Transcript Image Artifacts

Image Artifacts
Chapter 8
Bushong
Image Artifacts
Voluntary and involuntary patient motion can
result in a motion artifact
 The motion artifact appears as streaks or steplike patterns at high contrast edges
 Respiratory motion artifacts in computed
tomography angiography can simulate vascular
stenosis or aneurysm
 Metal artifacts occur because the x-ray
absorption results in incomplete projection
profiles
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Image Artifacts
Metal in tissue gives rise to streak and star
shaped artifacts
 With penetration of cranial bone, the x-ray
beam is selectively filtered and “hardened”
 The hardened x-ray beam presents a false
low linear attenuation coefficient and false
low CT number
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Image Artifact
The bean hardening artifact appears as a
dark ring inside cranial bone and cupping
at the center of the image
 When an object (calcification) is not fully
within a slice thickness, the CT number
representing that object will be false
 Partial volume artifacts can be reduced by
overlapping scans but that increases the
patient dose
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Image Artifacts
Partial volume artifacts can be reduced by using
thinner slice thickness but at the expense of a
higher image noise and/or patient dose
 Partial volume artifacts can be reduced in spiral
CT by moving the plane of reconstruction
 Multiple reconstruction along the z-axis during
spiral CT reduces partial volume artifacts
 Ring artifacts can occur in third-generation CT
imagers because of detector malfunction
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Image Artifacts
Partial volume artifacts can be reduced by
combining several thin slice reconstructed
images
 Pulsation artifact is observed in CTA
 Pulsation artifact can simulate vascular
stenosis
 Pulsation artifact can be reduced by using
360 degree interpolation
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Image Artifacts
The stair-step artifact is associated with
spiral CT
 The stair-step artifact is most apparent on
inclined vessels during spiral CTA
 The height of a stair step artifact is
proportional to couch increment
 The height of a stair-step artifact is
independent of collimation or
reconstruction interval
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