Sun Kook Yoo

Yonsei University Hospital, Sŏul, Seoul, South Korea

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Publications (23)13.07 Total impact

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    Bo Kyu Kang, Sun Kook Yoo
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    ABSTRACT: Recently, as we move toward a society with an increasingly aged population, wearable U-health devices in various shapes with smart wear have been developed in order to conveniently measure health variables without using hands in daily life or at home. However, the problem is that only supply of the wearable U-health devices is focused and its applicable devices are studied and developed, which has resulted in lack of awareness of importance of performance evaluation. In this study, two electrodes were fabricated using conductive fabric which can be used as electrode if attached to wearable U-health devices or smart wear in order to measure ECG signal. Two electrodes those were fabricated using conductive fabric were compared the correlation, impedance and CMRR with patch typed Ag-AgCl electrode-normally used for measurement of ECG signal, so that the study would find out if the fabricated electrode can be used with the wearable U-health devices by testing and evaluating performances.
    Journal of the Institute of Electronics and Information Engineers. 01/2013; 50(2).
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    Jungchae Kim, Sun Kook Yoo
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    ABSTRACT: Exchanging personal health information(PHI) is an essential process of healthcare services using information and communication technology. But the process have the inherent risk of information disclosure, so the PHI should be protected to ensure the reliability of healthcare services. In this paper, we designed encryption module for wearable personal health devices(PHD). A main goal is to guarantee that the real-time encoded and transmitted PHI cannot be allowed to be read, revised and utilized without user's permission. To achieve this, encryption algorithms as DES and 3DES were implemented in modules operating in Telos Rev B(16bit RISC, 8Mhz). And the experiments were performed in order to evaluate the performance of encryption and decryption using vital-sign measured by PHD. As experimental results, an block encryption was measured the followings: DES required 1.802 ms and 3DES required 6.683 ms. Also, we verified the interoperability among heterogeneous devices by testing that the encrypted data in Telos could be decoded in other machines without errors. In conclusion, the encryption module is the method that a PHD user is given the powerful right to decide for authority of accessing his PHI, so it is expected to contribute the trusted healthcare service distribution.
    Journal of the Institute of Electronics and Information Engineers. 01/2013; 50(2).
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    Jungchae Kim, Sun Kook Yoo
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    ABSTRACT: PACS is a medical system for digital medical images, and PACS expand to web-based service using public network, DICOM files should be protected from the man-in-the-middle attack because they have personal medical record. To solve the problem, we designed flexible secure transmission system using IPSec and adopted to a web-based three-dimensional medical image system. And next, we performed the performance evaluation changing integrity and encryption algorithm using DICOM volume dataset. At that time, combinations of the algorithm was 'DES-MD5', 'DES-SHA1', '3DES-MD5', and '3DES-SHA1, and the experiment was performed on our test-bed. In experimental result, the overall performance was affected by encryption algorithms than integrity algorithms, DES was approximately 50% of throughput degradation and 3DES was about to 65% of throughput degradation. Also when DICOM volume dataset was transmitted using secure transmission system, the network performance degradation had shown because of increased packet overhead. As a result, server and network performance degradation occurs for secure transmission system by ensuring the secure exchange of messages. Thus, if the secure transmission system adopted to the medical images that should be protected, it could solve server performance gradation and compose secure web PACS.
    Journal of the Institute of Electronics and Information Engineers. 01/2013; 50(3).
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    ABSTRACT: The purpose of this study was to assess whether gadoxetate disodium-enhanced hepatobiliary phase MRI could predict the histologic factors of hepatocellular carcinomas (HCCs). Fifty-three HCCs histopathologically proved by surgery in 51 patients were evaluated retrospectively. All patients underwent gadoxetate disodium-enhanced MRI before surgical resection. The differences in contrast enhancement ratio of the lesions and differences in contrast-to-noise ratio (CNR) among the histologic grades of HCC were compared by using the Kruskal-Wallis test. The Spearman method was used to determine the correlations among contrast enhancement ratio, CNR, cell density ratio, and positivity for anti-hepatocyte antibody, keratin 7, and keratin 19. Of 53 HCCs, 50 showed low signal intensity on hepatobiliary phase images, whereas three HCCs were hyperintense on hepatobiliary phase images compared with surrounding hepatic parenchyma. Although well-differentiated HCCs tended to show higher contrast enhancement, there was no statistical significance between contrast enhancement ratio of the tumors and histologic grade (p = 0.414). No significant difference was observed between CNR and histologic grade (p = 0.965). The contrast enhancement ratios of the tumors were significantly lower in the keratin 19-positive group than in the keratin 19-negative group (p = 0.015). There was no significant correlation among contrast enhancement ratio, anti-hepatocyte antibody positivity, cell density ratio, and keratin 7 positivity (p > 0.05). The contrast enhancement ratio and CNR of HCCs were not correlated with histologic grades. The contrast enhancement ratio was significantly lower in keratin 19-positive HCCs.
    American Journal of Roentgenology 08/2011; 197(2):399-405. · 2.90 Impact Factor
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    ABSTRACT: This study is part of the ongoing development of treatment methods for metabolic syndrome (MS) project, which involves monitoring daily physical activity. In this study, we have focused on detecting walking activity from subjects which includes many other physical activities such as standing, sitting, lying, walking, running, and falling. Specially, we implemented an integrated solution for various physical activities monitoring using a mobile phone and PC. We put the iPod touch has built in a tri-axial accelerometer on the waist of the subjects, and measured change in acceleration signal according to change in ambulatory movement and physical activities. First, we developed of programs that are aware of step counts, velocity of walking, energy consumptions, and metabolic equivalents based on iPod. Second, we have developed the activity recognition program based on PC. iPod synchronization with PC to transmit measured data using iPhoneBrowser program. Using the implemented system, we analyzed change in acceleration signal according to the change of six activity patterns. We compared results of the step counting algorithm with different positions. The mean accuracy across these tests was 99.6 ± 0.61%, 99.1 ± 0.87% (right waist location, right pants pocket). Moreover, six activities recognition was performed using Fuzzy c means classification algorithm recognized over 98% accuracy. In addition we developed of programs that synchronization of data between PC and iPod for long-term physical activity monitoring. This study will provide evidence on using mobile phone and PC for monitoring various activities in everyday life. The next step in our system will be addition of a standard value of various physical activities in everyday life such as household duties and a health guideline how to select and plan exercise considering one's physical characteristics and condition.
    Healthcare informatics research. 03/2011; 17(1):76-86.
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    Chung Ki Lee, Han Gue Jo, Sun Kook Yoo
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    ABSTRACT: Soft-computing techniques are commonly used to detect medical phenomena and to help with clinical diagnoses and treatment. The purpose of this paper is to analyze the single electroencephalography (EEG) signal with the chaotic methods in order to identify the sleep stages. Data acquisition (polysomnography) was performed on four healthy young adults (all males with a mean age of 27.5 years). The evaluated algorithm was designed with a correlation dimension and Lyapunov's exponent using a single EEG signal that detects differences in chaotic characteristics. The change of the correlation dimension and the largest Lyapunov exponent over the whole night sleep EEG was performed. The results show that the correlation dimension and largest Lyapunov exponent decreased from light sleep to deep sleep and they increased during the rapid eye movement stage. These results suggest that chaotic analysis may be a useful adjunct to linear (spectral) analysis for identifying sleep stages. The single EEG based nonlinear analysis is suitable for u-healthcare applications for monitoring sleep.
    Healthcare informatics research. 03/2010; 16(1):46-51.
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    ABSTRACT: This paper suggests the experimental guidelines to evaluate the electro-mechanical safety of belt type equipment. The electro-mechanical safety was determined by using the International Electrotechnical Commission guidelines, which are widely used as important factors for assessing the electro-mechanical safety of belt type equipment. However, the local guidelines on wearable healthcare sensors are currently not well-established. Therefore, safety guidelines suited for the actual circumstances in Korea are required, and this paper attempts to try a new experimental safety test procedure of the wearable healthcare sensor. This belt type device measures the electrocardiogram (ECG) and heart rates by attaching to the chest. Examination lists were selected by analyzing the common standards ofelectro-mechanical safety (IEC 60601-1) and environment tests (IEC 60068-1, IEC 60068-2) of home-healthcare equipment. The essential electrical safety, which was required for the RS300G3 as a medical device, was evaluated, and most of the examination lists were selected by considering the circumstances of the users. The device passed all the selected examinable lists that are applicable to the Korean environment. This study has limitations to estimate and to conduct electro-mechanical safety experiments because our study focused on the belt type of heart-rates equipment. We are not taking into account the overall electro-mechanical home-healthcare measurements. According to industrial and technological development, there are infinite possibilities for the advancement of home-healthcare equipment, so more examination lists for safety are being added in addition to what we have done.
    Healthcare informatics research. 03/2010; 16(1):30-5.
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    ABSTRACT: The purpose of this study was to review an implementation of u-Severance information system with focus on electronic hospital records (EHR) and to suggest future improvements. Clinical Data Repository (CDR) of u-Severance involved implementing electronic medical records (EMR) as the basis of EHR and the management of individual health records. EHR were implemented with service enhancements extending to the clinical decision support system (CDSS) and expanding the knowledge base for research with a repository for clinical data and medical care information. The EMR system of Yonsei University Health Systems (YUHS) consists of HP integrity superdome servers using MS SQL as a database management system and MS Windows as its operating system. YUHS is a high-performing medical institution with regards to efficient management and customer satisfaction; however, after 5 years of implementation of u-Severance system, several limitations with regards to expandability and security have been identified.
    Healthcare informatics research. 03/2010; 16(1):60-4.
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    ABSTRACT: Main objective of this pilot study was to present a method to convenient monitoring of detailed ambulatory movements in daily life, by use of a portable measurement device employing single tri-axial accelerometer. In addition, the purpose of this review article is to provide researchers with a guide to understanding some commonly-used accelerometers in physical activity assessment. Specially, we implemented a small-size wearable data storing system in real time that we used Micro SD-Memory card for convenient and long period habitual physical activity monitoring during daily life. Activity recognition on these features was performed using Fuzzy c means classification algorithm recognized standing, sitting, lying, walking and running with 99.5% accuracy. This study was pilot test for our developed system’s feasibilities. Further application of the present technique may be helpful in the health promotion of both young and elderly.
    01/2010;
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    Lecture Notes in Engineering and Computer Science. 01/2009;
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    ABSTRACT: The aim of this paper is to develop nonintrusive type ECG monitoring system based on active electrode with conductive fabric. Our developed electrode can measure ECG signal without the electrolyte gel or the adhesives causing skin trouble. For the stable measurement of ECG signal, the buffer amplifier with high input impedance and the noise bypassing shield with conductive fabric were developed. This system involves real-time ECG signal monitoring, and wireless communication using the Zigbee protocol. We show experimental results for developing wearable ECG monitoring system and demonstrate how it can be applied to the design of nonintrusive electrode with conductive fabric.
    Human-Computer Interaction. Ambient, Ubiquitous and Intelligent Interaction, 13th International Conference, HCI International 2009, San Diego, CA, USA, July 19-24, 2009, Proceedings, Part III; 01/2009
  • Sun Kook Yoo, Kwanghyun Lee, Moon H Lee
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    ABSTRACT: It is important to consider electrocardiogram (ECG) data compression that does not sacrifice diagnostic quality significantly before applying ECG data compression to mobile telecardiology applications. In this paper, we assessed the reconstructed ECG quality after compression with a wavelet-based low-delay algorithm, using both subjective and objective indices. We included diverse ECG databases including both normal and abnormal ECG data, and evaluated the relationship between the subjective and objective indices, paying close attention to specific cases in which there was a large discrepancy between the objective and subjective quality. Based on our observations, an empirically determined compression ratio can be applied to compress continuous ECG signals in limited-bandwidth mobile telecardiology applications.
    Telemedicine and e-Health 04/2008; 14(2):156-63. · 1.40 Impact Factor
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    ABSTRACT: Mobile computing system using mobile Web Services now supports advanced methods for application integration through the internet at distributed computing environments. Mobile Web Services on mobile networks is the foundation for ubiquitous healthcare that gives patients better medical services anytime and anywhere. However, available existing web contents are mainly used for desktops on wired networks, but are not yet compatible with mobile Web Services. in this paper, we suggested the cooperative mobile healthcare information support system. The designed system can achieve the advanced inquiring manner of medical information for collaborate diagnosis at both desktop and mobile machines, and also afford to support wider accessibility of users over wireless and wired network environments.
    Cooperative Design, Visualization, and Engineering, 4th International Conference, CDVE 2007, Shanghai, China, September 16-20, 2007, Proceedings; 01/2007
  • Ubiquitous Computing Systems, Third International Symposium, UCS 2006, Seoul, Korea, October 11-13, 2006, Proceedings; 01/2006
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    ABSTRACT: As part of an ongoing investigation into the development of a dental digital radiographic (DDR) system using a complementary metal-oxide semiconductor (CMOS) sensor, this study developed hardware and software with a graphical user interface to acquire and display intra-oral images from a prototype DDR system. The aim of this study was to develop a DDR system using a CMOS sensor and evaluate its characteristics. Electrical signals that were generated by the CMOS sensor were transformed into digital images by a control computer equipped using a USB board. The distance between the X-ray tube and the CMOS sensor was adjusted within the range of 10-40 cm to provide the optimal image quality. In order to evaluate the image quality according to variations in the dose, phantom images (60 kVp, 7 mA) were obtained at exposure times of 0.03, 0.05, 0.08, 0.10, and 0.12 s, and the signal-to-noise ratio (SNR) was calculated from the phantom image data. The modulation transfer function (MTF) was obtained from a Fourier transform of the line spread function, which was itself derived from the edge spread function of a sharp edge image acquired using the exposure conditions of 60 kVp, 7 mA, and 0.08 s exposure time. The best contrast and focus were obtained at 20 cm. The SNR level was found to increase with increasing exposure time ranging from 0.03 to 0.08 s. The results obtained at 10% of the MTF showed that the resolution of the DDR system was approximately 6.2 line pairs per millimeter. The characteristics of the prototype DDR system have potential applications in intra-oral dental radiographic imaging. The fully developed DDR system can be used for making a clinical diagnosis with further improvements in the acquisition time and spatial resolution.
    IEEE Transactions on Nuclear Science 03/2005; · 1.22 Impact Factor
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    ABSTRACT: In order to build a human-computer interface that is sensitive to a user’s expressed emotion, we propose a neural network based emotion estimation algorithm using heart rate variability (HRV) and galvanic skin response (GSR). In this study, a video clip method was used to elicit basic emotions from subjects while electrocardiogram (ECG) and GSR signals were measured. These signals reflect the influence of emotion on the autonomic nervous system (ANS). The extracted features that are emotion-specific characteristics from those signals are applied to an artificial neural network in order to recognize emotions from new signal collections. Results show that the proposed method is able to accurately distinguish a user’s emotion.
    Advances in Natural Computation, First International Conference, ICNC 2005, Changsha, China, August 27-29, 2005, Proceedings, Part I; 01/2005
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    ABSTRACT: High bit rate wireless cellular service using CDMA 1X-EVDO is now popular in Korea, particularly in urban areas, since it was launched commercially in 2002. This cellular service allows the real-time transmission of patient images and vital sign signals simultaneously in a moving ambulance application. In this paper, we designed a prototype emergency telemedicine system that can transfer both biological signal and patient motion video from a moving vehicle using a CDMA 1X-EVDO reverse link. To cope with the limited bandwidth of the reverse link (transmission bandwidth of cellular device) relative to the the forward link (receiving bandwidth), priority control between the vital sign and video images, frame rate control using MPEG-4 compression, and error control using automatic repeat request were incorporated into the application layer protocol of the designed prototype system. Many on-road experiments have been performed to evaluate the actual performance and to demonstrate the applicability in a real situation. In most cases, the biological signal and patient video images with reduced frame rate were successfully transmitted from the moving vehicle in urban areas.
    Computational Science and Its Applications - ICCSA 2005, International Conference, Singapore, May 9-12, 2005, Proceedings, Part II; 01/2005
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    ABSTRACT: The image display is an important component of the Picture Archiving and Communication System (PACS) and of digital imaging in general. In this paper, we assess the display performance of 32 different flat panel LCD devices, in terms of their reflection, luminance response, luminance uniformity, resolution, noise, veiling glare and color uniformity included in the tentative guidelines of the AAPM TG18 document version 8.1. We also report on the angular dependencies of luminance and contrast, which constitute one of the miscellaneous tests. The tools used included a telescopic photometer, which was also used as a colorimeter, an illuminance meter, light sources for the reflection assessment, light-blocking devices, and digital TG18 test patterns. The luminance ratio (LR), maximum luminance difference (ALmax) and deviation of contrast response with respect to that of DICOM GSDF were 379.2+/-61.0, 1.6+/-1.1%, and 4.84+/-0.58%, respectively. The maximum luminance nonuniformity was 9.2+/-3.9% for the 10% luminance of the TG18-UNL10 test pattern. In the luminance-based resolution test, the percent luminance difference (deltaL) at the center was 0.78+/-0.42%. In all cases of noise testing, the rectangular target in each square in the three quadrants was visible, as were all 15 targets, except for the smallest one, in each corner pattern and the center pattern. The glare ratio (GR) was 2350+/-1460. The average color uniformity parameter, delta(u',v'), across the display area of each display device was 0.002+/-0.001. Nevertheless, not all of the color uniformity parameters of the display devices associated with a workstation met the acceptance criteria. For 7 selected flat panel displays, the mean specular and diffuse reflection coefficients were 0.0061+/-0.0010 and 0.0017+/-0.0005 cd/m2 per lux, respectively. All of the test results conformed to the criteria recommended by AAPM TG18, indicating that the displays were fully acceptable for diagnostic image interpretation. The maximum viewing angle conforming to the DICOM 3.14 standard luminance responses with a 10% tolerance was found to be approximately 50 degrees in both directions along the vertical axis, 10 degrees in the upper direction and 20 degrees in the lower direction along the horizontal axis, and 20 degrees in the upper direction and 10 degrees in the lower direction along the diagonal axis. Therefore, a radiologist should interpret a displayed image by considering the physical characteristics of the narrow viewing angle of the AMLCD displays. The acceptance testing protocol described herein demonstrates the successful clinical implementation of the guidelines for the viewing conditions of medical displays, and if implemented with a QC program, can be used to determine when LCD devices used for diagnostic interpretation need to be upgraded.
    Medical Physics 08/2004; 31(7):2155-64. · 2.91 Impact Factor
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    ABSTRACT: This study evaluated the migration to full-PACS of medical image data archived using mini-PACS at two hospitals of the Yonsei University Medical Center, Seoul, Korea. A major concern in the migration of medical data is to match the image data from the mini-PACS with the hospital OCS (Ordered Communication System). Prior to carrying out the actual migration process, the principles, methods, and anticipated results for the migration with respect to both cost and effectiveness were evaluated. Migration gateway workstations were established and a migration software tool was developed. The actual migration process was performed based on the results of several migration simulations. Our conclusions were that a migration plan should be carefully prepared and tailored to the individual hospital environment because the server system, archive media, network, OCS, and policy for data management may be unique.
    Journal of Digital Imaging 07/2004; 17(2):100-8. · 1.10 Impact Factor
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    ABSTRACT: It is clinically important to examine the effect of the heart rate and its variation on the image quality and selection of the optimized window in coronary angiography using multidetector row CT (MDCT). This study performed contrast-enhanced coronary angiography using MDCT on 83 patients. Fifty-two cases with information on the heart rate available were enrolled in this study. The effect of heart rate and its variation were systemically analyzed. Two radiologists rated the image quality as follows: 4-excellent; 3-good; 2-fair; 1-bad. Cardiac cycle windows at 40% and 70% were routinely selected for image reconstruction. The optimized window was rated as 1 when a 40% reconstruction had a better quality than the 70% reconstruction, as 2 when the 40% reconstruction was the same as the 70% reconstruction, and as 3 when the 70% reconstruction was better than the 40% reconstruction. The image quality was more affected by a variation of the heart rate than by the high heart rate. The selection of the optimized reconstruction window for a good image quality was mostly affected by the heart rate and there was a tendency for the 40% phase reconstruction to have a better image quality than the 70% reconstruction at higher heart rates.
    IEEE Transactions on Nuclear Science 03/2004; · 1.22 Impact Factor