• Proceedings of the Optical Society of Korea Conference
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• 2009.10a
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• pp.30-31
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• 2009

• Journal of the Korean Institute of Telematics and Electronics D
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• v.35D no.1
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• pp.1-7
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• 1998

In this paper, an incoherent imaging of a conducting cylinder illuminated by the single-frequency time-harmonic plane wave is obtained via the back-projections of the intensity patterns of the forward total electric field scattered from this object in the circular rotational measurement configuration. The pheonmenon that interference fringes generated in the itesity patterns is removed in the back-projection process is interpreted numerically. This imaging method is validated by imagining conducting circular cylinders and the conditions to ge beter image are investigated.

• Proceedings of the Safety Management and Science Conference
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• 2010.11a
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• pp.103-112
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• 2010

This study was done to provide basic data on the safety of professionals in medical imaging system by measuring the electromagnetic waves generated in the medical imaging system being used in medical organization. The studied medical imaging systems were general X-ray system, computed tomography(CT), ultrasonographic system, magnetic resonance imaging(MRI), PET-CT and fluoroscopic system, and through these devices, electric field and magnetic field were measured and analyzed. As a result of the analysis, the measured values classified by the medical organizations were not much significant, but in the measurement by the medical imaging systems, there were high hazard elements in the sequential order of electric field PET-CT($17.7{\pm}22.9$)v/m, CT($10.3{\pm}8.7$)v/m, general X-ray system ($8.8{\pm}8.8$)v/m, magnetic field general X-ray system($5.06{\pm}8.26$)mG, CT($2.71{\pm}4.53$)mG and PET-CT($0.74{\pm}0.34$)mG, the systems that adopted X-ray as main ray source, and the more aged the medical imaging systems, the greater the effects of electro-magnetic waves($10.6{\pm}15.93v/m$ for 5 years or more, $6.14{\pm}5.60v/m$ for 5 years or less). The effects of electromagnetic waves on medical imaging systems or facilities were not much when the notification of ministry of knowledge economy is considered, but in the overall perspective considering all the equipments and facility of the medical organization, such effects were significant. It is determined that sustainable safety managements of electric field and magnetic field must be done during process from medical imaging system installation to maintenance to rule out such factors.

• Journal of the Korea Safety Management & Science
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• v.12 no.4
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• pp.67-72
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• 2010

This study was done to provide basic data on the safety of professionals in medical imaging system by measuring the electromagnetic waves generated in the medical imaging system being used in medical organization. The studied medical imaging systems were general X-ray system, computed tomography(CT), ultrasonographic(USG) system, magnetic resonance imaging(MRI), PET-CT and fluoroscopic(R/F) system, and through these devices, electric field and magnetic field were measured and analyzed. As a result of the analysis, the measured values classified by the medical organizations were not much significant, but in the measurement by the medical imaging systems, there were high hazard elements in the sequential order of electric field PET-CT($17.7{\pm}22.9$)v/m, CT($10.3{\pm}8.7$)v/m, general X-ray system($8.8{\pm}8.8$)v/m, magnetic field general X-ray system($5.06{\pm}8.26$)mG, CT($2.71{\pm}4.53$)mG and PET-CT($0.74{\pm}0.34$)mG, the systems that adopted X-ray as main ray source, and the more aged the medical imaging systems, the greater the effects of electro-magnetic waves($10.6{\pm}15.93v/m$ for 5 years or more, $6.14{\pm}5.60v/m$ for 5 years or less). The effects of electromagnetic waves on medical imaging systems or facilities were not much when the notification of ministry of knowledge economy is considered, but in the overall perspective considering all the equipments and facility of the medical organization, such effects were significant. It is determined that sustainable safety managements of electric field and magnetic field must be done during process from medical imaging system installation to maintenance to rule out such factors.

• Journal of Biomedical Engineering Research
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• v.30 no.2
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• pp.113-121
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• 2009

This study aims at designing and evaluating light source devices that can stably generate light with various wavelengths in order to make possible PDD using a photosensitizer and diagnosis using auto-fluorescence. The light source was a Xenon lamp and filter wheel, composed of an optical output control through Iris and filters with several wavelength bands. It also makes the inducement of auto-fluorescence possible because it is designed to generate a wavelength band of 380-420nm, 430-480nm, and 480-560nm. The transmission part of the light source was developed to enhance the efficiency of light transmission. To evaluate this light source, the characteristics of light output and wavelength band were verified. To validate the capability of this device as PDD, the detection of auto-fluorescence using mouse models was performed.

• Journal of radiological science and technology
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• v.40 no.3
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• pp.407-413
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• 2017

Medical radiation offers significant benefits in diagnosing and treating patients, but it also generates unnecessary radiation exposure to those nearby. Accordingly, the objective of the present study was to analyze spatial dose rate according to types of radiation source term in multi-bed hospital rooms occupied by patients and general public. MCNPX was used for geometric simulation of multi-bed hospital rooms and radiation source terms, while the radiation source terms were established as whole body bone scan patients and imaging using a portable X-ray generator. The results of simulation on whole body bone scan patients showed $3.46{\mu}Sv/hr$ to another patient position, while experimental results on imaging using a portable X-ray generator showed $1.47{\times}10^{-8}{\mu}Sv/irradiation$ to another patient position in chest imaging and $2.97{\times}10^{-8}{\mu}Sv/irradiation$ to another patient position in abdomen imaging. Multi-bed hospital room, unnecessary radiation generated in the surrounding patients, while legal regulations and systematic measures are needed for radiation exposure in multi-bed hospital rooms that are currently lacking in Korea.

• Journal of the Optical Society of Korea
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• v.15 no.3
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• pp.293-299
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• 2011

In this study, we demonstrated Fourier-domain/swept-source optical coherence tomography (FD/SS-OCT) at a center wavelength of 800 nm for in vivo human retinal imaging. A wavelength-swept source was constructed with a semiconductor optical amplifier, a fiber Fabry-Perot tunable filter, isolators, and a fiber coupler in a ring cavity. Our swept source produced a laser output with a tuning range of 42 nm (779 to 821 nm) and an average power of 3.9 mW. The wavelength-swept speed in this configuration with bidirectionality is 2,000 axial scans per second. In addition, we suggested a modified zero-crossing method to achieve equal sample spacing in the wavenumber (k) domain and to increase the image depth range. FD/SS-OCT has a sensitivity of ~89.7 dB and an axial resolution of 10.4 ${\mu}m$ in air. When a retinal image with 2,000 A-lines/frame is obtained, an acquisition speed of 2.0 fps is achieved.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.11
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• pp.1078-1088
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• 2010

In order to analyze the quantitative characteristics of acoustic streaming, experimental setup of 3-D stereoscopic PIV(particle imaging velocimetry) was designed and quantitative ultrasonic flow fields in the gap between the ultrasonic vibrator and heat source were measured. Utilizing acoustic streaming induced by ultrasonic vibration, surface temperature drop of cooling object was also measured. The study on smart cooling method by acoustic streaming induced by ultrasonic vibration was performed due to the empirical relations of flow pattern, average flow velocity, different gaps, and enhancement on cooling rates in the gap. Average velocity fields and maximum acoustic streaming velocity in the open gap between the stationary cylindrical heat source and ultrasonic vibrator were experimentally measured at no vibration, resonance, and non-resonance. It was clearly observed that the enhancement of cooling rates existed owing to the acoustic air flow in the gap at resonance and non-resonance induced by ultrasonic vibration. The ultrasonic wave propagating into air in the gap creates steady-state secondary eddy called acoustic streaming which enhances heat transfer from the heat source to encompassing air. The intensity of the acoustic streaming induced by ultrasonic vibration experimentally depended upon the gap between the heat source and ultrasonic vibrator. The ultrasonic vibration at resonance caused the increase of the acoustic streaming velocity and convective heat transfer augmentation when the flow fields by 3D stereoscopic PIV and temperature drop of the heat source were measured experimentally. The acoustic streaming velocity of air enhancement on cooling rates in the gap is maximal when the gap agrees with the multiples of half wavelength of the ultrasonic wave, which is specifically 12 mm.

• Imaging Science in Dentistry
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• v.51 no.2
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• pp.107-115
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• 2021

Purpose: This study aimed to demonstrate the presence of dental caries through a photoacoustic imaging system with visible and near-infrared wavelengths, highlighting the differences between the 2 spectral regions. The depth at which carious tissue could be detected was also verified. Materials and Methods: Fifteen permanent molars were selected and classified as being sound or having incipient or advanced caries by visual inspection, radiography, and optical coherence tomography analysis prior to photoacoustic scanning. A photoacoustic imaging system operating with a nanosecond pulsed laser as the light excitation source at either 532 nm or 1064 nm and an acoustic transducer at 5 MHz was developed, characterized, and used. En-face and lateral(depth) photoacoustic signals were detected. Results: The results confirmed the potential of the photoacoustic method to detect caries. At both wavelengths, photoacoustic imaging effectively detected incipient and advanced caries. The reconstructed photoacoustic images confirmed that a higher intensity of the photoacoustic signal could be observed in regions with lesions, while sound surfaces showed much less photoacoustic signal. Photoacoustic signals at depths up to 4 mm at both 532 nm and 1064 nm were measured. Conclusion: The results presented here are promising and corroborate that photoacoustic imaging can be applied as a diagnostic tool in caries research. New studies should focus on developing a clinical model of photoacoustic imaging applications in dentistry, including soft tissues. The use of inexpensive light-emitting diodes together with a miniaturized detector will make photoacoustic imaging systems more flexible, user-friendly, and technologically viable.

• Proceedings of the Korean Vacuum Society Conference
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• 1996.06a
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• pp.40-41
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• 1996

Nitridation technique has been receiving much attention for the formation of a thin nitrided buffer layer on which high quality nitride films can be formedl. Particularly, gallium nitride (GaN) has been considered as a promising material for blue-and ultraviolet-emitting devices. It can also be used for in situ formed and stable passivation layers for selective growth of $GaAs_2$. In this work, formation of a thin nitrided layer is investigated. Nitrogen electron cyclotron resonance(ECR)-plasma is employed for the formation of thin nitrided layer. The plasma source used in this work is a compact ECR plasma gun3 which is specifically designed to enhance control, and to provide in-situ monitoring of plasma parameters during plasma-assisted processing. Microwave power of 100-200 W was used to excite the plasma which was emitted from an orifice of 25 rnm in diameter. The substrate were positioned 15 em away from the orifice of plasma source. Prior to nitridation is performed, the surface of n-type (001)GaAs was exposed to hydrogen plasma for 20 min at $300{\;}^{\circ}C$ in order to eliminate a native oxide formed on GaAs surface. Change from ring to streak in RHEED pattern can be obtained through the irradiation of hydrogen plasma, indicating a clean surface. Nitridation was carried out for 5-40 min at $RT-600{\;}^{\circ}C$ in a ECR plasma-assisted molecular beam epitaxy system. Typical chamber pressure was $7.5{\times}lO^{-4}$ Torr during the nitridations at $N_2$ flow rate of 10 seem.(omitted)mitted)