CT Artifact Recognition & Reduction

What is the definition of an artifact in CT?

A distortion or error in an image unrelated to the subject being studied

How else is a CT artifact defined based on attenuation?

A discrepancy between reconstructed CT numbers and true attenuation coefficients

What is another definition of a CT artifact related to detectors?

Anything causing incorrect measurement of transmission readings by detectors

How else can an artifact be defined in CT images?

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

What are the three main categories of CT artifacts?

Physics-based, patient-based, and equipment-induced

What causes physics-based CT artifacts?

The physical processes associated with data acquisition

What causes patient-based CT artifacts?

Patient motion, positioning, or anatomy

What causes equipment-induced CT artifacts?

Scanner hardware or technical failures

What is beam hardening in CT?

An increase in the mean energy of the x-ray beam as it passes through the patient

Why does beam hardening occur?

Lower energy photons are absorbed, leaving higher energy photons

What is the typical appearance of beam hardening artifact?

Dark bands or streaks with the periphery appearing lighter than the center

What is the cupping artifact?

A beam hardening artifact where the periphery appears lighter than the center

What is partial volume averaging?

Mathematical averaging of voxel tissue attenuations when more than one tissue is in a voxel

What causes partial volume artifact?

A dense object lying at the edge of the FOV with too few views for accurate description

How can partial volume artifacts be reduced?

By using thinner slices

What is an edge gradient artifact?

Artifact caused by sampling attenuation profiles around complex structures with sharp density differences

What does an edge gradient artifact look like?

Streaks and shading that can be light or dark

How can edge gradient artifacts be reduced?

By using thinner slices

What is voluntary patient motion in CT?

Motion controlled by the patient such as swallowing or breathing

What is involuntary patient motion in CT?

Motion the patient cannot control such as peristalsis or cardiac motion

What is the appearance of patient motion artifacts?

Shading, ghosting (shadow), streaking, or blurring

What are metallic artifacts in CT?

Star-shaped streaks caused by metal blocking x-ray transmission

Why do metallic artifacts appear white on CT?

Because no transmission reaches the detector

How can metallic artifacts be reduced?

Remove external metal, use metal artifact reduction software, adjust scan range or gantry tilt, increase kVp

What is an out-of-field artifact?

Occurs when part of the patient lies outside the scan FOV

Why do out-of-field artifacts occur?

Anatomy outside the FOV contributes to attenuation but is ignored in reconstruction

What is the appearance of out-of-field artifacts?

White shading or streaks

How can out-of-field artifacts be reduced?

Ensure all anatomy is inside the FOV, properly center the patient, and use correct scan FOV

What is a ring artifact?

An artifact that appears as concentric rings on the image

What causes ring artifacts?

A bad detector

Which CT scanner generation commonly produced ring artifacts?

Third-generation scanners

How can ring artifacts be reduced?

Recalibration or replacement of the bad detector

What is tube arcing?

An undesired surge of electrical current within the x-ray tube

What causes tube arcing?

Vacuum compromise in the x-ray tube

What is the appearance of tube arcing artifact?

Streaks and noisy or non-diagnostic images

How is tube arcing artifact reduced?

Routine equipment maintenance

What is a cone beam artifact?

An artifact caused by the geometry of cone-shaped x-ray beams in multidetector CT

What is the appearance of cone beam artifact?

Irregular borders and shading around object edges

Why is cone beam artifact considered problematic?

It does not represent the true shape of the object

How can cone beam artifacts be reduced?

Using cone beam reconstruction algorithms and using only center detector rows

What is the main goal of CT artifact recognition?

To correctly identify image distortions and avoid misdiagnosis

Why is CT artifact reduction important?

To improve image accuracy and diagnostic quality

Which artifact type is caused by physical x-ray interactions?

Physics-based artifacts

Which artifact type is caused by patient movement?

Patient-based artifacts

Which artifact type is caused by scanner malfunction?

Equipment-induced artifacts

Which artifacts are reduced by thinner slice thickness?

Partial volume and edge gradient artifacts

Which artifact produces star-shaped streaks?

Metallic artifact

Which artifact produces concentric rings?

Ring artifact

Which artifact produces irregular object borders?

Cone beam artifact

Which artifact produces dark streaks due to high-density material?

Beam hardening artifact

Which artifact produces ghosting and blur?

Patient motion artifact

What is the best general method to prevent equipment-induced artifacts?

Routine quality control and maintenance

Why is proper patient centering critical in CT?

To prevent out-of-field artifacts and beam hardening

Why should metal be removed before CT scanning?

To prevent severe streak artifacts and image degradation