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Magnetic Resonance
Imaging (MRI) of the Brain
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What is the
test?
MRI is a noninvasive technique for visualizing
many different body tissues. Unlike x-rays, MRI
does not use any radiation. Instead, it uses
radio waves, a large magnet, and a computer to
create images.As with a CT scan, which does use
x-rays, each MRI picture shows a different
"slice," or cross-section, of the area being
viewed. Because these slices usually are spaced
about a quarter-inch apart, your doctor can get
a detailed representation of a particular area.
An MRI of the brain can identify tumors and
areas of brain damage caused by a stroke or another
neurological condition.
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How
do I prepare for the test?
Tell your doctor if you have a pacemaker, artificial
hip, or any metal pins, plates, screws, or surgical
staples. The magnet used in an MRI is so strong
that it can interfere with pacemakers and pull
on some metal objects implanted in the body.
If you know you have an implant, or are concerned,
discuss the issue with your doctor, as other
options may exist. (Some pacemakers, for example,
can be reprogrammed prior to an MRI so that they
are not disrupted.)
An IV is inserted into a vein if the particular
scan you're having requires a dye to make areas
of inflammation or abnormality easier to detect.
This dye is called gadolinium, and is different
from the contrast dye used for x-rays or CT scans.
Before undergoing the scan, remove metal objects
such as belt buckles or watches, which could
dislodge in the presence of the magnet and hurt
you.
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What
happens when the test is performed?
The MRI is a large machine with a circular tunnel
built through it, like the hole of a donut. You
lie on your back on a narrow table that can be
moved back and forth into the tunnel.When MRI
scans are taken, expect to hear some loud noises
from the machine. Some MRI departments offer
earplugs or a stereo headset to block this noise.
A technician moves your table using an automatic
control.When each picture is taken, he or she
asks you to hold your breath for a few seconds.
If you need to have dye injected through the
IV, this is usually done halfway through the
scanning. An MRI typically takes 30-90 minutes.
It can be difficult if you are uneasy in tight
spaces or have trouble lying flat for that amount
of time. If you think you might have trouble
getting through the procedure, talk to your doctor
beforehand and discuss whether an anti-anxiety
medicine might help. After the test is done,
you can go about your normal activities.
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What
risks are there from the test?
There are no risks from the MRI scan unless
you have a pacemaker or metal implants from previous
surgeries. The MRI causes no side effects, and
allergic reactions to the dye are rare.
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Must
I do anything special after the test is over?
No.
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How
long is it before the result of the test is
known?
MRI images are often recorded on film; if so,
it will take at least an hour for the MRI department
to develop the images and additional time for
a doctor to examine and interpret them. If the
images are stored in and displayed by a computer,
there is no time required to develop the images,
although the doctor's interpretation still takes
time. You can probably get preliminary results
within a day or two, but the complete results
might take four to seven days.
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