What is Magnetoencephalography (MEG)?

MEG is an imaging technique which has millisecond time resolution and an excellent ability to localize brain function precisely. It is entirely non-invasive, with no applied magnetic fields, radiation or injections of any kind. Preparation and measurement times are short. Unlike MRI, it is completely silent and well tolerated, even by children.

What are its applications?

Currently, the main clinical (reimbursable) applications are for epilepsy and pre-surgical functional mapping. In clinical use MEG has been shown to lead to improved surgical outcomes. The clinical utility of MEG is however expanding fast to include the characterisation and diagnosis of a broad range of neurological and psychiatric conditions.

How does it work?

MEG operates by detecting at several hundred locations the extremely tiny magnetic fields generated by currents within the neurons of the brain. The pattern of these fields is used to precisely determine the parts of the brain that are functionally active. These locations can then be accurately superimposed on an MRI or CT scan to provide information about both the anatomy and function of the brain.

How does MEG compare with other brain imaging modalities?

MEG data differs from the information provided by CT or MRI alone, which provide only structural information. MEG shows active areas, whether they be important for normal brain function, or a marker of pathology.

MEG is much more spatially accurate than EEG, because the skull and the tissue surrounding the brain affect the magnetic fields much less than they do the electric. Therefore, MEG offers greater localization accuracy than traditional EEG tests.

MEG works in conjunction with other tech

MEG is well placed as a multi-modality imaging tool. It combines well with EEG, since each technology detects an orthogonal component to the other. For example, MEG detects epileptic spikes in about 75% of patients, whereas EEG detects them in about 60%. When MEG and EEG are combined, almost all spikes are detectable. MEG combines with MRI or CT scans to give a functional-anatomical image known as a Magnetic Source Image (MSI). fMRI and PET each provide vascular information, which add confirmations to the direct neurophysiological measurement of MEG.

What's unique about MEG?

The unique features of MEG include:

  • Direct measure of brain function. This is unlike fMRI, PET and SPECT, which are secondary measures of metabolism.
  • High temporal resolution. Events with millisecond duration/frequency can be resolved, unlike fMRI, PET and SPECT, which have much longer time scales.
  • High spatial resolution. Sources can be localized with millimetre accuracy. This includes those who have had past brain surgery, where EEG is severely distorted.
  • Completely non-invasive, safe and silent

How MEG benefits patients with epilepsy

For patients with intractable epilepsy, surgery is often the best solution to end seizures. MEG is used to localize interictal (between seizure) activity, which is usually the source of the seizures themselves. MEG is particularly useful when MRI is negative (does not show a lesion), or if routine EEG is inconsistent. MEG then guides the surgeon to a successful resection. Some findings may suggest a more complex situation, with a need for more investigations, or even the impossibility of surgery.

How MEG benefits patients with concussion

Concussion diagnosis has traditionally been highly subjective especially with regards to mild traumatic brain injuries which cannot be detected with MRI or CT. Using MEG, the classic slow waves that indicate a concussion injury can be reviewed by a clinician who is then able to recommend an accurate treatment plan for this injury.

How MEG is helping with Oncology

Another routine application of MEG is pre-surgical functional mapping (PSFM). This is useful for patients who have tumours, other lesions, vascular malformations, epilepsy and/or brain injury. MEG is used to map the exact location of the healthy areas near the pathology, so that surgery does not result in postoperative weakness or loss of function. These functional areas, known as eloquent cortex, can include those used for audition, vision, motor control, language, etc.

What's next for MEG technology?

There are a number of emerging clinical applications for MEG, including brain injury, post-traumatic stress disorder, Alzheimer’s disease, autism, stroke recovery, dyslexia, stuttering and others.

Due to its fidelity and high temporal resolution, MEG can discern human brain networks with unprecedented accuracy. Neuroscientists believe that many clinical disorders are caused by brain network interruptions. For example, evidence has shown that disruptions in the brain’s network can lead to both Alzheimer’s and autism. This positions MEG as the brain imaging modality of choice for studying and diagnosing these disorders.