Reconstruction of three-dimensional organ of Corti micromechanical motion patterns via optical coherence tomography

Optical coherence tomography (OCT) is used in cochlear mechanics research to image and measure vibrations in the organ of Corti complex (OCC), the sensory tissue that spirals within the cochlea. OCT can be used to measure sub-nanometer vibrations at many points along the optical axis simultaneously. However, this optical axis does not generally bear a straightforward relation to the anatomy of the cochlea. This results in two ambiguities: 1) the measured motion is a projection of the true three- dimensional motion onto an axis that is not anatomically important, and 2) the relative locations of measured structures are known only along the optical axis, which is not sufficient to relate the structures anatomically. This results in limitations for the interpretation of OCT data, as measurements taken at two different orientations cannot be reasonably compared to one another. Even simultaneously measured structures in a single measurement cannot be adequately compared, as their relative locations are not necessarily known. The purpose of this project is to overcome these limitations of contemporary OCT experiments and gain a full three-dimensional picture of micromechanics in the base of the gerbil cochlea. These quantitative three-dimensional measurements will reveal mechanical properties governing cochlear tuning and transduction, such as the OCC effective mass and stereocilia pivoting. In Aim 1, we propose the use of densely spaced OCT measurements in a volume of the gerbil cochlea base at three different orientations to reconstruct the three-dimensional OCC motion. In Aim 2, we propose the use of compressed sensing to reduce the number of spatial samples required for this reconstruction, and consequently reduce the acquisition time of this three-dimensional vibration data. Aim 2 is based in the expectation - which will be tested in this project - that the motion pattern of the OCC can be expressed sparsely in some set of basis functions, for example, a wavelet basis. Finding such a basis would give significant insight into the spatial structure of in vivo cochlear micromechanics. The method will be made available through a public GitHub repository.