It is not easy to demonstrate the fine structure of human bones like the stapes and long process of the incus with three-dimensional(3-D)images using helical CT. In this study, fine structural imaging of the normal ossicular chain was investigated using helical CT with virtual endoscopy(VE). In cases of normal hearing, axial helical CT of the temporal bones was performed with a GE HSA. The endoscopic views were produced with commercially available software. VE images were studied with different threshold settings, and the measured CT values of these structures(incus long process, stapes crus)tended to vanish at various threshold settings(-800 to 0 H.U.). Accurate VE images of the assicular chain could be obtained at a threshold setting of about -600 H.U.. Furthermore, three elements of the superstructure of the stapes(two cruses and a head) were separately visualized with VE images using helical CT in 93.3% of all ears. Although VE using helical CT has some limitations at this time, this procedure when used for ossicular chain imaging in patients with ossicular lesions may provide important information for imaging diagnosis and preoperative planning. The combination of axial images and VE could be useful for ossicular chain abnormalities.
