What is Magnetoencephalography (MEG)?

3-D model obtained from MRI
and MEG scan displays epileptic
seizure source.
(Source: Illinois MEG Center)

Magnetoencephalography is a technique that measures magnetic fields generated by the electrical activity of neurons (nerve cells) in the brain. MEG may be used in a similar way to an EEG to identify abnormal brain activity and to determine from where it is coming. MEG is a functional imaging technique, meaning that it looks at brain activity, not simply brain structure.

MEG is most often used to identify abnormal magnetic signals of epileptic activity. Advanced computer analysis of these signals determines their likely source within the brain and, by mapping these locations on a patient’s MRI images, the epileptic focus and source of a patient’s seizures can be pinpointed. This information will help doctors more successfully plan surgical therapies. MEG can also localize important normally functioning areas of the brain so that surgery for brain tumors or vascular malformations can remove only what is absolutely necessary.

The benefits of a MEG , when compared to other brain imaging technologies, include:

2-D MRI Scan
(Source: Illinois MEG Center)

• Direct measure of brain function. Other brain functional imaging techniques, such as fMRI, PET, and, SPECT are secondary measures of brain function, reflecting brain metabolism or blood flow.
• Very high temporal resolution. Brief events that occur in milliseconds can be resolved using the MEG, which differentiates it from fMRI, PET, and SPECT, that require a much longer time scale.
• Excellent spatial resolution and accuracy. Sources can be localized within half an inch.—the most precise functional localization of any other imaging device on the market.

The Illinois MEG Center houses a 306-channel whole-head MEG system with capabilities for recording 64-channels of simultaneous EEG data. Together MEG and EEG are used to map out control centers for critical brain functions, and for the localization of epileptic activity.

For patients with brain tumors or vascular malformations, MEG is typically used to map out the location of critical control centers for functions like motor control, touch, hearing, sight, language and memory. The specific functions to be evaluated will depend on the location of the brain lesion. In most cases, an additional set of MRI examinations will need to be performed. These may include both structural and functional MRI, and perhaps MRI spectroscopy (especially if there is a question of tumor invasion into nearby tissue).