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Common Questions
about MRI Scans
A COMMON DIAGNOSTIC TOOL UTILIZED IN THE CARE OF ORTHOPAEDIC
INJURIES IS THE MRI, WHICH IS USED TO ASSIST THE TREATING PHYSICIAN
TO
DIAGNOSE DIFFERENT CONDITIONS AND DISORDERS OF THE BONE, JOINT,
MUSCLE AND SPINE. ORGANS, TUMORS AND OTHER PATHOLOGY CAN ALSO
BE IDENTIFIED. LISTED BELOW ARE SOME OF THE MOST COMMON QUESTIONS
WE RECEIVE FROM PATIENTS AND REFERRAL SOURCES RELATED TO MRI’S.
What is MRI?
MRI stands for Magnetic Resonance Imaging. It uses a large
magnet and radiofrequency waves to produce cross sectional images
of the body. There is no radiation (x-rays) involved. This test
is a painless procedure that takes 30 to 60 minutes, depending upon
the type of exam ordered.
Can anyone
have a MRI?
NO. Patients with pacemakers cannot have an MRI. Certain aneurysm
clips, hearing implants, heart valves and neurostimulators may not
be scanned. This is why a complete surgical history is taken before
any MRI scan is performed.
Does this
mean those patients with hip and knee replacements (for example)
cannot be done?
NO. People with joint replacements, screws, cages, heart bypasses
and certain heart valves can have an MRI scan.
How do patients
prepare for an MRI exam?
For the majority of MRI procedures, there is no preparation at all.
Patients may eat and drink up until the time of the exam. The exception
would be for MRI’s of the abdomen, liver or for breastfeeding mothers.
Are all MRI
scanners the same?
NO. MRI scanners vary greatly. First of all, MRI scanners are set
apart by their magnetic field strength and homogeneity. Magnetic
field strength is measured in Telsa (T) units. Magnetic field strengths
used in clinical settings range from less than .35T to 1.5 T or
higher. As the strength of the magnetic field increases other parameters
also change, such as signal to noise ratio. The higher the field
strength the better the image quality. Second, MRI scanners are
known as either open or closed scanners. Open scanners are usually
low field magnets (.25T or .35T) and are open on one side or shaped
like a C. Closed scanners are usually high field magnets ranging
from 1.0T and up. Closed scanners have a large bore (tunnel) that
is open at both ends and is shaped like a donut. Patients lie comfortably
on their back on either machine and listen to music while the test
is performed. Depending upon the manufacturer of the machine, the
scanners will have weight limits ranging from 300 to 420 pounds.
What is the
significance of ACR accreditation?
The ACR (American College of Radiology) is a voluntary accreditation
program that was established to attest to the quality of the performance
of MRI images and equipment. This certification ensures to the patients
and physicians that only certified or well-trained competent staff
using properly functioning MRI equipment perform MRI’s. Quality
control is done daily on the equipment before any patients are scanned
to ensure the highest quality of scans.
Is claustrophobia
a big factor?
NO. Claustrophobic patients can be scanned on either machine comfortably.
We rarely send anyone away(less than 1%) because they cannot complete
the test due to claustrophobia. Most patients at DMOS think we have
an open MRI scanner, but it is actually a scanner with a large opening.
It has a lot to do with our room layout. We have windows on two
sides of the scanner in a very large room, where many scanners are
pushed up against a wall, in a basement, without windows or on a
semi-truck, for example. Many patients at DMOS leave feeling relieved
and comment on how easy and comfortable the test was.
Can pregnant
women have a MRI scan?
Yes, if the benefits outweighthe risks. Most scanners do not scan
pregnant patients at all in the first trimester and some not at
all. As far as we know, to date, there are no known risks involved
with MRI but the long-term effects are not known. A second concern
is that the MRI Scanners increase internal body temperature (known
as SAR). For the benefit of the fetus it is recommended to identify
the necessity of the test before taking any risk. The decision whether
to perform an MRI should be seriously
discussed with the expectant mother and the treating physician(s).
Is contrast used for MRI? Yes, contrast can be used for MRI exams,
but many people confuse it with contrast that is used for radiography
examinations such as angiograms, CT’s and IVP’s. The most common
contrast that is used for MRI’s is called gadolinium DTPA. It is
used for MRI exams only and doesn’t have the adverse effects of
x-ray contrast.
Contrast for MRI’s is used for patients that have had previous back
surgeries, metastatic disease or other abnormalities. There are
other contrasts that are used for MRI, but are not as common. One
(an IV solution) is used to show up abnormalities of the liver,
and there is another that is used orally to differentiate bowel
in the abdomen and pelvis.
You may have
other questions about MRI that we have not answered. If so, please
contact the MRI Imaging Center at DMOS at 515-224-5111. We are more
than happy to help!
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