Nondestructive Three-dimensional Analysis of Electrode to Modiolus Proximity

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Abstract
To propose a nondestructive method for three-dimensional analysis of inner ear morphology after cochlear implantation for isolated petrous bones. After implantation of cochlear implant electrode arrays, fresh temporal bones were investigated on a new C-arm–based radiographic device permitting the generation of cross-sectional images and of three-dimensional models from multiple two-dimensional radiographic images taken under different projections (cone-beam computed tomography). Cross-sectional images and multiplanar reformations with a slice thickness of 0.15 mm were acquired. The relationship of the electrode to the modiolus was analyzed (distance between electrode and the modiolus; position of the electrode inside the tympanic or vestibular scale). Histologic preparation was used as a gold standard. In all cases, cone-beam computed tomography gave similar information concerning the position of the electrode compared with histologic analysis (tympanic scale versus vestibular scale, proximity versus distance to the modiolus). Perforation of the electrode from the tympanic to the vestibular scale could be assessed three-dimensionally in the cross-sectional images. In contrast to histology, cross-sectional imaging based on radiography is performed in less than 10 minutes and needs no preparation of the object. Because it is nondestructive, it can be repeated and used as a control after position-correcting maneuvers. Cross-sectional imaging based on radiography is a valuable tool for the analysis of the electrode-modiolus relationship after cochlear implantation in isolated temporal bones, which may confirm histologic analysis.