• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.372-377
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• 2007

For more than 2,500 years, surgical teaching has been based on the so called "see one, do one, teach one" paradigm, in which the surgical trainee learns by operating on patients under close supervision of peers and superiors. However, higher demands on the quality of patient care and rising malpractice costs have made it increasingly risky to train on patients. Minimally invasive surgery, in particular, has made it more difficult for an instructor to demonstrate the required manual skills. It has been recognized that, similar to flight simulators for pilots, virtual reality (VR) based surgical simulators promise a safer and more comprehensive way to train manual skills of medical personnel in general and surgeons in particular. One of the major challenges in the development of VR-based surgical trainers is the real-time and realistic simulation of interactions between surgical instruments and biological tissues. It involves multi-disciplinary research areas including soft tissue mechanical behavior, tool-tissue contact mechanics, computer haptics, computer graphics and robotics integrated into VR-based training systems. The research described in this paper addresses the problem of characterizing soft tissue properties for medical virtual environments. A system to measure in vivo mechanical properties of soft tissues was designed, and eleven sets of animal experiments were performed to measure in vivo and in vitro biomechanical properties of porcine intra-abdominal organs. Viscoelastic tissue parameters were then extracted by matching finite element model predictions with the empirical data. Finally, the tissue parameters were combined with geometric organ models segmented from the Visible Human Dataset and integrated into a minimally invasive surgical simulation system consisting of haptic interface devices and a graphic display.

• Journal of Periodontal and Implant Science
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• 제53권3호
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• pp.207-217
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• 2023

Purpose: Non-crosslinked and crosslinked collagen membranes are known to exhibit distinct degradation characteristics, resulting in contrasting orientations of the adjacent tissues and different biological processes. The aim of this study was to conduct a histomorphometric assessment of non-crosslinked and crosslinked collagen membranes regarding neovascularization, tissue integration, tissue encapsulation, and biodegradation. Methods: Guided bone regeneration was performed using either a non-crosslinked (BG) or a crosslinked collagen membrane (CM) in 15 beagle dogs, which were euthanized at 4, 8, and 16 weeks (n=5 each) for histomorphometric analysis. The samples were assessed regarding neovascularization, tissue integration, encapsulation, the remaining membrane area, and pseudoperiosteum formation. The BG and CM groups were compared at different time periods using nonparametric statistical methods. Results: The remaining membrane area of CM was significantly greater than that of BG at 16 weeks; however, there were no significant differences at 4 and 8 weeks. Conversely, the neovascularization score for CM was significantly less than that for BG at 16 weeks. BG exhibited significantly greater tissue integration and encapsulation scores than CM at all time periods, apart from encapsulation at 16 weeks. Pseudoperiosteum formation was observed in the BG group at 16 weeks. Conclusions: Although BG membranes were more rapidly biodegraded than CM membranes, they were gradually replaced by connective tissue with complete integration and maturation of the surrounding tissues to form dense periosteum-like connective tissue. Further studies need to be performed to validate the barrier effect of the pseudoperiosteum.

• Journal of Genetic Medicine
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• 제2권1호
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• pp.31-34
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• 1998

The N-methylpurine-DNA glycosylase (MPG), a ubiquitous DNA repair enzyme, removes N-methylpurine and other damaged purines induced in DNA. Tissue-specific mRNA levels of the N-methylpurine-DNA glycosylase (MPG) were investigated in Balb/c mice of four different growing stages; newborn, 1, 4 and 8-weeks postpartum. MPG expressions in the newborn and the 8-week-old mice were the highest in thymus and testis, respectively. The tested tissues of the newborn mice had consistently higher MPG mRNA level than 8-week-old adults except in testis and thymus. The MPG mRNA level in testis was the lowest in the newborn mice, but it attained the highest in the 8-week-old mice. The levels of MPG mRNA among the different tissues in the newborn and the 8-week-old mice were more than 9.0 and 19.0-fold respectively. These results suggest that the of MPG expression was dependent on the growing stage and had tissue-specificity.

• Journal of Chest Surgery
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• 제24권11호
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• pp.1074-1080
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• 1991

A total and consecutive 62 patients between 13 and 58 years of age receiving biological prosthetic heart valves at the Korea University Hospital from January 1978 through October 1983 were analyzed. Out of 71 valves replaced, 64 were Carpentier-Edwards valves, 4 were Ionescu-Shiley valves, 2 were Angell-Shiley valves, 1 was Hancock valve. Early mortality within 30 days after operation was noted in 4 cases[6.4%]. There were no cases of valve-related early death. The 58 early survivors were followed-up for a total 387 patient-year over a period of 3 years to 12 years[Mean$\pm$S.D: 6.37$\pm$2.51 years] at the follow-up end of April 1991. During follow-up, seven patients died and late mortality rate was 12%. There were two major late complications: the one is thromboembolism[1.6% /patient-year], the other is primary tissue failure[2.76% /patient-year]. Ten patients underwent re-replacement of 13 tissue valves because of primary tissue failure[nine Carpentier-Edwards, two Ionescu-Shiley, two Angell-Shiley]. There was operative mortality. The probabilities of freedom from primary tissue failure were 95.4% and 75.3% at 5 and 10 years after operation respectively, The actuarial survival rates were 86.2% and 81.8% at 5 and 10 years after initial surgery respectively.

• 대한의용생체공학회:의공학회지
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• 제14권1호
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• pp.31-40
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• 1993

It is well known that nonlinear propagation characteristics of the wave in the tissue may give very useful information for the medical diagnoisis. In this paper, a new method to detect nonlinear propa gation characteristics of the internal vibration in the tissue for the low frequency mechanical vibra lion by using bispectral analysis is proposed. In the method, low frequency vibration of $f_0(=100Hz)$ is applied on the surface of the object, and the waveform of the internal vibration ${\times}{\;}(t)$ is measured from Doppler frequency modulation of silmultaneously transmitted probing ultrasonic waves. Then, the bispectra of the signal ${\times}{\;}(t.)$ at the frequencies ($f_0,{\;}f_0$) and ($f_0,{\;}2f_0$) are calculated to estimate the nonlinear propagation characteristics as their magnitude ratio, where since bispectrum is free from the gallssian additive noise we can get the value with high S/N. Basic experimental system is con structed by using 3.0 MHz probing ultrasonic waves and the several experiments are carried out for some phantoms. Results show the superiority of the proposed method to the conventional method using power spectrum and also its usefulness for the tissue characterization.

• 대한의용생체공학회:의공학회지
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• 제10권2호
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• pp.165-172
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• 1989

본 논문에서는 초음파 반사신호에 내포되어 있는 정량적인 정보로부터 감쇠계수, 전파속도 파라메타를 매개로 조직의 온도특성에 대해 검토하고 이를 기초로 무침습적인 심부 온도추정의 가능성에 대해서 고찰하였다. 실험에 사용한 기초시료는 아크릴과 돼지의 근육, 간, 지방이며 온도분해능이 $0.25^{\circ}C$이하로 조절되는 항은수조를 제작하여 시료의 온도를 변화시켰다. 일련의 실험을 통하여 조직의 온도변화에 따른 초음파 파라메타의 변화가 근시적 선형성을 가짐이 확인되었으며 이는 표준적인 실험조건과 기준치의 설정을 전제로 무침습적 심부 온도추정이 가능함을 시사하는 것이다.

• 전자공학회논문지T
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• 제36T권2호
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• pp.70-76
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• 1999

최근에 휴대전화기가 저 연령층까지 널리 보급되어 어린이들의 두부내에 열점(hot-spot)형성문제가 염려되고 있는 실정이다. 전자파의 인체영향이 체온상승의 열적작용에 의한 것이라고 생각한다면 휴대전화기에 의해 발생하는 두부내 국소SAR의 인체영향도 두부의 온도상승과 연관된다고 추정된다. 본 논문은 휴대전화기를 실사용 상황에서 시간대별 두부의 국소부위에 대한 온도변화를 측정하였다. 그 결과 휴대전화기의 통화시작점에서 계속적인 온도상승을 보이다가 통화가 끝나는 시점에서 두부의 국소적인 온도변화는 빠르게 회복되지만 생체전신의 평균온도는 상승함을 알 수 있었다.

• Smart Structures and Systems
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• 제7권3호
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• pp.213-222
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• 2011

The native extracellular matrix (ECM) consists of an integrated fibrous protein network and proteoglycan-based ground (hydrogel) substance. We designed a novel electrospinning technique to engineer a three dimensional fiber-hydrogel composite that mimics the native ECM structure, is injectable, and has practical macroscale dimensions for clinically relevant tissue defects. In a model system of articular cartilage tissue engineering, the fiber-hydrogel composites enhanced the biological response of adult stem cells, with dynamic mechanical stimulation resulting in near native levels of extracellular matrix. This technology platform was expanded through structural and biochemical modification of the fibers including hydrophilic fibers containing chondroitin sulfate, a significant component of endogenous tissues, and hydrophobic fibers containing ECM microparticles.

• 대한의용생체공학회:의공학회지
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• 제27권3호
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• pp.117-124
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• 2006

Recently, active research has been going on to measure the elastic modulus of human soft tissue with medical ultrasound imaging systems for the purpose of diagnosing cancers or tumors which have been difficult to detect with conventional B-mode imaging techniques. In this paper, a real-time ultrasonic elasticity imaging system is implemented in software on a Pentium processor-based ultrasonic diagnostic imaging system. Soft tissue is subjected to external vibration, and the resulting tissue displacements change the phase of received echoes, which is in turn used to estimate tissue elasticity. It was confirmed from experiment with a phantom that the implemented elasticity imaging system could differentiate between soft and hard regions, where the latter is twice harder than the former, while operating at an adequate frame rate of 20 frames/s.

• 대한의용생체공학회:의공학회지
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• 제28권2호
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• pp.169-173
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• 2007

During laser irradiation, mechanically deformed cartilage undergoes a temperature dependent phase transformation resulting in accelerated stress relaxation. Clinically, laser-assisted cartilage reshaping may be used to recreate the underlying cartilaginous framework in structures such as ear, larynx, trachea, and nose. Therefore, research and identification of the biophysical transformations in cartilage accompanying laser heating are valuable to identify critical laser dosimetry and phase transformation of cartilage for many clinical applications. quasi-elastic light scattering was investigated using Ho : YAG laser $(\lambda=2.12{\mu}m\;;\;t_p\sim450{\mu}s)$ and Nd:YAG Laser $(\lambda=1.32{\mu}m\;;\;t_p\sim700{\mu}s)$ for heating sources and He : Ne $(\lambda=632.8nm)$ laser, high-power diode pumped laser $(\lambda=532nm)$, and Ti : $Al_2O_3$ femtosecond laser $(\lambda=850nm)$ for light scattering sources. A spectrometer and infrared radiometric sensor were used to monitor the backscattered light spectrum and transient temperature changes from cartilage following laser irradiation. Analysis of the optical, thermal, and quasi-elastic light scattering properties may indicate internal dynamics of proteoglycan movement within the cartilage framework during laser irradiation.