Image ArtifactsImage Artifacts

Chapter 8Chapter 8

BushongBushong

Image ArtifactsImage Artifacts

Voluntary and involuntary patient motion Voluntary and involuntary patient motion can result in a motion artifactcan result in a motion artifact

The motion artifact appears as streaks or The motion artifact appears as streaks or step-like patterns at high contrast edgesstep-like patterns at high contrast edges

Respiratory motion artifacts in computed Respiratory motion artifacts in computed tomography angiography can simulate tomography angiography can simulate vascular stenosis or aneurysmvascular stenosis or aneurysm

Metal artifacts occur because the x-ray Metal artifacts occur because the x-ray absorption results in incomplete projection absorption results in incomplete projection profilesprofiles

Image ArtifactsImage Artifacts

Metal in tissue gives rise to streak Metal in tissue gives rise to streak and star shaped artifactsand star shaped artifacts

With penetration of cranial bone, the With penetration of cranial bone, the x-ray beam is selectively filtered and x-ray beam is selectively filtered and “hardened”“hardened”

The hardened x-ray beam presents a The hardened x-ray beam presents a false low linear attenuation false low linear attenuation coefficient and false low CT numbercoefficient and false low CT number

Image ArtifactImage Artifact

The bean hardening artifact appears The bean hardening artifact appears as a dark ring inside cranial bone and as a dark ring inside cranial bone and cupping at the center of the imagecupping at the center of the image

When an object (calcification) is not When an object (calcification) is not fully within a slice thickness, the CT fully within a slice thickness, the CT number representing that object will number representing that object will be falsebe false

Partial volume artifacts can be Partial volume artifacts can be reduced by overlapping scans but that reduced by overlapping scans but that increases the patient doseincreases the patient dose

Image ArtifactsImage Artifacts

Partial volume artifacts can be reduced by using Partial volume artifacts can be reduced by using thinner slice thickness but at the expense of a thinner slice thickness but at the expense of a higher image noise and/or patient dosehigher image noise and/or patient dose

Partial volume artifacts can be reduced in spiral Partial volume artifacts can be reduced in spiral CT by moving the plane of reconstructionCT by moving the plane of reconstruction

Multiple reconstruction along the z-axis during Multiple reconstruction along the z-axis during spiral CT reduces partial volume artifactsspiral CT reduces partial volume artifacts

Ring artifacts can occur in third-generation CT Ring artifacts can occur in third-generation CT imagers because of detector malfunctionimagers because of detector malfunction

Image ArtifactsImage Artifacts

Partial volume artifacts can be Partial volume artifacts can be reduced by combining several thin reduced by combining several thin slice reconstructed imagesslice reconstructed images

Pulsation artifact is observed in CTAPulsation artifact is observed in CTA Pulsation artifact can simulate Pulsation artifact can simulate

vascular stenosisvascular stenosis Pulsation artifact can be reduced by Pulsation artifact can be reduced by

using 360 degree interpolationusing 360 degree interpolation

Image ArtifactsImage Artifacts

The stair-step artifact is associated The stair-step artifact is associated with spiral CTwith spiral CT

The stair-step artifact is most The stair-step artifact is most apparent on inclined vessels during apparent on inclined vessels during spiral CTAspiral CTA

The height of a stair step artifact is The height of a stair step artifact is proportional to couch incrementproportional to couch increment

The height of a stair-step artifact is The height of a stair-step artifact is independent of collimation or independent of collimation or reconstruction intervalreconstruction interval