Magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to take pictures of the head. In many cases, MRI gives information that can't be seen on an X-ray, ultrasound, or computed tomography (CT) scan.
For an MRI of the head, you lie with your head inside a special machine (scanner) that has a strong magnet. The MRI can show tissue damage or disease, such as infection or inflammation, or a tumour, stroke, or seizure. Information from an MRI can be saved and stored on a computer for more study. Photographs or films of certain views can also be made.
In some cases, a dye (contrast material) may be used during the MRI to show pictures of structures more clearly. The dye may help show blood flow, look for some types of tumours, and show areas of inflammation.
MRI of the head may be used to look for the cause of headaches.
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Magnetic resonance imaging (MRI) of the head is done to:
Before your MRI test, tell your doctor and the MRI technologist if you:
You may need to arrange for someone to drive you home after the test if you are given a medicine (sedative) to help you relax.
You will be asked to sign a consent form that says you understand the risks of the test and agree to have it done. Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form( What is a PDF document? ).
A magnetic resonance imaging (MRI) test is done by an MRI technologist. The pictures are read by a radiologist. But some other types of doctors (such as a neurologist or neurosurgeon) can also read an MRI scan of the head.
You may be able to have an MRI with an open MRI machine that doesn't enclose your entire body. But open MRI machines aren't available everywhere. The pictures from an open MRI may not be as good as those from a standard MRI machine.
You will need to remove all metal objects (such as hearing aids, dentures, jewellery, watches, and hairpins) from your body because these objects may be attracted to the powerful magnet used for the test. If you have had an accident or you work around metal, there is a chance that you have metal pieces in your head, eyes, skin, or spine. An X-ray may be taken before the MRI to see if you can have the test.
You may need to take off some of your clothes. You will be given a gown to wear during the test. If you keep your clothes on, empty your pockets of any coins and cards (such as credit cards or ATM cards) with scanner strips on them because the MRI magnet may erase the information on the cards.
During the test you will lie on your back on a table that is part of the MRI scanner. Your head, chest, and arms may be held with straps to help you lie still. The table will slide into the space with the magnet. A device called a coil may be placed over or wrapped around your head.
Some people feel nervous (claustrophobic) inside the MRI magnet. If this keeps you from lying still, you can be given a medicine (sedative) to help you relax.
Inside the scanner you will hear a fan and feel air moving. You may also hear tapping or snapping noises as the MRI pictures are taken. This is normal. You may be given earplugs or headphones with music to reduce the noise. It is very important to hold completely still while the scan is being done. You may be asked to hold your breath for short periods of time.
During the test, you may be alone in the scanner room. The technologist will watch you through a window. You will be able to talk through a speaker.
If contrast material is needed, the technologist will put it in an intravenous (IV) line in a vein in your arm or hand. The material may be given over 1 to 2 minutes. Then more MRI scans are done.
An MRI test usually takes 30 to 60 minutes but can take as long as 2 hours.
You will not have pain from the magnetic field or radio waves used for the MRI test. The table you lie on may feel hard and the room may be cool. You may be tired or sore from lying in one position for a long time.
If a contrast material is used, you may feel some coolness when it is put into your IV.
In rare cases, you may feel:
There are no known harmful effects from the strong magnetic field used for MRI. But the magnet is very powerful. The magnet may affect pacemakers, implantable cardioverter-defibrillators (ICDs), artificial limbs, and other medical devices that contain iron. The magnet will stop a watch that is close to the magnet.
Metal parts in the eyes can damage the retina. If you may have metal fragments in the eye, an X-ray of the eyes may be done before the MRI. If metal is found, the MRI will not be done.
Iron pigments in tattoos or tattooed eyeliner can cause skin or eye irritation.
An MRI can cause a burn with some medicine patches. Be sure to tell your health professional if you are wearing a patch.
There is a slight risk of an allergic reaction if contrast material is used during the MRI. But most reactions are mild and can be treated using medicine. There also is a slight risk of an infection at the IV site.
A dye (contrast material) that contains gadolinium may be used in this test. Be sure to tell your doctor if:
Health Canada has safety warnings about gadolinium. But for most people, the benefit of its use in this test outweighs the risk.
If you breastfeed and are concerned about whether the dye used in this test is safe, talk to your doctor. Most experts believe that very little dye passes into breast milk and even less is passed on to the baby. But if you prefer, you can store some of your breast milk ahead of time and use it for a day or two after the test.
Magnetic resonance imaging (MRI) is a test that uses a magnetic field and pulses of radio wave energy to take pictures of the head.
The radiologist may tell you some of the results of the MRI right after the test. Full results are sent to your doctor or specialist in 1 to 2 days.
All structures of the head—the brain, its vessels, spaces, nerves, and surrounding structures—are normal.
No abnormal growths, such as tumours, in or around the brain are present.
No bleeding, abnormal blood vessels (AV malformations), abnormal pockets of fluid, blockage in the flow of blood, or bulges in the blood vessels ( aneurysm) are present.
No signs of infection or inflammatory disease, such as encephalitis or meningitis, are present.
Tumours in the brain or in areas outside the brain, such as an acoustic neuroma, are present.
Bleeding or swelling (edema) in or around the brain is present.
Areas of infection or inflammatory disease, such as encephalitis or meningitis, are present.
Abnormal areas in the brain may mean that certain diseases, such as Huntington's disease, multiple sclerosis, Parkinson's disease, or Alzheimer's disease, are present.
Bulges or weak areas (aneurysms) or abnormal blood vessels (such as an AV malformation) are present.
Reasons you may not be able to have the test or why the results may not be helpful include:
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
ByHealthwise StaffPrimary Medical ReviewerKathleen Romito, MD - Family MedicineDonald Sproule, MDCM, CCFP - Family MedicineE. Gregory Thompson, MD - Internal MedicineAdam Husney, MD - Family MedicineMartin J. Gabica, MD - Family MedicineHoward B. Schaff, MD - Diagnostic Radiology
Current as ofJune 26, 2018
Current as of: June 26, 2018
Kathleen Romito, MD - Family Medicine
& Donald Sproule, MDCM, CCFP - Family Medicine & E. Gregory Thompson, MD - Internal Medicine & Adam Husney, MD - Family Medicine & Martin J. Gabica, MD - Family Medicine & Howard B. Schaff, MD - Diagnostic Radiology
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