Dynamic microtomography of human tympanic membrane motions.

Understanding middle ear biomechanics is crucial for clarifying sound transmission and surgical techniques. Conventional interferometry-based techniques for motion quantification are highly sensitive but are often limited to small surfaces, while conventional microtomography is volumetric but cannot adequately resolve soft tissues and temporal dynamics. We used dynamic synchrotron-based X-ray phase-contrast microtomography on three fresh-frozen human temporal bones under acoustic stimulation at 128, 256, and 512Hz with sound pressure levels of 120, 126, 141, and 151dB. This method achieved micrometer spatial and kHz temporal resolution, allowing 4D visualization of the ossicles and tympanic membrane (TM). Non-rigid registration quantified micrometer-scale TM motion and was validated with anatomical landmarks. Displacement 'hot spots' were consistently observed in the posterosuperior quadrant of the TM and the pars flaccida, although their relative contributions varied between specimens. Displacement amplitudes also varied strongly between specimens, with peaks ranging from <0.15 to nearly 2 μm/Pa. The magnitude of displacement changed with the level and frequency of the sound pressure, while the motion patterns remained stable. These findings demonstrate that dynamic synchrotron-based X-ray phase-contrast microtomography is a reliable and powerful approach for studying the non-rigid motion of TM. The variability between samples underscores the need for correlative imaging to characterize both motion and tissue microstructure such as fiber orientation and density. Future studies should also investigate how the motion of the TM correlates with the movement of the umbo and entire ossicular chain to provide a more complete understanding of the mechanics of the middle ear.