Magnetic resonance imaging (MRI) of the head is a painless, noninvasive test that produces detailed images of your brain and brain stem. The test is carried out with an MRI machine, which produces the images using a magnetic field and radio waves. This test is also known as a brain MRI or a cranial MRI. The test will be carried out at a hospital or radiology center.
An MRI is different from a computed tomography (CT) scan or an X-ray in that it does not use radiation to produce images. The images can be combined to form 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
If you have had a stroke or head injury, an MRI can help determine whether any damage was caused. Your doctor may also order a head MRI to get to the bottom of symptoms such as dizziness, weakness, seizures, changes in thinking or behavior, blurry vision, or chronic headaches. These symptoms may be caused by 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 that are used for speech and language, as well as, for movement of the body. It does this by measuring metabolic changes that take place in the brain when you perform certain tasks. During this test, you may be asked 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 is used to examine certain blood vessels in the brain.
The medical staff will need to know if you have inner ear implants, artificial joints, 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 are 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 will not be permitted to have electronic devices in the MRI room.
You may be asked to not eat or drink anything for four to six hours before the exam.
If you are pregnant, tell the test staff. The way in which an MRI’s magnetic field affects unborn children is not yet fully understood.
Additionally, it is important to let the staff know if you suffer from claustrophobia. If you are 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 is important to stay still in order 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 be asked to lie down on a table that slides into the MRI machine. The table slides through a large magnet, which is 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. A contrast solution, usually gadolinium, may be given to you intravenously in order to allow certain parts of the brain to be seen more easily, particularly your blood vessels. You may be given earplugs or headphones to block the MRI machine’s noises or you may be allowed to listen to music during the test.
There are no risks associated with the MRI itself. If a contrast solution is used, there is a very slight chance that you may have an allergic reaction. You should tell the test staff if you have decreased kidney function because 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, you may be moved to a recovery area until you wake up—usually one to two hours after the sedative was administered.
A radiologist will analyze your MRI images. He or she will provide your doctor with the results. If the test was conducted in an emergency situation, your results will be available quickly. Next steps will depend on whether the results revealed anything unusual or the cause of any abnormalities was discovered.