CT ARTIFACTS Flashcards
Anything appearing on the
image that is not present in the
object scanned
IMAGE ARTIFACT
Classification of CT artifacts
• Physics-based artifacts
• Patient-based artifacts
• Equipment-induced artifacts
Has:
• BEAM HARDENING
• PARTIAL VOLUME
EFFECT
• ALIASING
• EDGE GRADIENT
PHYSICS-BASED ARTIFACTS
A result of the attenuation of
the beam as it passes through
the patient
BEAM HARDENING
Caused by: polychromatic
nature of x-ray
BEAM HARDENING
• Appearance:
• Broad dark bands or
streaks(cupping artifact)
• Vague areas of high density
• Dark bands or streaks between
dense objects in the image
• Decrease in CT number
BEAM HARDENING
Types of PHYSICS-BASED ARTIFACTS
• BEAM HARDENING
• PARTIAL VOLUME
EFFECT
• ALIASING
• EDGE GRADIENT
Correction for BEAM HARDENING artifacts?
• Filtering the x-ray beam
• Calibration correction
• Beam hardening correction
software
• Increased kVp setting
• To select appropriate SFOV
Occurs when the data from the
entire section thickness is
averaged together
• Caused by:
• Thick slice
• Large pixel size
PARTIAL VOLUME EFFECT
Appearance: shading artifact to
appear in the image
PARTIAL VOLUME EFFECT
Corrections for PARTIAL VOLUME EFFECT
• Corrections:
• Thin slice
• Small pixel size
Occurs when there’s inadequate
number of projections available
for reconstruction
ALIASING ARTIFACT
• Caused by:
• Greater helical pitch
• Fast gantry rotation
• Decrease scan time
• Small FOV
ALIASING ARTIFACT
• Appearance: fine stripes or
streaks
ALIASING ARTIFACT
corrections for ALIASING ARTIFACT
• Corrections:
• Reduce helical pitch
• Slow gantry rotation
• Increase scan time
• Large FOV
• Results from irregularly shaped
objects that have a pronounced
difference in density from
surrounding structures
EDGE GRADIENT EFFECT
Caused by: Barium and air lie
adjacent to each other
EDGE GRADIENT EFFECT
• Appearance: streaks or
shading(both light and dark)
EDGE GRADIENT EFFECT
• Corrections:
• Thin slice
• Low-HU oral contrast
• Increase scan time
EDGE GRADIENT EFFECT
Types of PATIENT -BASED ARTIFACTS
• MOTION ARTIFACT
• METAL ARTIFACT
• OUT-OF-FIELD ARTIFACT
• Results from patient movement
during the scan
• Caused By:
• Involuntary motion
• Voluntary motion
MOTION ARTIFACT
Appearance: shading, ghosting,
streaking or blurring
MOTION ARTIFACT
Corrections:
• Proper instruction
• Immobilization device
• Sedation
• Short scan time
MOTION ARTIFACT
• Results from attenuation of
nearly 100% of the primary beam
• Caused By: presence of metallic
materials within the SFOV
• Star artifact
METAL ARTIFACT
Appearance: streaks or star
artifact
METAL ARTIFACT
Corrections:
• Angle the gantry
• Software algorithm
• Increased kVp
• Thin slice
METAL ARTIFACT
Occurs because the anatomy
outside the SFOV attenuates the
beam but is ignored in image
reconstruction
• Caused by: anatomy that extends
outside of the selected SFOV
OUT -OF-FIELD ARTIFACT
• Appearance: streaks or shading
OUT -OF-FIELD ARTIFACT
Corrections:
• Place the arms away from the
SFOV
• Large SFOV
OUT -OF-FIELD ARTIFACT
Types of EQUIPMENT -INDUCED ARTIFACTS
• RING ARTIFACT
• TUBE ARCING ARTIFACT
• HELICAL INTERPOLATION
ARTIFACT
• CONE BEAM ARTIFACT
• Annular artifact
• Occurs with 3rd generation
scanners
• Caused by: imperfect detector
elements (faulty or out of
calibration)
RING ARTIFACT
• Appearance: ring or concentric
rings on the rotational axis
RING ARTIFACT
• Corrections:
• Detector calibration
• Repair (service engineer)
RING ARTIFACT
Occurs when there is a large
difference in electrical
potential(undesirable surge of
electric current)
TUBE ARCING ARTIFACT
• Caused by:
• Short circuit
• Degradation of vacuum within
the tube
TUBE ARCING ARTIFACT
• Corrections:
• Remove residual gas(service
engineer)
• Install new tube
TUBE ARCING ARTIFACT
Appearance: no specific pattern
• Single slight streak to multiple
streaks
TUBE ARCING ARTIFACT
• Appearance: subtle inaccuracies
in CT number
• Corrections: low pitch
HELICAL INTERPOLATION ARTIFACT
• Occurs when the table moved
continuously and the views
collected for reconstruction were
not all in the same plane
• Caused by: high pitch
HELICAL INTERPOLATION ARTIFACT
CONE BEAM ARTIFACT are also known as?
• Windmill artifact
Occurs only on multidetector CT
helical system
CONE BEAM ARTIFACT
• Common Sites:
• Edge of the FOV
• Outer detector row
CONE BEAM ARTIFACT
• Appearance:
• Streaks or bright and dark shading
near areas large density differences
CONE BEAM ARTIFACT
Corrections:
• Do not use all available detectors
• Use pitch recommended by the
manufacturer
CONE BEAM ARTIFACTS
