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 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

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

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

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

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

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