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 is different from a CT scan or an X-ray in that it doesn’t use radiation to produce images. An MRI combines images to create a 3-D picture of your internal structures, so the MRI is more effective than other scans at detecting abnormalities in the pituitary gland and brain stem.
A head MRI is a useful tool for detecting a number of brain conditions, including:
- aneurysms (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 syndrome)
- bleeding (hemorrhage)
- problems with development or structure
- blood vessel issues
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 dizziness, weakness, seizures, changes in thinking or behavior, blurry vision, or chronic headaches. These symptoms may be due to a brain issue, which an MRI can help detect.
A functional MRI, or 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 the 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 examines certain blood vessels in the brain.
The medical staff will need to know if you have inner ear implants, artificial joints, a defibrillator or pacemaker, particular types of heart valves, vascular stents, brain aneurysm clips, or if you have ever worked with sheet metal. All of these things can affect the outcome of an MRI. In the case of implants and pacemakers, those items can stop working properly due to an MRI’s magnetic field.
If you’re wearing anything that contains metal, including jewelry or sunglasses, you will need to remove these items. Metal interferes with the MRI machine’s ability to produce a clear image. Braces and dental fillings will typically not 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.
You may have to refrain from eating or drinking anything for four to six hours before the exam.
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 you’re claustrophobic, you might need to use 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 intravenous or oral sedation. 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 the testing staff.
The test normally takes 30 to 60 minutes. You may receive a contrast solution, usually gadolinium, intravenously to allow the MRI machine to see certain parts of the brain more easily, particularly your blood vessels. The MRI scanner will make loud banging noises during the procedure. You may wear earplugs or headphones to block the MRI machine’s noises, or you may listen to music during the test.
There are no risks associated with the 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. They will 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.