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fMRI is a non-invasive neuroimaging technique that tracks blood flow in different areas of the brain based on mental tasks performed by the patient. It can help develop our understanding of brain function and organization, but its disadvantages include difficulty distinguishing hemodynamic responses due to neural activity from responses due to other events in the body.
Functional magnetic resonance imaging (fMRI) is a specialized version of an MRI. Instead of focusing only on brain tissue imaging, it also tracks blood flow in different areas, based on certain mental tasks performed by the patient. This reactive blood flow is called hemodynamic activity. The availability of fMRI has increased dramatically since the early 1990s and has become one of the most common forms of neuroimaging.
It has long been known that changing areas of neural activity in the brain cause changes in blood flow through these areas. When nerve cells in the brain or elsewhere become active, they consume oxygen from the blood. Unlike muscle cells, they don’t have nearby stores of glucose and oxygen, and blood flow must immediately change to accommodate increased neural activity. This leads to localized areas of deoxygenated blood where nerve activity has taken place, and these areas are what fMRI can see.
The magnetic properties of blood differ depending on whether it is oxygenated or deoxygenated. This magnetic signature is what is read by a functional magnetic resonance scanner. The technology for this was first developed in 1990 and has opened up many potential opportunities for developing our understanding of brain function and organization.
When a patient undergoes an fMRI procedure, it can last anywhere from 15 minutes to two hours, depending on its purpose. It is very important that the patient remains completely still throughout this time in order to obtain usable images. This can be problematic for young children or those with certain psychological conditions, but attempts can be made to meet the needs of these patients. Subjects may be presented with various sensory information or asked to perform mental tasks such as memorization during the course of the exam, while a physician reads and interprets areas of brain activity as they are displayed on a screen.
The greatest advantage of fMRI is that it is completely non-invasive and does not require the injection of radioactive contrast dye or similar material. This means that the patient is not exposed to unnecessary radiation. The duration of the procedure can also be very short if necessary.
The disadvantages of these procedures are related to the nature of what they measure. That is, hemodynamic responses due to neural activity are sometimes difficult to distinguish from responses due to other events in the body. For this reason, when fMRI data is published, it usually takes the form of aggregated images, lumped together from data collected over time from many different subjects.
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