MIDDLE EAR MORPHOMETRY FROM CADAVERIC TEMPORAL BONE MICRO-CT IMAGING

摘要

An anatomically based three-dimensional (3D) compuational model requires detailed morphometry of middle ear structures. We report methods and results using the microCT imaging modality for the middle ear. Stacks of images were obtained from cadaveric temporal bone ears of human, cat, chinchilla and guinea pig. The images were segemented and 3D structures reconstructed. The structures include the eardrum (thickness map and 3D shape), volumes of each of the three middle ear bones, and suspensory ligaments and tensor tympani tendon. The volume reconstruction of the malleus indicates that it has a solid rod-like shape in human, is a hollow cylinder in cat, and has an I-beam like shape in guinea pig and chinchilla. From the ossicle volumes, principal axis of rotation and principal moments of inertia, both around the center of gravity, were calculated. The results indicate that for the guinea pig and chinchilla, where the malleus-incus joint is fused, the clasical axis of rotation through the malleus and incus heads holds. However, the data also indicate a new mode of operation at high frequencies in animals where the malleus-incus joint is mobile (human and cat). We hypothesize that the malleus shape, along with a mobile joint, provides optimal transfer of energy to the cochlea at high frequencies through a rotation motion (torsion) around the long axis (superior-inferior) of the malleus.