High speed Holographic Shape and Vibration Measurement of the Semi-transparent Tympanic Membrane

Abstract

Holographic interferometric methods have been used by our group to quantify the shape and full-field vibrations of the tympanic membrane (TM) in the human cadaveric ear. Previously, we integrated a high-speed holographic system using a 532 nm wavelength laser for displacement measurement and a 770–789 nm tunable wavelength laser for shape measurement. However, because of the semi-transparency of the TM and the short exposure time (<13 μs) from high-speed recording (>75,000 fps), the TM surface needs to be painted with a thin layer of white paint to increase reflection of the laser beam to obtain quantifiable interference patterns. The need for painting is not practical for in-vivo live human ear measurement. In this paper, we describe our efforts to measure the unpainted semi-transparent TM. We adapted a multi-angle illumination shape measurement method into the existing holographic system to eliminate the need for the tunable laser source. It allows us to use the single wavelength (532 nm) high power laser to perform both shape and displacement measurements on the unpainted TM. We show results from three fresh postmortem human ears before and after experimentally simulated common middle-ear pathologies. The Frequency Response Function (FRF) of the displacement normalized by the sound stimulus at each pixel point of the entire TM surface was calculated. Vibration parameters such as dominant frequency, rise time, settling time over the entire surface of the TM are then determined and compared among different middle ear conditions. We observe distinguishable changes in these vibration parameters, which may be useful for the differential diagnosis of middle ear pathologies.