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BOSTON, Mass., Oct. 18, 2018 – A vibrating imaging tool based on optical coherence tomography (OCT) provides new information on how the ear receives and processes sound waves. Called OCT vibrography, the tool was designed by a team from the Wellman Photomedicine Center at Massachusetts General Hospital to visualize how sound-induced vibrations propagate in the ear. OCT vibrography visualizes the middle ear through the intact eardrum and measures the tiny vibrations in the ear that contribute to sound perception.
The researchers reconstructed the movement of the ossicular bones in a corpse of chinchilla. With the kind permission of the Wellman Center for Photomedicine, Massachusetts General Hospital.
The researchers demonstrated the capabilities of their system by measuring the eardrum and sound-oriented ossicular movement of chinchillas cadavers exposed to high-frequency sound. The chinchilla is commonly used in research on hearing because its ears are similar to those of humans in terms of size and sensitivity to different sound frequencies.
For this experiment, the team has synchronized an OCT measurement system with the sound of a high fidelity speaker. When the sound of the speakers pushed onto the eardrum, the bones began to move and were visualized with OCT. Researchers have developed algorithms to extract accurate measurements of vibration from OCT images. They observed a hitherto unknown mode of ossicular movement at high frequencies, which was consistent with some of the theories describing how high frequency sounds propagate in the inner ear.
"There are many theories about how high frequency sounds are routed to the inner ear, and the ability to visualize the sound-based motion of large portions of the ossicular chain will help us understand what's going on. really, "said the head of the research team, Seok-Hyun Yun.
The combination of high-resolution imaging and high-sensitivity vibration measurements available via OCT vibrography enabled researchers to simultaneously measure structure and motion in more than 10,000 points on the ossicular surface and eardrum.
One of the reasons the team used corpses was that it took almost 60 seconds to get the measurements. The team felt that during this period, the breathing and heart rate of a live animal could cause artifacts in movement measurements.
Colleagues at Dalhousie University are investigating whether 3 to 5-point movement measurements, combined with an OCT anatomical analysis of the entire eardrum and middle ear, could provide sufficient information to diagnose ear disease in living organisms.
The researchers plan to use their instrument to study the ears of human cadavers to determine if the new mode of ossicular motion they found in chinchillas also applies to humans. Future research will also examine in more detail how this new tool could be applied to specific clinical applications such as the diagnosis of a particular disease or hearing problem.
"If our approach is clinically accepted, clinicians could differentiate different middle ear problems and plan a treatment strategy before or instead of performing surgery to visualize the area," said John Rosowski of the Massachusetts Eye and Ear.
The search was published in Biomedical Optical Express, a publication of OSA, The Optical Society (https://doi.org/10.1364/BOE.9.005489).
Using their new OCT vibrography tool, researchers reconstructed the movement of bone in a chinchilla exposed to high frequency sound. The new technology has allowed them to observe a previously unknown mode of ossicular motion at high frequencies. With the kind permission of the Wellman Center for Photomedicine, Massachusetts General Hospital.
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