1. Articles from Yeh-Chan Ahn

    1-24 of 24
    1. Stiffness Comparison of Tissue Phantoms using Optical Coherence Elastography without a Load Cell

      Stiffness Comparison of Tissue Phantoms using Optical Coherence Elastography without a Load Cell

      Mechanical property of tissue is closely related to diseases such as breast cancer, prostate cancer, cirrhosis of the liver, and atherosclerosis. Therefore measurement of tissue mechanical property is important for a better diagnosis. Ultrasound elastography has been developed as a diagnostic modality for a number of diseases that maps mechanical property of tissue. Optical coherence elastography (OCE) has a higher spatial resolution than ultrasound elastography. OCE, therefore, could be a great help for early diagnosis. In this study, we made tissue phantoms and measured their compressive moduli with a rheometer measuring the response to applied force. Uniaxial strain of the ...

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      Mentions: Min Yong Jeon
    2. Preliminary study of optical coherence tomography imaging to identify microscopic extrathyroidal extension in patients with papillary thyroid carcinoma

      Preliminary study of optical coherence tomography imaging to identify microscopic extrathyroidal extension in patients with papillary thyroid carcinoma

      Background and Objectives We evaluated the feasibility of using optical coherence tomography (OCT), to identify microscopic extrathyroidal extension (mETE) in ex vivo thyroidectomy specimens of patients who underwent thyroidectomy for the treatment of papillary thyroid carcinoma (PTC). Methods A total of 170 ex vivo OCT images of the tumor, were acquired just after completion of thyroidectomy in 17 patients. The OCT images of each patient were separately evaluated by two blinded investigators, and the outcomes were compared with the histopathology reports. Results The sensitivity and specificity of mETE identification from the OCT images were 81.4% and 86.0%, respectively ...

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    3. Multimodal imaging using optical coherence tomography and endolaryngeal ultrasonography in a new rabbit VX2 laryngeal cancer model

      Multimodal imaging using optical coherence tomography and endolaryngeal ultrasonography in a new rabbit VX2 laryngeal cancer model

      Background and Objective Optical coherence tomography (OCT) provides ultrahigh-resolution imaging of tissues within a depth of a few millimeters, whereas ultrasonography provides good imaging further below the surface. We aimed to develop a minimally invasive rabbit model of VX2 laryngeal cancer, suitable for these two imaging modalities through a transoral approach. We also sought to study the utility of combined OCT and endolaryngeal ultrasonography (EUS) for evaluation of early and advanced laryngeal cancer, using this model. Materials and Methods VX2 tumor suspension was inoculated into the vocal folds of ten rabbits by injection through the trans-thyrohyoid membrane. The tumor model ...

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    4. Ultra-thin and flexible endoscopy probe for optical coherence tomography based on stepwise transitional core fiber

      Ultra-thin and flexible endoscopy probe for optical coherence tomography based on stepwise transitional core fiber

      We present an ultra-thin fiber-body endoscopy probe for optical coherence tomography (OCT) which is based on a stepwise transitional core (STC) fiber. In a minimalistic design, our probe was made of spliced specialty fibers that could be directly used for beam probing optics without using a lens. In our probe, the OCT light delivered through a single-mode fiber was efficiently expanded to a large mode field of 24 μm diameter for a low beam divergence. The size of our probe was 85 μm in the probe’s diameter while operated in a 160-μm thick protective tubing. Through theoretical and ...

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    5. In vivo Optical Coherence Tomography Imaging of the Mesothelium Using Developed Window Models

      In vivo Optical Coherence Tomography Imaging of the Mesothelium Using Developed Window Models

      The mesothelium is an essential lining for maintaining the normal homeostasis of the closed body cavity and a central component of pathophysiologic processes. The mesothelium has been known as the end target for asbestos which induces asbestos-related lung diseases. Malignant mesothelioma (MM) is a rare and fatal neoplasm predominantly due to asbestos exposure. Adaptation of an advanced and reliable technology is necessary for early detection of MM because it is difficult to diagnose this disease in its early stages. Optical coherence tomography (OCT) provides cross-sectional images of micro-tissue structures with a resolution of 2-10 μm that can image the mesothelium ...

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    6. In vivo real-time imaging of airway dynamics during bronchial challenge test

      In vivo real-time imaging of airway dynamics during bronchial challenge test

      Background and Objective Asthmatic patients exhibit airway hyper-responsiveness, which induces bronchoconstriction and results in a ventilation defect. The bronchial challenge test using methacholine is a useful way to measure airway hyper-responsiveness with airway constriction. Anatomical optical coherence tomography has been used to image airway hyper-responsiveness of medium sized bronchus with the aid of an endoscopic probe. Recently, a thoracic window was reported that allows direct visualization of terminal airway such as alveolus. A multi-scale integrated airway dynamics was assessed in this study. We imaged in vivo changes in the right intermedius bronchus and alveolar structure during the bronchial challenge test ...

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    7. Multimodal Imaging of Sarcopenia using Optical Coherence Tomography and Ultrasound in Rat Model

      Multimodal Imaging of Sarcopenia using Optical Coherence Tomography and Ultrasound in Rat Model

      Sarcopenia, or reduced muscle mass and volume, is due to various factors such as senile change, neuronal degeneration, drug, malignancy, and sepsis. Sarcopenia with the aging process has been evidenced by the decline in muscle mass by 0.5 to 1% per year with 3-5% reduction in muscle strength for 10 years between the ages of 40 and 50, and a 1-2% of decline of mass every year in people aged 60-70. Therefore, early diagnosis and understanding the mechanism of sarcopenia are crucial in the prevention of muscle loss. However, it is still difficult to image changes of muscle microstructure ...

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    8. Optical imaging of subacute airway remodeling and adipose stem cell engraftment after airway injury

      Optical imaging of subacute airway remodeling and adipose stem cell engraftment after airway injury

      Acquired airway injury is frequently caused by endotracheal intubations, long-term tracheostomies, trauma, airway burns, and some systemic diseases. An effective and less invasive technique for both the early assessment and the early interventional treatment of acquired airway stenosis is therefore needed. Optical coherence tomography (OCT) has been proposed to have unique potential for early monitoring from the proliferative epithelium to the cartilage in acute airway injury. Additionally, stem cell therapy using adipose stem cells is being investigated as an option for early interventional treatment in airway and lung injury. Over the past decade, it has become possible to monitor the ...

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      Mentions: Joseph A. Izatt
    9. Visualization and measurement of capillary-driven blood flow using spectral domain optical coherence tomography

      Visualization and measurement of capillary-driven blood flow using spectral domain optical coherence tomography

      Capillary-driven flow (CD-flow) in microchannels plays an important role in many microfluidic devices. These devices, the most popular being those based in lateral flow, are becoming increasingly used in health care and diagnostic applications. CD-flow can passively pump biological fluids as blood, serum or plasma, in microchannels and it can enhance the wall mass transfer by exploiting the convective effects of the flow behind the meniscus. The flow behind the meniscus has not been experimentally identified up to now because of the lack of high-resolution, non-invasive, cross-sectional imaging means. In this study, spectral-domain Doppler optical coherence tomography is used to ...

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    10. Simple Spectral Calibration Method and Its Application Using an Index Array for Swept Source Optical Coherence Tomography

      Simple Spectral Calibration Method and Its Application Using an Index Array for Swept Source Optical Coherence Tomography
      In this study, we report an effective k-domain linearization method with a pre-calibrated indexed look-up table. The method minimizes k-domain nonlinear characteristics of a swept source optical coherence tomography (SS-OCT) system by using two arrays, a sample position shift index and an intensity compensation array. Two arrays are generated from an interference pattern acquired by connecting a Fabry-Perot interferometer (FPI) and an optical spectrum analyzer (OSA) to the system. At real time imaging, the sample position is modified by location movement and intensity compensation with two arrays for linearity of wavenumber. As a result of evaluating point spread functions (PSFs ...
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    11. Investigating in vivo airway wall mechanics during tidal breathing with optical coherence tomography

      Investigating in vivo airway wall mechanics during tidal breathing with optical coherence tomography
      Optical coherence tomography (OCT) is a nondestructive imaging technique offering high temporal and spatial resolution, which makes it a natural choice for assessing tissue mechanical properties. We have developed methods to mechanically analyze the compliance of the rabbit trachea in vivo using tissue deformations induced by tidal breathing, offering a unique tool to assess the behavior of the airways during their normal function. Four-hundred images were acquired during tidal breathing with a custom-built endoscopic OCT system. The surface of the tissue was extracted from a set of these images via image processing algorithms, filtered with a bandpass filter set at ...
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    12. Multimodality approach to optical early detection and  mapping of oral neoplasia

      Multimodality approach to optical early detection and  mapping of oral neoplasia
      Early detection of cancer remains the best way to ensure patient survival and quality of life. Squamous cell carcinoma is usually preceded by dysplasia presenting as white, red, or mixed red and white epithelial lesions on the oral mucosa (leukoplakia, erythroplakia). Dysplastic lesions in the form of erythroplakia can carry a risk for malignant conversion of 90%. A noninvasive diagnostic modality would enable monitoring of these lesions at regular intervals and detection of treatment needs at a very early, relatively harmless stage. The specific aim of this work was to test a multimodality approach [three-dimensional optical coherence tomography (OCT) and ...
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    13. Calibration and characterization protocol for spectral-domain optical coherence tomography using fiber Bragg gratings

      Calibration and characterization protocol for spectral-domain optical coherence tomography using fiber Bragg gratings
      We present a calibration protocol to obtain the alignment factors of a custom-made spectrometer and the nonlinear fitting function between the measured CCD pixel domain and the wavelength domain to apply to the spectral-domain optical coherence tomography (SD-OCT) using fiber Bragg gratings. We have used five gratings with different center wavelengths covering the broadband source spectral range. All have a narrow spectral bandwidth (0.05 nm) and the same reflectivity (92%) to calibrate and align the custom-made spectrometer. The implemented SD-OCT system following the proposed protocol showed the alignment factors as 44.37 deg incident angle, 53.11 deg diffraction ...
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    14. Ability of optical coherence tomography to detect caries beneath commonly used dental sealants

      Ability of optical coherence tomography to detect caries beneath commonly used dental sealants
      Background and Objective The onset and progression of early tooth decay is often preventable with dental sealants. However, occasionally decay progresses underneath the sealant. Current technology does not permit monitoring of potential lesion progression or arrest. Dental sealants themselves mask the visual cues that identify early tooth decay, and radiographs are not sufficiently sensitive. Therefore, clinicians can be reluctant to use dental sealant. The objective of this ex vivo study was to evaluate the ability of dentists to detect decay beneath commonly used dental sealants using optical coherence tomography (OCT) imaging. Study Designs/Materials/Methods Forty extracted teeth were divided ...
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    15. Efficient and facile delivery of gold nanoparticles in vivo using dissolvable microneedles for contrast-enhanced optical coherence tomography

      Efficient and facile delivery of gold nanoparticles in vivo using dissolvable microneedles for contrast-enhanced optical coherence tomography
      Obtaining sufficient contrast is an indispensable requirement for detecting early stage cancer using optical coherence tomography (OCT), an emerging diagnostic tool that detects abnormal lesions with micrometer resolutions in real time. PEGylated gold nanoparticles (Au NPs; 87 nm in diameter) were formulated in aqueous dissolvable microneedles (dMNs; 200 μm height) for efficient, precisely controlled, and convenient delivery of Au NPs into hamster oral tissue in vivo. The Au NPs were then further briefly dissipated by ultrasound (US). The results showed 33% and 20% increase in average optical scattering intensity (contrast level) in dysplastic and normal tissues, respectively, and pinpointed pathological ...
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    16. Calibration protocol for Fourier-domain OCT using optical fiber gratings

      Calibration protocol for Fourier-domain OCT using optical fiber gratings
      We present a calibration protocol to get the alignment factors of a custom-made spectrometer and the nonlinear fitting function between the measured CCD pixel domain and the wavelength domain to apply the Fourier-domain optical coherence tomography (FD-OCT) using optical fiber gratings. We have used 5 different center wavelength gratings covered the broadband source spectral range with a narrow spectral bandwidth (<0.05 nm) and the same reflectivity (>92 %) to calibrate and align the custom-made spectrometer. The implemented SD-OCT system following the proposed protocol showed the alignment factors as 44.37o incident angle, 53.11o diffraction angle, and 70.0 mm focal length. The spectral resolution of 0 ...
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    17. Overcoming barriers in topical administration of gold nanoparticles for optical coherence tomography using multimodal delivery

      Overcoming barriers in topical administration of gold nanoparticles for optical coherence tomography using multimodal delivery
      Optical coherence tomography (OCT) is a non-invasive and promising imaging modality with high resolution that is an order of magnitude higher than current diagnostic techniques. However, its use in detecting early-stage cancer is limited due to insufficient contrast level in biological tissue, which can be enhanced by harnessing contrast agents [e.g., gold nanoparticles (Au NPs)]. Enhanced penetration by creating micropassages and distribution by ultrasonic force (multimodal topical delivery) was proven to overcome two major barriers (stratum corneum and epithelial barriers) in topically administering Au NPs using an in vivo oral dysplasia hamster model (overall 150% enhanced OCT contrast). Expanded ...
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    18. Multimodality bronchoscopic imaging of recurrent respiratory papillomatosis

      Objectives/Hypothesis. Recurrent respiratory papillomatosis (RRP) of the central airways requires removal to potentially reduce recurrence and risk for malignant transformation. Analogous to the principles of treatment for early lung cancer, a precise determination of the extent of cartilage invasion could help guide therapeutic decisions and monitor response to treatment. The purpose of this study was to determine whether a bronchoscopy platform comprised of white light bronchoscopy (WLB), endobronchial ultrasound (EBUS), and optical coherence tomography (OCT) could identify layered microstructure of RRP and underlying cartilage. Study Design. Case study. Methods. A bronchoscopy platform consisting of commercially available WLB, EBUS using ...
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    19. Multimodality bonchoscopic imaging of tracheopathica osteochondroplastica

      Results of a commercial optical coherence tomography system used as part of a multimodality diagnostic bronchoscopy platform are presented for a 61-year-old patient with central airway obstruction from tracheopathica osteochondroplastica. Comparison to results of white-light bronchoscopy, histology, ... [J. Biomed. Opt. 14, 034035 (2009)] published Thu Jun 25, 2009.
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    20. Enhanced detection of early-stage oral cancer in vivo by optical coherence tomography using multimodal delivery of gold nanoparticles

      Contrast in optical coherence tomography (OCT) images can be enhanced by utilizing surface plasmon resonant gold nanoparticles. To improve the poor in vivo transport of gold nanoparticles through biological barriers, an efficient delivery strategy is needed. In this study, the improved penetration a ... [J. Biomed. Opt. 14, 034008 (2009)] published Tue May 12, 2009.
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    21. Axial resolution and depth range of high-resolution spectral domain optical coherence tomography at 1.3 um

      We built a high-speed, real-time spectral domain optical coherence tomography (SD-OCT) system at the 1.3 µm region using an InGaAs line-scan camera with 1024 pixels and 46.99 klines/s. In SD-OCT, the actual spatial resolution can be different from the theoretical one due to the large bandwidth of the light source and the finite number of detector pixels, especially for a long center wavelength. We calculated and compared the axial resolutions obtained from the point spread function and the physical pixel size of the OCT image. We found that the axial resolution of the SD-OCT system could be ...
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    22. Thermoelastic optical Doppler tomography of biological tissues

      Thermoelastic optical Doppler tomography of biological tissues
      In this presentation, we demonstrate a novel optical tomography technique, thermoelastic optical Doppler tomography (ODT). Short laser pulses are used to generate thermoelastic waves in biological samples. Optical phase variations in response to wave propagation are detected using ODT. It is shown that areas of different elastic property in the phantom can be clearly resolved.
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    23. Analysis of surface-tension-driven blood flow using spectral domain optical coherence tomography

      Yeh-Chan Ahn, Salvatore Cito, Ioanis Katakis et al. A passive pumping for lab-on-a-chip using surface tension only is the most effective method because the effect of surface tension on a flow is significant in microscale. The movement of the triple point at a meniscus is driven by surface tension, resisted by viscous stress, and balanced by inertial ... [Proc. SPIE Int. Soc. Opt. Eng. 6886, 68860S (2008)] published Wed Feb 13, 2008.
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      Mentions: Zhongping Chen
    24. In vivo three-dimensional spectral domain endoscopic optical coherence tomography using a microelectromechanical system mirror

      Woonggyu Jung, Daniel T. McCormick, Yeh-Chan Ahn, Ali Sepehr, Matt Brenner, Brian Wong, Norman C. Tien, Zhongping Chen A biopsy is a well-known medical test used to evaluate tissue abnormality. Biopsy specimens are invasively taken from part of a lesion and visualized by microscope after chemical treatment. However, diagnosis by means of biopsy is not only variable due to depth and location of specimen but may also ... [Opt. Lett. 32, 3239-3241 (2007)]
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    1-24 of 24
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  2. Topics in the News

    1. (14 articles) UC Irvine
    2. (13 articles) Zhongping Chen
    3. (5 articles) Petra E. Wilder-Smith
    4. (3 articles) Pusan National University
    5. (3 articles) Matthew Brenner
    6. (2 articles) Gwangju Institute of Science and Technology
    7. (2 articles) Sang-Won Lee
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    Calibration protocol for Fourier-domain OCT using optical fiber gratings Overcoming barriers in topical administration of gold nanoparticles for optical coherence tomography using multimodal delivery Ability of optical coherence tomography to detect caries beneath commonly used dental sealants Calibration and characterization protocol for spectral-domain optical coherence tomography using fiber Bragg gratings Investigating in vivo airway wall mechanics during tidal breathing with optical coherence tomography Visualization and measurement of capillary-driven blood flow using spectral domain optical coherence tomography Line-field confocal optical coherence tomography-Practical applications in dermatology and comparison with established imaging methods Optical coherence tomography detection of changes in inner retinal and choroidal thicknesses in patients with early retinitis pigmentosa Feasibility of combined optical coherence tomography and autofluorescence imaging for visualization of needle biopsy placement Characterization of microvascular tortuosity in retinal vein occlusion utilizing optical coherence tomography angiography Evaluation of retinochoroidal tissues in third trimester pregnants: An optical coherence tomography angiography study Evaluation of retinal and choroidal variations in thyroid-associated ophthalmopathy using optical coherence tomography angiography