside of the participant's head, so that the MEG data can be lined up with MRI data. While the MEG Tech digitizes, the RA sets up the stimulus.
- If needed, make a pair of eyeglasses for participant (if the participant needs them to perform a visual task adequately, or for their comfort)
- Demagnetize the participant's dental work (if needed)
- Double-check that the participant has no significant metal on them
Setting up participant in the MSR:
- Have the participant sit in chair. Warn them to sit back slowly so that they don't hit their head on the helmet. Place your hand on the helmet behind their head to protect their head.
- Check the participant's height in the chair. If short, remove the top black cushion and put the yellow neck cushion behind their neck.
- Connect HPI coils, bi-polar and single electrodes, and EEG to the scanner.
- If desired or part of protocol, put the tray in the chair for the participant to lay their arms on.
- Put a pillow under the participant's arms if desired.
- Ask the participant if they want their legs up or down.
- Have the participant put in earbuds (if used).
- Place response devices on participant's hands (if used).
- Put projector screen in place.
- Let participant know about camera and intercom.
- Make sure that the participant understands the first task.
- Leave the MSR and close the door.
- Immediately check with the participant over the intercom to make sure they can hear you. Let participant know that you'll be taking a few minutes to get set up.
Running tasks / data collection: Run tasks and collect MEG data during the tasks. It is important to make sure that the participant is safe and comfortable at all times. The RA will run the experiment stimulus. The MEG Tech will run the Acquisition program to collect data.
General steps for running a task:
- Tech: Start the Acquisition program and check all channels -- MEG, EEG, and bipolar. Heat, reset, tune, and/or fix channels as needed.
- RA: Prepare first task per protocol -- instructions, practice run, protocol set up, etc.
- Tech: Once the channels are all checked and the task preparation is complete, you are ready to begin recording. For most studies, you'll record 15 seconds of raw data, check the HPI coils, start average and hCPI, then let the RA know that you're ready to start recording data from the task.
- RA: Begin the task.
- Both Tech and RA: Each study will have something you need to watch to make sure that the participant understands the task and is responding appropriately and that the Acquisition Program is receiving the responses. This is usually a combination of raw data, button presses, averages, and the plotted averages. It's also important to watch the participant to make sure they are comfortable, awake, responding, and not moving excessively.
- Tech: When the task ends, stop the Acquisition recording and save the file/s (usually an average file and a raw file).
- Both Tech and RA: In between tasks (or during tasks, if they are long), either the RA or the Tech checks in with the participant to make sure they are okay. Often, the participant will get sleepy. Encourage them to wiggle and take deep breaths between tasks to wake themselves up.
Clean-up: The MEG Tech will assist the participant with clean up and the investigator will clean up the equipment. In general, clean up includes:
- Sanitize the chair, helmet, response devices
- Remove washables - pillow cases, etc
- Throw away used ear buds
- Turn off projector
- Restore stimulus equipment to standard setup
- Move projector screen out of the way
- Sanitize digitizer pen & goggles
- Have participant sit in digitizing chair in MEG control room (or prep room if they have an EEG cap)
- Remove HPI coils, bi-polar electrodes, and EEG Cap (if used). If participant's skin is too sensitive to tape removal, apply baby oil to tape before removing.
- Give participant a clean washcloth to remove electrode paste in bathroom. Also give them their locker key. Ask them to return to the MEG room for de-briefing.