Artifacts

Question 1

Beam hardening

Answer 1

Cause: attenuation
Appearance: shading or streaks
How to fix/avoid: 
-select appropriate SFOV
-beam hardening reducing software

Question 2

Partial volume

Answer 2

Cause: more than 1 type of tissue in a voxel
Appearance: shading
How to avoid/fix: 
-thinner slices
-smaller pixels

Question 3

Motion

Answer 3

Cause: the patient, voluntary and involuntary 
Appearance: shading, streaking or blurring
How to avoid/fix: 
-software correction
-cardiac gating
-communication
-immobilization
-sedation
-short scan times

Question 4

Metallic

Answer 4

Cause: density of metal exceeds HU value range of the system
Appearance: streaks
How to avoid/fix:
-metal reducing software
-removal of external metallic objects
-⬆️ kVp
-thinner slices

Question 5

Out-of-field

Answer 5

Cause: anatomy that is outside the SFOV
Appearance: streaks and shading
How to fix/avoid:
-move anatomy out of the way
-⬆️ SFOV

Question 6

Cone beam

Answer 6

Cause: helical and MDCT scans, data interpolation, cone beam geometry
Appearance: streaks or shading
How to avoid/fix: ⬇️ pitch, use cone beam reconstruction algorithms

Question 7

Rings and bands

Answer 7

Cause: malfunctioning or miscalibrated detector elements
Appearance: rings or bands
How to avoid/fix: recalibration, service engineer

Question 8

Noise

Answer 8

Cause: quantum noise, inherent physical limitations, reconstruction parameters
Appearance: salt and pepper 
How to avoid/fix: 
-⬆️ mAs
-use a low-noise DAS system
-smoothing reconstruction algorithms