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 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 tumor, 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 tumors, and show areas of inflammation.

MRI of the
head may be used to look for the cause of headaches.

Health Tools

Health Tools help you make wise health decisions or take action to improve your health.


Decision Points focus on key medical care decisions that are important to many health problems.

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.
  • 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 doctor
and the MRI technologist if you:

  • Are allergic to any medicines. The
    contrast material used for MRI does not have iodine.
    If you know that you are allergic to the contrast material used for the MRI, tell your doctor before having another test.
  • Have any other health conditions,
    such as kidney problems or
    sickle cell disease, that may prevent you from having
    an MRI using contrast material.
  • Are or might be
    pregnant.
  • Have any metal implanted in your body. This helps your doctor know if the test is safe for you. Tell your doctor if you have:
    • Heart and blood vessel devices such as a coronary artery stent, pacemaker, ICD (implantable cardioverter-defibrillator), or metal heart valve.
    • Metal pins, clips, or metal parts in your body, including artificial limbs and dental work or braces.
    • Any other implanted medical device, such as a medicine infusion pump or a cochlear implant.
    • Cosmetic metal implants, such as in your ears, or tattooed eyeliner.
  • 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 medicine 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 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?).

How It Is Done

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, 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

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.

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
when 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
medicine patches. Be sure to tell your doctor if you are wearing a
patch.

There is a small chance of an allergic reaction
if
contrast material is used during the MRI. But most
reactions are mild and can be treated with medicine. Contrast material that contains gadolinium may cause a
serious problem (called nephrogenic systemic fibrosis) in people with
kidney failure. If you have decreased kidney function
or serious kidney disease, tell your doctor before having an MRI scan.

There also is a slight risk of an infection at the IV site if contrast
material was used.

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.

If you are pregnant, be sure to tell your doctor. The contrast material that contains gadolinium could be harmful to your baby.

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.

Magnetic resonance imaging (MRI) of the head

Normal:

All structures of the head-the brain, its vessels,
spaces, nerves, and surrounding structures-are normal.

No abnormal growths, such as tumors, 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.

Abnormal:

Tumors 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.

What Affects the Test

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

  • 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:

  • Being unable to lie still during the
    test.

What To Think About

  • Sometimes your MRI results may be different from earlier test
    results because you were tested at a different medical center or you had a
    different kind of test.
  • 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 angiography (MRA) 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. To learn more, see the topic
      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.
    • Functional MRI (fMRI) measures small chemical changes in the brain, which can show the part of the brain being used for functions such as speech, thought, or movement of body parts. Results from fMRI can be used to locate areas of the brain to avoid during brain surgery. These results can also be used to see how well the brain is functioning in people who have certain conditions.

References

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.

Credits

ByHealthwise Staff
Primary Medical Reviewer Kathleen Romito, MD – Family Medicine
E. Gregory Thompson, MD – Internal Medicine
Adam Husney, MD – Family Medicine
Martin J. Gabica, MD – Family Medicine
Specialist Medical Reviewer Howard Schaff, MD – Diagnostic Radiology

Current as ofOctober 9, 2017