Physics

Question 1

What 2 artifacts are present?

Answer 1

Undersampling artifacts

• View aliasing - Fine stripes radiating from the edge of a dense a object at a distance. Fixed by acqcuiring the plargest possible number of projects per roation - slowing the rotation speed
• Ray aliasing - Strips appearing close to a structing due to under sampling within a projection. This is fixed by using specialized high resolution techniques

Question 2

How to improve this artifact?

Answer 2

• Metal artifact has several mechanisms: beam hardening, partial volume, aliasing and density ranges higher than what can be handled by computer.
• Fixing metal artifact: ask patient to remove it, Increase kVP, use thinner slices, certain interpolation software can help

Question 3

Name the artifact and how to reduce

Answer 3

Helical artifact

Must reduce the variation in the Z direction

• use a low pitch,
• use 180 degree instead of 360 degree when possible
• using thin sections instead of thick

Question 4

Name the artifact

Answer 4

Windmill artifact

• aka as helical artifact in multi-section
• worsens with increased helical ptich
• a “Z-filter” is done to reduce the severity

Question 5

Name the artifact and how to correct

Answer 5

Stair Step Artifact

• Fixed by making thin slices
• Less severe with helical scanner

Question 6

Artifact?

Answer 6

Zebra artifact

• reformat artifact seen in 3D imaging which manifests as stripes