MEG as an Imaging Tool: A Comparison

fMRI vs MEG: 

Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow within the brain. This technique is predominantly used to localize brain functions prior to surgery.

The difference between these two techniques predominantly lies in that fMRI measures blood flow relying on the fact that cerebral blood flow and neuronal activation are coupled. MEG directly measures brain activity through the magnetic field the neuronal activation produces. Due to these different measurement methods, MEG has much higher temporal resolution than fMRI, meaning that the measurement of the timing and location of brain activity is more precise with MEG.

EEG vs MEG: 

Similar to MEG, EEG measures and records electrical activity in the brain. However, unlike EEG, MEG can tell where in the brain this functional activity originates. This is because the human skull and the tissue surrounding the brain distort the electrical signals an EEG picks up, but affects magnetic fields produced by those electric signals much less and in a measurable way that can be accounted for.

EEG and MEG are great tools to use in conjunction with one another as the information they offer complement one another.

 

SPECT and PET vs MEG: 

A single photon emission computed tomography (SPECT) scan and a positron emission tomography (PET) are imaging modalities that show how blood flows to tissues and organs. Both are nuclear imaging scans that integrates computed tomography (CT) and a radioactive tracer. The tracer is what allows doctors to see how blood flows to tissues and organs. Before the scan, a tracer is injected into the bloodstream. This imaging technique is used to form a 3D image of the brain.

The difference between these two techniques predominantly lies in that, similar to fMRI, SPECT and PET measure blood flow averaging the measurements over a few minutes. This relies on the fact that cerebral blood flow and neuronal activation are coupled. MEG directly measures brain activity through the magnetic field the brain produces. Due to these different measurement methods, MEG has much higher temporal resolution than SPECT and PET, meaning that the measurement of the timing of brain activity is more precise with MEG. Due to the radioactive tracer required for SPECT and PET images, they are highly invasive and give rise to concern about radiation exposure in patients. MEG, however, is entirely non-invasive and with no radiation exposure.

iEEG vs MEG: 

Intracranial electroencephalography (iEEG) is a type of imaging that measures and records electrical activity in the brain just as EEG does. However unlike EEG, which uses electrodes placed outside the head, iEEG places those electrodes directly on the surface of the brain to record the same electrical activity from the cerebral cortex. This allows it to be much more accurate with respect to the location and timing of electrical activity in the brain. However, this method requires brain surgery. And because of this, iEEG cannot be used for all brain areas due to difficulty of access to all parts of the brain. MEG allows for accurate measurement of the location and timing of electrical activity in the brain, in a quick and easy non-invasive scan.

 

MEG vs CT: 

A computerized tomography (CT) scan combines a series of X-ray images taken from different angles around your body and uses computer processing to create cross-sectional images of the bones, blood vessels and soft tissues inside your body. A CT scan is a standard imaging modality used to assess the brain right after injury. However, because it only creates a structural image of the brain, it is not an imaging technique that can determine how the brain is functioning. Many brain injuries are not visible but show up in brain activation which MEG detects and measures. In addition, CT scans use ionizing radiation which has given rise to concern about radiation exposure in patients who have had many scans.

CT scans are a great complement to MEG scan data. MEG scan data can be superimposed on top of the structural image created by a CT scan to give a 3D image and recording of the brain and the electrical data it produces.

MEG vs MRI: 

Magnetic resonance imaging (MRI) is a medical imaging technique used to form pictures of the anatomy and the physiological processes of the body. MRI scanners use strong magnetic fields, magnetic field gradients, and radio waves to generate images of the organs in the body. Because of it’s use of magnets to image the body, some patients with certain types of implants are not able to have an MRI scan. However similar to CT, MRIs creates a structural image of the brain and therefore isn’t an imaging technique that can asses how the brain is functioning. Many brain injuries are not visible structurally but show up in brain activation and connectivity which MEG detects and measures.

However, MRI scans are a great complement to MEG scan data. MEG scan data can be superimposed on top of the structural image created by an MRI scan to give a 3D image and recording of the brain and the electrical data it produces.

 

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