Magnetic resonance imaging (MRI) of the head is a painless, noninvasive test that produces detailed images of your brain and brain stem. An MRI machine creates the images using a magnetic field and radio waves. This test is also known as a brain MRI or a cranial MRI. You will go to a hospital or radiology center to take a head MRI.
An MRI scan is different from a CT scan or an X-ray in that it doesn’t use radiation to produce images. An MRI scan combines images to create a 3-D picture of your internal structures, so it’s more effective than other scans at detecting abnormalities in small structures of the brain such as the pituitary gland and brain stem. Sometimes a contrast agent, or dye, can be given through an intravenous (IV) line to better visualize certain structures or abnormalities.
A head MRI is a useful tool for detecting a number of brain conditions, including:
- aneurysms, or bulging in the blood vessels of the brain
- multiple sclerosis
- spinal cord injuries
- hydrocephalus, a buildup of spinal fluid in the brain cavities
- hormonal disorders, such as acromegaly and Cushing’s syndrome
- hemorrhage, or bleeding
- problems with development or structure (such as a Chiari malformation)
- blood vessel issues
- an issue due to a previous head injury
A head MRI can help determine whether you sustained any damage from a stroke or head injury. Your doctor may also order a head MRI to investigate symptoms such as:
- changes in thinking or behavior
- blurry vision
- chronic headaches
These symptoms may be due to a brain issue, which an MRI scan can help detect.
A functional MRI (fMRI) of the brain is useful for people who might have to undergo brain surgery. An fMRI can pinpoint areas of the brain responsible for speech and language, and body movement. It does this by measuring metabolic changes that take place in your brain when you perform certain tasks. During this test, you may need to carry out small tasks, such as answering basic questions or tapping your thumb with your fingertips.
Additionally, there is a type of MRI called magnetic resonance angiography (MRA), which better examines the blood vessels in the brain.
The medical staff will need to know if you have any metal in your body, including:
- inner ear implants
- artificial joints
- a defibrillator or pacemaker
- particular types of heart valves
- vascular stents
- brain aneurysm clips
They’ll also ask whether you’ve ever worked with sheet metal or been injured with metal shrapnel. All of these things can affect how safely you can undergo an MRI. In the case of implants and pacemakers, those items can stop working properly due to an MRI’s powerful magnetic field.
If you’re wearing anything that contains metal, including jewelry or sunglasses, you will need to remove those items. Metal interferes with the MRI machine’s ability to produce a clear image. Braces and dental fillings typically won’t pose a problem, but pocketknives, pens, pins, and certain dental appliances can interfere. The staff may ask you to wear a hospital gown or clothing that doesn’t contain metal fasteners. You can’t have electronic devices in the MRI room.
Tell the medical staff if you’re pregnant. An MRI’s magnetic field affects unborn children in a way that isn’t yet fully understood.
Additionally, it’s important to let the staff know if you have claustrophobia. If so, you might need to take sedatives during the exam or have an “open” MRI. Open MRI machines have wider tunnels, which tend to be more tolerable for claustrophobic patients.
During the exam, it’s important to stay still to obtain the clearest images. Children who have difficulty staying still may need sedation, administered either orally or through an IV line. Sedation can also be helpful for adults who are claustrophobic.
You will lie down on a table that slides into the MRI machine. The table slides through a large magnet shaped like a tube. You may have a plastic coil placed around your head. After the table slides into the machine, a technician will take several pictures of your brain, each of which will take a few minutes. There will be a microphone in the machine that allows you to communicate with staff.
The test normally takes 30 to 60 minutes. You may receive a contrast solution, usually gadolinium, through an IV to allow the MRI machine to see certain parts of your brain more easily, particularly your blood vessels. The MRI scanner will make loud banging noises during the procedure. You may be offered earplugs to block the MRI machine’s noises, or you may listen to music during the test.
There are no risks associated with an MRI itself. There is a very slight chance that you will have an allergic reaction to a contrast solution. Tell the medical staff if you have decreased kidney function. It may not be safe to use contrast solution if this is the case.
After the test, you can get dressed and leave the testing facility. If you were sedated for the exam, staff may move you to a recovery area until you wake up — usually one to two hours after you received the sedative.
A radiologist will analyze your MRI images and provide your doctor with the results. Your results will be available quickly if your head MRI was an emergency procedure.
Next steps will depend on whether the results revealed anything unusual or discovered the cause of any abnormalities.