Clinical neurophysiology

IFCN-endorsed practical guidelines for clinical magnetoencephalography (MEG)

The first IFCN-endorsed clinical guidelines for magnetoencephalography

This article presents the first IFCN-endorsed clinical guidelines for MEG.1

The first part deals with general features of MEG signals and their similarities and differences in comparison to EEG. Locations and time courses of the underlying neuronal generators can be inferred more accurately from MEG than from scalp EEG data.

The second part is about acquisition and analysis of MEG signals. MEG records extremely weak magnetic fields in the presence of a very noisy background generated by external electrical and magnetic equipment. Therefore, properly designed hardware and software are essential. To date, commercial MEG systems include about 300 magnetic-field sensors in a cryogenic vessel. The system’s main components, which characteristics may vary, are:

-the superconducting quantum interference device (SQUID) sensors with their related electronics

-the flux transformers that couple the neuromagnetic field to the SQUIDs

-the “Dewar”, a cryogenic vessel containing liquid helium.

In the third part, the authors review the clinical application of MEG, the most important being epilepsy. When structural brain MRI is negative, the selection of good candidates for epilepsy surgery is aided by MEG. Moreover, MEG has been found more effective than EEG in epilepsy screening.2 MEG has also proved to be helpful in brain pre-operative evaluation, including mapping of language function.3 The authors, then, describe possible future clinical applications of the method.

Finally the fourth part concerns practical considerations for clinical MEG recordings and considerations regarding special requirements for exploring functions of sensory cortices and motor system.

Key Points

-    The article presents the first IFCN-endorsed clinical guidelines for magnetoencephalography

 -    Locations and time courses of the underlying neuronal generators can be inferred more accurately from MEG than from scalp EEG data

- The most important indications for MEG are epilepsy and brain pre-operative evaluation

References

1) Hari R, Baillet S, Barnes G, Burgess R, Forss N, Gross J, Hämäläinen M, Jensen O, Kakigi R, Mauguière F, Nakasato N, Puce A, Romani GL, Schnitzler A, Taulu S. IFCN-endorsed practical guidelines for clinical magnetoencephalography (MEG). Clin Neurophysiol. 2018;129:1720-1747.

 

2) Ossenblok P, de Munck JC, Colon A, Drolsbach W, Boon P. Magnetoencephalography is more successful for screening and localizing frontal lobe epilepsy than electroencephalography. Epilepsia 2007;48:2139–49.

 

3) Tanaka N, Liu H, Reinsberger C, Madsen JR, Bourgeois BF, Dworetzky BA, et al. Language lateralization represented by spatiotemporal mapping of magnetoencephalography. AJNR Am J Neuroradiol 2013;34:558–63.