Artefact on CT brain images caused by the presence of air bubbles in the cooling oil of the X-ray tube.

Introduction: We report a series of patients who had computed tomography (CT) of their brains which showed an uncommon artefact caused by excess air bubbles in the cooling oil around the X-ray tube.

Methods: In November and December 2015, it was recognised that artefacts appearing on CT brain images acquired at our department were caused by a scanner fault. The test images were reviewed and the service engineer for the CT scanner was questioned about the artefact cause. A retrospective audit was then performed of images acquired on the CT scanner from December 2015 back to the date that the CT scanner was last serviced in September 2015 to identify any other scans affected by the artefact.

Results: Seven patients were identified whose CT brain scans showed the artefact. The artefact manifested in the form of an ill-defined low density area in varying locations. The artefact also appeared on CT phantom test images. It was discovered to be caused by the presence of excess air bubbles within the cooling oil of the X-ray tube. The fault was then rectified.

Conclusions: The artefact described may not be easily recognised and could lead to misinterpretation and unnecessary investigation. We aim to promote awareness of this artefact and to reinforce the importance of frequent quality control testing of CT systems.