Magnetoencephalography (MEG)

MEG is a noninvasive brain mapping technique that records brain activity with great accuracy, based on the magnetic fields produced by the brain.

It's extremely accurate as to time (millisecond precision) and location (millimeter precision) of the brain activity.

Because the equipment is very sensitive to stray electromagnetic signals, the MEG system is housed in a special magnetically shielded room.

Using MEG to Plan for Brain and Epilepsy Surgery

When planning for brain surgery, doctors may use MEG to help identify areas of the brain that are responsible for functions such as speech, movement, and the senses, so that they may avoid these critical areas.

In people with brain tumors, MEG can localize the precise areas that are still healthy and functioning, despite the brain tumor and associated brain swelling.  Knowledge of these regions helps the surgeon to determine a successful surgical approach and how aggressively to resect a given area.

With a MEG-based roadmap of which areas to avoid, the surgeon has a better chance of performing the procedure without affecting critical brain functions.

Doctors also use MEG before epilepsy surgery to identify the specific part of the brain that is causing the seizures (seizure focus). The results of MEG studies, combined with MRI scans, allow surgeons to locate the specific areas of interest and plan for surgery.

How MEG Works

At UPMC, surgeons use MEG to:

• Identify which side of the brain (left vs. right) has dominant control over language.
• Localize specific language-related regions of the brain that are responsible for speech comprehension and production.

At UPMC we have developed a new method to localize brain functions and project these on brain MRI. Surgeons can use the results of MEG, in combination with MRI, during image-guided brain surgery.

How MEG Differs from Other Brain Imaging Techniques

Compared to other brain imaging procedures, MEG:

• Offers a direct measure of brain function. Other techniques — such as PET, SPECT, and fMRI — are secondary measures of brain function reflecting brain metabolism.
• Can record the brain events with time scales on the order of milliseconds. PET, SPECT, and fMRI have much longer time scales.
• Is completely noninvasive. It does not require an injection of isotopes or exposure to X-rays or magnetic fields. It's safe for children and infants, and to perform repeat tests.