Test Overview
An MRI is a
test that uses a magnetic field and pulses of radio wave energy to make
pictures of the
spine. In many cases an MRI gives different information
than an
X-ray
, an
ultrasound
, or a
CT scan
. An MRI also may show
problems that cannot be seen with other imaging tests.
For an
MRI, your body is placed inside a machine that contains a strong
magnet. Pictures from an MRI can be saved and
stored on a computer for further study. In some cases, a
contrast material
may be used during the MRI to
show certain parts of the body more clearly.
The MRI can find changes in the spine and in other tissues. It also can find problems
such as infection or a tumor. MRI can look at the spine in the neck (cervical), upper back (thoracic), or lower back (lumbosacral). The
entire spine can be seen in one series of pictures to find a tumor. More
detailed pictures of one area,
such as the lumbar spine,
may be taken.
MRI may be used to check low
back problems.
-
Low Back Pain: Should I Have an MRI?
You may be able to have an
MRI with an open 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
.
Why It Is Done
An MRI of
the spine is done to:
- Find problems of the
spinal discs, such as a ruptured disc. The test may
also show if a disc is pressing on a nerve, causing symptoms such as
sciatica
.
- Find areas of the spine where
the canal is abnormally narrowed (
spinal stenosis
) and may need surgery.
- Find
tumors affecting the bones or nerves of the spine. The
tumors that most commonly spread to the spine include those from
prostate, breast, or lung cancer.
- Check
areas of joint inflammation (
arthritis
) or bone loss found during an
X-ray test or a
bone scan
.
- Find areas of the spine that do
not have good blood supply.
- Find an infection.
- Find
nerve damage caused by injury or disease, such as
multiple sclerosis
.
- Check problems of the
spine that have been present since birth (congenital).
An MRI may be done using contrast material to see abnormal
tissue more clearly. The contrast material also may help tell the difference between
old surgical scars and a new disease or injury.
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 contain iodine. If you know that you are allergic to the contrast material used for the MRI, tell your doctor before having another test.
- 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, a pacemaker, an ICD (implantable cardioverter-defibrillator), or a 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.
- Had recent 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 confined spaces. You need to lie very still inside the MRI magnet, so you may need medicine to help you relax. Or you may be able to have the test done with open MRI equipment. It is not as confining as standard MRI machines.
- Have any other health conditions, such as kidney problems or sickle cell anemia, that may prevent you from having an MRI using contrast material.
- Wear any medicine patches. The MRI may cause a burn at the patch site.
You may 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
An MRI is usually done by an MRI technologist. The pictures are usually
read by a
radiologist
. But some other types of doctors can also
read an MRI scan.
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.
You will need to take off all or most of your clothes,
depending on which area is examined. (You may be allowed to keep on your
underwear if it is not in the way.) You will be given a gown to use during the
test. If you are allowed to keep some of your clothes on, you should empty your
pockets of any coins and cards (such as credit cards or ATM cards) with scanner
strips on them. The MRI magnet may erase the information on the
cards.
During the test you usually 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 remain still. The table will slide into the space that contains the
magnet. A device called a coil may be placed over or wrapped around the area to
be scanned. A belt strap may be used to sense your breathing or
heartbeat. This triggers the machine to take the scan at the right time.
If you feel very nervous inside the machine, you may be given a sedative to help you
relax. You may be able to have an
MRI with an open 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
.
Inside the scanner you will hear a fan and feel
air moving. You may also hear tapping or snapping noises as the MRI scans are
taken. 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. But the technologist will watch
you through a window. You will be able to talk with the technologist through a
two-way intercom.
If contrast material is needed, the technologist
will put it in an
intravenous (IV)
line in your arm. The material may be
given over 1 to 2 minutes. Then more MRI scans are done.
An MRI 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. 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 the area being examined. 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, artificial limbs, and other medical devices that contain
iron. The magnet will stop a watch that is close to the magnet. Any loose metal
object has the risk of causing damage or injury if it gets pulled toward the
strong 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.
Results
The
radiologist may discuss some of the results of the MRI
with you right after the test. Complete results are usually ready for your
doctor in 1 to 2 days.
MRI of the spine
| Normal: |
The bones of the spine, discs, and nerves
are normal.
|
|
No tumors, inflammation, or areas of nerve
damage in the spine are present.
|
|
No disease or bone loss in the spine is present.
|
|
No ruptured discs are present. There are no
structures pressing on a nerve.
|
|
No structural problems that have been
present from birth (congenital problems) are found.
|
| Abnormal: |
Tumors, inflammation, or areas of nerve
damage in the spine are present. A disease of the spinal cord, such as
multiple sclerosis
, is found.
|
|
Narrowing of the spinal canal (
spinal stenosis
) is present.
|
|
Broken bones or bone loss in the spine
caused by injury or disease, such as
arthritis
, is found.
|
|
One or more
discs of the spine are bulging or ruptured or pressing
on a nerve.
|
|
A condition that has been present from
birth (congenital condition) is found in the spine or the
vertebrae.
|
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
- Pregnancy. An MRI test usually is not done
during pregnancy.
- Medical devices that use electronics, such as a
pacemaker or medicine infusion pump. The MRI magnet may cause problems with
these devices, and that may keep you from having an MRI.
- Medical devices that have metal in them. The metal might make
some of the detailed MRI pictures blurry. This may prevent your doctor from
seeing the organ that is being looked at. For example, any metal in your spine
may prevent your doctor from seeing it clearly.
- Inability to remain
still during the test.
- Obesity. A
person who is very overweight may not fit into standard MRI machines.
Many modern medical devices that do not use
electronics—such as heart valves, stents, or clips—can be safely placed in most
MRI machines. But some newer MRI machines have stronger magnets. The safety of
MRI scans with these stronger MRI magnets in people with medical devices is not
known.
What To Think About
- Sometimes your MRI test results may be
different from the results of
CT
, ultrasound, or
X-rays
tests, because the MRI
scan shows tissue differently.
- Magnetic resonance imaging (MRI) of
the spine can often be used instead of other tests that use
X-rays, such as a
computed tomography (CT) scan or
myelography
.
- MRI is a safe test for
looking at structures and organs inside the body. It costs more than other
methods and may not be available in your area.
- Open MRI machines
are now made so that the magnet does not completely surround you. But these
machines may not be available in all medical centers. Open MRI is useful for
people who are claustrophobic or obese.
-
Contrast material
that contains gadolinium may cause a serious skin problem
(called nephrogenic fibrosing dermopathy) in people with
kidney failure
. Before having an MRI scan, tell your
doctor if you have serious kidney disease or if you have had a kidney
transplant.
References
Other Works Consulted
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Saunders.
- Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Credits
|
By
| Healthwise Staff |
|
Primary Medical Reviewer
| Kathleen Romito, MD - Family Medicine |
|
Specialist Medical Reviewer
| Howard Schaff, MD - Diagnostic Radiology |
|
Last Revised
| May 16, 2011 |
