Holographic Measurement of Semi-transparent Tympanic Membrane Shape Using Multiple Angle Illuminations

Abstract

The shape of the tympanic membrane (TM) plays an important role in conducting acoustic energy from the environment to the ear for hearing. Changes of the TM shape also have the diagnostic value, e.g., bulging of the TM is a sign of middle ear effusion. Previously we developed a high-speed holographic system employing a tunable wavelength laser for rapid TM shape measurement. However, because of the semi-transparency of the TM and the short-exposure time required for the high-speed acquisition, the illumination intensity (0.01 mW/mm2) of the tunable laser was insufficient for measurements on the semi-transparent TM surface. Here, we describe a multi-angle illumination technique that allows us to use a single wavelength (532 nm) laser with higher illumination intensity (0.06 mW/mm2) to perform shape measurements of the semi-transparent TM. The accuracy of the proposed method is demonstrated by measurements of a stepwise gauge provided by the National Institute of Standards and Technology. We successfully applied the abovementioned method to resolve the shape of the fresh postmortem human TM. We see a potential for miniaturization of the apparatus into a holographic otoscope for in-vivo measurements.KeywordsHigh-speed holographyHuman tympanic membraneSingle wavelength shape measurement