• Proceedings of the Korean Society of Medical Physics Conference
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• 2003.09a
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• pp.45-45
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• 2003

The aim of this study was the characterization and performance validation of new prototype avalanche photodiode (APD) arrays for positron emission tomography (PET). Two different APD array prototypes (noted A and B) developed by Radiation Monitoring Device (RMD) have been investigated. Principal characteristics of the two APD array were measured and compared. In order to characterize and evaluate the APD performance, capacitance, doping concentration, quantum efficiency, gain and dark current were measured. The doping concentration that shows the impurity distribution within an APD pixel as a function of depth was derived from the relationship between capacitance and bias voltage. Quantum efficiency was measured using a mercury vapor light source and a monochromator used to select a wavelength within the range of 300 to 700 nm. Quantum efficiency measurements were done at 500 V, for which the APD gain is equal to one. For the gain measurements, a pencil beam with 450 nm in wavelength was illuminating the center of each pixel. The APD dark currents were measured as a function of gain and bias. A linear fitting method was used to determine the value of surface and bulk leakage currents. Mean quantum efficiencies measured at 400 and 450 nm were 0.41 and 0.54, for array A, and 0.50 and 0.65 for array B. Mean gain at a bias voltage of 1700 V, was 617.6 for array A and 515.7 for type B. The values based on linear fitting were 0.08${\pm}$0.02 nA 38.40${\pm}$6.26 nA, 0.08${\pm}$0.0l nA 36.87${\pm}$5.19 nA, and 0.05${\pm}$0.00 nA, 21.80${\pm}$1.30 nA in bulk surface leakage current for array A and B respectively. Results of characterization demonstrate the importance of performance measurement validating the capability of APD array as the detector for PET imaging.

• Journal of radiological science and technology
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• v.29 no.3
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• pp.125-132
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• 2006

The PET/CT scanner is an evolution in image technology. The two modalities are complementary with CT and PET images. The PET scan images are well known as low resolution anatomic landmak, but such problems may help with interpretation detailed anatomic framework such as that provided by CT scan. PET/CT offers some advantages-improved lesion localization and identification, more accurate tumor staging. etc. Conventional PET employs tranmission scan require around 4 min./bed position and 30 min. for whole body scan. But PET/CT scanner can reduced by 50% in whole body scan. Especially nowadays PET scanner LSO scintillator-based from BGO without septa and operate in 3-D acquisition mode with multidetectors CT. PET/CT scanner fusion problems solved through hardware rather than software. Such device provides with the capability to acquire accurately aligned anatomic and functional images from single scan. It is very important to effective detection from gamma ray source in PETdetector. And can be offer high quality diagnostic images. So we have study about detection processing of PET detector and high quality imaging process.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.334-334
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• 2013

In the past decade, the infrared detectors based on intersubband transition in quantum dots (QDs) have attracted much attention due to lower dark currents and increased lifetimes, which are in turn due a three-dimensional confinement and a reduction of scattering, respectively. In parallel, focal plane array development for infrared imaging has proceeded from the first to third generations (linear arrays, 2D arrays for staring systems, and large format with enhanced capabilities, respectively). For a step further towards the next generation of FPAs, it is envisioned that a two-dimensional metal hole array (2D-MHA) structures will improve the FPA structure by enhancing the coupling to photodetectors via local field engineering, and will enable wavelength filtering. In regard to the improved performance at certain wavelengths, it is worth pointing out the structural difference between previous 2D-MHA integrated front-illuminated single pixel devices and back-illuminated devices. Apart from the pixel linear dimension, it is a distinct difference that there is a metal cladding (composed of a number of metals for ohmic contact and the read-out integrated circuit hybridization) in the FPA between the heavily doped gallium arsenide used as the contact layer and the ROIC; on the contrary, the front-illuminated single pixel device consists of two heavily doped contact layers separated by the QD-absorber on a semi-infinite GaAs substrate. This paper is focused on analyzing the impact of a two dimensional metal hole array structure integrated to the back-illuminated quantum dots-in-a-well (DWELL) infrared photodetectors. The metal hole array consisting of subwavelength-circular holes penetrating gold layer (2DAu-CHA) provides the enhanced responsivity of DWELL infrared photodetector at certain wavelengths. The performance of 2D-Au-CHA is investigated by calculating the absorption of active layer in the DWELL structure using a finite integration technique. Simulation results show the enhanced electric fields (thereby increasing the absorption in the active layer) resulting from a surface plasmon, a guided mode, and Fabry-Perot resonances. Simulation method accomplished in this paper provides a generalized approach to optimize the design of any type of couplers integrated to infrared photodetectors.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.11
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• pp.6432-6439
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• 2014

The NAUT (Non-contact Air coupled Ultrasonic Testing) technique is one of the ultrasonic testing methods that enables non-contact ultrasonic testing by compensating for the energy loss caused by the difference in acoustic impedance of air with an ultrasonic pulser receiver, PRE-AMP and high-sensitivity transducer. As the NAUT is performed in a state of steady ultrasonic transmission and reception, testing can be performed on materials of high or low temperatures or specimens with a rough surface or narrow part, which could not have been tested using the conventional contact-type testing technique. For this study, the internal defects of spot weld, which are often applied to auto parts, and CFRP parts, were tested to determine if it is practical to make the NAUT technique commercial. As the spot welded part had a high ultrasonic transmissivity, the result was shown as red. On the other hand, the part with an internal defect had a layer of air and low transmissivity, which was shown as blue. In addition, depending on the PRF (Pulse Repetition Frequency), an important factor that determines the measurement speed, the color sharpness showed differences. With the images obtained from CFRP specimens or an imaging device, it was possible to identify the shape, size and position of the internal defect within a short period of time. In this paper, it was confirmed in the above-described experiment that both internal defect detection and image processing of the defect could be possible using the NAUT technique. Moreover, it was possible to apply NAUT to the detection of internal defects in the spot welded parts or in CFRP parts, and commercialize its practical application to various fields.

• Journal of the Korean Society of Radiology
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• v.11 no.4
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• pp.221-225
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• 2017

To evaluate the performance of ultrasound imaging system, we investigated the change of spatial resolution according to changing sonic velocity change parameter provided by ultrasound equipment. Ultrasound phantom images were obtained using a 3.0 ~ 5.0 MHz convex transducer in an ultrasound diagnostic device used at a medical institution located at Iksan. N-365 multi-purpose ultrasound phantom was used to measure longitudinal distance measurement accuracy and longitudinal and transverse resolution. In the same manner, the sonic velocity of the ultrasound equipment was changed from 1580 m/sec to 1400 m/sec in six steps, and the full width at half maximum(FWHM) was measured using the image J program to determine whether the measured values were different. As a result, lateral resolution was measured from 1.91 mm to 5.3 mm according to the speed change, and the smallest FWHM was 1.91 mm at 1420 m/sec. The axial resolution was measured from 1.03 mm to 1.14 mm according to the speed change, and the smallest FWHM was 1.03 mm at 1400 m/sec. The slower the sound velocity of the ultrasound equipment, the shorter the length of longitudinal measurement.

• Korean Journal of Optics and Photonics
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• v.18 no.4
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• pp.246-255
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• 2007

The floating image system (FIS) is a device to display input source in the space between fast surface of the display and an observer and it provides pseudo 3D depth to an observer when input source as real object or 2D image was displayed through the optical lens system in the FIS. The Advanced floating image system (AFIS) was designed to give more effective 3D depth than existing FIS by adding front and rear depth cues to the displayed stereogram, which it was used as input source. The magnitude of disparity and size of stereogram were strongly related each other and they have been optimized for presenting 3D depths in a non-optical lens systems. Thus, if they were used in optical lens system, they will have reduced or magnified parameters, leading to problem such as providing incorrect 3D depth cues to an observer. Although the size of stereogram and disparity were demagnified by total magnifying power of optical system, the viewing distance (VD) from the display to an observer and base distance (BD) for the gap between the eyes were fixed. For this reason, the quantity of disparity in displayed stereogram through the existing FIS has not kept the magnifying power to the total optical system. Therefore, we proposed the methods to provide correct 3D depth to an observer by compensating quantity of disparity in stereogram which was satisfied to keep total magnifying power of optical lenses system by AFIS. Consequently, the AFIS provides a good floating depth (pseudo 3D) with correct front and rear 3D depth cues to an observer.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.42 no.2 s.302
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• pp.69-80
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• 2005

In these days, the technology development of the imaging/optic industry and the digital broadcasting replace the classic CRT with the new display devices that is getting slimmer and larger. Especially, when the general TV signal is applied directly to the wide gamut display using LED or laser, which can display higher chromatic colors that can't be reproduced on CRT, the color distortion occurs and it causes serious problems. Thus, in this paper the gamut mapping is studied, which gets rids of the color distortion and utilizes the wider color gamut than that of the CRT sufficiently. In the gamut mapping the general mapping concept is the increasement of the chroma on the same hue plane but it causes the over chromatic enhancement. So, the vector mapping, which increases the lightness md the chroma at the same time, is proposed to prevent the side effect. In the vector mapping the chromaticity is maintained constantly, hence the image can be seen more natural than that of the chroma mapping. By using the gamut fitting, it is compensated that the tone disappearance or the contour effect that is arose from the geometric properties of the input and the output color gamut. These gamut mapping and gamut fitting can prevent the color distortion and reproduce the natural image on the wide gamut displays.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.46 no.3
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• pp.44-51
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• 2009

It is very important to verify generated setup errors in cancer therapy by using a high energy radiation and to perform the precise radiation therapy. Specially, the verification of treatment position is very crucial in special therapies like fractionated stereotatic radiotherapy (FSRT). The FSRT uses normally high-dose, small field size for treating small intracranial lesions. To estimate the developed FSRT system, the isocenter accuracy of gantry, couch and collimator were performed and a total of inaccuracy was less than ${\pm}1mm$. Precise beam targeting is crucial when using high-dose, small field size FSRT for treating small intracranial lesions. The EPID image of the 3mm lead ball mounted on the isocenter with a 25mm collimator cone was acquired and detected to the extent of one pixel (0.76mm) after comparing the difference between the center of a 25mm collimator cone and a 3 mm ball after processing the EPID image. In this paper, the radiation treatment efficiency can be improved by performing precise radiation therapy with a developed video based EPID and FSRT at near real time

• Imaging Science in Dentistry
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• v.44 no.4
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• pp.257-262
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• 2014

Purpose: This study was performed to evaluate the effect of changing the orientation of a reconstructed image on the accuracy of linear measurements using cone-beam computed tomography (CBCT). Materials and Methods: Forty-two titanium pins were inserted in seven dry sheep mandibles. The length of these pins was measured using a digital caliper with readability of 0.01 mm. Mandibles were radiographed using a CBCT device. When the CBCT images were reconstructed, the orientation of slices was adjusted to parallel (i.e., $0^{\circ}$), $+10^{\circ}$, $+12^{\circ}$, $-12^{\circ}$, and $-10^{\circ}$ with respect to the occlusal plane. The length of the pins was measured by three radiologists, and the accuracy of these measurements was reported using descriptive statistics and one-way analysis of variance (ANOVA); p<0.05 was considered statistically significant. Results: The differences in radiographic measurements ranged from -0.64 to +0.06 at the orientation of $-12^{\circ}$, -0.66 to -0.11 at $-10^{\circ}$, -0.51 to +0.19 at $0^{\circ}$, -0.64 to +0.08 at $+10^{\circ}$, and -0.64 to +0.1 at $+12^{\circ}$. The mean absolute values of the errors were greater at negative orientations than at the parallel position or at positive orientations. The observers underestimated most of the variables by 0.5-0.1 mm (83.6%). In the second set of observations, the reproducibility at all orientations was greater than 0.9. Conclusion: Changing the slice orientation in the range of $-12^{\circ}$ to $+12^{\circ}$ reduced the accuracy of linear measurements obtained using CBCT. However, the error value was smaller than 0.5 mm and was, therefore, clinically acceptable.

• Progress in Medical Physics
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• v.26 no.1
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• pp.52-58
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• 2015

The automated dental cavity detection program for a new concept intra-oral dental x-ray imaging device, an auxiliary diagnosis system, which is able to assist a dentist to identify dental caries in an early stage and to make an accurate diagnosis, was to be developed. The primary theory of the automatic dental cavity detection program is divided into two algorithms; one is an image segmentation skill to discriminate between a dental cavity and a normal tooth and the other is a computational method to analyze feature of an tooth image and take an advantage of it for detection of dental cavities. In the present study, it is, first, evaluated how accurately the DRLSE (Direct Regularized Level Set Evolution) method extracts demarcation surrounding the dental cavity. In order to evaluate the ability of the developed algorithm to automatically detect dental cavities, 7 tooth phantoms from incisor to molar were fabricated which contained a various form of cavities. Then, dental cavities in the tooth phantom images were analyzed with the developed algorithm. Except for two cavities whose contours were identified partially, the contours of 12 cavities were correctly discriminated by the automated dental caries detection program, which, consequently, proved the practical feasibility of the automatic dental lesion detection algorithm. However, an efficient and enhanced algorithm is required for its application to the actual dental diagnosis since shapes or conditions of the dental caries are different between individuals and complicated. In the future, the automatic dental cavity detection system will be improved adding pattern recognition or machine learning based algorithm which can deal with information of tooth status.