Magnetic Resonance Imaging (MRI
scan)
An MRIscan is a completely different
technology from an x-ray and CT scan and represents
the single most useful imaging study available
for spine surgery.
An MRI scan is particularly useful as an aid
in the assessment of certain back conditions
by providing detail of the spinal disc (such
as for degenerative disc disease, isthmic spondylolisthesis)
and nerve roots (such as for lumbar disc herniation,
lumbar spinal stenosis). MRI scans are also useful
to rule out tumors or spinal infections.
How an MRI scan works
An MRI images the spine by using a magnet that
goes around the body to excite hydrogen atoms.
After the atoms return to their normal level of
excitation, they emit energy that is picked up
on an MRI scanner. Since humans are composed primarily
of water (which is two parts hydrogen), MRI scans
provide highly refined detail of the spine's anatomy
(see Figure
1).
Unlike an x-ray beam, there is no radiation
with the magnet so the MRI scans may be done
for pregnant women. However, patients with
a pacemaker implanted in their heart should
not have an MRI scan because the magnetic
field will cause the pacemaker to malfunction.
Also, anyone who works around metal should
first have an x-ray of their eye sockets
to ensure that they do no have any metal
filings in their eyes, which the magnetic
field may cause to migrate and damage the
eye during the MRI scan.
New developments in MRI scan equipment
Because most MRI scanners are fairly tight,
certain patients may feel uncomfortable,
or may not tolerate, lying in a tight tunnel
for 45 to 60 minutes while the scan is being
performed. To address this issue, newer generation
MRI scanners are designed with more open
space, although a more open tube does sacrifice
the excellent detail provided by the tight
tubes.
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