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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 step-like patterns at high contrast edges

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Image Artifacts

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  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

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