• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.23 no.11
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• pp.1307-1314
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• 2012

To reduce the effects of clutters with subsurface inhomogenities in ground-penetrating radar(GPR) images, an eigenimage based signal-processing technique is presented. If the conventional eigenimage filtering technique is applied to B-scan images of a GPR survey, relatively homogeneous clutters such as antenna ringing, direct coupling between transmitting and receiving antennas, and soil-surface reflection, can be removed sufficiently. However, since random clutters of subsurface inhomogenities still remain in the images, target signals are distorted and obscured by the clutters. According to a comparison of the eigenimage filtering results, there is different coherency between subsurface clutters and target signals. To reinforce the pixels with high coherency and reduce the pixels with low coherency, the pixel-by-pixel geometric-mean process after the eigenimage filtering is proposed here. For the validity of the proposed approach, GPR survey for detection of a metal target in a randomly inhomogeneous soil is numerically simulated by using a random media generation technique and the finite-difference time-domain(FDTD) method. And the proposed signal processing is applied to the B-scan data of the GPR survey. We show that the proposed approach provides sufficient enhancement of target signals as well as remarkable reduction of subsurface inhomogeneous clutters in comparison with the conventional eigenimage filtering.

• Imaging Science in Dentistry
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• v.46 no.2
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• pp.103-108
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• 2016

Purpose: The current study investigates the feasibility of a platform for a nationwide dose monitoring system for dental radiography. The essential elements for an unerring system are also assessed. Materials and Methods: An intraoral radiographic machine with 14 X-ray generators and five sensors, 45 panoramic radiographic machines, and 23 cone-beam computed tomography (CBCT) models used in Korean dental clinics were surveyed to investigate the type of dose report. A main server for storing the dose data from each radiographic machine was prepared. The dose report transfer pathways from the radiographic machine to the main sever were constructed. An effective dose calculation method was created based on the machine specifications and the exposure parameters of three intraoral radiographic machines, five panoramic radiographic machines, and four CBCTs. A viewing system was developed for both dentists and patients to view the calculated effective dose. Each procedure and the main server were integrated into one system. Results: The dose data from each type of radiographic machine was successfully transferred to the main server and converted into an effective dose. The effective dose stored in the main server is automatically connected to a viewing program for dentist and patient access. Conclusion: A patient radiation dose monitoring system is feasible for dental clinics. Future research in cooperation with clinicians, industry, and radiologists is needed to ensure format convertibility for an efficient dose monitoring system to monitor unexpected radiation dose.

• Journal of the korean academy of Pediatric Dentistry
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• v.39 no.2
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• pp.139-144
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• 2012

The purpose of this study was to evaluate the accuracy and reproducibility of measuring the size of unerupted permanent tooth via cone beam computed tomography(CBCT). Ten children were scanned with dental CBCT, and 3-dimensional reconstruction of the dentitions were generated CBCT. Mesio-distal dimension and buccolingual dimension of the teeth were made directly on the model with a high-precision digitalcaliper and on the CBCT by using three-dimensional dental imaging software. Reliability and accuracy were assessed by using intraclass correlation and paired $t$-tests. ($p$ <0.05) The results were as follows : 1. Intraclass correlations were above 0.9 for Both the CBCT and the model measurements, showinghigh reliability. 2. Although there were high correlation values(r=0.91) between CBCT and model messurement methods, comparisons between the CBCT and model messurement methods showed a statistically significant difference($p$ <0.05). 3. The CBCT measurements tended to slightly underestimate by 0.2 mm. But, the systematic difference of CBCT measurements were clinically acceptable Therefore, CBCT measurement method can be used to measure the size of unerupted teeth in a sufficiently accurate way.

• Journal of the Korean Chemical Society
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• v.48 no.6
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• pp.553-560
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• 2004

In this experiment, a three dimensional structure analysis was carried out to examine the surface defects of semiconductor made artificially on known scale. It was investigated the three dimensional imaging according to the sample depth and the thermal diffusivity as well as the carrier transport properties. The thermal diffusivity measurement of the intrinsic GaAs semiconductor was also analyzed by the difference of frequency-dependence photoacoustic signals from the sample surface of different conditions. Thermal properties such as thermal diffusion length or thermal diffusivity of the Si wafer with and without defects on the surface were obtained by interpreting the frequency dependence of the PA signals. As a result, the photoacoustic signal is found to have the dependency on the shape and depth of the defects so that their structure of the defects can be analyzed. This method demonstrates the possibility of the application to the detection of the defects, cracks, and shortage of circuits on surface or sub-surface of the semiconductors and ceramic materials as a nondestructive testing(NDT) and a nondestructive evaluation(NDE) technique.

• Investigative Magnetic Resonance Imaging
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• v.2 no.1
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• pp.73-82
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• 1998

Purpose : A precise NMR technique for measuring the rate of water exchange and cell membrane permeability across the hepatocyte membrane using liver-specific MR contrast agent is described. Materials and Methods : The rat hepatocytes isolated by perfusion of the livers were used for the NMR measurements. All experiments were performed on an IBM field cycling relaxometer operating from 0.02MHz to 60 MHz proton Larmor frequency. spin-echo pulse sequence was empolyed to measure spin-lattice relaxation time, T1. The continuous distribution analysis of water proton T1 data from rat hepatocytes containing low concentrations of the liver specific contrast agent, Gd-EOB-DTPA, modeled by a general two compartment exchange model. Results : The mean residence time of water molecule inside the hepatocyte was approximately 250 msec. The lower limit for the permeability of the hepatocyte membrane was $(1.3{\pm}0.1){\;}{\times}{\;}10^{-3}cm/sec$. The CONTIN analysis, which seeks the natural distribution of relaxation times, reveals direct evidence of the effect of diffusive exchange. the diffusive water exchange is not small in the intracellular space in the case of hepatocytes. Conclusions : Gd-EOB-DTPA, when combined with continuous distribution analysis, provides a robust method to study water exchange and membrane permeability in hepatocytes. Water exchange in hepatocyte is much slower thatn that in red blood cells. Therefore, tissue-specific contrast agent may be used as a functional agent to give physiological information such as cell membrane permeability.

• Investigative Magnetic Resonance Imaging
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• v.19 no.2
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• pp.88-98
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• 2015

Purpose: To compare the interobserver and intraobserver reliability of mean apparent diffusion coefficient (ADC) values using contrast-enhanced (CE) T1 weighted image (WI) and T2WI as structural images between manual and semiautomatic segmentation methods. Materials and Methods: Between January 2011 and May 2013, 28 patients who underwent brain MR with diffusion weighted image (DWI) and were pathologically confirmed as having glioblastoma participated in our study. The ADC values were measured twice in manual and semiautomatic segmentation methods using CE-T1WI and T2WI as structural images to obtain interobserver and intraobserver reliability. Moreover, intraobserver reliabilities of the different segmentation methods were assessed after subgrouping of the patients based on the MR findings. Results: Interobserver and intraobserver reliabilities were high in both manual and semiautomatic segmentation methods on CE-T1WI-based evaluation, while interobserver reliability on T2WI-based evaluation was not high enough to be used in a clinical context. The intraobserver reliability was particularly lower with the T2WI-based semiautomatic segmentation method in the subgroups with involved $lobes{\leq}2$, with partially demarcated tumor borders, poorly demarcated inner margins of the necrotic portion, and with perilesional edema. Conclusion: Both the manual and semiautomatic segmentation methods on CE-T1WI-based evaluation were clinically acceptable in the measurement of mean ADC values with high interobserver and intraobserver reliabilities.

• Journal of the Korea Society of Computer and Information
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• v.13 no.7
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• pp.117-126
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• 2008

Recent advances in medical imaging technologies have enabled the high-resolution data acquisition. Therefore visualization of such large data set on standard graphics hardware became a popular research theme. Among many visualization techniques, we focused on bricking method which divided the entire volume into smaller bricks and rendered them in order. Since it switches bet\W8n bricks on main memory and bricks on GPU memory on the fly, to achieve better performance, the number of these memory swapping conditions has to be minimized. And, because the original bricking algorithm was designed for regular volume data such as CT and MR, when applying the algorithm to ultrasound volume data which is based on the toroidal coordinate space, it revealed some performance degradation. In some areas near bricks' boundaries, an orthogonal viewing ray intersects the single brick twice, and it consequently makes a single brick memory to be uploaded onto GPU twice in a single frame. To avoid this redundancy, we divided the volume into bricks allowing overlapping between the bricks. In this paper, we suggest the formula to determine an appropriate size of these shared area between the bricks. Using our formula, we could minimize the memory bandwidth. and, at the same time, we could achieve better rendering performance.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.113.1-113.1
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• 2012

The characteristics of Doppler shifts in a quiet region of the Sun are investigated by comparing between the $H{\alpha}$ line and the Caii infrared line at 854.2 nm. A small area of $16^{\prime\prime}{\times}40^{\prime\prime}$ was observed for about half an hour with the Fast Imaging Solar Spectrograph (FISS) of the 1.6 meter New Solar Telescope (NST) at Big Bear Solar Observatory. The observed area contains a network region and an internetwork region, and identified in the network region are $H{\alpha}$ fibrils, Caii fibrils and bright points. We infer the Doppler velocity from each line profile at a point with the lambdameter method as a function of half wavelength separation ${\Delta}{\lambda}$. It is confirmed that the bisector of the spatially-averaged Caii line profile has an inverse C-shape of with a significant peak redshift of +1.8 km/s. In contrast, the bisector of the spatially-averaged $H{\alpha}$ line profile has a different shape; it is almost vertically straight or, if not, has a C-shape with a small peak blueshift of -0.5 km/s. In both the lines, the bisectors of bright network points are much different from those of other features in that they are significantly redshifted not only at the line centers, but also at the wings. We also find that the spatio-temporal fluctuation of Doppler shift inferred from the Caii line is correlated with those of the $H{\alpha}$ line. The strongest correlation occurs in the internework region, and when the inner wings rather than the line centers are used to determine Doppler shift. In this region, the RMS value of Doppler shift fluctuation is the largest at the line center, and monotonically decreases with ${\Delta}{\lambda}$. We discuss the physical implications of our results on the formation of the $H{\alpha}$ line and Caii 854.2 nm line in the quiet region chromosphere.

• Journal of Biomedical Engineering Research
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• v.24 no.4
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• pp.267-273
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• 2003

The present study attempted to observe what changes the supply of highly concentrated (30%) oxygen cause to people's ability of visuospatial cognition, compared to air of normal oxygen concentration (21%). This study sampled eight male university students (the average age : 23.5) as subjects for functional Magnetic Resonance Imaging (MRI) study It also developed equipment that supplies 21% and 30% oxygen) at a constant rate of 8L/min. Two questionnaires containing 20 questions were developed to measure the ability of visuospatial cognition, and accuracy was calculated from the result of task performance. The experiment paradigm consisted of the run conducting tasks at 30%'s concentration of oxygen and another run at 21%'s concentration of oxygen. Each run was composed of four blocks and each block included eight control tasks and five visuospatial taks. 3T MRI was used and fMRI was obtained through the single-shot EPI method. The activation in the occipital-associated area, bilateral superior parietal lobes, bilateral inferior parietal lobes. bilateral precuneus, bilateral postcentral gyri, bilateral middle frontal gyri, bilateral inferior frontal gyri, bilateral medial frontal gyri, bilateral superior frontal gyri, bilateral cingulate gyri was significantly increased at the 30%'s concentration of oxygen rather than 21%'s. Furthermore, the result of task performance showed the accuracy increased at 30%'s concentration of oxygen rather than 21%'s. From the result of this study, it is concluded that the supply of highly concentrated oxygen has a positive effect on the ability of visuospatial cognition.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.3
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• pp.1294-1300
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• 2013

The purpose of this study is to increase contrast to noise ratio(CNR) in myocardial viability test by using contrast agent which highly content gadolinium(1mmol/mL) maximizing diagnostic value. This research method that four hundred four patients were underwent the MRI scanning two hundred eighty four of them were injected commercial contrast media which have 0.5mmol/L and the rest of them were injected new contrast media(gadobutrol) which have 1mmol/mL of molarity to study the contrast difference depending on the molarity of the contrast agent signal intensities of normal ventricle and left ventricle were measured to compare and evaluate signal to noise ratio(SNR) and CNR of the images. As result, 1mmol/mL contrast agent showed higher SNR by 25.13% in myocardium and 30.74% in left ventricle. CNR was proved to be better in 1mmol/mL contrast agent by 31.29%. The results above were all statistically meaningful. Therefore, contrast agent contenting more gadolinium which was 1mmol/mL in this study, could more effectively shorten T1 relaxation time, increase the signal intensity and at the same time maximize CNR and diagnostic value. This study firstly report the usefulness of 1mmol/mL contrast agent in patients allegedly suffering cardiac diseases and it is considered to increase diagnostic value.