Introduction:
The brain is an integral and vital organ of the central nervous system. The brain functions primarily by receiving and sending certain chemical and electrical impulses through the neurons. Therefore, assessing the structure and functioning of the brain can help diagnose various neurological conditions. Diagnostic techniques such as computed tomography and magnetic resonance imaging are well-versed in imaging the brain's structure; however, specialized techniques are required to measure electrical activity to assess brain functioning. Functional MRI (fMRI) and electroencephalography (EEG) are the most commonly used tools to determine brain functioning. EEG is a non-invasive test that employs sensors to assess the electrical activity in the brain. However, one of the most significant drawbacks of EEG is the inability to trace the origin of electrical activity combined with a decreased spatial resolution of the images. Hence there was a need for a more precise diagnostic neuroimaging tool.
What Is Magnetoencephalography?
Magnetoencephalography is a non-invasive diagnostic technique used to evaluate the electrical activity in the brain. It can precisely measure brain activity every milli-second and localize its origin. The neuronal electrical activity produces a certain magnetic field which can be analyzed and superimposed over the brain images to evaluate the brain's structure and function. It is an advanced and novel technique that measures brain activity while functioning. MEG is considered the gold standard in diagnosing and treating epileptic seizures as it is more accurate than EEG in mapping the seizure-generating areas.
What Is the Working Principle of Magnetoencephalography?
MEG examination uses a specialized helmet-like device that constitutes multiple magnetic sensors lined from the inside. The nerve cells within the brain receive and send signals by utilizing electrical and chemical signals as messengers. This results in a flow of electric current throughout the brain, producing magnetic fields that can be detected by the magnetic sensors used in MEG. By measuring this magnetic field, neuronal activity can be assessed in real-time while the brain functions. This can be conducted while the patient performs various activities like sleeping, listening to music, reading, or seeing pictures, thus helping to assess neuronal activity under various circumstances. However, the magnetic field produced in the brain is small; hence numerous sensors (>300) are required, which concurrently offer high-resolution images.
Where Is Magnetoencephalography Indicated?
MEG is indicated for the following conditions:
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To assess the functional areas of the brain (sensory and motor)
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To identify the source of epileptic seizures.
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To map the motor and sensory areas before brain surgery.
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To identify sensory and motor areas associated with autism, Alzheimer's disease, and traumatic brain injury.
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For advanced research on various psychological and neurological disorders.
What Are the Instructions to Be Followed Before the Procedure?
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Patients are advised to wear loose and comfortable clothes.
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There are no dietary restrictions; if any, the patients will be advised by their healthcare professionals.
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Patients can continue taking their routine prescription medicines.
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There is no fear of claustrophobia as MEG examinations are not conducted in closed units. However, if the patient is anxious, they may be given a mild sedative before the examination.
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In children, MEG may be conducted under general anesthesia.
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Patients are advised not to wear jewelry or metallic accessories such as hair clips, earrings, belts, buckles, eyeglasses, or hearing aids, as they may interfere with the magnetic field during the procedure.
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Removable dental appliances, watches, credit cards, pins, and mobile phones should be avoided.
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Patients should also avoid facial makeup or hair products such as hair spray or other cosmetics with metallic substances.
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Patients with cochlear implants, pacemakers, defibrillators, artificial heart valves, or other metal implants are not ideal candidates for MEG examination.
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Patients must carry their previous MRI or EEG reports to the diagnostic center.
How Is Magnetoencephalography Done?
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It is usually performed as an outpatient procedure. The patient will be assisted to the MEG procedure room, which is shielded from external electrical or magnetic fields.
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A few coils may be positioned and attached with tape to the head to place them relatively per the MEG sensors.
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The patient will be made to lie on an examination table or may be asked to sit on a chair.
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The patient will be positioned beneath the MEG helmet that contains the magnetic sensors.
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Depending on the study, the patient may be asked to perform various activities, and the brain functioning will be recorded.
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To identify the brain's sensory areas, patients may be asked to listen to sounds or music or observe a few images.
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The patient may be asked to push buttons or press a compressible ball for motor assessment.
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For language assessment, the patient may be asked to read.
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The procedure may take roughly around two to three hours, depending on the areas of functional mapping.
What Are the Post-procedure Instructions?
MEG is a non-invasive and painless procedure. Hence no special instructions are required. Patients can resume their routine activity and regular diet after the procedure.
What Are the Benefits and Risks Associated With the Procedure?
Benefits:
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It is non-invasive and painless.
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Highly sensitive and accurate in assessing brain functioning.
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No radiation is involved.
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It aids in the real-time evaluation of brain functioning.
Risks:
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MEG examination has no known risk to humans.
What Are the Limitations of the Procedure?
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MEG is contraindicated in patients with metal implants, pacemakers, and drug ports.
How Is MEG Superior to EEG or fMRI?
MEG is superior and more efficient than EEG or fMRI. It provides high-resolution images with a time resolution of milliseconds. fMRI and PET scans measure brain activity indirectly as they depend on oxygen consumption and radiotracer uptake to determine neuronal functioning. In contrast, MEG detects brain functioning directly from the electrical activity of the neurons. MRI units have the drawback of making loud noises and possibly making the patients feel claustrophobic. MEG units are devoid of noise, and only a helmet-like device is used hence no fear of enclosed spaces. MRI also requires the patients to remain still while capturing the images; however, no such restriction exists in MEG. MEG provides better temporal characteristics and spatial localization of brain activity than EEG or fMRI.
Similarly, EEG records the electrical activity where the electrodes must be placed on the scalp. However, in MEG, the sensors are attached to a helmet and hence do not touch the head of the patient. In addition, EEG is highly sensitive to extracellular electrical fields, thus resulting in reduced spatial resolution. Also, electrical fields tend to get distorted more easily than magnetic fields by factors such as cerebrospinal fluid, bone, or scalp.
Conclusion:
Magnetoencephalography is a novel, advanced neuroimaging technique promising in diagnosing and treating epilepsy. In addition, the meticulous application of MEG and cutting-edge research studies may prove valuable and extend its applications to various other neurological conditions.