• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.66.2-66.2
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• 2013

In this study, we present a pore-selection technique to estimate the size of pore. The estimation of the size of pore is important to examine the temporal evolution of size itself and corresponding intensity. The size of pore is typically estimated by applying the intensity threshold technique to the fixed box which contains the entire pore. The typical method has disadvantages in the following circumstances; there are small features near the pore or the image has low spatial resolution. In the former, it is difficult to define a box containing the pore only, excluding the small features near the pore. In the latter, the background and threshold intensity are insignificant due to the insufficient number of pixel in the box. To avoid these difficulties, we use a pore-selection technique which is simply based on the measurement of distances from the pore center. In addition, we will discuss the advantage of the technique for the imaging spectrograph data like the NST FISS.

• Korean Journal of Optics and Photonics
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• v.17 no.2
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• pp.159-164
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• 2006

We demonstrate a compact optical coherence tomography(OCT) system based on the optical fiber delay line controlled by a cylindrical piezo-electric transducer(PZT). An 18-m length of single mode fiber is wrapped under constant tension around a PZT. Approximately 134 windings are used. Wraps of the long length of fiber allow the small expansion of the PZT to be magnified to an optical path length delay of 0.78 m. The OCT system shows characteristics for 2-dimensional imaging, exhibiting 96.9dB of signal-to-noise ratio(SNR), $18.6{\pm}0.5\;{\mu}m$ of axial resolution, and $5\;{\mu}m$ of lateral resolution with samples.

• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.5
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• pp.520-526
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• 2016

Squeal noise is a typical brake noise that is annoying to both passengers and pedestrians. Its frequency range is fairly wide from 1 kHz to 18 kHz, which can be distressful to people. The brake squeal noise occurs due to various mechanisms, such as the mode coupling of the brake system, self-excited vibration, unstable wear, and others. In this study, several parameters involved in the generation of a squeal noise are investigated experimentally by using a brake noise dynamometer. The speed, caliper pressure, torque, and friction coefficient are measured as functions of time on the dynamometer. The contact pressure and temperature distributions of the disc and the pad are also measured by using a thermal imaging camera and a pressure mapping system. As a result of the simultaneous measurement of the friction coefficient and squeal amplitude as functions of the velocity, it is found that the onset of the squeal may be predicted from the ${\mu}-v$ curve. It is also found that a non-uniform contact pressure causes instability and, in turn, a squeal. Based on the analysis results, design modifications of the pad are suggested for improved noise characteristics.

• Journal of the Optical Society of Korea
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• v.17 no.1
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• pp.68-72
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• 2013

We developed an SD-OCT (Spectral Domain-Optical Coherence Tomography) system which uses a GPU (Graphics Processing Unit) for processing. The image size from the SD-OCT system is $1024{\times}512$ and the speed is 110 frame/sec in real-time. K-domain linearization, FFT (Fast Fourier Transform), and log scaling were included in the GPU processing. The signal processing speed was about 62 ms using a CPU (Central Processing Unit) and 1.6 ms using a GPU, which is 39 times faster. We performed an in-vivo retinal scan, and reconstructed a 3D visualization based on C-scan images. As a result, there were minimal motion artifacts and we confirmed that tomograms of blood vessels, the optic nerve, and the optic disk are clearly identified. According to the results of this study, this SD-OCT can be applied to real-time 3D display technology, particularly auxiliary instruments for eye operations in ophthalmology.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.58-60
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• 2007

Magnetic Resonance Imaging(MRI) has become a very widely used medical procedur e. Clo.sed and open systems are typically used with static magnetic fields at or below 2 Tesla. BWhole body SAR(specific absorbsion rate) is the value of SAR averaged over the entire body of the patient over any period of 15 minutes. Head SAR is the value of SAR averaged over the head of the patient for any period of 10 minutes. SAR is a measure of the absorption of electromagnetic energy in the body' (typically in watts per kilogram (W/kg)). The normal operating mode comprises values of head SAR not higher than 3 W/kg. The second level controlled operating mode comprises values higher than 3 W/kg. Current FDA guidance limits the SAR in the whole body. including the head to a range of 1.5 to 4.0 W/kg, depending on the patient's clinical condition. SAR, limit restrictions are incorporated in all MRI systems. and domestic' s guidance limits the SAR in a part body. including the head to 3.2w/kg and less. The purpose of this study is to evaluate on change of head SAR in using MRI pulse sequence and to check if exceed 3.2(w/kg) level in domestic a part exposure through measured head SAR. 23 patient's the average head SAR of pulse sequence is that T2WI sagittal is 0.5375. T2WI axial(FSE) is 0.4817, T1WI axial(SE) is, 0.8179. FLAIR axial is 0.4580. GRE axial is 0.0077, Diffusion is 0.0824w/kg. The head SAR exposed per patient was proved 2.3845w/kg less than the international standard. Coefficient of correlation for the relations body weight and SAR or for the relations ETL(echo train length) and SAR is 1 value. Coefficient of correlation for the relations between TR(time to repeat) and SAR is -0.602 value. so SAR increased relative to weight body and ETL. But the relations between TR and SAR is negative definite.

• Journal of the Korean Academy of Child and Adolescent Psychiatry
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• v.23 no.2
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• pp.57-62
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• 2012

Objectives : Characteristic symptoms, including hyperactivity and easy distractibility, in children with attention-deficit hyperactivity disorder (ADHD) suggest that their brain status, even at rest, might differ from that of healthy children. This study was conducted in order to determine whether resting state brain activity is compromised in medication-naive children with ADHD. Methods : Twenty medication-naive children with ADHD (mean age $10.3{\pm}2.5$) and 28 age- and gender-matched healthy volunteers (mean age $10.3{\pm}2.0$) underwent measurements for resting state brain activity using functional magnetic resonance imaging (fMRI). Among resting state related-independent components (RSICs) extracted from fMRI data using independent component analysis, a significant difference in RSICs was observed between groups, using a mixed Gaussian/gamma model. Results : Except for IQ, which was higher in the healthy control group, no demographic difference was observed between the two groups (p<.001). Significantly less activation of one RSIC, which includes the bilateral precuneus/posterior cingulate cortex, occipito-temporal junction, and anterior cingulate cortex, was observed in the ADHD group, compared with the control group (p<.05). Conclusion : An abnormal RSIC, posterior default mode network (DMN), was observed in the medication-naive ADHD group. Results of our study suggest that abnormality of posterior DMN is one of the main pathophysiologies of ADHD.

• Journal of Yeungnam Medical Science
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• v.24 no.2
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• pp.119-128
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• 2007

Purpose : The purpose of this study was a phantom study to measure the diffusion properties of water molecules by steady-state free precession diffusion-weighted imaging (SSFP- DWI) with a low b-value and to determine if this sequence might be useful for application to the evaluation of bone marrow pathology. Materials and methods : 1. The phantom study: A phantom study using two diffusion weighted sequences for the evaluation of the diffusion coefficient was performed. Three water-containing cylinders at different temperatures were designed: phantom A was $3^{\circ}C$, B was $23^{\circ}C$ and C was $63^{\circ}C$. Both SSFP and echo planar imaging (EPI) sequences (b-value: $1000s/mm^2$) were performed for comparison of the diffusion properties. The Signal to noise ratios (SNR) and apparent diffusion coefficient (ADC) values of the three phantoms using each diffusion-weighted sequence were assessed. 2. The Clinical study: SSFP-DWI was performed in 28 patients [sacral insufficiency fractures (10), osteoporotic lumbar compression fractures (10), malignant compression fractures (8)]. To measure the ADC maps, a diffusion-weighted single shot stimulated echo-acquisition mode sequence ($650s/mm^2$) was obtained using the same 1.5-T MR imager Results : For the phantom study, the signal intensity on the SSFP as well as the classic EPI-based DWI was decreased as the temperature increased in phantom A to C. The ADC values of the phantoms on EPI-DWI were $0.13{\times}10^{-3}mm^2/s$ in phantom A, $0.22{\times}10^{-3}mm^2/s$ in B and $0.37{\times}10^{-3}mm^2/s$. in C. The SSFP can be regarded as a DWI sequence in view of the series of signal decreases. Conclusion : Bone marrow pathologies with different diffusion coefficients were evaluated by SSFP-DWI. All benign fractures were hypointense compared to the adjacent normal bone marrow where as the malignant fractures were hyperintense compared to the adjacent normal bone marrow.

• The Korean Journal of Nuclear Medicine Technology
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• v.16 no.1
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• pp.86-90
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• 2012

Purpose: Quantification of myocardial blood flow (MBF) using dynamic PET imaging has the potential to assess coronary artery disease. Rb-82 plays a key role in the clinical assessment of myocardial perfusion using PET. However, MBF could be overestimated due to the underestimation of left ventricular input function in the beginning of the acquisition when the scanner has non-linearity between count rate and activity concentration due to the scanner dead-time. Therefore, in this study, we evaluated the count rate linearity as a function of the activity concentration in PET data acquired in list mode. Materials & methods: A cylindrical phantom (diameter, 12 cm length, 10.5 cm) filled with 296 MBq F-18 solution and 800 mL of water was used to estimate the linearity of the Biograph 40 True Point PET/CT scanner. PET data was acquired with 10 min per frame of 1 bed duration in list mode for different activity concentration levels in 7 half-lives. The images were reconstructed by OSEM and FBP algorithms. Prompt, net true and random counts of PET data according to the activity concentration were measured. Total and background counts were measured by drawing ROI on the phantom images and linearity was measured using background correction. Results: The prompt count rates in list mode were linearly increased proportionally to the activity concentration. At a low activity concentration (<30 kBq/mL), the prompt net true and random count rates were increased with the activity concentration. At a high activity concentration (>30 kBq/mL), the increasing rate of the prompt net true rates was slightly decreased while the increasing rate of random counts was increased. There was no difference in the image intensity linearity between OSEM and FBP algorithms. Conclusion: The Biograph 40 True Point PET/CT scanner showed good linearity of count rate even at a high activity concentration (~370 kBq/mL).The result indicates that the scanner is useful for the quantitative analysis of data in heart dynamic studies using Rb-82, N-13, O-15 and F-18.

• Asian Pacific Journal of Cancer Prevention
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• v.15 no.13
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• pp.5487-5492
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• 2014

Ultrasonography is non-invasive and can give useful clues in the diagnosis of cervical lymphadenopathy, However, differential diagnosis is difficult in some situations even combined with color Doppler imaging. The present study was conducted to evaluate the clinical value of real time elastography in patients with unexplained cervical lymphadenopathy using a quantitative method. From May 2011 to February 2012, 39 enlarged lymph nodes from 39 patients with unexplained cervical lymphadenopathy were assessed. All the patients were examined by both B-mode ultrasound, color Doppler flow imaging and elastography. The method of analyzing elasto-graphic data was the calculation of the 10 parametres ("mean", "sd", "area%", "com", "kur", "ske", "con", "ent", "idm", "asm") offered by the software integrated into the Hitachi system. The findings were then correlated with the definitive tissue diagnosis obtained by lymph node dissection or biopsy. Final histology revealed 10 cases of metastatic lymph nodes, 11 cases of lymphoma, 12 cases of tuberculosis and 6 cases of nonspecific lymphadenitis. The significant distinguishing features for conventional ultrasound were the maximum short diameter (p=0.007) and absent of echogenic hilum (p=0.0293). The diagnostic accuracy was 43.6% (17/39 cases) and there were 17 patients with equivocal diagnosis. For elastography, "mean" (p=0.003), "area%" (p=0.009), "kurt" (p=0.0291), "skew" (p=0.014) and "cont" (p=0.012) demonstrated significant differences between groups. With 9 of the 17 patients with previous equivocal diagnoses (52.9%) definite and correct diagnoses could be obtained. The diagnostic accuracy for conventional ultrasound combined elastography was 69.2% (27/39 cases). There were differences in the diagnostic sensitivity of the two methods (p=0.0224). Ultrasound combined with elastography demonstrated higher rates of conclusive and accurate diagnoses in patients with unexplained cervical lymphadenopathy than conventional ultrasound. The quantitative program showed good correlation with the pathology of different lymph node diseases.

• Korean Journal of Digital Imaging in Medicine
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• v.14 no.2
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• pp.39-46
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• 2012

Purpose : The purpose of this study was to reduce Entrance Surface Dose and maintain image quality by changing Source to Image receptor Distance. And we'd like to compare ESD on this study to DRLs in other contries. Materials and Methods : We used indirect DR system(Definium 8000, General Electric, USA)and phantom(ART-200X, Flukebiomedical, USA),glass dosimeters(GD-352M, Asahi Techno Glass, Japan)for this study. The imagies were obtained throuh 80kVp fixed, and different tube currents using AEC mode in $16{\times}16$(inch) field size and changing Source to Image receptor Distance from 100 cm to 130 cm per 10 cm unit. The phantom with attaching 5 glass dosimeters on abdomonal skin was set at supine and erect position as a anterioposterial projection on detector For measuring Entrance Surface Dose. Image analysis was conducted by histograms of Image J(1.46r) which was given from National Institutes of Health(NIH). Results : Due to inverse square law of distance, the tube currents were increasing 42.6 % in supine position and 32.6 % in erect position according to the change of Source to Image receptor Distance. While Entrance Surface Doses were rapidly decreasing 14.2 % in supine position and 29.4 % in erect position according to the change of Source to Image receptor Distance. As the results of histogram using Image J, pixel mean values from 100 cm to 110 cm, 120 cm and 130 cm were decreasing each 1.4%, 2.5%, 2.7%, 4.5%, 2.2 %, 5.8 % in supine, erect position. While standard deviations from 100 cm to 110 cm, 120 cm and 130 cm were increasing each 1.4 %, 2.5 %, 2.5 %, 4.0 %, 2.0 %, 4.9 % Consequently, there are no significant differences in abdomen images taken. Conclusion: As the results described above, we strongly recommend using long Sourceto Image receptor Distance than 100cm that we have been using. So, we should deliver less Entrance Surface Dose to the patients while maintaining image quality in abdomen radiography.