Measuring the Acoustic Reflex through the Tympanic Membrane.

INTRODUCTION: The acoustic reflex is the active response of the middle ear to loud sounds, altering the mechanical transfer function of the acoustic energy into the inner ear. Our goal was to observe the effect of the acoustic reflex on the tympanic membrane by identifying a significant nonlinear increase in membrane oscillations. METHODS: By using interferometric spectrally encoded endoscopy, we record the membrane oscillations over time in response to a loud, 200-ms-long acoustic stimulus. RESULTS: A gradual reflex activation is measured between approximately 40 and 100 ms, manifested as a linear 42% increase in the umbo oscillation amplitude. CONCLUSION: The measured oscillations correlate well with those expected from a mechanical model of a damped harmonic oscillator, and the results of this work demonstrate the potential of interferometric spectrally encoded endoscopy to observe unique dynamical processes in the tympanic membrane and in the middle ear.

In vivo optical mapping of the tympanic membrane impulse response.

The wide frequency range of the human hearing could be narrowed by various pathologies in the middle ear and in the tympanic membrane that lead to conductive hearing loss. Diagnosing such hearing problems is challenging, however, often relying on subjective hearing tests supported by functional tympanometry. Here we present a method for in vivo 2D mapping of the impulse response of the tympanic membrane, and demonstrate its potential on a healthy human volunteer. The imaging technique is based on interferometric spectrally encoded endoscopy, with a handheld probe designed to scan the human tympanic membrane within less than a second. The system obtains high-resolution 2D maps of key functional parameters including peak response, rise and decay times, oscillation bandwidth and resonance frequency. We also show that the system can identify abnormal regions in the membrane by detecting differences in the local mechanical parameters of the tissue. We believe that by offering a full 2D mapping of broad-bandwidth dynamics of the tympanic membrane, the presented imaging modality would be useful for effective diagnosis of conductive hearing loss in patients.

Rapid imaging of tympanic membrane vibrations in humans.

Functional imaging of the human ear is an extremely challenging task because of its minute anatomic structures and nanometer-scale motion in response to sound. Here, we demonstrate noninvasive in vivo functional imaging of the human tympanic membrane under various acoustic excitations, and identify unique vibration patterns that vary between human subjects. By combining spectrally encoded imaging with phase-sensitive spectral-domain interferometry, our system attains high-resolution functional imaging of the two-dimensional membrane surface, within a fraction of a second, through a handheld imaging probe. The detailed physiological data acquired by the system would allow measuring a wide range of clinically relevant parameters for patient diagnosis, and provide a powerful new tool for studying middle and inner ear physiology.

Plasmonic targeting of cancer cells in a three-dimensional natural hydrogel.

Using specifically designed gold nanoparticles and local laser irradiation, individual cells and small cell clusters could be targeted on a microscopic scale with minimal toxicity to nearby tissue. To date, most scientific studies and technological demonstrations of this approach were conducted on two-dimensional cultures, while most feasibility tests and preclinical trials were conducted using animal models. For bridging the gap between two-dimensional cell cultures and animal experiments, we propose and demonstrate the use of a natural hydrogel for studying the effect of intense, ultrashort laser pulses on a gold nanoparticle targeted tissue. Using illumination parameters comparable to those used with two-dimensional cultures, we show the complete eradication of multilayered cell colonies comprising normal fibroblasts and malignant epithelial cells co-cultured on a hydrogel scaffold. By evaluating the extent of cell damage for various pulse durations at off-resonance irradiation, we find that the observed damage mechanism was dominated by rapid thermal transitions around the gold nanospheres, rather than by photoionization. The work provides a new tool for understanding the complex pulse-particle-tissue interactions and demonstrates the important role of nanoparticle mediated cavitation bubbles in a thick, multilayered tissue.