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오동인,백상민,이재상,우응제 대한의용생체공학회 2004 의공학회지 Vol.25 No.4
인체내부의 각 조직은 서로 다른 저항률(resistivity)분포를 가지며, 조직의 생리학적, 기능적 변화에 따라 임피던스가 변화한다. 본 논문에서는 주로 기능적 영상을 위한 임피던스 단층촬영 (EIT, electrical impedance tomography) 시스템의 설계와 구현 결과를 기술한다. EIT 시스템은 인체의 표면에 부착한 전극을 통해 전류를 주입하고 이로 인해 유기되는 전압을 측정하여, 내부 임피던스의 단층영상을 복원하는 기술이다. EIT 시스템의 개발에 있어서는 영상복원의 난해함과 아울러 측정시스템의 낮은 정확도가 기술적인 문제가 되고 있다. 본 논문은 기존 EIT 시스템의 문제점을 파악하고 디지털 기술을 이용하여 보다 정확도가 높고 안정된 시스템을 설계 및 제작하였다. 크기와 주파수 및 파형의 변화 가능한 50KHz의 정현파 전류를 인체에 주입하기 위해 필요한 정밀 정전류원을 설계하여 제작한 결과, 출력 파형의 고조파 왜곡(THD, total harmonic distortion)이 0.0029%이고 진폭 안정도가 0.022%인 전류를 출력 할 수 있었다. 또한, 여러개의 정전류원을 사용함으로써 채 널간 오차를 유발하던 기존의 시스템을 변경하여, 하나의 전류원에서 만들어진 전류를 각 채널로 스위칭하여 공급함으로써 이로 인한 오차를 줄였다. 주입전류에 의해 유기된 전압의 정밀한 측정을 위해 높은 정밀도를 갖는 전압측정기가 필요하므로 차동증폭기, 고속 ADC및 FPGA(field programmable gate array)를 사용한 디지털 위상감응복조기 (phase-sensitive demodulator )를 제작하였다. 이때 병렬 처리를 가능하게 하여 모든 전극 채널에서 동시에 측정을 수행 할 수 있도록 하였으며, 제작된 전압측정기의 SNR(signal-to-noise ratio)은 90dB 이다. 이러한 EIT 시스템을 사용하여 배경의 전해질 용액에 비해 두 배의 저항률을 가지는 물체(바나나)에 대한 기초적인 영상복원 실험을 수행하였다. 본 시스템은 16채널로 제작되었으나 전체를 모듈형으로 설계하여 쉽게 채널의 수를 늘릴 수 있는 장점을 가지고 있어서 향후 64채널 이상의 디지털 EIT시스템을 제작할 계획이며, 인체 내부의 임피던스 분포를 3차원적 으로 영상화하는 연구를 수행 할 예정이다. Different biological tissues have different values of electrical resistivity. In EIT (electrical impedance tomography), we try to provide cross-sectional images of a resistivity distribution inside an electrically conducting subject such as the human body mainly for functional imaging. However, it is well known that the image reconstruction problem in EIT is ill-posed and the quality of a reconstructed image highly depends on the measurement error. This requires us to develop a high-performance EIT system. In this paper, we describe the development of a 16-channel digital EIT system including a single constant current source, 16 voltmeters, main controller, and PC. The system was designed and implemented using the FPGA-based digital technology. The current source injects 50KHz sinusoidal current with the THD (total harmonic distortion) of 0.0029% and amplitude stability of 0.022%. The single current source and switching circuit reduce the measurement error associated with imperfect matching of multiple current sources at the expense of a reduced data acquisition time. The digital voltmeter measuring the induced boundary voltage consists of a differential amplifier, ADC, and FPGA (field programmable gate array). The digital phase-sensitive demodulation technique was implemented in the voltmeter to maximize the SNR (signal-to-noise ratio). Experimental results of 16-channel digital voltmeters showed the SNR of 90dB. We used the developed EIT system to reconstruct resistivity images of a saline phantom containing banana objects. Based on the results, we suggest future improvements for a 64-channel muff-frequency EIT system for three-dimensional dynamic imaging of bio-impedance distributions inside the human body.
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도전율 및 유전율이 다른 병소의 검출을 위한 320-채널 다주파수 Trans-Admittance Scanner(TAS)
오동인,이민형,김희진,우응제,Oh, Tong-In,Lee, Min-Hyoung,Kim, Hee-Jin,Woo, Eung-Je 대한의용생체공학회 2007 의공학회지 Vol.28 No.1
In order to collect information on local distribution of conductivity and permittivity underneath a scan probe, we developed a multi-frequency trans-admittance scanner (TAS). Applying a sinusoidal voltage with variable frequency on a chosen distal part of a human body, we measure exit currents from 320 grounded electrodes placed on a chosen surface of the subject. The electrodes are packaged inside a small and light scan probe. The system includes one voltage source and 17 digital ammeters. Front-end of each ammeter is a current-to-voltage converter with virtual grounding of a chosen electrode. The rest of the ammeter is a voltmeter performing digital phase-sensitive demodulation. Using resistor loads, we calibrate the system including the scan probe to compensate frequency-dependent variability of current measurements and also inter-channel variability among multiple. We found that SNR of each ammeter is about 85dB and the minimal measurable current is 5nA. Using saline phantoms with objects made from TX-151, we verified the performance of the lesion estimation algorithm. The error rate of the depth estimation was about 19.7%. For the size estimate, the error rate was about 15.3%. The results suggest improvement in lesion estimation algorithm based on multi-frequency trans-admittance data.
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오동인,조성필,김상민,구환,우응제,Oh, Tong-In,Cho, Seong-Phil,Kim, Sang-Min,Koo, Hwan,Woo, Eung-Je 대한의용생체공학회 2007 의공학회지 Vol.28 No.1
We have developed a multi-channel, multi-frequency EIT system with operating frequency of 10Hz to 500KHz. The number of digital voltmeters using phase-sensitive demodulation can be varied from 8 to 64 and we found that 16 and 32-channels are most practical. This paper describes the design, implementation, and construction of 16 and 32-channel systems. The performance of the system was thoroughly tested and we found that CMRR of the developed voltmeter is about 85dB with $100{\Omega}$ unbalancing series resistor. The SNR is greater than 99.6dB and the output impedance of the constant current source is $1{\Omega}W$ at least for all frequencies. Imaging experiments using a banana with frequency-dependent conductivity and permittivity show that frequency-difference imaging is possible using the developed system. Future works of animal and human experiments are discussed.
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오동현,박지은,이언숙,오상우,조성일,장숙랑,백현욱 대한내과학회 2012 The Korean Journal of Internal Medicine Vol.27 No.4
Background/Aims: Falls among older people are a major public health problem and may result in fracture, medical complications that require hospitalization, and fear of additional falls. Given the prevalence and impact of the fear of falling again, reducing the incidence of falls is important to prevent additional falls. This study analyzed whether exercise programs decrease the fear of future falls in elderly patients who have fallen previously. Methods: A randomized controlled study was performed that included 65 elderly community-dwelling subjects who had fallen in the previous year. Subjects were randomized into two groups: an exercise group (EG, n = 36) and a control group (CG, n = 29). The EG participated in three exercise sessions per week for 12 weeks. Muscle strength, balance, agility, flexibility, and muscular endurance were measured at baseline and after 12 weeks. Results: After the 12-week exercise program, the subjects in the EG demonstrated remarkable improvement in their walking speed, balance (p = 0.003), back strength (p = 0.08), lower extremity strength (p = 0.004), and flexibility (p < 0.001). When asked whether they were afraid of falling, more participants in the EG than in the CG responded “not at all” or “a little.”Conclusions: The 12-week exercise program described here reduced the fear of falling (p = 0.02). It also improved the balance, flexibility, and muscle strength of the participants and was associated with improved quality of life.
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吳東晟 한국중국언어문화연구회 2008 한중언어문화연구 Vol.- No.16
作者簡介 : 吳東晟 (Tung-cheng WU), 1977年生,臺灣南投人。現為成功大學中文所博士生,成功大學中文系、實踐大學高雄校區博雅學部兼任講師,《藍星詩學季刊》執行編輯,瀛社社員。創作領域兼賅新舊文學。著有現代詩集《上帝的香煙》、古典詩集《愛悔集》、現代詩讀本《織錦入春闈》(合著)、編有《臺灣詩道─府城詩選》(合編)。 內容題要 : 余光中是臺灣當代首屈一指的重要詩人,其詩歌創作取材豐富多元,其中地理書寫更是其一貫關心之主題。這個主題在余光中遷居高雄以後,表現得特別明顯。余光中的地理書寫,有以詩傳地之企圖,他透過大量詩歌的浸染、以及生活於斯地的實踐,將詩人的光輝銘刻於土地之上。本文以余光中的詩歌為觀察對象,探討其詩歌地理書寫的具體內容及文化意涵。
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