A digital holographic interferometry (DHI) system with three object-illumination beams is used for the first time to measure micro-deformations along the x, y and z axes (3D) on the tympanic membrane (TM) surface of a post-mortem cat. In order to completely and accurately measure the TM surface displacements its shape is required to map on it the x, y and z micro-deformations. The surface contour is obtained by applying small shifts to the object illumination source position. A cw laser in stroboscopic mode and a CCD camera were used and synchronized to the acoustic excitation wave that produces a resonant vibration mode on the tympanic membrane surface. This research work reports on the 3D full field of view response of the TM to sound pressure, and has as its main goal the presentation of DHI as an alternative technique to study the TM real displacement behavior when subjected to sound waves, so it can be used as a diagnostic tool to prevent and treat TM diseases.
The data acquisition from the shape of an object is a must to complete its quantitative
displacement measurement analysis. Over the past years whole field of view optical non-invasive
testing has been widely used in many areas, from industrial ones to, for instance, biomedical
research topics. To measure the surface contour from the tympanic membrane (TM) of ex-vivo cats
digital holographic interferometry (DHI) is used in combination with a two-illumination
positions method: the shape is directly measured from the phase change between two source
positions by means of a digital Fourier transform method. The TM shape data in conjunction with
its displacement data renders a complete and accurate description of the TM deformation, a
feature that no doubt will serve to better comprehend the hearing process. Acquiring knowledge
from the tissue shape indicates a mechanical behavior and, indirectly, an alteration in the
physiological structure due to middle ear diseases or damages in the tissue that can
deteriorate sound transmission. The TM shape contour was successfully measured by using two
source positions within DHI showing that the TM has a conical shape. Its maximum depth was
found to be 2 mm, considering the umbo as the reference point with respect to the TM annulus
plane, where the setup is arranged in such a manner that it is capable of measuring a height of
up to 7 mm.
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