Test Overview

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 cannot be seen on an X-ray, ultrasound, or computed tomography (CT) scan.

For an MRI test, 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, inflammation, or a tumor. 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. See MRI images of a person who has had a stroke or a seizure.

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 tumors, and show areas of inflammation.

MRI of the head may be used to look for the cause of headaches. For more information, see:

Should I have imaging tests to look for the cause of my headaches?

See pictures of a standard MRI machine and an open MRI machine.

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	Should I have image tests to evaluate my headaches?

Why It Is Done

Magnetic resonance imaging (MRI) of the head is done to:

• Look for the cause of headaches.
• Help diagnose a stroke or blood vessel problems in the head. Problems with blood vessels may include an aneurysm or abnormal twisted blood vessels that are present at birth (this is called an arteriovenous [AV] malformation).
• Check blood flow or blood clots to the brain. MRI can show bleeding in or around the brain.
• Check symptoms of a known or suspected head injury.
• Check symptoms such as change in consciousness, confusion, or abnormal movements. These symptoms may be caused by brain diseases, such as Huntington's disease, multiple sclerosis (MS), Parkinson's disease, or Alzheimer's disease. See an MRI showing MS in the brain.
• Check for "water on the brain" (hydrocephaly).
• Look for tumors, infections, an abscess, or conditions of the brain or brain stem, such as encephalitis or meningitis.
• Check the eyes, the nerves from the eyes to the brain (optic nerves), the ears, and the nerves from the ears to the brain (auditory nerves).
• Look for problems of the pituitary gland.
• Investigate or follow a finding seen on another test.

How To Prepare

Before your MRI test, tell your health professional and the MRI technologist if you:

• Have allergies, such as hay fever, asthma, food or medicine allergies. The contrast material used for MRI does not have iodine. If you have a known allergy to the contrast material used for MRI, tell your health professional to prevent an allergic reaction. Sometimes the benefits of having this test outweigh the risks.
• Have any other health conditions, such as kidney problems or sickle cell anemia, that may prevent you from having an MRI using contrast material.
• Are or might be pregnant.
• Have a pacemaker, implantable cardioverter-defibrillator (ICD), artificial limb, any metal pins or metal parts in your body (especially in the eyes), metal heart valves, metal clips in your brain, metal implants in your ear, tattooed eyeliner, or metallic-based tattoos, or any other implanted or prosthetic medical device (such as a medication infusion pump). Also, tell your health professional if you have worked around metal or if you have recently had surgery on a blood vessel. In some cases, you may not be able to have the MRI test.
• Have an intrauterine device (IUD) in place. An IUD may prevent you from having the MRI test done.
• Become very nervous in small, tight spaces. You need to lie very still inside the MRI magnet. You may need medicine to help you relax.
• Wear any medication patches. The MRI may cause a burn at the patch site.

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 need to sign a consent form that says you understand the risks of an MRI and agree to have the test done. Talk to your health professional 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?).

How It Is Done

A magnetic resonance imaging (MRI) test is done by an MRI technologist. The pictures are read by a radiologist. However, some other types of doctors (such as a neurologist or neurosurgeon) can also read an MRI scan of the head.

You will need to remove all metal objects (such as hearing aids, dentures, jewelry, 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 MRI machines (called open MRI) are now made so that the magnet is not around your whole body.

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. Open MRI machines may be helpful if you are claustrophobic.

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. 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.

How It Feels

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 and flushing as it is put into your IV.

In rare cases, you may feel:

• A tingling feeling in the mouth if you have metal dental fillings.
• Warmth in your head. This is normal. Tell the technologist if you have nausea, vomiting, headache, dizziness, pain, burning, or breathing problems.

Risks

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 pieces in the eyes can damage the retina. If you might have metal pieces in your 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 medication patches. Be sure to tell your health professional if you are wearing a patch.

There is a small chance of developing an allergic reaction if contrast material is used during the MRI. However, most reactions are mild and can be treated with medicine. There also is a small chance of an infection at the IV site.

Results

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.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include:

• Being pregnant. An MRI test is not usually done during pregnancy even though the strong magnetic field is not known to be harmful.
• Having medical devices with metal. The MRI magnet may cause these devices to not work right or to have problems during an MRI scan. This test may not be done if you have:
  • An intrauterine device (IUD) in place.
  • Metal parts or clips in the head or eye.
  • A pacemaker.
  • An implantable cardioverter-defibrillator (ICD).
  • Certain types of artificial limbs.
  • A medication infusion pump in place.
• You cannot lie still during the test.

What To Think About

• Sometimes your MRI results may be different because you were tested at a different medical center or earlier test results are not available to compare to the new test findings.
• Several special MRI methods have been developed to look at the brain.
  • Magnetic resonance spectroscopy shows changes in brain chemistry that may occur in certain areas of the brain. These changes may help show diseases that affect the brain.
  • Magnetic resonance angiogram (MRA) is a special MRI method that can be used to study blood vessels. Dye may be injected into the blood vessels so blood flow can be seen clearly. MRA can also be used to show the speed and direction of blood flow. For more information, see the medical test Magnetic Resonance Angiogram (MRA).
  • Diffusion-perfusion imaging shows the water content and character of the brain. This method can give an early diagnosis of a stroke and may help predict the outcome of stroke. It can also be used to find tumors or inflammation of the brain.
• Contrast material that contains gadolinium may cause a serious skin problem (called nephrogenic fibrosing dermopathy) in people with kidney failure. Tell your doctor if you have serious kidney disease before having an MRI scan.

References

Other Works Consulted

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.

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