CT ARTIFACTS Flashcards by Cyril Macalintal

Anything appearing on the
image that is not present in the
object scanned

IMAGE ARTIFACT

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Classification of CT artifacts

• Physics-based artifacts
• Patient-based artifacts
• Equipment-induced artifacts

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Has:
• BEAM HARDENING
• PARTIAL VOLUME
EFFECT
• ALIASING
• EDGE GRADIENT

PHYSICS-BASED ARTIFACTS

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A result of the attenuation of
the beam as it passes through
the patient

BEAM HARDENING

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Caused by: polychromatic
nature of x-ray

BEAM HARDENING

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• 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

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Types of PHYSICS-BASED ARTIFACTS

• BEAM HARDENING
• PARTIAL VOLUME
EFFECT
• ALIASING
• EDGE GRADIENT

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Correction for BEAM HARDENING artifacts?

• Filtering the x-ray beam
• Calibration correction
• Beam hardening correction
software
• Increased kVp setting
• To select appropriate SFOV

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Occurs when the data from the
entire section thickness is
averaged together
• Caused by:
• Thick slice
• Large pixel size

PARTIAL VOLUME EFFECT

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Appearance: shading artifact to
appear in the image

PARTIAL VOLUME EFFECT

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Corrections for PARTIAL VOLUME EFFECT

• Corrections:
• Thin slice
• Small pixel size

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Occurs when there’s inadequate
number of projections available
for reconstruction

ALIASING ARTIFACT

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• Caused by:
• Greater helical pitch
• Fast gantry rotation
• Decrease scan time
• Small FOV

ALIASING ARTIFACT

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• Appearance: fine stripes or
streaks

ALIASING ARTIFACT

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corrections for ALIASING ARTIFACT

• Corrections:
• Reduce helical pitch
• Slow gantry rotation
• Increase scan time
• Large FOV

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• Results from irregularly shaped
objects that have a pronounced
difference in density from
surrounding structures

EDGE GRADIENT EFFECT

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Caused by: Barium and air lie
adjacent to each other

EDGE GRADIENT EFFECT

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• 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