CT artifacts are image features that do not accurately represent the anatomy scanned. They can obscure findings, mimic pathology or make an examination harder to interpret. Recognizing the pattern is the first step; the next is to check its possible cause and decide with the radiologist whether the existing images answer the clinical question. [1]
Before repeating a scan
Review the acquisition and available reconstructions, involve the radiologist, and follow local protocols. A repeat adds radiation exposure and should be justified by clinical need. Optimize dose for the image quality required by the clinical task. [2]
CT artifacts at a glance
| Artifact | Typical appearance | First check |
|---|---|---|
| Motion | Blur, ghosting, double contours or streaks | Review location, patient movement and scan timing. |
| Beam hardening | Dark bands, shading or streaks near dense material | Look for dense bone or metal along the affected paths. |
| Metal | Bright and dark streaks around implants or dental work | Review conventional and available metal artifact reduction images. |
| Ring | Rings or arcs, often centered near the scanner isocenter | Check for recurrence and review scanner quality control. |
| Partial volume | Blurred edges or averaged attenuation | Review thinner reconstructions if available and appropriate. |
| Noise or photon starvation | Graininess or streaks through highly attenuating regions | Check positioning, protocol and exposure-control information. |
| Sampling and stair-step | Distorted edges or steps on reformatted images | Review source images, slice thickness and reconstruction interval. |
These appearances are clues, not definitive diagnoses: several mechanisms can occur together. [1]
1. Motion: the blurry chest CT
Blurred lung markings or double contours near the diaphragm can suggest respiratory motion. Swallowing, cardiac pulsation and other patient movement can also cause artifacts. Check where the artifact occurs and whether available images answer the clinical question. If another acquisition is justified, clear instructions and comfortable, safe positioning may help; follow a protocol suited to the patient's ability. [1]
2. Beam hardening: dark bands near bone
Lower-energy photons are preferentially absorbed as the X-ray beam passes through the patient. This changes its energy distribution and can cause shading or dark bands, including near dense skull-base bones. Look for the relationship to dense anatomy and review available reconstructions. Photon starvation and other effects can contribute to similar appearances, so do not assume a single cause. Protocol adjustments require local radiologist and medical physicist guidance. [1]
3. Metal: streaks around an implant
Bright and dark streaks around prostheses or dental work have multiple contributing mechanisms, including beam hardening, scatter and photon starvation. Review available metal artifact reduction (MAR) and conventional reconstructions according to local practice; corrected images can contain their own distortions and do not recover every obscured detail. Ask the radiologist whether the clinical question can be answered. [1]
4. Ring artifacts: a recurring pattern
Detector response inconsistencies or calibration problems can produce rings or arcs. If the same pattern recurs on different patients, check the scanner's QC status and follow the approved procedure for phantom assessment. Document the finding and notify the lead technologist, medical physicist or service team as required. Perform calibration only when authorized by local and manufacturer instructions. The ACR includes artifact evaluation in CT quality control under qualified medical physicist supervision; local requirements may differ. [3]
5. Partial volume: a small structure looks blurred
When more than one tissue contributes to a voxel, their attenuation is averaged. This can blur boundaries or change how a small structure appears. Review thinner reconstructions when available and suitable. Thinner images may improve visualization of small structures but can also appear noisier, so the reconstruction must suit the diagnostic task. [1, 5]
6. Noise and photon starvation: streaks through the shoulders
Highly attenuating anatomy can leave too few detected photons along some paths, producing noise and contributing to streaks. Check patient centering, the selected protocol, safe arm positioning and available reconstructions. Simply increasing exposure is not automatically the right response; use approved protocols and balance image quality with dose. [1, 2]
When to escalate
- The artifact obscures anatomy needed for the clinical question.
- A pattern recurs across patients or phantom images.
- Quality control fails or the scanner displays a warning.
- A possible equipment problem could affect later examinations.
Communicate with the radiologist and follow the department's escalation process. Scanner-specific corrective actions must follow manufacturer and local guidance.
Key points
- Recognize the pattern, then investigate possible causes.
- Different mechanisms can produce similar appearances.
- Review existing data before considering additional exposure.
- Escalate recurring artifacts through quality control.
For an introduction to CT physics and image quality, see our CT scan overview. The same troubleshooting logic applies to projection imaging: our guide to digital radiography artifacts covers the checks for CR and DR images.
References
- Common computed tomography artifact: source and avoidance. Review of CT artifact mechanisms.
- U.S. Food and Drug Administration. Medical X-ray Imaging. Dose optimization and quality assurance.
- American College of Radiology. Quality Control: CT.
- Health Canada. Safety Code 35. Safety and quality assurance for medical radiological facilities.
- Cardiac CT blooming artifacts: clinical significance, root causes and potential solutions.
Educational information; follow institutional protocols and professional judgment. Clinical review has not been claimed.