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