3D-motion mapping of the malleus–incus complex using a robot-mounted optical coherence tomography vibrometry system

Significance: Optical coherence tomography vibrometry (OCTv) allows measuring the surface and subsurface nanometer vibrations of the mammalian ossicular chain. However, existing multidimensional OCTv setups remain expensive, complex, or limited in accuracy. Aim: We developed a 3D OCTv setup with a rotational component and provided a theoretical framework that clarifies the main determinants of measurement accuracy in 3D vibrometry. Approach: A commercially available OCTv system is mounted on a robotic arm to allow multidimensional measurements. The relative positions of measured structures and the optical axes orientation are defined with a custom volume registration algorithm. Results: We present a mathematical framework for decomposing the measured motion components into a Cartesian space and identify key factors that influence the decomposition accuracy. The angular accuracy of optical axis estimation was 0.4 deg. Experimental validation was performed on an oscillating phantom and on the malleus-incus complex (MIC) of a fresh human temporal bone specimen, replicating previous evidence on the MIC's frequency-dependent vibratory behavior. Conclusions: The robot-mounted 3D OCTv setup provides a cost-effective, robust, and integral solution for mapping middle ear 3D vibrations, accurately orienting optical axes across measurements. Future work should integrally map the ossicular chain to test the commonly assumed rigid-body behavior of ossicular motion.