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93 results on '"Cho, Nam Hyun"'

3. Differential transverse motion of individual outer hair cells measured in gerbil high-frequency region.

Author

Puria, Sunil, Cho, Nam Hyun, and Guinan, John

Subjects
*HAIR cells, *GERBILS, *AUDIO frequency, *COCHLEA, *CYTOARCHITECTONICS
Abstract

The great sensitivity and frequency selectivity of mammalian hearing originates in the mechanical properties of the cochlea. Cochlear motions in response to sound are amplified using metabolic energy. The motor element of this cochlear amplification is presumed to be the outer hair cell (OHC), that expands and contracts lengthwise in response to a change in receptor potential at audio frequencies. How thousands of OHCs, acting through the local cytoarchitecture, work to achieve cochlear amplification is not fully understood. The properties of individual OHCs measured in micro-chamber environments are low-pass with a corner frequency of, at most, a few kHz. OHC corner frequencies within the cochlea have been estimated to be ∼3 kHz. Since in-vivo cochlear motion measurements show amplified frequency responses that extend up to many tens of kHz, but OHCs have corner frequencies of a few kHz, it has been suggested that OHCs are not active at the highest frequencies. How to reconcile these measurements has been a challenge. To address this, we made transverse cochlear motion measurements using a high-resolution optical-coherence-tomography (OCT) system at approximately the two ends of the OHC axial length: at the OHC bottom near the OHC-Deiter-Cell junction and at the OHC top near the reticular lamina. From these in-vivo measurements near the 42 kHz best frequency (BF) region of the gerbil cochlea, we determined the transverse differential response of OHCs. To remove phase from the traveling wave, we calculated the ratio of the RL motion to the motion at the OHC-Deiter-Cell junction. The OHC top-to-bottom phase difference was almost exactly ½-cycle at frequencies up to 35-40 kHz. As frequency increased above 40 kHz, the phase difference decreased until near BF there was very little phase difference. The OHC top-to-bottom amplitude ratio transitioned from the OHC top moving less than the bottom at low frequencies, to the OHC top moving more than the bottom, at about 30 kHz, which is approximately the frequency above which there is traveling-wave amplification. Our data show that OHCs had length changes at frequencies up to 50 kHz, more than a decade above their low-pass corner frequency in vitro. [ABSTRACT FROM AUTHOR]

Published
2024
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21. Wavelength-Filter Based Spectral Calibrated Wave number - Linearization in 1.3 mm Spectral Domain Optical Coherence

Author

Wijeisnghe, Ruchire Eranga Henry, Cho, Nam Hyun, Park, Kibeom, Shin, Yongseung, and Kim, Jeehyun

Subjects
Astrophysics::Instrumentation and Methods for Astrophysics, Article
Abstract

In this study, we demonstrate the enhanced spectral calibration method for 1.3 μm spectral-domain optical coherence tomography (SD-OCT). The calibration method using wavelength-filter simplifies the SD-OCT system, and also the axial resolution and the entire speed of the OCT system can be dramatically improved as well. An externally connected wavelength-filter is utilized to obtain the information of the wavenumber and the pixel position. During the calibration process the wavelength-filter is placed after a broadband source by connecting through an optical circulator. The filtered spectrum with a narrow line width of 0.5 nm is detected by using a line-scan camera. The method does not require a filter or a software recalibration algorithm for imaging as it simply resamples the OCT signal from the detector array without employing rescaling or interpolation methods. One of the main drawbacks of SD-OCT is the broadened point spread functions (PSFs) with increasing imaging depth can be compensated by increasing the wavenumber-linearization order. The sensitivity of our system was measured at 99.8 dB at an imaging depth of 2.1 mm compared with the uncompensated case.

Published
2013

25. Optical assessment of the in vivo tympanic membrane status using a handheld optical coherence tomography-based otoscope.

Author

Park, Kibeom, Cho, Nam Hyun, Jeon, Mansik, Lee, Sang Heun, Jang, Jeong Hun, Boppart, Stephen A., Jung, Woonggyu, and Kim, Jeehyun

Subjects
*TYMPANIC membrane surgery, *DIAGNOSIS, *EAR examination, *ENDOSCOPES, *OTOSCOPES, *STATISTICS, *SURGICAL complications, *TYMPANIC membrane, *DATA analysis, *OPTICAL coherence tomography, *TYMPANIC membrane perforation, *IN vivo studies
Abstract

Objective: Conventional otoscopes and oto-endoscopes, which are used to examine the tympanic membrane (TM), do not provide tomographic information. Optical coherence tomography (OCT) non-invasively reveals the depth-resolved internal microstructure of the TM with very high spatial resolution. We designed this study to examine the TMs with middle ear diseases using a handheld otoscope employing 860nm spectral domain (SD)-OCT, combined with video camera and to demonstrate the clinical applicability of this system. Design: A total of 120 patients with otologic symptoms were enrolled. TM images were obtained using the handheld OCT-based otoscope (860nm central wave length, 15 lm axial resolution, 15 lm lateral resolution, and 7mm scanning range using relay lens). Both OCT and oto-endoscope images were compared according to the clinical characteristics such as perforation, retraction, and postoperative healing process. Results: The objective grade about the thickness of perforation margins and the accurate information about the extent of TM retraction that was not distinguishable by oto-endoscopic exam could be identified using this system. The postoperative healing process of TMs could be also followed using the OCT device. Conclusion: These analyses from the surgeon-oriented perspective suggest another useful application of the handheld OCT device. [ABSTRACT FROM AUTHOR]

Published
2018
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49. Bio-Photonic Detection and Quantitative Evaluation Method for the Progression of Dental Caries Using Optical Frequency-Domain Imaging Method

Author

Wijesinghe, Ruchire Eranga, Cho, Nam Hyun, Park, Kibeom, Jeon, Mansik, and Kim, Jeehyun

Subjects
optical frequency domain imaging (OFDI), optical coherence tomography, dental caries, demineralization, Bio-photonic detection
Abstract

The initial detection of dental caries is an essential biomedical requirement to barricade the progression of caries and tooth demineralization. The objective of this study is to introduce an optical frequency-domain imaging technique based quantitative evaluation method to calculate the volume and thickness of enamel residual, and a quantification method was developed to evaluate the total intensity fluctuation in depth direction owing to carious lesions, which can be favorable to identify the progression of dental caries in advance. The cross-sectional images of the ex vivo tooth samples were acquired using 1.3 μm spectral domain optical coherence tomography system (SD-OCT). Moreover, the advantages of the proposed method over the conventional dental inspection methods were compared to highlight the potential capability of OCT. As a consequence, the threshold parameters obtained through the developed method can be used as an efficient investigating technique for the initial detection of demineralization.

Published
2016
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