A numerical study of the effects of destructive preprocessing on bone conduction transfer path measurements
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For modelling impacts and energy propagation in human heads, numerical models have become increasingly popular for understanding the underlying mechanisms [1,2]. In bone conduction hearing research, many quantities inside the human head are not measurable without destructive preprocessing, e.g. cochlear pressure and promontory or intracochlear bone motion. Therefore, several modifications can be done by performing mastoidectomy or upper dome removal [3,4]. Quantities of interest mainly involve the acoustic wave transfer path within the audible frequency range (0.1 to 20 kHz) from the excitation position at the mastoid or so-called BAHA position to the inner ear. To measure the importance of removed regions, we perform finite element analysis (FEA) of a validated 3D printed human skull. A CT scan of the 3D printed skull is used for the segmentation of the cranial anatomical structure, resulting in the major bone plates — parietal, occipital, temporal, frontal, zygomatic — as well as nasal and facial bones. By conducting FEA, we measure the energy distribution per frequency in different bone plates and facial regions. This gives a clear indication of the importance of these structures for the bone conduction transfer path. By removing individual bone plates of the cranium, correlations between the energy distribution and the transfer path can be quantified. While the removal of the face or zygomatic arc significantly affect the low frequency region up to 2 kHz along the entire structure, some regions such as the nose have a spatially localized impact on the bone conduction transfer path, e.g. only the lateral side.
