What Is an fMRI?

This imaging method shows activity in different areas of the brain.

Functional magnetic resonance imaging, or fMRI, is a special type of magnetic resonance imaging (MRI) that measures brain activity by detecting changes in blood flow.

When a brain area is more active, it consumes more oxygen, so blood flow increases in that area.

An fMRI can reveal which areas of the brain perform specific functions such as thought, speech, or movement.

The imaging method is used to help doctors see the effects of a stroke, trauma, brain tumors, or diseases such as Alzheimer's.

It can also help guide doctors as they perform radiation, surgery, or other treatments for the brain.

The technology was developed in the 1990s by scientists Seiji Ogawa and Ken Kwong.

The fMRI Procedure

Like all MRI procedures, an fMRI uses a large device (about the size of a truck), a powerful magnet, and radio waves to view organs and structures in the body.

An fMRI typically takes about an hour or less to perform.

Before the procedure, you may need an injection of a contrast medium to help provide more detail in the images.

You'll receive this through an intravenous (IV) line in your hand or arm.

If you suffer from anxiety or claustrophobia, you may be given sedation before your fMRI.

You'll be positioned on a moveable exam table. Your head may be placed in a device that's designed to keep you still. You may also be given special goggles or earphones to wear.

A technician or radiologist will move you into the magnet of the MRI unit. Doctors will perform the imaging test while working at a computer outside the exam room.

A technician will be able to see, hear, and talk with you over an intercom.

It's important that you remain still during the procedure. You may even be asked to hold your breath at times.

An fMRI should be painless, but you may find it uncomfortable to lie still.

When the procedure is complete, your IV will be removed.

Before an fMRI

Before having an fMRI, let your doctor know if you have any serious health conditions, especially severe kidney disease.

Also, let your doctor know if you've recently had any surgery or if there's a chance you might be pregnant.

Be sure to remove all jewelry and any metal or electronic items before having an fMRI.

Tell your doctor and radiologist ahead of time if you have any metal objects or medical devices in your body.

After an fMRI

You can resume your normal activities immediately after an fMRI unless your doctor tells you otherwise.

In rare cases, some people experience side effects such as nausea, pain, or an allergic reaction to the injected contrast medium. Tell your doctor if you notice any unusual symptoms.