• 대한의용생체공학회:의공학회지
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• 제41권5호
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• pp.179-184
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• 2020

Purpose: The purpose of this study was to evaluate the effect according to the NEX, VENC, targeted cardiac phases on the velocity measurement of 4D phase-contrast MRI. Materials and Methods: The abdominal aortic phantom was made to experiment. The working fluid was mixed with water and glycerin to mimic the density and viscosity of human blood. The inlet velocity was Reynolds number 2000. The experimental conditions were NEX 1 and 4, VENC 102 cm/s and 200 cm/s, and 10 and 15 targeted cardiac phases, respectively. The average flow rate, average velocity, maximum velocity, and cross-section area were measured. Results: As a result of the case-by-case comparison, the error rate was less than 5%. There was no significant difference (p > 0.05). Conclusion: It is expected that this result will be useful for acquiring blood flow information in clinical practice.

• 한국방사선학회논문지
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• 제15권3호
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• pp.281-291
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• 2021

본 연구는 자기공명영상을 이용한 TOF MRA 검사에서 flow rate 2.0 ml 이하의 유속을 표현함에 있어 Compressed sensing의 사용에 따른 영상의 변화를 정량적으로 측정하고자 하였다. Auto-injector와 Flow phantom을 이용하여 각각의 혈류속도 구간을 설정하고 CS를 사용하지 않은 TOF without CS 기법과 CS를 이용한 TOF with CS 기법에서 CS factor의 변화에 따른 SNR, CNR, SSIM, RMSE 등을 측정하여 비교하였다. CS factor의 증가에 따라 나타나는 영상의 영향을 검증하고자 일원배치 분산분석(One-way ANOVA)을 시행하였다. 실험 결과 CS를 사용한 TOF MRA는 CS를 사용하지 않은 TOF MRA와 비교하여 SNR 및 CNR의 유의한 차이 없이 scan time이 현저하게 감소하였다. 반면 CS factor의 증가에 따라 SSIM 및 RMSE는 TOF without CS 영상과의 차이가 증가함을 나타내었다. 따라서 TOF MRA 검사 시 CS 기법을 통해 scan time을 효율적으로 감소시키되 적절한 CS factor의 범위를 충분히 고려해야 한다. 또한 CS factor와 영상의 유사도, 정밀성에 대한 지속적인 연구가 필요할 것으로 사료된다.

• 한국통신학회논문지
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• 제38B권11호
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• pp.861-869
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• 2013

본 논문에서는 정보시스템에 바이러스가 ${\lambda}$의 비율을 갖는 포아송 프로세스를 따라 도착한다고 가정한다. 정보시스템에는 바이러스를 검출하고 치료하기 위해 실시간스캔과 배치스캔의 두가지 방식으로 안티바이러스시스템을 운용하고 있다. 실시간스캔 방식에서는 바이러스가 시스템에 도착하자마자 스캔하게 되어 무한 용량의 안티바이러스시스템을 보유한 것과 같은 효과가 있다. 스캔과 치료에 소요되는 시간은 일반분포를 따르는 것으로 가정한다. 배치스캔 방식에서는 시스템 관리자가 일정한 시간 간격마다 정기적으로 시스템을 스캔하여 시스템에 존재하는 바이러스들을 동시에 치료한다. 본 논문에서는 안티바이러스시스템의 동작을 확률적으로 모형화하고 경제적으로 최적운용정책이 달성되는 조건을 유도한다. 비용 요소를 고려하여 실제적인 운용 환경에서의 시사점을 제시할 수 있는 수치예제도 제시한다.

• Investigative Magnetic Resonance Imaging
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• 제19권4호
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• pp.212-217
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• 2015

Purpose: For a single time-point hyperpolarized $^{13}C$ magnetic resonance spectroscopy imaging (MRSI) of animal models, scan-time window after injecting substrates is critical in terms of signal-to-noise ratio (SNR) of downstream metabolites. Pre-scans of time-resolved magnetic resonance spectroscopy (MRS) can be performed to determine the scan-time window. In this study, based on two-site exchange model, protocol-specific simulation approaches were developed for $^{13}C$ MRSI and the optimal scan-time window was determined to maximize the SNR of downstream metabolites. Materials and Methods: The arterial input function and conversion rate constant from injected substrates (pyruvate) to downstream metabolite (lactate) were precalibrated, based on pre-scans of time-resolved MRS. MRSI was simulated using two-site exchange model with considerations of scan parameters of MRSI. Optimal scan-time window for mapping lactate was chosen from simulated lactate intensity maps. The performance was validated by multiple in vivo experiments of BALB/C nude mice with MDA-MB-231 breast tumor cells. As a comparison, MRSI were performed with other scan-time windows simply chosen from the lactate signal intensities of pre-scan time-resolved MRS. Results: The optimal scan timing for our animal models was determined by simulation, and was found to be 15 s after injection of the pyruvate. Compared to the simple approach, we observed that the lactate peak signal to noise ratio (PSNR) was increased by 230%. Conclusion: Optimal scan timing to measure downstream metabolites using hyperpolarized $^{13}C$ MRSI can be determined by the proposed protocol-specific simulation approaches.

• Journal of Welding and Joining
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• 제32권6호
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• pp.41-46
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• 2014

In this study, cracking susceptibility of laser cladding was investigated according to the processing parameters such as laser power, scan speed and feeding rate with blended powders of stellite#6 and technolase40s (WC+NiCr). The solidification microstructure of clad was composed of Co-based dendrite structures with ${\gamma}+Cr7C3$ eutectic phases at the dendritic boundaries. The crack propagation showed transgranular fracture along dendritic boundaries due to brittle chrome carbide at the eutectic phases. From results of fractography experiments, the fracture surface was typical cleavage brittle fracture in the clad and substrate. The number of clad cracks, caused by a tensile stress after the solidification, increased with increase of laser power, scan speed and feeding rate. Increase of the laser power caused large pores by facilitating WC decarburizing reaction. And the pores affected increase of crack susceptibility. High scan speed caused increment of clad cracks due to thermal stress and WC particle fractures. Also, increase of the feeding rate accompanied an amount of WC particles causing crack initiation and decarburizing reaction.

• 소성∙가공
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• 제19권8호
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• pp.517-522
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• 2010

Selective laser melting (SLM) is emerged as a new manufacturing technique to directly fabricate precise parts using metallic materials. The final characteristics of a component fabricated through the SLM process are strongly dependent upon various parameters such as laser power, scan rate and pulse duration, etc. This paper, therefore, focuses on the dimensional characteristics of melted $20{\mu}m$ Fe-Cr-Ni powder by fiber laser for the selective laser melting process. With energy density decrease, the height and depth were decreased. Although the conditions are of the same energy density, the shape is different by laser power and scan rate. The shapes at various laser parameters were divided into 3 groups based on depth over height. The smooth regular shape is obtained under the conditions of $50{\mu}m$ of powder height and $15-20{\mu}s$ of pulse duration. And the laser power influenced the variation of shape more significantly than the scan rate.

• Corrosion Science and Technology
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• 제11권6호
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• pp.218-224
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• 2012

Liquid droplet impingement erosion (LDIE) known to be generated in aircraft and turbine blades is recently appeared in nuclear piping. UT thickness measurements with both A-scan and B-scan UT inspection equipments were performed for a component estimated as susceptible to LDIE in feedwater heater vent system. The thickness data measured with B-Scan equipment were compared with those of A-Scan. Thermal hydraulic analysis based on ANSYS FLUENT code was performed to analyze the behavior of liquid droplets inside piping. The wall thinning rate and residual lifetime based on both existing Sanchez-Caldera equation and measuring data were also calculated to identify the applicability of the existing equation to the LDIE management of nuclear piping. Because Sanchez-Caldera equation do not consider the feature of magnetite formed inside piping, droplet size, colliding frequency, the development of new evaluation method urgently needs to manage the pipe wall thinning caused by LDIE.

• 한국정보통신학회논문지
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• 제14권9호
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• pp.2023-2030
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• 2010

본 논문에서는 3차원 그래픽스 시스템에 적용 가능한 고성능 스캔변환회로를 설계하고 FPGA로 구현한 내용을 기술한다. 스캔변환회로의 성능을 높이기 위하여 본 논문에서는 계층적 타일기반 탐색기법과 SIMD 구조를 적용한 스캔변환회로 구조를 제안한다. 제안한 스캔변환회로는 Xilinx Vertex4 LX100 FPGA 디바이스에서 약 124Mhz로 동작가능하며, 실제 연산결과의 올바른 출력을 확인하기 위해 셰이더, 텍스처 매핑회로 그리고 $240{\times}320$ 컬러 TFT-LCD의 컨트롤러를 설계하여 통합하였다. FPGA상에 구현된 스캔변환회로는 약 311Mpixels/sec의 픽셀 생성율을 가지므로 데스크 탑 PC용 3차원 그래픽스 시스템뿐만 아니라 고성능을 요구하는 모바일 3차원 그래픽스 시스템에도 적용 가능하다.

• 대한의용생체공학회:의공학회지
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• 제5권1호
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• pp.85-92
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• 1984

A new architecture of the Digital Scan Converter (DSC) for the linear-scan ultrasound medical imaging systems is proposed and its hardware implementation is reported. While the conventional DSC merely displays the acquisited data and does nor allow access to the frame memory, it is possible, in the new system, to access to the frame memory for further imaging processing so as to obtain useful information for medical diagnosis. Image processing can be performed either by a special pupose processor, or by VAX 11/780. The system is made to operate asyncronously to increase the frame rate with tags assigned to the data. The proposed DSC was designed to be used without much modification for the sector scan system as well.

• 전자공학회논문지
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• 제52권4호
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• pp.62-70
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• 2015

최근 스마트폰의 발달과 더불어 대형 TV, 의료용 장비 및 전자 칠판에도 터치스크린의 수요가 급증하고 있다. 스크린 사이즈가 증가 할수록 고해상도를 위하여 훨씬 더 많은 채널이 추가 되면서 한 프레임을 스캔하는데 긴 시간이 소요되어 터치감지 지연이 큰 문제가 되고 있다. 본 논문에서는 이러한 문제를 해결하기 위하여 새로운 드라이빙 및 센싱 기법을 제안한다. 이 기법은 differential 드라이빙 방법으로 2 단계로 수행되어진다. 먼저 고속 센싱 프로세스를 통해 터치가 발생된 센싱 라인들을 우선 대략적으로 도출해 낸 후 정확한 터치 위치 스캔을 위해서 터치된 라인에서만 감지가 수행되어 진다. 이 방법을 사용하면 터치 패널의 frame refresh rate를 향상 시킬 수 있다. 제안된 구조는 FPGA와 개발된 AFE board로 구현되었으며, 23인치 상용 터치패널을 사용하여 테스트하였다. 이 기법은 기존 대비 frame scan rate를 8.4배 향상시킨다.