Magnetoencephalography, or MEG, is a technique for identifying and analyzing brain activity based upon the normal magnetic fields generated by the brain. Although this technique has been available for several decades, it is only recently that scanners involving the whole head have been available.
Because the physical properties of magnetic waves differ from those of electrical waves, MEG provides different, complementary information than the EEG. MEG recording is achieved using detectors that are placed near the head. The test is non-invasive, painless and safe.
Unlike MRI, the patient is not exposed to any magnets; metal objects do not pose any risk to the patient, however, metal (magnetic) objects can produce artifacts. Even metallic flakes in make-up and hairspray can alter the signal, so it is important to avoid using these products the morning of a test. Pacemakers and vagus nerve stimulators will not be harmed or altered in any way by this study, however, the wires can produce artifacts and the physician and technologist should be made aware of these devices prior to the test.
The magnetic waves recorded between seizures can be mapped in three dimensions onto an image of the patient’s brain derived from an MRI or CT, referred to as magnetic source images (MSI).
MEG has been approved for clinical use by Medicare as well as the Food and Drug Administration. Presently, many insurance companies are covering MEG. However, this is often on a case-by-case basis and may require efforts on the part of the patient, the patient’s epileptologist and the MEG center to coordinate this process.
MEG’s primary clinical use focuses on two areas: localizing the area or areas from which seizures arise in patients with epilepsy and identifying regions of normal brain function (e.g. vision, hearing, sensation, movement, language) in patients preparing to undergo brain surgery either for epilepsy or removal of a tumor or other mass lesion. MEG plays an important role in identifying the seizure focus in patients with epilepsy, particularly in those with seizures arising from areas other than the mesial (inner) temporal lobe. MEG also plays an important role in facilitating the planning of surgery and preservation of normal brain functions.