HIGH-SPEED SHAPE AND DISPLACEMENT MEASUREMENTS BY HOLOGRAPHY AND APPLICATIONS IN MIDDLE-EAR RESEARCH

Tang, Haimi

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HIGH-SPEED SHAPE AND DISPLACEMENT MEASUREMENTS BY HOLOGRAPHY AND APPLICATIONS IN MIDDLE-EAR RESEARCH

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The human ear comprises three parts: the outer-ear, middle-ear, and inner-ear. The middle-ear is an air- filled space, separated from the outer ear by the tympanic membrane (TM), which is the first structure that moves in response to sound. The mechanical response of the TM to sound is intricate in space and time. A method that simultaneously gathers relevant data from the entire TM surface is needed to characterize these spatiotemporal responses. This work describes the development of a holographic system that measures the shape and sound-induced motions of the TM using high-speed image acquisition to provide a complete description of TM mechanics, including 3D shape information and full-field TM surface normal vibration in the time and frequency domains. Three non-contact optical methodologies are implemented to measure TM shape with sub-mm resolution, while we refined our high-speed holographic methods to measure sound-induced motion of the TM surface with nanometer and microsec resolutions. The processing algorithm for the high-speed holography is optimized to facilitate near real-time examination of data quality during the experiment. Using a broad-band transient sound stimulus, the holographic measurements are used to describe the frequency response function (FRF) and impulse response function (IRF) for each measured pixel of the entire TM surface. Motion parameters based on FRF and IRF are extracted and then spatially averaged over regions of the TM surface to characterize the TM's mechanical properties. Statistically significant differences in the region-averaged motion parameters separate several pathological middle-ear conditions from the normal condition in a cadaveric human temporal bone study. The developed measurement system and analyses are also applied to study the ears of live chinchillas with and without Otitis Media with Effusion (OME). The holographic measurement results are compared to the results of functional hearing tests, including: auditory brainstem responses (ABR) and distortion product otoacoustic emissions (DPOAE). The holographic results describe significant differences in the TM's mechanical response to sound in normal and the OME-infected ears that are consistent with elevated ABR and DPOAE thresholds in the OME ears. The correlation between measured TM-function and hearing deficits suggest that high-speed holography may provide a rapid diagnostic tool for middle-ear diseases.

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