Functional MRI (fMRI)

What is functional MRI?

Functional magnetic resonance imaging (fMRI) is an imaging scan that shows activity in specific areas of the brain. In medical settings, fMRI mainly helps plan brain surgeries and similar procedures.

A standard MRI scan uses an extremely powerful magnet, radio waves and computer processing to generate highly detailed 3D pictures of the inside of your body. It doesn’t use radiation like an X-ray or computed tomography (CT) scan, so there’s no radiation to worry about.

An fMRI scan uses the same MRI machine, but is special because it tracks blood flow in different parts of your brain. Your brain cells use more oxygen when they’re working. That means following the blood flow shows the areas of your brain that are working hardest. Those areas appear brighter on an fMRI scan.

What is functional MRI used for?

Mapping out the areas of your brain based on their blood flow and activity lets clinicians know what specific parts of the brain control certain actions and abilities. It’s useful for planning brain surgery or other procedures that might affect your brain. If you need surgery on a specific part of your brain, fMRI can help a neurosurgeon plan the surgery and know which areas to leave undisturbed because they handle critical jobs. Adults and children can undergo fMRI scans.

For example, a specific part of your brain’s frontal lobe handles muscle movements. Having you tap your fingers during an fMRI scan shows which areas handle that job. The neurosurgeon then knows to avoid disturbing those areas.

Conditions or procedures that might need this kind of planning include:

• Epilepsy. When epilepsy doesn’t respond to medications or other treatments, epilepsy surgery may be an option.
• Brain tumors. Growths of any kind, including cancer and benign tumors, may need surgery to remove them.
• Radiation therapy to the brain. Precision radiation therapies can treat cancer, circulatory problems and many other brain conditions.
• Post-treatment scans. Follow-up scanning can help show any differences in brain function following a medical procedure.

Researchers are also investigating other uses for fMRI. There’s evidence it might be useful for biofeedback therapy.

How common are fMRI scans?

Because fMRI doesn’t have many medical uses, it isn’t common in healthcare settings. Smaller hospitals and healthcare facilities may not be able to do an fMRI scan. You may need to travel to a larger medical center if you need one.

How should I prepare for this procedure?

On the day of your fMRI, you shouldn’t drink anything containing caffeine, as this may affect the results of an fMRI. If you take any medications, your healthcare provider will also instruct you on how to take (or not to take) them before the scan.

Like a standard MRI scan, an fMRI scan involves a very powerful magnet. It’s strong enough to damage certain items or pull magnetic objects to it at high speed. Even simple metallic items can become dangerous projectiles near an MRI.

You’ll need to remove any clothing, accessories or jewelry that contains any kind of metal, including piercings. This includes ALL metals, regardless of whether or not they’re magnetic. Even nonmagnetic metals can still affect the scan quality.

Items you shouldn’t take or wear near an MRI include:

• Jewelry, watches, credit cards and hearing aids.
• Pins, metal hair accessories, underwire bras and metal zippers, which can distort MRI images.
• Removable dental work, such as dentures.
• Pens, pocketknives or multitools.
• Body piercings.
• Cell phones, electronic watches and tracking devices.

It’s critical that you tell your healthcare provider before the MRI if you have any of the following:

• A heart pacemaker or defibrillator.
• Electronic or implanted stimulators or devices, including deep brain stimulators, vagus nerve stimulators, bladder stimulators, spine stimulators, neurostimulators and implanted electrodes or wires.
• Replacement joints.
• Cochlear implants or other ear implants.
• Implanted drug pumps, such as those that pump narcotic/pain medications or drugs to treat spasticity.
• Programmable shunts.
• Aneurysm clips and coils.
• Stents not located in your heart.
• Filters, such as blood clot filters.
• Metal fragments lodged anywhere in your body or eye (like bullets, shrapnel, metal pieces or shavings).
• A continuous glucose monitor (CGM).
• An insulin pump.
• A medication patch you’re wearing anywhere on your body.

You should also tell your healthcare provider before the fMRI if:

• You are or might be pregnant.
• There’s a reason you can’t lie on your back for the full duration of the procedure.
• You have claustrophobia (fear of enclosed spaces).

If you have claustrophobia, your provider may recommend giving you an anti-anxiety medication during or just before the scan. This can vary, so you should ask your healthcare provider whether medication is an option to help fear and anxiety during an fMRI.

Children can also undergo fMRI but may need medication to help them relax. Your child’s healthcare provider can tell you more about the options available and which ones they recommend.

What happens during a functional MRI scan?

An fMRI scan works very similarly to a standard MRI. During the procedure, you’ll lay on a table that can move your body toward the MRI machine. Most of the time, fMRI uses a traditional ring-shaped MRI scanner because open MRI machines usually don’t have a strong enough magnet.

During an fMRI, your head will be inside a special helmet-like device called a head coil. The coil helps with producing clearer images. You’ll also wear special sound-canceling headphones that block out sound from the MRI machine. The headphones also let healthcare providers, such as MRI technologists or radiologists, talk to you during the scan and give you instructions.

The main difference between a standard MRI and an fMRI scan is activity. During an fMRI scan, healthcare providers will have you talk, tap a finger or do other simple tasks. While you do these tasks, the fMRI tracks the blood flow in your brain to see which areas are most active and compare it to what you were doing at the time. That lets them “map” the areas of your brain and what they’re responsible for.

The tasks can happen using either an event system or a block system.

• Block system: This system has you do a task for a short period and then rest for a short period. The periods are called blocks.
• Event system. This involves going through a series of tasks without rest periods in between.

Your provider may also want part of your fMRI to involve a “resting state” scan. During this time, you’ll simply lie in the scanner (your provider may ask you to keep your eyes open or closed). That lets the provider see and measure the difference between activity and rest in your brain.

Functional MRI with contrast

Like a standard MRI scan, fMRI scans may involve a contrast material containing gadolinium. Infusing gadolinium into a vein using an intravenous (IV, through your vein) line can help with certain imaging tests. It can make certain structures inside your body or brain easier to see.

How long does a functional MRI scan take?

In all, an fMRI scan generally takes up to an hour. It may take a little longer if your provider wants to collect additional scans to be sure they have enough data to analyze, or if they want to run another type of MRI scan alongside an fMRI.

What happens after this procedure?

You can typically go home right after an fMRI scan. If you received medication to help with anxiety during your fMRI, you’ll need someone to drive you home. A radiologist will review and analyze the scan and provide the results to you and the healthcare provider who referred you for the scan (such as a neurologist or neurosurgeon).

What are the benefits of fMRI?

Functional MRI is especially useful for pre-surgery planning. It can help neurosurgeons better understand the activity of different brain structures. That helps them avoid critical areas, if possible, reducing the chance that you’ll lose any abilities that rely on those areas.

Other tests can also help with planning, but fMRI is usually a better choice. Other tests that can help are usually more invasive, involve medications with a greater chance of side effects or aren’t as accurate at mapping the brain areas in question.

What are the disadvantages or risks of fMRI?

Functional MRI has a few disadvantages compared to other procedures. One of the biggest disadvantages has to do with fMRI scan timing vs. how fast your brain works. An fMRI captures scan data from second to second. Brain activity changes in tiny fractions of a second, so fMRI can’t scan fast enough to capture very detailed brain activity.

There are very few risks from fMRI itself and they’re generally similar to the risks of standard MRI. Side effects from gadolinium contrast are rare. Metal safety is the main concern. Be sure to follow all guidance from healthcare providers and clinical staff about metal safety. If you have any questions, don’t hesitate to ask them for input.

What is the difference between an EEG and an fMRI?

An electroencephalogram (EEG) is a diagnostic test that measures and records your brain activity. An EEG machine shows brain activity as a series of waves on paper or a digital display. They both record similar data, but an fMRI displays it as an image.

A note from Cleveland Clinic

Functional MRI is a relatively new technology. While it’s only been around for a little over 30 years, it’s opened the door to a new understanding of how the brain works. Today, it’s most useful for mapping brain activity and showing which areas are active during certain tasks or events. Whether it’s you or your child undergoing an fMRI, this type of scanning can be very helpful for neurosurgeons as they plan procedures and try to avoid critical areas as much as possible.