An MRI scan is a type of medical imaging scan that provides a static, or still, picture of certain parts or all of the inside of the body. They’re regularly used to diagnose a wide range of conditions. MRI scans are very useful in determining the causes of unexplained pain and help doctors diagnose or rule out cancer affecting various different organs and parts of the body.
A functional MRI, or fMRI, however, is a type of MRI scan that only looks at the brain or a specific part of the brain and is used to gain a dynamic, or moving, picture of brain activity. It’s helpful in diagnosing conditions that affect the blood flow to the brain, such as a stroke or a brain aneurysm, and in gaining a detailed image of parts of the brain prior to surgery.
In this article, we’re going to look more deeply into an fMRI vs MRI scan, what the similarities are, how the two scans differ and each of their benefits.
What is an MRI?
MRI stands for magnetic resonance imaging. An MRI scan is a type of scan that produces highly detailed images of the organs, tissues, bones and other physical structures of the body.
What is an fMRI?
Functional magnetic resonance imaging, known as an fMRI scan, is a type of MRI scan that focuses only on the brain and brain activity and blood flow.
MRI vs fMRI
An MRI scan of the brain will show the structures such as brain tissue and blood vessels - an fMRI of the brain will show how the brain is working. There are lots of similarities and differences between an fMRI scan and a regular MRI scan that are important to doctors when deciding which one to perform.
Similarities
Both an MRI scan and an fMRI scan are painless, non-invasive types of medical imaging scan. They both take place inside an MRI scanner; a long, tube-like machine with a large hollow centre, connected to various computers, and both utilise strong magnetic fields and radio waves to create images. During both an MRI and an fMRI scan, you will lay still on a bed that moves slowly into the MRI machine. Neither scan uses X-rays, meaning that there’s no risk of radiation exposure (like there is with CT or PET scans).
Differences
In terms of the brain, both scans can diagnose conditions such as a stroke or Alzheimer’s. An MRI will do this by highlighting a blocked or burst blood vessel in the case of a stroke, or a build-up of protein plaques and shrinkage of brain tissue seen in Alzheimer’s patients. An fMRI does this by taking a series of images over time, to measure blood flow to certain parts of the brain whilst you’re performing physical or mental tasks to highlight where there might be problems.
Although very similar, there are some distinct differences between an fMRI vs MRI including why they’re used and what they measure.
Uses
The main difference between an MRI scan and a functional MRI is why they might be used.
MRI
An MRI scan is used to create a detailed, standalone image of the organs and structures inside the body. It can be used on any part of the body, including the brain, to diagnose conditions ranging from degenerative disc disease in the back, Crohn’s disease, Alzheimer’s disease, strokes and certain cancers.
fMRI
An fMRI scan is used to measure dynamic changes in brain activity and blood flow to parts of the brain that may be interrupted by conditions such as a stroke or brain injury.
Key Measurement
The differences in the key measurements are important to doctors when considering whether to perform an fMRI vs MRI.
MRI
An MRI produces a snapshot of a one-off moment in time of the physical organs and structures inside the body and is extremely useful in diagnosing many conditions that affect many different parts of the body.
fMRI
Rather than a snapshot, an fMRI scan provides doctors with a better understanding of brain activity over time, so it’s a dynamic measurement, rather than a static one. During an fMRI scan, you’ll be asked to perform a number of tasks such as tapping a finger, squeezing one hand into a fist, thinking of a particular word or answering a question.
When we’re concentrating on such a task or we’re thinking, reasoning, recalling a memory or learning (mental processes that contribute to our cognitive function), our brains require more oxygen, plus more energy in the form of glucose. Oxygen and glucose are carried around the body to the organs, including the brain, by the blood. As such, when we’re moving, concentrating or mentally processing, we require more blood flow to the brain to supply it with oxygen and glucose.
During a functional MRI scan, blood flow to the brain changes as we carry out a task or think of something we’re asked to do. Doctors can then monitor these changes in blood flow and subsequent brain activity to ascertain which areas of the brain are activated when certain tasks are performed and which may be negatively affected by a lack of blood flow.
Temporal Resolution
Temporal resolution is a measure of how accurately medical imaging of the brain can measure changes in brain activity when it changes from a resting state to an active state.
MRI
An MRI machine has a temporal resolution of around 60-90 seconds.
fMRI
The temporal resolution of an fMRI scan is better - around 1-4 seconds.
Scan Duration
Both types of medical imaging scan take a relatively short period of time.
MRI
An MRI scan takes around 30 minutes.
fMRI
An fMRI scan can take around 45 minutes to an hour.
Data Analysis
An fMRI and an MRI scan rely on computer programming and an experienced radiologist to interpret the results.
MRI
MRI scans produce static images of “slices” of the body that can then be viewed from different angles to confirm or rule out certain diseases.
fMRI
fMRI scans produce colour coded images that signal different levels of brain activity that are then used to diagnose or guide surgeons during surgery to the brain. Results can also be used to produce a treatment plan or to check how well medications may be working.
Application Areas
There are various reasons why your doctor may choose an fMRI vs MRI.
MRI
You may be referred for an MRI scan due to undiagnosed pain somewhere in your body, such as your back or a joint such as your knee or shoulder, or because you may be undergoing tests for cancer in a specific part of your body. Some patients have a full body MRI scan while others have an MRI scan that focuses on one certain area.
fMRI
If your doctor suspects you may have a condition that’s affecting your brain, they will suggest an fMRI scan. An fMRI can diagnose conditions such as:
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Alzheimer’s disease (or another type of dementia)
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Stroke
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Epilepsy
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Brain injury
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Brain tumour
You may also have an fMRI scan prior to brain surgery to help doctors determine which areas of the brain are activated by things such as movement, thinking, remembering and reasoning so that your surgeon can avoid these areas of brain activity as much as possible.
How They Work
An MRI scan and an fMRI work in very similar ways.
MRI
An MRI scan uses a strong magnetic field and radio waves to temporarily realign the hydrogen atoms in the body. As they return to their normal state, they emit different types of energy, depending on the tissue type. Computer programming then turns this energy into images that experienced radiologists can use to differentiate between normal tissue and tissue that indicates disease.
fMRI
An fMRI scan works in the same way as a standard MRI. The only difference is, that you will be asked to perform certain tasks throughout, as the MRI machine measures brain activity. You may also wear virtual reality (VR) glasses or a headset to read text or answer questions. During an fMRI scan, your radiologist will use a process called Blood Oxygen Level Dependent (BOLD) scanning which measures changes in blood flow and oxygen levels during tasks and activities. Brain activity in areas of the brain for example associated with movement or remembering is seen as brighter areas on fMRI scan results. Parts of the brain not being used and in resting state show as darker areas.
The Scan Processes
Preparation for both an fMRI and an MRI scan are essentially the same.
MRI
An MRI scan involves the following:
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You will be given a hospital gown to wear and you should remove all jewellery and removable medical devices such as a hearing aid
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You will then lay on a bed that will move slowly into the MRI machine
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You will be given earphones to wear that will help to reduce noise and enable you to communicate with your radiographer
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You may have a contrast dye injected into a vein in your arm that will help to produce better images
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If you struggle with claustrophobia, or you think you may not be able to keep still, you may be offered medication to help you relax
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Once the scan is complete, you will be moved out of the MRI scanner and you’ll be able to get dressed
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You’ll feel no pain or discomfort during an MRI scan, and you’ll be able to return home soon afterwards
fMRI
An fMRI follows much the same process, but you will also wear a VR headset or glasses in order to perform certain tasks whilst inside the MRI scanner. Your head may also be placed into a brace to ensure that you stay as still as possible.
Find an MRI Scan
If you’re thinking about having an MRI scan or you’d like a second opinion, use our simple booking system to book a private MRI scan at one of our UK-wide centres. It can be difficult to know if you’d benefit more from an fMRI vs MRI scan. If so, or if you're unsure what scan is right for you and your symptoms, book an appointment to see one of our private doctors to help you decide.
References
Functional MRI of the brain. (2022, August 13). Yale Medicine. https://www.yalemedicine.org/conditions/functional-mri-imaging-the-brain
Professional, C. C. M. (2024a, May 1). Functional MRI (FMRI). Cleveland Clinic. https://my.clevelandclinic.org/health/diagnostics/25034-functional-mri-fmri
Radiological Society of North America (RSNA) and American College of Radiology (ACR). (n.d.-b). Functional MRI (FMRI). Radiologyinfo.org. https://www.radiologyinfo.org/en/info/fmribrain
