What is MEG?Magnetoencephalography (mag-ne-toe-en-sef-a-log-ruff-ee) offers unparallelled functional information about brain activity and networks.
What is Magnetoencephalography (MEG)?
Magnetoencephalography (MEG) is a non-invasive imaging technique for investigating human brain activity. It allows the measurement of ongoing brain activity on a millisecond-by-millisecond basis, and it shows where in the brain the activity is produced. It is entirely non-invasive, silent, and with no applied magnetic fields, radiation or injections of any kind.
How does it work?
MEG operates by detecting and measuring the electromagnetic fields generated by individual neurons in the brain. The pattern of these electromagnetic fields is used to precisely determine the parts of the brain that are functionally active. These measurements and their patterns can then be accurately superimposed on an MRI or CT scan to provide information about the anatomy as well as the 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 structural information – or simplistically, they provide a picture of what the brain looks like in terms of its bones, vascular structure or soft tissues. MEG shows active areas of the brain, whether they be important for normal brain function, or a marker of an abnormality.
MEG is more similar to EEG, which measures and records electrical activity in the brain. However, MEG can much more accurately than EEG tell where in the brain this functionality originates. This is because the human skull and the tissue surrounding the brain distort the electrical signals an EEG picks up, but affects magnetic fields produced by those electric signals much less and in a measurable way that can be accounted for.
MEG works in conjunction with other imaging technology
MEG is a complement to other imaging methods. MEG is a great tool to use alongside EEG. 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 an anatomical image over which MEG data is superimposed so that you have a complete picture of the appearance and function of the brain, this is known as a Magnetic Source Image (MSI). Clinically, MSI provides mapped areas of function (language, hearing, touch, movement, visual) in presurgical patients. Additionally, fMRI and PET each provide vascular information of the brain, which add to the overall picture of brain health.
Indications for a MEG scan
MEG is predominantly used in the presurgical evaluation of patients with epilepsy and those with brain tumours undergoing tumor resection surgery. MEG is able to map the brain, specifically the areas used for motor control, language and our senses. This allows the surgeon to develop a surgical plan of how best to resect the area of the brain being removed, knowing how to approach this area, and which areas to avoid in order to best preserve the critical functions of the patient, while suffering minimal functional deficits (for example, loss of senses or control). For epilepsy, MEG has the added benefit of being able to localize, with precise accuracy, the location(s) where the epileptic activity originates. This information is used to determine if the patient is a good candidate for surgery and then similar as to what is done for tumour resections, to plan the operation itself.
What’s next for MEG technology?
There are a number of potential emerging clinical applications for MEG, including brain injury, post-traumatic stress disorder, Alzheimer’s disease, and autism.
Due to its fidelity and high temporal resolution, MEG can discern human brain networks with unprecedented accuracy. Neuroscientists believe that many brain 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 these disorders.