A CT artifact is an image feature that does not accurately represent the scanned anatomy. It can hide real detail, distort attenuation or resemble disease. Knowing the name helps; knowing why it appeared is what makes the next decision useful. [1, 2]
There is no single fix for every streak. A ring that recurs across scans calls for a different response from breathing motion, and a cleaner-looking metal-artifact reduction reconstruction does not necessarily recover every detail. Start by judging whether the finding affects the diagnostic target and which evidence can distinguish the causes.
What do you see first?
Four common clues worth recognizing. Open a card to understand the likely mechanism and choose a sensible first check.
01Ring artifactConcentric or partial circlesReveal mechanism and first check
Why it happens: A detector channel may be responding differently across rotations.
First useful check: Inspect adjacent slices and prior studies. If the pattern persists, follow site QC/escalation procedures rather than guessing at a patient cause.
02Beam hardeningDark bands or cupping near dense materialReveal mechanism and first check
Why it happens: Lower-energy photons are preferentially absorbed, leaving a harder X-ray spectrum and inconsistent attenuation estimates.
First useful check: Review anatomy, positioning and whether an approved reconstruction or artifact-correction series is available.
03Metal streakingBright and dark streaks radiating from metalReveal mechanism and first check
Why it happens: Photon starvation, beam hardening and other acquisition/reconstruction effects can occur together.
First useful check: Confirm removable external metal has been addressed and review approved MAR reconstructions with the radiologist; do not assume recovered detail is always faithful.
04MotionBlur, edge doubling or mismatched anatomyReveal mechanism and first check
Why it happens: Respiratory, cardiac or patient movement can create inconsistencies during data acquisition.
First useful check: Check timing, coaching, patient support and reconstruction options already acquired before considering another exposure.
Patterns overlap. In real CT images, several mechanisms can produce streaks, and the same artifact can vary with anatomy and reconstruction.
A quick distinction worth remembering
| Pattern | What may be happening | First useful check |
|---|---|---|
| Ring or partial ring | Detector-channel calibration or response problem | Persistence across slices/studies; QC escalation |
| Dark band between dense structures | Beam hardening, sometimes compounded by photon starvation | Anatomy and approved reconstructions |
| Streaks around metal | Mixed metal-related mechanisms | External objects and available MAR reconstructions |
| Blurring or double edges | Movement during acquisition | Breathing, timing and patient motion history |
| Smoothed edges or mixed tissue values | Partial-volume averaging within a voxel | Acquired resolution and appropriate thinner reconstructions |
| Grainy image / pronounced noise | Insufficient detected photons and reconstruction trade-offs | Patient size, available reconstructions and exposure/QC context |
Two less dramatic artifacts that still matter
Partial-volume averaging
A single voxel may contain more than one tissue. The reconstructed CT number then represents a mixture, and small structures can lose definition. Where the source data allow it, an appropriately thinner reconstruction can reduce averaging—but often increases visible noise. [1, 3]
Image noise and photon starvation
Fine grain can increase when too few useful photons reach the detector, especially through thicker or highly attenuating regions. Section thickness, reconstruction method and acquisition settings all affect the appearance. Lower noise is not automatically better if important detail is overly smoothed. [2, 3]
Pause on the cause, not just the picture.
- Locate the problem. Is it in one reconstruction, several contiguous slices or multiple studies? Is it near a dense object or recurring at a fixed scanner-centered location?
- Look for a less invasive explanation. Compare approved reconstructions, windows and relevant acquired series. Note patient motion, positioning, and removable objects.
- Decide whether it changes interpretation. A visible artifact is not automatically a failed exam; the diagnostic question and responsible radiologist determine whether essential anatomy is adequately shown.
- Escalate instead of improvising. Follow facility-approved protocol, QC and repeat-exposure processes; persistent rings or unexpected technical patterns warrant physicist/service review.
This guide does not authorize repeat radiation exposure, dose adjustments, diagnostic interpretation or equipment calibration. Decisions belong to the qualified clinical team under site protocols and manufacturer guidance. ACR expects formal CT quality control under a qualified medical physicist's oversight. [4]
Can you explain the next step?
Spotting a ring artifact is one thing. Connecting image quality, acquisition choices and reconstruction logic takes repeated practice.
The CT Core Concepts Workbook builds those connections through 39 teaching modules, 130 original practice questions and a structured approach to reviewing weak areas.
Explore the CT Core Concepts Workbook
Actual listing previewQuestions that come up in practice
Does every ring artifact mean a broken detector?
No. Detector miscalibration or abnormal channel response is a common mechanism, but the pattern alone does not diagnose a component failure. Report a recurring artifact and use the facility's quality-control process for investigation. [1, 4]
Will metal artifact reduction always restore the anatomy?
No. MAR may reduce prominent streaks but can introduce new image appearances or leave uncertainty near the metal–tissue interface. Review original and corrected images when available and follow the radiologist's assessment. [2, 3]
Is repeating the scan the first response to motion?
Not by default. First assess the affected anatomy and whether already acquired data, approved reconstructions or the planned clinical protocol are sufficient. A repeat examination involves additional radiation and requires an appropriate clinical decision. [4]
Sources and review notes
This article is an independently written educational synthesis. References support the imaging mechanisms and QC framework. The pattern descriptions are not a substitute for reviewing actual CT images in their clinical context.
- Barrett JF, Keat N. Artifacts in CT: Recognition and Avoidance. RadioGraphics (2004).
- Kalisz K, et al. Artifacts at Cardiac CT: Physics and Solutions. RadioGraphics (2016).
- Boas FE, Fleischmann D. CT Artifacts: Causes and Reduction Techniques. Imaging in Medicine (2012).
- American College of Radiology. Quality Control: CT (revised March 21, 2025).
Published October 23, 2026 · MRITechStudio independent educational resource · About our approach