Computed Tomography Artifact Created by Air in the X-ray Tube Oil.

A subtle artifact of patchy hypodensities in computed tomography images of the head mimicked acute or subacute cerebral infarct. The cause of the artifact was air in the oil of the x-ray tube. The artifact manifested only when the acquisition parameters included a rotation time of 0.5 second and a gantry tilt angle of 11 to 20 degrees. Routine quality control testing did not detect nonuniformities in the water phantom.