Magnetoencephalographic telemetry in epilepsy using OP-MEG sensors

Epilepsy is a common condition caused by episodes of abnormal electrical activity in the brain resulting in seizures. An important tool in the diagnosis of epilepsy has been the electroencephalogram (EEG). However EEG is limited by its spatial accuracy in locating exactly which area of the brain is producing the abnormal activity. In addition EEG signal is significantly distorted by muscle and movement artefact, which is especially problematic if the patient has a seizure during the recording. Magnetoencephalography (MEG) is another form of brain recording that is superior to EEG in localising abnormal activity. Moreover, MEG signal is only minimally affected by muscle or motion artefact. However, current limitations of traditional MEG include the fact that patients cannot move in the scanner, which is particularly limiting if the patient has seizures during the recording. Also, MEG systems are expensive which has meant that the technique has until now been reserved for research and only limited clinical scenarios.

We aim to introduce a new MEG technique (OP-MEG) that uses sensors worn within a helmet, so patients can move freely. This property also means that very long MEG recording of patients is possible, increasing the chances of capturing abnormal brain activity related to epilepsy. As the head is not fixed in the scanner, OPM-MEG recording of seizures is much safer. OPM-MEG sensors do not require super-cooling technology unlike traditional MEG, which will significantly reduce costs. By using OP-MEG in epilepsy patients, we aim to provide highly accurate information on the type of abnormal electrical activity associated with the epilepsy and where in the brain it originates. In addition, we will use OP-MEG to accurately map important brain areas for speech production, a key step in planning for epilepsy surgery. As such OP-MEG has the potential to revolutionise the way brain electrical activity is recorded.

Currently, scalp electroencephalography (EEG) is the key non-invasive investigation in the diagnosis and treatment of epilepsy. However, it has a number of significant limitations, including spatial and temporal filtering and susceptibility to artefacts from muscle and movement. Magnetoencephalography (MEG) is an alternative non-invasive brain scanning technique that gives a unique window into whole brain function. MEG offers specific advantages over scalp EEG, including superior source localization accuracy and better immunity to muscle artefact. However current limitations of conventional (superconducting) MEG are 1) it is a one-size-fits-all scanner, which means sub-optimal sensitivity in a number of people 2) the scanner environment is unnatural and claustrophobic and subjects must remain still, a significant factor when considering epilepsy 3) Due to the restrictive environment, recording time for clinical MEG studies are briefer than EEG (1-2 hours) meaning that MEG recording of seizures, the most useful electrophysiological data for surgical planning, are rare 4) MEG systems are expensive and support intensive, as a result there are only 10 systems in the UK. As such the clinical benefit of superconducting MEG systems has been limited.

The aim here is to bring a new type of MEG system (OP-MEG), which will be worn on the subject's head (allowing them to move freely whilst being scanned) into clinical practice. We expect OP-MEG to identify common electrophysiological abnormalities (e.g. epileptic spikes) with greater spatiotemporal accuracy than scalp EEG, and have much better immunity to muscle and motion artefact when recording seizures. OP-MEG will also make prolonged MEG recording of patients over several hours a possibility, a property not readily associated with traditional MEG. This technology has the potential to revolutionise how brain neurophysiology is performed in future.

Epilepsy is a common neurological condition that currently affects 600,000 people in the UK. A third of these cases are resistant to drug treatment (refractory epilepsy), but may respond to epilepsy surgery. Our initial aim is to validate OP-MEG as an additional investigatory tool for diagnosis and characterisation of a range of refractory focal epilepsies (affecting part of the brain), and to aid potential epilepsy surgery planning for suitable patients. In addition the use of OP-MEG post-surgery could be a valuable tool in assessing likelihood of seizure freedom for this group. We also aim to perform much longer MEG recording of patients with epilepsy than is done currently using OP-MEG, ultimately leading to an ambulatory OP-MEG telemetry service within the hospital.

One particular subset of epilepsy patients that would benefit greatly from this technology are children, as the restrictive nature of both scalp EEG and traditional MEG have made diagnostics challenging in this group. OP-MEG can be performed while the subject moves within their environment, thus theoretically improving the chance of capturing useful data during (ictal) and in between (interictal) seizures, and maintaining safety of the patient.

OP-MEG can also be translated to other conditions to provide further information on pathogenesis and direct future therapeutic avenues. Cortical plasticity during recovery from stroke, and understanding the motor networks underlying limb tremor are two such directions. At a physiological level, OP-MEG would be ideal to image sleep states in a comfortable setting (as opposed to head fixed associated with traditional MEG) and inform of the neural basis for critical processes during sleep such as memory consolidation and how this affected in sleep disorders. The translation and validation of OP-MEG has the potential to revolutionise how brain neurophysiology is performed in future, and so is of significant scientific and clinical relevance.