3D imaging and modeling of the middle and inner ear

The bones of the middle ear are the smallest bones in the body and are among the most complicated functionally. They are located within the temporal bone – rendering them difficult to access and study. An accurate 3D model can offer an excellent illustration of the complex spatial relationships between the ossicles and the nerves and muscles with which they intertwine. The overall objective was to create an educational module for learning the anatomy of the outer, middle and inner ear from MRI data. Such a teaching tool will provide surgeons, radiologists and audiologists with a detailed self-guided tour of ear anatomy. MRI images of the auditory canal were acquired using a 9 Tesla MR scanner. The acquired images were reformatted along obliquely oriented axes to obtain the desired orientation relative to anatomical planes. An automated segmentation algorithm was applied to the MRI data to separate the cochlea, auditory nerve and semi-circular canals in the inner ear. Semi-automated segmentation was used to separate the middle ear bones. This was necessary in order to detach the malleus from the incus and the tympanic membrane from the malleus, as the boundaries between these structures were not sufficiently distinct in the data. Each structure became an independent object to facilitate its interactive manipulation. Different angles of view of the 3D structures were rendered illustrating the anatomic pathway starting at the tympanic membrane, through the middle ear bones, to the semi-circular canals, cochlea and auditory nerve in the inner ear.