Magnetoencephalography (MEG)

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Overview

MEG is a non-invasive neurophysiological technique that measures the magnetic fields generated by neuronal activity of the brain. The spatial distributions of the magnetic fields are analysed to localize the sources of the activity within the brain, and the locations of the sources are superimposed on anatomical images, such as MRI, to provide information about both the structure and function of the brain.
Chart on how MEG works

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How does MEG work?

MEG is based on the ability to detect very weak magnetic fields that originate from electrical activity within the brain. These signals are detected with an array of devices known as Superconducting Quantum Interference Devices (SQUIDs) that are placed close to the scalp.


SQUIDs can detect tiny magnetic signals, much less than one-billionth the strength of the Earth’s magnetic field, and then convert these into recordable electric voltages. The SQUID array is mounted in a close-fitting helmet and is cooled with liquid helium. Neuronal signals may be events lasting from about a millisecond for an action potential, tens to hundreds of milliseconds for postsynaptic potentials or even multiple seconds for modulation of brain rhythms.

What is MEG used for ?

Common clinical applications include Detection of Epileptic Activity and Presurgical Functional Mapping. Researchers continue to use MEG to provide new insights into the neural basis of developmental disorders such as autism and dyslexia, as well as psychiatric diseases including depression, bipolar disorder and schizophrenia. Neurodegenerative diseases such as Alzheimer’s disease are also increasingly studied.

 

Brain with text on Sensory Function
Brain with text on Disorders
Brain with text on Epilepsy
Brain with text on Dyslexia

Core MEG System

306 Channel Magnetoencephalography (MEG) System

The core system at CoNiC is a state-of-the-art 306-channel system for MEG measurements (Elekta Neuromag TRIUX) with an integrated 128-channel EEG system (Elekta), located inside a 3-layer magnetically shielded room (Vacuumschmelze GmbH), and related amplifiers and acquisition systems. 

Elekta Neuromag TRIUX System

Magnetoencephalography (MEG) is rapidly becoming an indispensible brain imagingtechnology. Using sophisticated instrumentation, MEG detects the weak magneticactivity emanating from groups of neurons in the brain. Only MEG can precisely localize and record these millisecond phenomena that produce signals approximately a billion times smaller than the earth’s magnetic field.
 
 

Elekta Neuromag® TRIUX employs thin-film sensors of two different types integrated on 102 sensor elements. Each is equipped with three independent sensors with different sensitivity patterns.Each sensor element contains a magnetometer that measures the normal field component. These sensors are highly attuned to all signals, whether from deep or superficial sources - regardless of orientation. Each sensor element also provides two orthogonal planar gradiometer sensors for measuring the gradient components. The primary advantage of this triple-sensor design is that it provides a combination of three unique and mutually independent measurements instead of oversampling the same information as would be the case with an axial gradiometer or magnetometer-only system.

The lab is uniquely equipped with wide array of best-available equipment stimulation (visual, auditory, somatosensory, olfactory and more), measurement of and registration of responses (psychophysiology, eye tracking, behaviour and more) all handpicked, modified, installed and verified for millisecond timing in the MEG environment.

Integrated 128 Channel EEG

 

The Elekta Neuromag TRIUX MEG System has an integrated MEG-compatible 128 channel EEG system. It includes an EEG amplifier with 128 unipolar channels and a 32-channel EEG headbox for loose electrodes. We currently use 128 channel caps, 74 channel caps and 128-slit custom montage caps from EasyCap.
 

Integrated Bipolar Channels 

The Elekta Neuromag TRIUX also has 12 integrated bipolar channels, for recording of electrophysiological signal measurement system for measuring electrooculgraphy (EOG), electrocardiography (ECG), and electromyography (EMG).

Triggers and Time-Locking 

A total of 32 digital channels and 24 analog channels are sampled in parallell and synchronized to the MEG, EEG and biochannels data.

Magnetically Shielded Room (MSR)

All MEG/EEG recordings are done within a two-layer MSR, model Ak3B from Vacuumschmelze GmbH. It is a passive, magnetically shielded room with alternating layers of Permalloy (two layers) and aluminum (one layer). It also have coils for internal active shielding and coils for external active shielding.

 

Data Analysis Software

CoNiC is installed with a comprehensive data analysis suite for magnetoencephalographic and electroencephalographic data acquired with Elekta Neuromag.
 
  • Signal Processor
  • Signal Plotter
  • Source modeling
  • MRI integration
  • Minimum current estimation (for non-diagnostic use only)

 

Other than this, we also work with open source data analysis softwares (like MNE Python) to process time-resolved neural signals.
 

Data Storage & Management

The data generated per acquisition in MEG is of Gigabytes. The data generated is locally stored in the aquisition work station, and periodically will be transferred to our Network Attached Storage (NAS). The total capacity of NAS is about 50TB. The total storage has been fragmented to about 25TB for MRI and 20TB for MEG respectively. All the storage and back-up systems are connected by local network to ensure smooth & safe data transfer and storage. The NAS has been configured to be compatible to store the MEG data in the required format. The handling of data and its delivery to the collaborators are followed according to the SOP.

 

 

Equipment for Stimulation of Subjects

Stimulation Equipment

1. Auditory Stimulation
The MEG system is equipped with a binaural auditory stimulator with two tubal-insert earphone sets for eliciting auditory evoked fields. The audi­tory stim­u­la­tion paradigms for the subjects are typically controlled via Compumedics Neuroscan's STIM2 stim­u­lus presen­ta­tion and exper­i­men­tal design system.

STIM2 is fully integrated with the Cedrus StimTracker system which uses photocells and auditory threshold detection to identify stimulus onset with the greatest accuracy possible.

2. Somatosensory Stimulation
The MEG system is also equipped with an electrical stimulator for eliciting somatosensory evoked fields. It consist of Digitimer's DS7A single channel current stimulator system and a stimulus electrode with felt tips for median nerve stimulation.

A hand gripping in air
Equipment for Registration of Subject Responses

Response Equipment

Finger Response System. The MEG system is equipped with a bilateral finger response system working on fiber optics for detecting subject responses.

Processes

Workflow for Subject Preparation & MEG Measurement

MEG workflow chart

MEG system can provide real-time mapping of brain activity by non-invasively measuring the magnetic fields produced by the brain. The MEG system @ CoNiC is basically focused on studying cognitiion based tasks which includes basic research within cognitive neuroscience in the areas of memory, language, attention, perception, pain, music, decision making, emotion and others, performed on healthy adult populations.

The STIM2 system with our MEG is a comprehensive stimulus presentation system consisting of a library of sensory, cognitive and neuropsychological tasks. It contains well-defined and widely known paradigms for cognitive tasks.

STIM2 is fully integrated with the Cedrus Stim Tracker. This system uses photocells and auditory threshold detection to identify stimulus onset with the greatest accuracy possible.

Principle Categories of Tasks

Fourteen tasks are pre-programmed into the STIM2 software to provide a task library to build upon. Each task allows the user to modify parameters, such as, the duration, order of presentation, the inter-stimulus interval, performance feedback options, and many more. The programs are categorized as follow:

Additional tasks include pattern reversal, Naming, Visual tracking, spatial memory, Visual and Auditory continuous performance, Verbal learning, and Visual memory tasks.

MEG: A Safe Environment

MEG is safe for children and adults. Unlike with some imaging tests, the machinery is quiet and almost never produces a feeling of claustrophobia. During MEG testing, brain activity is ordinarily recorded in both wakefulness and sleep.

A MEG scan is noninvasive and painless with no injections, radioactivity or strong magnetic fields. MEGs have highly sensitive SQUID Sensors which needs to be protected from external magnetic fields and other noises. 
 
We are here to provide you the safest environment and make you aware about the potential safety hazards.

Getting Screened for Scan 

Precautions for Entering MEG Scanning Room

Safety Incharge

Please contact our safety in-charge regarding safety briefing and other safety issues:

 1. Dr. Sundramurthy Kumar, CoNiC Safety In-charge
     Email: s_kumar@ntu.edu.sg ; Phone: (65) - 6904 1185

 2. Dr. Sini Mathew, Assistant Director, Health & Safety, LKCMedicine
     Email: sinimathew@ntu.edu.sg ; Phone: (65) - 6592 3209