Doppler optical coherence microscopy for studies of cochlear mechanics.

The possibility of measuring subnanometer motions with micron scale spatial resolution in the intact mammalian cochlea using Doppler optical coherence microscopy (DOCM) is demonstrated. A novel DOCM system is described that uses two acousto-optic modulators to generate a stable 500-kHz heterodyne frequency. Images and motion measurements are obtained using phase-resolved analysis of the interference signal. The DOCM system permits imaging with micron-scale resolution and 85-dB sensitivity and motion measurements with 100-kHz bandwidth, directional discrimination, and 30-pm/Hz(0.5) noise floor. Images and motion measurements are presented that demonstrate the ability to resolve motions of structures of interest in a mammalian cochlea in vitro including the basilar membrane, reticular lamina, tectorial membrane, and outer hair cells.