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A vibrational imaging tool based on optical coherence tomography (OCT) is providing new insight into how the ear receives and processes sound waves. Called OCT vibrography, the tool was built by a team at the Wellman Center for Photomedicine at Massachusetts General Hospital to visualize how sound-induced vibrations travel through the ear. OCT vibrography images the middle ear through the intact eardrum and measures the tiny vibrations within the ear that contribute to sound perception.
The researchers reconstructed the motion of ossicular bones in a chinchilla cadaver. Courtesy of the Wellman Center for Photomedicine, Massachusetts General Hospital.
The researchers demonstrated the capabilities of their system by measuring sound-driven eardrum and ossicular motion in chinchilla cadavers exposed to high-frequency sound. The chinchilla is commonly used in hearing research because its ears are similar to those of humans in terms of size and sensitivity to different sound frequencies.
For this experiment, the team synchronized an OCT measurement system with sound from a high-fidelity speaker. As the sound from the speakers pushed on the eardrum, the bones began to move and were imaged with OCT. The researchers developed algorithms to extract accurate measurements of the vibration from the OCT images. They observed a previously unknown mode of ossicular motion at high frequencies that was consistent with some of the theories describing how high-frequency sounds travel to the inner ear.
“There are multiple theories of how high-frequency sounds are conducted to the inner ear, and the ability to view the sound-driven motion of large portions of the ossicular chain will help us understand what actually happens,” said research team leader Seok-Hyun Yun.
The combination of high-resolution imaging and high-sensitivity vibration measurements available through OCT vibrography allowed the researchers to simultaneously measure structure and motion at over 10,000 points on the ossicular surface and eardrum.
One reason the team used cadavers was that it took almost 60 seconds to acquire the measurements. The team believed that during the time period, the breathing and heartbeat of a live animal could cause artifacts in the motion measurements.
The team’s colleagues at Dalhousie University are exploring whether measurements of the motion taken from 3 to 5 points, combined with an anatomical OCT scan of the whole eardrum and middle ear, could provide enough information to diagnose ear disease in living organisms.
The researchers plan to use their instrument to study ears from human cadavers to find out if the new mode of ossicular motion they found in chinchillas also occurs in humans. Future research will also further examine how this new tool could be applied in specific clinical applications such as diagnosing a particular disease or hearing problem.
“If our approach is accepted clinically, it would allow clinicians to differentiate between different middle-ear problems and plan a treatment strategy before or instead of performing surgery to view the area,” said John Rosowski of Massachusetts Eye and Ear.
The research was published in Biomedical Optics Express, a publication of OSA, The Optical Society (https://doi.org/10.1364/BOE.9.005489). Using their newly developed OCT vibrography tool, the researchers reconstructed the motion of ossicular bones in a chinchilla exposed to high-frequency sound. The new technology allowed them to observe a previously unknown mode of ossicular motion at high frequencies. Courtesy of the Wellman Center for Photomedicine, Massachusetts General Hospital.READ MORE