magnetoencephalography- by anuj malik

Seminar On The Topic:

“MagnetoEncephaloGraphy”In this Presentation of mine; I’ll introduce you

regarding-

M.E.G.- Overview.

Origin of the Signal.

Entire Setup of the Process.

S.Q.U.I.D.S.

JosephSon Junctions.

Detecting Brain Activity.

Magnetic Shielding.

Benefits of Employing this Technology.

Future Scope of M.E.G. Technology.

Just An Overiew….. What Actually It Is…??

MagnetoenCephaloGraphy (MEG) is a technique for mapping brain activity by recording magnetic fields produced by electrical currents occurring naturally in the brain, using very sensitive magnetometers.

M.E.G. Signals were first measured using a copper

induction coil as the detector. 

V

Skull

CSF

Tissue

MEG

EEGB

- Non-Invasive Measurement.- Direct Measurement.

ScalpRecordingSurface

CurrentFlow.

Orientationof Magnetic Field.

Origin of the signal

Actual Phenomenon:

Currents in Neurons create very tiny Magnetic Fields.

MEG uses SQUIDs to detect these Magnetic Fields.

Magnetic Signals from the brain are only a few fT in strength.

Needs a Magnetically Shielded Room.

Entire Setup of the Process

S.Q.U.I.D.S….

Superconducting Quantum Interference Devices.

Superconducting material is niobium or lead alloy with Gold/Indium.

Cooled to low temperature with either liquid He (4K) or N (77K).

Manufactured at NIST in Boulder.

Noise levels about 3fT*Hz(-1/2).

Axial Gradiometer

Recording Surface

Neuronal Source

Capturing The Signal:

For a gradiometer of this type, a signal from cortex looks different between the two coils because of the distance between the two coils.

A signal from far away, however, will look similar in size to the two coils.

This gradiometer principle can help further with the challenging problem of measuring small source that exist in an electro-magnetic environment with many large source (subways, elevators,computers, etc.).

Josephson Junctions

Two superconductors separated by a thin insulating barrier:

A small current will tunnel across the barrier:

The constant current Ic depends on temperature and magnetic field.

SQUIDS measure fractions of the phase difference in terms of the flux quantum h/2e.

Detecting Brain Activity 50,000 neurons need to fire to generate a

Readable signal. Neurons near the outside of the brain generate

the strongest signals.

Magnetic Shielding

Rooms for MEGs have walls made of Aluminum and MU-metal (a type of nickel-iron alloy with extremely high magnetic permeability).

Aluminum shields from high frequency Noise. MU-metal shields from low frequency noise.

Let The Pictures Speak:

Sensor layout: recording from 160 channels

Response peak at 98ms after onset of an auditory stimulus, in the left and right temporal lobes.

What is the benefit of using MEG?

EEG

MEG

-As high temporal resolution as EEG … … but much easier and quicker to set up (kids, patients)

-Magnetic fields are not differentially attenuated …. …. easier to get a reasonable estimate of source over time.

- Sensitivity to within-subjects effects.

MEGs are used in research to measure the time course of brain activity.

MEGs can detect Epilepsy, as well as detect areas of the brain that are most important to avoid during surgery.

Does not depend on head geometry like EEG.

Magnetic fields decay faster over distance than electric fields.Few Other Notable PointS-

MEG is a technique that allows you to

(i) record brain activity directly, withexcellent temporal resolution (ms)

(ii) design within-subjects experiments and evaluate single-subject data

(iii) test models of cognitive processes and evaluate how these models map on to the brain.

SummmariSation:

THANK YOU ALL..

Presented By:Anuj Malik.

Roll No. MT-2112607[E.E.E.] M.Tech.

FOR YOURS PRECIOUS TIME....

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