fMRI: Definition, Uses & Limitations

Instructor: Danielle Haak

Danielle has a PhD in Natural Resource Sciences and a MSc in Biological Sciences

An fMRI is a type of medical imaging scan used to monitor changes in brain activity with varying blood flow. This lesson will explain why such a scan would be useful, how it works, and the strengths and weaknesses of using fMRI.

What Is fMRI?

As we all know, our brains are these incredibly complex organs that are responsible for making sense of all the stimuli we're confronted with every single second. This complexity can seem overwhelming, but there's actually a lot we can learn from studying how the brain responds in different scenarios. One way is to use fMRI.

Medical acronyms can be confusing, so let's break this down: fMRI stands for functional magnetic resonance imaging. An fMRI scan is used to get a picture of the brain and to assess what changes take place based on blood flow.

An example of what an fMRI scan of the brain might look like.
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How Does Magnetic Resonance Work?

You may already be familiar with a scan called an MRI - just like the fMRI, these letters stand for 'magnetic resonance imaging'. This family of tests uses a strong magnetic field and a series of radio frequency pulses to produce a map of the body.

Specifically, magnetic resonance scans target hydrogen atoms in the body without chemically altering any of the tissues. As a result, the procedure results in very detailed images with differentiated types of tissues, and is non-invasive, which is a huge benefit.

The fMRI is a specific type of magnetic resonance imaging that solely focuses on the small metabolic changes that take place when we're using a specific region of the brain. Without getting into too much of the nuts and bolts of the test, the detail of the image results from changes in blood flow.

We can zoom in to one region of the brain, and have the patient perform some activity. This stimulates the blood to flow in the activated region and the different amounts of oxygen in the blood result in different images during the scan.

Why Use fMRI?

Getting a detailed map of the brain sounds pretty cool, but why would someone need this information? There are two general reasons.

  1. First, scientists use fMRI to study normal functioning of healthy brains. (If you break apart the name, this makes sense: the fMRI is assessing the function of the brain.) fMRI can be used for brain mapping, which is the process of identifying which part of the brain is responsible for different activities, like reading, speaking, seeing, and hearing (among others).
  2. The information collected from brain mapping provides baseline data that can be used to then compare how different diseases alter brain functioning.

For example, if scientists understand which parts of the brain are active during walking, they can analyze how the brain functioning of a stroke patient has changed as a result of the incident. Or, they can monitor a progressive condition like dementia to study how brain activity changes as the disease progresses. In a patient with a growing brain tumor, the effects of the tumor on brain activity can be monitored as the tumor grows or as the patient undergoes various treatments.

In all of these cases, you can begin to understand the benefits of having a relatively fast (about one hour), non-invasive way to study the brain.

Benefits and Limitations of fMRI

As previously mentioned, benefits of fMRI include it being a fast, non-invasive procedure. The resulting images are more detailed than those produced by X-ray, CT scan, or ultrasound, and the tissues aren't chemically altered during the procedure. The scan is especially useful for identifying irregularities that might otherwise be visually blocked by another body part, like a bone.

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