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MRI
Other Tests
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Source: http://www.spinephysicians.org/dr0sqf.cfm |
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MR
Imaging (MRI) - Musculoskeletal
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What is MRI of the
Musculoskeletal System?
Magnetic resonance imaging
(MRI) uses radio waves and a strong magnetic field rather than
x-rays to provide clear and detailed pictures of internal organs
and tissues. The parts of the
musculoskeletal system that are most frequently imaged with
MRI are the spine, knee and shoulder. However, MRI has also been
used to study almost every joint in the body, including the
hips, wrists, and hands. MRI requires specialized equipment and
expertise and allows evaluation of some body structures that may
not be as visible with other imaging methods. |
What are some common uses of
the MRI procedure?
 Because
MRI can give such clear pictures of soft tissue structures
near and around bones, it is usually the best choice for
examination of the body's major joints, the spine for disk
disease, and soft tissues of the extremities. MRI is widely used
to diagnose sports-related injuries, as well as work-related
disorders caused by repeated strain, vibration, or forceful
impact.
Using MRI images, physicians
can locate and identify the cause of pain, swelling or bleeding
in the tissues in and around the joints and bones. The images
allow the physician to clearly see even very small tears and
injuries to tendons, ligaments and muscles, and even some
fractures that cannot be seen on
x-rays.
In addition, MRI images can
give physicians a clear picture of degenerative disorders such
as
arthritis, deterioration of joint surfaces, or a
herniated disk. Neurosurgeons often use MRI to evaluate the
integrity of the spinal cord after trauma.
Finally, MRI is also useful for
the diagnosis and characterization of infections (for example
osteomyelitis) and tumors (for example
metastases) involving bones and joints.
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How should I prepare for the
procedure?
Because the strong magnetic
field used for
MRI will pull on any
ferromagnetic metal object implanted in the body, MRI
staff will ask whether you have a prosthetic hip, an
aneurysm clip in the brain, heart pacemaker (or
artificial heart valve),
implanted port,
infusion catheter (brand names
Port-o-cath,
Infusaport,
Lifeport),
intrauterine device (IUD), or any metal plates, pins,
screws or surgical staples in your body. In most cases,
surgical staples, plates, pins and screws pose no risk
during MRI if they have been in place for more than 4-6
weeks. Dyes used in tattoos and permanent eyeliner may
contain metallic iron oxide and could heat up during MRI;
however, this is rare. You will be asked if you have ever
had a bullet or shrapnel in your body, or ever worked with
metal. If there is any question of metal fragments,
especially in the eye, you may be asked to have an
x-ray that will detect any such metal
objects. Tooth fillings usually are not affected by the
magnetic field, but they may distort images of the facial
area or brain, so the
radiologist should be aware of them. The same is true of
braces, which may make it hard to "tune" the MRI unit to
your body. You will be asked to remove anything that might
degrade MRI images of the head, including hairpins, jewelry,
eyeglasses, hearing aids, and any removable dental work.
The radiologist or
technologist may ask if you have any drug allergies and
whether you have undergone any surgery in the past. If you
are or might be pregnant, mention it to the MRI staff.
Some patients who undergo
MRI in an enclosed unit may feel confined or
claustrophobic. If you are not easily reassured, a
sedative may be administered. Roughly one in 20 patients
will require medication.
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What does the MRI equipment
look like?
The conventional
MRI unit is a closed cylindrical magnet in which the
patient must lie totally still for several minutes at a
time, and consequently may feel closed-in or truly
claustrophobic. However, new patient-friendly designs
are rapidly coming into routine use. These "short-bore"
systems are wider and shorter and do not fully enclose the
patient. Some newer units are open on all sides; however,
the image quality may vary.
An example of the
radiography equipment that may be used is shown at the top
of this page.
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How does the procedure work?
MRI is a unique imaging method because, unlike the usual
radiographs (x-rays),
radioisotope studies, or even
CT, it does not rely on
ionizing radiation. Instead, radio waves are directed at
protons, the nuclei of hydrogen atoms, in a strong magnetic
field. The protons are first "excited" and then "relaxed,"
emitting radio signals that can be computer-processed to
form an image. In the body, protons are most abundant in the
hydrogen atoms of water —the "H" of H2O—
so that an MRI image shows differences in the water content
and distribution in various body tissues. Even different
types of tissue within the same organ, such as the gray and
white matter of the brain, can easily be distinguished.
Typically an MRI exam consists of two to six imaging
sequences, each lasting two to 15 minutes. Each sequence has
its own degree of contrast and shows a cross section of the
body in one of several planes (right to left, front to back,
upper to lower).
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How is the procedure
performed?
 The
patient is comfortably positioned on a special table that
slides into the
MRI system opening where the magnetic field is created.
Then the
radiologist and
technologist leave the room and the individual MRI
sequences are performed. The patient will hear tapping
noises during the exam. The tapping is created when
magnetic field gradient coils are switched on and off to
measure the MRI signal reflecting back out of the patient's
body. The patient is able to communicate with the
radiologist or technologist at any time using an intercom.
Also, many MRI centers allow a friend or, if a child is
being examined, a parent to stay in the room.
Depending on how many
images are needed, the exam will generally take 15 to 45
minutes, although a very detailed study may take longer. You
will be asked not to move during the actual imaging process,
but between sequences some movement is allowed. Patients are
generally required to remain still for only a few seconds to
a few minutes at a time.
Depending on the part of
the body being examined, a contrast material may be used to
enhance the visibility of certain tissues or blood vessels.
A small needle connected to an intravenous line is placed in
an arm or hand vein. The
contrast material is injected about two-thirds of the
way through the exam.
When the exam is over the
patient is asked to wait until the images are examined to
determine if more images are needed.
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What will I experience during
the MRI procedure?
MRI causes no pain, but some patients can find it
uncomfortable to remain still during the examination. Others
experience a sense of being "closed in," though the more
open construction of newer MRI systems has done much to
reduce that reaction. You may notice a warm feeling in the
area under examination; this is normal, but if it bothers
you, the
radiologist or
technologist should be told.
Most bothersome to many
patients are the loud tapping or knocking noises heard at
certain phases of imaging. Ear plugs may help.
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Who interprets the results and
how do I get them?
 A
radiologist, who is a physician experienced in MRI and other
radiology examinations, will analyze the images and send
a signed report with his or her interpretation to the
patient's personal physician. The personal physician's
office will inform the patient on how to obtain their
results. New technology also allows for distribution of
diagnostic reports and referral images over the Internet at
some facilities.
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What are the benefits vs.
risks?
Benefits
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MR images of the soft
tissue structures of the body, such as the
muscles, tendons, joints and blood vessels, are
clearer and more detailed than with other
imaging methods.
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MR images can help
identify the causes of pain, swelling and
bleeding so that appropriate treatment can
begin.
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MRI contrast material is less likely to
produce an allergic reaction than the
iodine-based materials used for conventional
x-rays and
CT scanning.
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MRI enables the detection
of abnormalities, injuries and diseases that
might be obscured by bone tissue with other
imaging methods.
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MRI provides a fast,
noninvasive way to assess a variety of
muscle and joint injuries and disorders.
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The detail of MR images
makes them an invaluable tool in early diagnosis
and evaluation of tumors.
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Risks
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An undetected metal
implant may be affected by the strong
magnetic field. It may cause some distortion
of the images or the MRI system may have
difficulty "tuning" to your body if the
implant is in the area being imaged.
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MRI is generally
avoided in the first 12 weeks of pregnancy
although there are no proven hazards.
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What are the limitations
of a Musculoskeletal MRI?
Bone is better imaged
by conventional
x-rays, and
CT is preferred for unstable patients with severe
bleeding.
MRI may not always distinguish between tumor tissue
and
edema fluid, and does not detect calcium when this
is present within a tumor. In most cases the exam is
safe for patients with metal
implants, with the exception of a few types of
implants, so patients should inform the technician of an
implant prior to the test. The exam must be used
cautiously in early pregnancy. |
Source: http://www.radiologyinfo.org/content/mr_musculoskeletal.htm |
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