APPARENT WALL THICKENING IN FLUID-FILLED VERSUS AIR FILLED TYMPANIC BULLA IN COMPUTED-TOMOGRAPHY

A series of CT imaging experiments was performed to test the hypothesi s that when the tympanic bulla is filled with fluid there would be a f alse impression of bulla wall thickening, CT images were obtained befo re and after introduction of water in the tympanic bulla of a fresh ca nine cadaver, Images were acquired using different mA settings, slice thicknesses, reconstruction algorithms, and displayed at different win dow widths, The wall of the fluid filled bulla appeared thicker than t hat of the air filled bulla, This artifact was also demonstrated on a phantom composed of a thin (0.5 mm) and a thick (5 mm) piece of alumin um imaged in air and water, The effect was more apparent when images w ere acquired as thick slices (>5 mm), reconstructed with a soft tissue algorithm, or displayed with a narrow window (<250 CT numbers), The r adiologist must be aware of this artifact when interpreting CT images of the tympanic bullae.