Image Artifacts

1
Image Artifacts

• Chapter 8
• Bushong

2
Image Artifacts

• Voluntary and involuntary patient motion can
  result in a motion artifact
• The motion artifact appears as streaks or
  step-like 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

3
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

4
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

5
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

6
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

7
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