Ring artifact

Last revised by Andrew Murphy on 26 Jan 2024

Ring artifacts are a CT phenomenon that occurs due to the miscalibration or failure of one or more detector elements in a CT scanner. Less often, it can be caused by insufficient radiation dose or contrast material contamination of the detector cover 2.


This artifact usually occurs in 3rd generation CT machines because the detector row rotates around the patient. Miscaliberation of one detector will give erroneous readings around the patient as the detector moves, thus giving a circular artifact 1.

However, ring artifacts seen in phantom may not be seen in clinical images because a wide window is used 1.

They occur close to the isocenter of the scan and are usually visible on multiple slices at the same location. They are a common problem in cranial CT.


Selecting the correct scan field using calibration data that are more closely fit with the anatomy of the patient may reduce artifact 1.

Recalibration or repair of the detector will usually rectify the artifact 1. Occasionally detector elements need replacing, which can be costly. The referring clinician should be notified that the concerning ring shadows are artifactual. 

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