Comparison of three-dimensional visualization techniques for depicting thescala vestibuli and scala tympani of the cochlea by using high-resolution MR imaging

BACKGROUND AND PURPOSE: Cochlear implantation requires introduction of a st imulating electrode array into the scala vestibuli or scala tympani, Althou gh these structures can be separately identified on many high-resolution sc ans, it is often difficult to ascertain whether these channels are patent t hroughout their length, The aim of this study was to determine whether an o ptimized combination of an imaging protocol and a visualization technique a llows routine 3D rendering of the scala vestibuli and scala tympani. METHODS: A submillimeter T2 fast spin-echo imaging sequence was designed to optimize the performance of 3D visualization methods. The spatial resoluti on was determined experimentally using primary images and 3D surface and vo lume renderings from eight healthy subjects, These data were used to develo p the imaging sequence and to compare the quality and signal-to-noise depen dency of four data visualization algorithms: maximum intensity projection, ray casting with transparent voxels, ray casting with opaque voxels, and is osurface rendering. The ability of these methods to produce 3D renderings o f the scala tympani and scala vestibuli was also examined. The imaging tech nique was used in five patients with sensorineural deafness. RESULTS: Visualization techniques produced optimal results in combination w ith an isotropic volume imaging sequence. Clinicians preferred the isosurfa ce-rendered images to other 3D visualizations. Both isosurface and ray cast ing displayed the scala vestibuli and scala tympani throughout their length , Abnormalities were shown in three patients, and in one of these, a focal occlusion of the scala tympani was confirmed at surgery. CONCLUSION: Three-dimensional images of the scala vestibuli and scala tympa ni can be routinely produced. The combination of an MR sequence optimized f or use with isosurface rendering or ray-casting algorithms can produce 3D i mages with greater spatial resolution and anatomic detail than has been pos sible previously.