40 year old man found collapsed. Persisting headache but no neurological signs.
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There are no acute intracranial findings on this study. An artifact is seen, consisting of high density rings located in the same position on each slice. This is seen as a series of dots on the coronal reformatted image.
This artifact is known as a ring artifact. It is caused by CT detector breakdown or malfunction, and a reboot of the machine usually solves the problem. In the days of film, this may have been confused for a mark left on the films by a cup of barium!