The Importance of Reading Artifacts in MRI

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The Importance of Reading Artifacts in MRI
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By Vikki Harmonay
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Magnetic Resonance Imaging (MRI) uses magnetic
fields and radio waves to form images of the
body. Radiologists read these images to help
diagnose a lot of different health conditions.
Sometimes structures or artifacts can appear in
MRI imaging but arent actually anatomically
present. This can lead to improper diagnoses, so
its important to be able to recognize common
artifacts. Almost every MRI exam includes some
kind of artifact. There are three primary types
of MRI artifacts Physiologic, Inherent Physical
Artifacts and Hardware/Software Artifacts.
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Physiologic Artifacts are those caused by patient
motion during the MRI. These can be caused by
cardiac movement, breathing, CSF pulsation/blood
flow or patient movement that is intentional or
not. They typically look like blurring or
ghosting, especially in the phase-encoding
direction. Its very important to instruct a
patient to hold still during the exam in order to
reduce the possibility of motion artifacts since
these can help radiologists diagnose patients as
accurately as possible. Sometimes patients might
even require an antispasmodic medication to
reduce the possibility of motion artifacts. A
radiologist also mighty reduce motion artifacts
by using echo-planar imaging (EPI), which is a
very fast MRI technique.
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Inherent Physical Artifacts are artifacts that
are caused by the inherent physics of an MRI,
like the presence of metal or chemical shift.
Chemical shift artifacts happen during the
frequency encoding of the MRI process. However,
they tend to be less prominent on T1-weightd
images than on T2-weighted images. Fat and water
molecules show up differently during encoding
because they oscillate differently within the
magnetic field. This creates a bright or black
band at the edge of the patients anatomy and
sometimes is misinterpreted as pathology. This
kind of artifact can be minimized by increasing
the bandwidth, suppressing the fat-frequency
signal or reducing the matrix size.
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When a patient has an implant or medical device
in the MRI room that responds to the magnetic
field, magnetic susceptibility artifacts can
occur. This causes the image to have dark areas
and bright areas near the magnetic object that
are not anatomically correct. By avoiding
gradient echo sequences, this effect can be
reduced. However, sometimes this type of artifact
can actually be useful in diagnosing patients,
especially in the detection of hematomas. These
artifacts can also enhance the image quality when
used in certain circumstances. In addition,
metallic objects within the patients body or
also on the patient can result in
FLAIR-hyperintensity due to a magnetic
susceptibility artifact.
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There are three types of artifacts caused by
metallic and other foreign bodies that are found
in and one patients bodies.

• Foreign bodies that are connected with outfit or
  ornamentation of the body, like make-up, hair
  accessories, clothes and clothing labels. This
  can also include medical equipment like hearing
  aids.
• Foreign bodies that cant be eliminated like,
  surgical/neurosurgical staples or clips, dental
  implants and endoprostheses.

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• Foreign bodies that patients have forgotten to
  tell MRI unit personnel about or dont know about
  them, like a stent graft or other medical
  implants.
• In additional, spike noise artifacts caused by
  static electricity from clothing or blankets
  resemble checkered patterns on the clothes. This
  can be caused by acrylic materials.

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Hardware/Software Artifacts
When something in the environment interferes with
an MRI unit, it can create noise on the image
which makes it difficult to read. These zipper
artifacts can be caused by blinking light bulbs,
the door to the MR Room not being securely
closed, or even noise from nearby construction.
By removing the source of the interference the
artifact can be eliminated. By locating the MR
room in an isolated area thats strictly
controlled, the chance of interference can be
minimized.
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Conclusion
Yes, there are many types of artifacts and many
different causes of them. When radiologists can
identify them and minimize their effects, its
easier to make correct diagnoses.
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Talk To An Expert
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consider buying a refurbished or used MRI, CT
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Meet the author Vikki Harmonay
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