SEEING THE IMPULSE RESPONSE OF THE TYMPANIC MEMBRANE

The human auditory bandwidth encompasses a wide range of frequencies between20 Hz and 20 kHz, with a maximum sensitivity between 1-5 kHz. This range could be narrowed, however, due to various conduction loss pathologies such as otitis media and otosclerosis, which may limit sound transduction into the inner ear. Our research group has recently demonstrated a technique for directly imaging the vibrations on the tympanic membrane using in vivo interferometric spectrally encoded imaging. Here we demonstrate the measurement of the impulse response of the tympanic membrane across its entire surface, and form a 2D map of its relaxation time and oscillation bandwidth. This measurement is accomplished using a specifically tailored series of ‘click’ sound excitations as the imaging spectrally encoded line is scanned across the membrane, resulting in a time-bandwidth data collected from each point on the membrane surface. Initial measurements within the left ear of a human volunteer show that the oscillation bandwidth of the membrane is smaller compared to the bandwidth measured at the umbo region, and reveal the natural frequency of the damped membrane oscillations as approximately 2.5 kHz. The system could be operated conveniently using a handheld probe, and completes the measurement within less than a second. Its ability to map the impulse response of the tympanic membrane may assist the diagnosis of hearing problems associated with possible conduction loss.