CT - Semis Pt. 2

• streaks

• cupping

• low density

Beam-Hardening Artifact Manifestation

• Petrous pyramids of skull

• Chest and shoulder

• Hips

Beam-Hardening Artifact Common Locations

Beam-Hardening

Cause

• X-ray beams are composed of different energies

Remedy

• Use appropriate filtration

• Calibration and correction software

• Increase kVp setting

Partial Volume Effect

Cause

• More than one type of tissue in a voxel

• Dense object at edge of FOV (off-center)

Remedy

• Use thinner slices

Fine lines

Aliasing Effect Manifestation

Aliasing Effect

Cause

• Too few samples

Remedy

• If partial scan used → rescan using complete arc

• Increase scan time

• Reduce pitch

• Straight line from high-contrast areas

• barium adjacent to air

Edge Gradient Effect Manifestation

Edge Gradient Effect

Cause

• Angle of x-ray beam varies between two similar views

Remedy

• Largely unavoidable

• Reduced by:

  • Thinner slices

  • Use low or neutral HU-value oral contrast instead of barium

• Shading

• Streaking

• Blurring

• Ghosting

Motion Artifact Manifestation

Motion Artifact

Cause

• Voluntary or involuntary patient motion

Remedy

• Give clear breathing instructions

• Reinforce importance of staying still

• Use positioning aids / immobilization devices

• Consider sedation (especially pediatric)

• Use shortest scan time

• For cardiac → consider β-blockers

Streaks

Metallic Artifact (Star Artifact) Manifestation

Metallic Artifact (Star Artifact)

Cause

• Objects beyond dynamic range of scanner

• Object absorbs photons

Remedy

• Remove metallic objects from SFOV

• Angle gantry

• Increase technique (kVp)

• Use thin slices

Single ring or concentric rings

Ring Artifact Manifestation

Ring Artifact

Cause

• Detector problem

Remedy

• Recalibrate

• If persistent → call service

• No specific pattern:

  • Single streak → severe mottling

Tube Arcing Manifestation

Tube Arcing

Cause

• Electrical surge in x-ray tube

Remedy

• Call service

• Tube replacement

Subtle inaccuracies in CT number

Spiral Interpolation Artifact Manifestation

Spiral Interpolation

Cause

• Images created from views not in same plane

Remedy

• Lower pitch

Lines in windmill formation

Cone Beam Effect Manifestation

Cone Beam Effect

Cause

• Occurs in MDCT

• Due to cone-shaped x-ray beam

Remedy

• Use manufacturer-recommended pitch

Out-of-Field Artifact

Cause

• Anatomy extends outside SFOV

• Patient body obstructs detectors

Remedy

• Select SFOV larger than patient

Bright and dark streaks

Photon Starvation (Noise) Manifestation

Photon Starvation (Noise)

Cause

• Poor exposure technique

• Photons pass through thicker anatomy

Remedy

• Increase mA

• Use filtering

Step-like appearance

Staircase Artifact Manifestation

Staircase Artifact

Cause

• Improper:

  • Slice thickness

  • Slice incrementation

• Occurs in MPR and 3D images

Remedy

• Increase mA

• Use filtering