What Is an fMRI?

fMRI stands for Functional magnetic resonance imaging. An fMRI scan is a special type of MRI that shows how different parts of your brain are working. They help doctors measure blood flow in the brain without having to do surgery. fMRI imaging is a safe, non-invasive way to diagnose conditions and to find out if certain treatments are working.

How Does an fMRI Work?

A functional magnetic resonance imaging (fMRI) scanner uses a powerful magnetic field to detect brain activity. When an area of the brain becomes more active, such as when you wave your hand, there is an increase in blood flow to that region.

An fMRI imaging scan takes advantage of activated neurons requiring more oxygen from red blood cells. This increase in activity leads to a change in blood flow. fMRI detects these changes. By indirectly measuring the alterations in blood flow and electrical activity, fMRI assesses brain activity.

Doctors also call this indirect measurement a way to study the blood-oxygen-level-dependent (BOLD) response.

fMRIs can be used to study a variety of cognitive processes, including everything from decision-making to memory formation. In addition, fMRIs can be used to examine how different disorders affect brain function. fMRI scans create a color-coded map of your brain activity.

What Is an fMRI used for?

fMRI is used to assess how your brain is working. Doctors also use fMRIs to help determine the potential risk of surgeries or other invasive procedures.

fMRI scans help diagnose:

  • Stroke
  • Brain tumors
  • Brain injury
  • Alzheimer's Disease
  • Epilepsy

What Are the Benefits of an fMRI?

There are several benefits of receiving a functional MRI scan. 

Benefits of fMRI include:

  • Noninvasive—An fMRI does not require surgery.
  • Detects abnormalities—Doctors can use fMRIs to detect abnormalities in your brain.
  • Structure and function—fMRI scans help doctors assess both the structure and function of your organs.
  • Observe around bone—fMRI scans allow doctors to see abnormalities hidden behind bones. 

How Should I Prepare for an fMRI?

Your doctor will provide you with information about fMRI preparation. They will likely give you advice on what to expect before, during, and after your fMRI procedure.

Before the Scan

There is often no active preparation required for an fMRI scan, but there are a few things to keep in mind. First, it is important to remove all metal objects from your body, as these can interfere with the magnetic field. This includes items such as jewelry, hair clips, and glasses. You may also need to leave your phone outside of the scanning room, as the signal can interfere with the images. It is also important to inform your doctor if you have any medical implants, such as a pacemaker, or if you are pregnant.

During the Scan

When you arrive for your fMRI scan, you will be asked to lie down on a flat table with wheels. Then, you will be slid into the MRI machine, which is a large, tube-shaped machine. The noise and small space of the machine can feel uncomfortable, but it is not painful.

During your functional MRI scan, the technician may ask you to perform certain tasks, like flexing your fingers or toes. These tasks trigger specific brain activity that can be seen in the images. The scan itself usually takes about 40 to 55 minutes.

After the Scan

After your fMRI imaging scan, your technician will help you exit the machine and scanning table. You will then collect your belongings, get dressed, and leave the scanning room. Once your doctor receives a copy of the fMRI images and report, they will review the results with you.

Risk Factors

There are no fMRI scan risks for most patients.

Potential fMRI risks include:

  • Allergic reaction—There is a low risk of a mild allergic reaction to any contrast material used during the fMRI.
  • Sedation—There is a low risk of receiving excess sedation. The medical staff is highly trained to deliver the optimum dosage and will closely watch your vital signs to further mitigate your risk.
  • Magnetic interference—The magnet field used during the test is not painful. However, it may interfere with implanted devices in your body.
  • Contrast material—According to the makers of contrast material used during an fMRI, mothers should wait for 24-48 hours after receiving the contrast material before breastfeeding their babies.


There are several limitations to fMRIs. Functional MRI scans can be affected by movement or unsteadiness. This means that if you move around during the procedure, the movement can skew the results. Not following breathing instructions can cause slight changes in the position of your head, which can then affect the fMRI results.

Another fMRI limitation is that metal objects often interfere with the results of the scan. This is because the metal can distort the magnetic field, which then affects the accuracy of the fMRI. In addition, there is also a weight limit for fMRIs. The machine itself is only designed to accommodate people of a certain weight. 

Serious injuries can cause damage to the nervous system, which can then distort fMRI scans. Finally, an irregular heartbeat can alter the accuracy of the images.


After completing an fMRI scan, a radiologist will interpret the results and send a report to your doctor. Your doctor will then discuss the results with you and explain what they mean for your health. With this information, you and your doctor can make decisions about your care and treatment.

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