• 대한디지털의료영상학회논문지
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• 제14권2호
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• pp.57-61
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• 2012

To compare the accuracy of breath-hold magnetic resonance imaging sequences to establish the most effective superparamagnetic iron oxide-enhanced sequence for detection of hepatic metastases. A total of 100 patients(50men and 50women, mean age: 60years) with liver disease(including malignant and benign liver lesions) were investigated at 3.0T machine (GE, General Electric Medical System, Excite HD) with 8Ch body coil. Pulse sequence for MR imaging decided to the FS-T2-FSE-RT(TR/TE/Thick./Freq./Phase=12857ms/100ms/7mm/512/384), MGRE(TR/TE/Thick./Freq./Phase=100ms/9.7ms/7mm/384/288), in-out of phase echo(TR/$TE_1$, $TE_2$/Thick./Freq./Phase=140ms/2.4, 5.8ms/7mm/352/300), Images obtained before the injection of SPIO. Six sequences were optimized for lesion detection: FS-T2-FSE-RT, multigradient recalled echo data image(MGRE), T2-weighted MGRE with an 9.7msec echo time. Images were reviewed independently by five blinded observers. The accuracy of each sequence was measured by using picture archiving communication system analysis. All results were correlated with findings at multidectator computed tomography examination. Differences between the mean results of the six observers were measured by using paired student t-test analysis. Postcontrast T2-weighted MGRE sequences were the most accurate and were significantly superior to postcontrast FS-T2-FSE-RT, T2-weighted MGRE, in-out of phase MR sequences(p < .05). For all lesions that were malignant or smaller than 1 cm, respectively, contrast to noise ratio of pre and postcontrast sequences were -1and -0.3 for T2-weighted FSE, 0.53 and 4.5 in-out of phase, 7, 7.08, 5.08, 3.32, 1.7, 1.16, 0.79, 0.68 for GRE with 2.9, 7.5, 12.1, 16.6, 21.2, 25.8, 30.4, 35.0 TE values. Breath-hold various TE precontrast sequences offer improvement in sensitivity compared with fixed multigradient recalled echo sequences alone.

• 한국통신학회논문지
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• 제28권10A호
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• pp.816-829
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• 2003

본 논문에서는 동일 상관 신호군을 이용하는 M-ary UWB (Ultra Wide Band) 다원 접속 시스템에서 PN(Pseudo Noise) 부호 기반의 시간 도약 시퀀스를 이용하는 경우의 성능을 평가하였다. 특히 심벌 수 M이 증가해도 신호 펄스열의 길이가 변화하지 않아 M에 관계없이 동일 심벌 전송률을 갖게 되는 M-ary UWB 시스템 (시스템 #1)과 신호 펄스열의 길이가 M의 증가에 따라 확장되어 M이 증가하여도 동일 비트 전송률을 갖게 되는 M-ary UWB 시스템 (시스템 #2)을 모두 고려하여, UWB 실내 무선 다중 경로 채널 하에서의 심벌오율 성능을 이상적인 랜덤 시간 도약 시퀀스를 적용한 다원 접속 시스템의 성능과 비교 분석하였다. 모의 실험 결과, PN 부호 기반의 시간 도약 시퀀스가 이상적인 랜덤 시퀀스와 거의 유사한 매우 우수한 성능을 나타냄을 알 수 있었다. 또한, 심벌수가 증가함에 따라 시스템 #2의 경우가 시스템 #1의 경우보다 다원 접속 간섭에 대한 강인성 측면에 있어서 월등히 우수함을 확인하였다.

• 대한의용생체공학회:의공학회지
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• 제24권4호
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• pp.275-280
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• 2003

일반적으로 MR Angiography(MRI)는 사전 포화방법(presaturation)을 이용하여 동맥과 정맥의 분리된 영상을 획득한다. 하지만 이러한 일반적인 사전포화방법으로 동맥과 정맥영상을 획득하기 위해서는 두 번의 영상획득이 필요하다. 따라서 본 연구에서는 동맥과 정맥의 구분된 영상을 한번의 영상획득으로 얻을 수 있는 SAAV 기법을 0.3T MRI system에 적용하고, 획득한 동맥과 정맥의 두 MRA 영상을 Colot-Mapping으로 동$.$정맥을 한 영상에 구분하여 나타냄으로써 0.3T MRI system에서 MRI의 임상적 적용 및 활용 가능성을 높이고자 하였다. 마산 삼성병원의 0.3T MRI system (Magfinder, AILab. Korea)어서 SAAV sequence를 이용하여 정상적인 피험자로부터 목 부위의 동맥과 정맥 혈관영상 (volume : 256${\times}$256${\times}$64)을 동시에 얻었다. 그리고. 이들의 각 2D 영상들에서 위치정보를 획득한 후 MIP 기법과 Color Mapping으로 조합하여 3D Artery-Vein Color Mapping(AVCM) MRA 영상으로 재구성하였다.

• Korean Journal of Radiology
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• 제22권5호
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• pp.782-791
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• 2021

Objective: To evaluate the signal intensity of the periosteum using ultrashort echo time pulse sequence with three-dimensional cone trajectory (3D UTE) with or without fat suppression (FS) to distinguish from artifacts in porcine tibias. Materials and Methods: The periosteum and overlying soft tissue of three porcine lower legs were partially peeled away from the tibial cortex. Another porcine tibia was prepared as three segments: with an intact periosteum outer and inner layer, with an intact periosteum inner layer, and without periosteum. Axial T1 weighted sequence (T1 WI) and 3D UTE (FS) were performed. Another porcine tibia without periosteum was prepared and subjected to 3D UTE (FS) and T1 WI twice, with positional changes. Two radiologists analyzed images to reach a consensus. Results: The three periosteal tissues that were partially peeled away from the cortex showed a high signal in 3D UTE (FS) and low signal on T1 WI. 3D UTE (FS) showed a high signal around the cortical surface with an intact outer and inner periosteum, and subtle high signals, mainly around the upper cortical surfaces with the inner layer of the periosteum and without periosteum. T1 WI showed no signal around the cortical surfaces, regardless of the periosteum state. The porcine tibia without periosteum showed changes in the high signal area around the cortical surface as the position changed in 3D UTE (FS). No signal was detected around the cortical surface in T1 WI, regardless of the position change. Conclusion: The periosteum showed a high signal in 3D UTE and 3D UTE FS that overlapped with artifacts around the cortical bone.

• 대한의용생체공학회:의공학회지
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• 제28권1호
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• pp.132-138
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• 2007

MR(magnetic resonance) image of moving organ such as heart shows serious distortion of MR image due to motion itself. To eliminate motion artifacts, MRI(magnetic resonance imaging) scan sequences requires a trigger pulse like ECG(electro-cardiography) R-wave. ECG-gating using cardiac cycle synchronizes the MRI sequence acquisition to the R-wave in order to eliminate image motion artifacts. In this paper, we designed ECG/PPG(photo-plethysmography) gating system which is for eliminating motion artifacts due to moving organ. This system uses nonmagnetic carbon electrodes, lead wire and shield case for minimizing RF(radio-frequency) pulse and gradient effect. Also, we developed a ECG circuit for preventing saturation by magnetic field and a finger plethysmography sensor using optic fiber. And then, gating pulse is generated by adaptive filtering based on NLMS(normalized least mean square) algorithm. To evaluate the developed system, we measured and compared MR imaging of heart and neck with and without ECG/PPG gating system. As a result, we could get a clean image to be used in clinically. In conclusion, the designed ECG/PPG gating system could be useful method when we get MR imaging of moving organ like a heart.

• 한국통신학회논문지
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• 제25권7A호
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• pp.943-950
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• 2000

본 논문에서는 실내 비방향성 분산채널에서 비동기 다중전송률 광무선 펄스위치변조기법을 적용한 부호분할다원 접속 시스템을 제안한다. 부호분할다원접속을 위한 시그너쳐 시퀀스로는 광직교부호를 사용하고, 비트오류률을 향상시키기 위해 간섭제거기법을 적용한다. PPM-CDMA은 전력효율이 다른 변조기법에 비해 우수하고, 고정된 펄스구간에 대해 변조레벨을 변화시켜 다중전송률 서비스를 제공하는 데에 용이하다. 본 논문에서 제안한 다중전송률 PPM-CDMA 시스템은 각 전송률에 대해 칩전송률 및 샘플링 시간을 변화시키지 않으므로써 전체 시스템 구조를 단순화할 수 있다.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.713-722
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• 2020

This article aims to illustrate the damped dynamic responses of layered functionally graded (FG) thick 2D beam under dynamic pulse sinusoidal load by using finite element method, for the first time. To investigate the response of thick beam accurately, two-dimensional plane stress problem is assumed to describe the constitutive behavior of thick beam structure. The material is distributed gradually through the thickness of each layer by generalized power law function. The Kelvin-Voigt viscoelastic constitutive model is exploited to include the material internal damping effect. The governing equations are obtained by using Lagrange's equations and solved by using finite element method with twelve -node 2D plane element. The dynamic equation of motion is solved numerically by Newmark implicit time integration procedure. Numerical studies are presented to illustrate stacking sequence and material gradation index on the displacement-time response of cantilever beam structure. It is found that, the number of waves increases by increasing the graduation distribution parameter. The presented mathematical model is useful in analysis and design of nuclear, marine, vehicle and aerospace structures those manufactured from functionally graded materials (FGM).

• 대한전기학회:학술대회논문집
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• 대한전기학회 1993년도 하계학술대회 논문집 A
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• pp.284-286
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• 1993

Software and hardware for cochlear implant system have been developed to create a speech signal processing system which, in real-time, extracts model parameter including formants, pitch, amplitude information. The system is based on the Texas Instruments TMS320 family. In hardware, computer interface has been desisted and implemented that allows presentation of biphasic pulse stimuli to patients with the hearing handicapped. The host computer sends a stream of bytes to the parallel port. Upon receipt of the data the interface generates the appropriate burst sequence that is delivered to the patient's external transmitter coil. The coded information is interpreted by the Nucleus-22 internal receiver that delivers the pulse to the specified electrodes at the specified amplitude and pulse width.

• 한국자기공명학회논문지
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• 제3권1호
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• pp.27-35
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• 1999

Quadrupolar interaction is a strong line broadening agent for nuclei of half-integer spin except the central line. The two-pulse quadrupolar echo technique is widely used, which refocuses the quadrupolar broadening. Echo formation is due to the cancellation of quadrupolar broadening effect by the applied two pulses. Since the central line is not quadrupolar broadened, it should not be involved in the echo formation. However, the central line peak always appears in experiments. This is explained qualitatively here by close examination on the time development of individual coherence. This explanation is used to predict the number of echoes that will be formed with 2 pulse sequence for nuclei of I=3/2, 5/2, 7/2, 9/2 with ease.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2009년도 정보 및 제어 심포지움 논문집
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• pp.296-298
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• 2009

In this paper, we are performance analysis of IEEE 802.15.4b LR-WAPN(Low-Rate Wireless Personal Area Network; Zigbee) system noncoherent receivers at 915MHz under Jamming. IEEE 802.15.4b concerns itself with devices at 915MHz, which employ a higher data rate of up to 250 kbps, and which use O-QPSK(Offset Quradrature Phase Shift Keying modulation with DSSS(Direct Sequence Spread Spectrum). Communication between devices can still be hampered by the presence of interferers outside the network, whether the interference be intentional or not. Hence the receivers can not have stable receiving condition due to worse BER. To solve this problem, we present a mere stabilized receiver system of using noncoherent detection. In this paper, we look instead at the effect of jamming, i.e. intentional interference, on the BER performance of IEEE 802.15.4 devices.