적응형 총변이 기법을 이용한 가우시안 잡음 제거 방법 : CBCT 치과 영상에 적용

김중혁(Joong-Hyuk Kim),김정채(Jung-Chae Kim),김기덕(Kee-Deog Kim),유선국(SunK. Yoo) 대한전자공학회 2012 電子工學會論文誌-SC (System and control) Vol.49 No.1

의료 영상의 획득하는 과정에서 발생하는 잡음은 영상판독 및 진단을 방해하는 요소로 작용한다. 이러한 잡음으로 오염된 영상으로부터 원본영상을 복원하기 위하여 R.O.F(L.Rudin, S Osher, E. Fatemi)에 의해서 제안된 총변이 최적화 알고리즘은 정규화와 적합도의 균형을 맞춰 잡음을 제거할 수 있는 방법이다. 그러나 잡음 제거율을 높이기 위한 반복연산을 수행하는 과정에서 발생하는 경계영역의 몽롱화 현상은 피할 수 없다. 본 논문에서는 총변이 최적화 알고리즘의 제어 파라미터를 잡음 분산과 영상의 지역분산 특성에 따라서 가변적으로 변환시켜 치아영상의 경계 영역의 왜곡을 최소화 하고 전체 영상의 잡음을 제거하고자 하였다. CBCT 치아영상 464장을 대상으로 제안된 알고리즘을 적용한 결과, 기존의 R.O.F가 제안한 방법에 비해 PSNR측면에서 약 3dB 정도 향상됨을 보였다. 또한 처리된 결과영상을 3D 볼륨으로 재구성하여 비교한 결과, 기존의 방법보다 치아모델의 경계영역이 더 잘 보존됨을 보여주었다. The noise generated in the process of obtaining the medical image acts as the element obstructing the image interpretation and diagnosis. To restore the true image from the image polluted from the noise, the total variation optimization algorithm was proposed by the R.O. F (L.Rudin, S Osher, E. Fatemi). This method removes the noise by fitting the balance of the regularity and fidelity. However, the blurring phenomenon of the border area generated in the process of performing the iterative operation cannot be avoided. In this paper, we propose the adaptive total variation method by mapping the control parameter to the proposed transfer function for minimizing boundary error. The proposed transfer function is determined by the noise variance and the local property of the image. The proposed method was applied to 464 tooth images. To evaluate proposed method performance, PSNR which is a indicator of signal and noise's signal power ratio was used. The experimental results show that the proposed method has better performance than other methods.

의료용 로봇 원격 응용을 위한 영상처리 시스템 개발

김주영,김중혁,김정채,김기덕,유선국,Kim, Joo Young,Kim, Joong Hyuk,Kim, Jung Chae,Kim, Kee Deog,Yoo, Sun K. 한국의학물리학회 2012 의학물리 Vol.23 No.4

본 논문에서는 원격제어가 가능한 의료용 로봇 응용을 위한 웹기반-영상처리 시스템을 구현하였다. 개발된 소프트웨어 시스템은 다양한 영상처리 모듈과 원격 제어동작 모듈로 계층적으로 구성되어 있으며, 계층적 구성은 상위계층의 복잡한 응용을 위한 확장성과 웹에서의 접근성을 만족하였다. 또한, 응용환경의 변화에 따른 처리된 영상의 표시, 전송, 저장 및 공유를 위하여 다양한 DICOM, VRML, CAD (STL) 파일형식을 지원하였다. 메시지를 기반으로 한 데이터 교환과 객체-지향 모듈과 오픈소스 기반의 소프트웨어 구성은 다양한 원격 의료 응용에 따른 다양한 요구조건에 맞는 효율적인 동적 조합이 가능할 것이다. In this paper, web-base image processing system has been implemented for remote-controlled medical robot applications. The developed software system was hierarchically composed of diverse image processing and remote operation modules, and the hierarchical composition was satisfied the expandability to higher level application and the accessibility over the web. It can also support diverse file formats including DICOM, VRML, and CAD(STL) to display, transmit, store and share the processed images depending on application environment. Message-based data exchange, object-oriented module and open-source based software configuration will enable the dynamic combination associated with diverse remote medical application requirements.

PSC범 교량의 교좌장치 교체시 상부구조물의 안전성평가에 관한 연구

박선규 ( Park Bun Kyu ),김중혁 ( Kim Joong Hyuk ) 한국구조물진단유지관리공학회 1997 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.1 No.1

Serviceability and durability deteriorates because of crack and corrosion, therefore, the bridge requires repair and maintenance in case of heavy loss, it is need to replace. At the same time, bearing is necessary to replace on the occasion of serious loss. Especially when bearing is needed to replace, it is necessary to lift deck to make enough space for work. At that time, the stress in deck varies because of the effect of displacement. The work should depend on experience. The reason is lack of technique and study on this field. Object of this study is to find the effect of displacement caused by oil jack which is necessary to life deck, and to show the direction in safe work.

주간사와 기관투자자간의 거래관계가 IPO 배정(Allocation)에 미치는 영향

정재웅 ( Jai Woong Chung ),김중혁 ( Joong Hyuk Kim ) 한국금융연구원 2015 금융연구 Vol.29 No.1

Prior studies focusing on the U.S. market show that underwriters favor certain institutional investors in IPO allocation due to various reasons explained by book-building hypothesis (e.g., Benveniste and Spindt, 1989; Benveniste and Wilhelm, 1990; Spatt and Srivastava, 1991 etc.), agency problem based hypothesis (e.g., Loughran and Ritter, 2002; Reuter, 2006; Ritter and Zhang, 2007 etc.) and so on. In this study, we examine if and how the strength of prior business relationship between underwriters and institutional investors affects IPO initial allocation in Korean market. To address the issue, we use monthly mutual fund holding information and IPOs listed in KOSDAQ market during 2002 to 2012. To our best knowledge, this is the first study that examines the IPO initial allocation in Korean market. Studies on IPO allocation generally suffer from data availability since the allocation data is not publicly available. They all used either quarterly or semi-annual mutual fund holding information to proxy for initial IPO allocation to institutional investors, which has clear limitation. We try to overcome the data limitation by using monthly mutual fund holding information for the first time in the literature and applying additional screening procedures to identify initial IPO allocation to mutual funds. We measure the strength of prior business relationship by (1) the total investment amount by each mutual fund in IPOs underwritten by each underwriter, (2) the number of participation by each mutual fund in IPOs underwritten by each underwriter, and (3) the average investment amount by each mutual fund in each IPO underwritten by an underwriter, based on prior one and two years of IPO participation information by each mutual fund. We find that about 78.4% of our IPO sample was allocated to mutual funds at the time of IPOs. The results show that underwriters allocate more IPOs to funds with stronger prior business relationship, especially when IPOs are more underpriced (positive initial returns). On the other hand, when IPOs are overpriced (negative initial returns), mutual funds with stronger prior relationship receive relatively less IPOs. On average, the higher institutional investors’ demands are, the smaller IPO allocation to individual fund is. However, even in IPOs with higher institutional investors` demands, mutual funds with stronger prior business relationship receive relatively more IPO allocation. In addition, consistent with Sherman and Titman (2002), we find that mutual funds that were allocated with overpriced IPOs (or IPOs with negative initial returns) in the past receive more underpriced IPOs in the current allocation. Park et al. (2011) argues that there is a higher probability that Korean securities firms allocate IPOs underwritten by themselves to their affiliated mutual funds. We find that underwriters, on average, allocate less IPO shares to affiliated funds. For underpriced IPOs, however, they allocate more shares to affiliated funds, which is consistent with the conflict of interests argument. Overall our results indicate that underwriters favor regular investors with stronger business relationship in IPO allocation in Korean market.

기업의 사회적 책임 활동, 조세회피와 기업가치

임현일 ( Hyun Il Lim ),김중혁 ( Joong Hyuk Kim ) 한국금융연구원 2015 금융연구 Vol.29 No.4

We examine the effects of tax avoidance on firm value and the role of corporate social responsibility (CSR) in the relationship between tax avoidance and firm value. The prior studies on the relationship between tax avoidance and firm value report mixed results using both the U.S. and Korean data. Thus, the effect of tax avoidance on firm value becomes an unresolved empirical question that requires more evidence to understand the issue better. In a separate strain of research, previous studies explain that corporate social responsibility (CSR) activities can reduce potential conflicts among various stakeholders of a firm and improve firm value in the long run (Stakeholder theory, e.g, Schwart, 1968; Bruyn, 1987). Prior studies also argue that CSR activities help firms build their good reputation and result in positive effects on various aspects of firm performance and valuation (e.g, Clarkson, 1995; Klein and Dawar, 2004; Spicer, 1978, Turban and Greening, 1997). In particular, Hanlon and Slemrod (2009) show that tax avoidance by firms that are expected to engage less in tax avoidance affects firm value less negatively. Thus, we expect that tax avoidance by firms who engage more actively in CSR will affect firm value differently from those who are less active in CSR. In this study, using Korean firms listed in KOSPI between 2004 to 2011, we attempt to shed another light on the unresolved issue: effects of tax avoidance on firm value. In addition, we examine how active engagement in CSR activities affect this relationship. We use Korea Economic Justice Institute Index (KEJI Index) as a proxy for the degree of CSR activities. Our results confirm that tax avoidance affects firm value negatively, supporting the agency problem based argument in the literature. However, we find that the negative effect on firm value from tax avoidance can be alleviated when a firm actively engage in CSR activities. Moreover, the alleviating effect becomes greater when a firm consistently, not just temporarily, engages actively in CSR activities, and when a firm increases CSR activities. These results are robust when we use different measures for tax avoidance and the degree of CSR activity and even when we control for firm fixed effects and potential endogeniety problem using system GMM method.

What determines the Pricing of underwriting services in Korean IPO Market?

안옥화 ( Ok Hwa Ahn ),김중혁 ( Joong Hyuk Kim ),손판도 ( Pan Do Son ) 한국증권학회 2006 한국증권학회 발표논문집 Vol.2006 No.4

척추외과 의사의 직업성 근골격계 질환

최성우(Sung-Woo Choi),이재철(Jae Chul Lee),장해동(Hae-Dong Jang),전민철(Min-Chul Jeon),김중혁(Joong Hyuk Kim),김충현(Chung-Hyun Kim),박수연(Suyeon Park),신병준(Byung-Joon Shin) 대한정형외과학회 2016 대한정형외과학회지 Vol.51 No.6

목적: 척추외과 의사들의 근골격계 질환의 유병률과 발생 위험요소를 조사하고자 한다. 대상 및 방법: 근골격계 질환에 대한 수정된 discomfort survey를 사용한 설문지를 대한척추외과학회 회원들에게 e-mail로 발송하였다. 설문지의 구성은 인류사회학적 요소, 수술 업무 관련 요소, 근골격계 질환 관련 요소로 이루어졌다. 근골격계 질환의 호발 부위와 발생 위험요소에 대하여 조사하였다. 결과: 총 대상자 420명 중 80명(19.0%)이 응답하였다. 78.8%에서 최근 1년 동안 수술로 인한 근골격계 통증이 있었고, 흔히 발생하는 부위는 목(52.5%), 허리(46.3%), 어깨(18.8%)였다. 척추 수술 집도 개수가 많은 군(>200건/year)에서 그렇지 않은 군보다 주관절/전완부 통증이 많았고(p=0.033), 대수술을 많이 시행하는 군(>10건/year)에서 그렇지 않은 군보다 손목/손의 통증(p=0.008)과 허리의 통증이 더 많았다(p=0.042). 결론: 척추외과 의사들의 78.8%에서 최근 1년 동안 수술로 인한 근골격계 통증이 있었고, 일반인과 비교하였을 때 높은 유병률을 보였다. 이런 현 상태에 대한 정확한 인식과 척추외과 의사들의 근골격계 질환의 예방에 대해 많은 관심이 필요하다. Purpose: To investigate the prevalence and risk factors of musculoskeletal disorder (MSD) among spine surgeons. Materials and Methods: A modified version of discomfort survey was sent via e-mail to surgeons that belong to the Korean Society of Spine Surgery. The survey questionnaires were composed of demographics, factors relating to spine surgery, and MSD. We investigated the common sites of occurrence of MSD and its risk factors. Results: The survey was sent to a total of 420 subjects; of which, 80 subjects (19.0%) responded. About 78.8% of the respondents had MSD for the past year. The common sites of occurrence included the neck (52.5%), back (46.3%), and shoulder (18.8%). The prevalence of pain in the elbow joint/forearm was higher in the group performing a higher frequency of spine surgeries (p=0.033). Moreover, the prevalence of pain in the wrist/hand (p=0.008) and in the back (p=0.042) was higher in those with greater frequency of major surgeries (>10 case/year) as compared with those with lower frequency of major surgeries. Conclusion: As shown, about 78.8% of spine surgeons experienced MSD for the past one year. Its prevalence was higher as compared with the general population. Thus, more attention should be paid to the prevention of MSD among spine surgeons.