• Journal of the Korean Society of Radiology
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• v.16 no.3
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• pp.203-209
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• 2022

One of the typical methods for lowering radiation dose while maintaining image quality of computed tomography (CT) is the use of model-based iterative reconstruction (MBIR). This study is to evaluate the image quality by adjusting the strength of the advanced modeled iterative reconstruction (ADMIRE), which is well known as a representative model of MBIR. The study was conducted using phantom, and CT images were obtained while adjusting the strength of ADMIRE in units of 1 to 5. Quantitative evaluation includes noise levels using coefficient of variation (COV) and contrast to noise ratio (CNR), as well as natural image quality evaluation (NIQE) and blind/referenceless image spatial quality evaluator (BRISQUE). As a result, in both noise level and blind quality evaluation results, the higher the strength of ADMIRE, the better the results were derived. In particular, it was confirmed that COV and CNR were improved 1.89 and 1.75 times at ADMIRE 5 compared to ADMIRE 1, respectively, and NIQE and BRISQUE were proved to be improved 1.35 and 1.22 times at ADMIRE 5 compared to ADMIRE 1, respectively. In conclusion, this study was proved that the reconstruction strength of ADMIRE had a great influence on the noise level and overall image quality evaluation of CT images.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.67-76
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• 2006

This paper describes the analysis method to define the system specification for conducted EMI environment and verification method to evaluate the conducted EMI performance. Conducted EMI environment is characterized by the electrical power subsystem which is mainly issued by the switching circuit noise, common ground impedance coupling. To define and control these EMI problems, EMI assesment through system analysis are preceded at the early design phase and then EMI reduction methods are applied during the unit/system development phase. System EMC should be carefully controlled and designed in the consideration of EMC safety margin and its performance is fully evaluated at the whole development period.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.287-292
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• 2001

당과 같은 실내 음향 문제는 강당의 사용자와 관리자의 주관적인 평가가 배제되기 힘든 것이므로 문제를 개선하기 위해 물리적 측정이나 실험, 해석 등을 통한 다각적인 정량적 분석 자료를 산출하는 과정이 선행되어야 한다 이를 위해 본 논문에서는 기존의 강당에 대한 고유 음향 특성-잔향시간, 명료도, 음압레벨-을 실험과 컴퓨터 시뮬레이션을 통해 얻어 음향 분포를 파악하고, 현재 설치되어 있는 스피커의 지향성 및 위치 등에 따른 음향 특성을 알아보았다. 대표적인 음향평가 지수인 잔향 시간은 랜덤노이즈를 음원으로 사용하여 음향측정을 수행하였으며, 이 결과를 시뮬레이션과 비교함으로써 컴퓨터 시뮬레이션의 신뢰성 또한 검토하였다.

• Journal of the Korean Society of Radiology
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• v.15 no.1
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• pp.9-14
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• 2021

Recently, magnetic resonance imaging (MRI), which can acquire images with good contrast without exposure to radiation, has been widely used for diagnosis. However, noise that reduces the accuracy of diagnosis is essentially generated when acquiring the MR images, and by adjusting the parameters, the noise problem can be solved to obtain an image with excellent characteristics. Among the parameters, the number of excitation (NEX) can acquire images with excellent characteristics without additional degradation of image characteristics. In contrast, appropriate NEX setting is required since the scan time increases and motion artifacts may occur. Therefore, in this study, after fixing all MRI parameters through the MRiLab simulation program, we tried to evaluate the tendency of image characteristics according to changing NEX through quantitative evaluation of brain T2 weighted images acquired by adjusting only NEX. To evaluate the noise level and similarity of the acquired image, signal to noise ratio (SNR), contrast to noise ratio (CNR), root mean square error (RMSE) and peak signal to noise ratio (PSNR) were calculated. As a result, both noise level and similarity evaluation factors showed improved values as NEX increased, while the increasing width gradually decreased. In conclusion, we demonstrated that an appropriate NEX setting is important because an excessively large NEX does not affect image characteristics improvement and cause motion artifacts due to a long scan.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.27 no.2
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• pp.147-155
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• 2016

This paper presents a jamming detection and suppression algorithm of a frequency-modulated continuous-wave(FMCW) radar altimeter. The radar altimeter measures the noise level at the noise measuring period before the transmitting and receiving period and finds the number of sampled noise data over the jamming threshold for detecting the jamming. For a jamming suppression technique, we design the time domain jamming suppression, transmit/receive power control and frequency hopping methods. To assess more realistic operation, the radar altimeter was performed a field test. Through the field test, we verified the algorithms successfully.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.05a
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• pp.5-12
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• 2000

본 연구에서, Daubechies'Mother Wavelet를 이용한 이산 웨이블렛 변환(Discrete Wavelet Transform)에 기초한 새롭고 효과적인 특정추출방법을 제안하였다. 특정추출을 이용하여 응용방향을 설명하고 또는 통계적 파라메터의 평가를 행하였다. 본 연구에서는 다음과 같은 몇 가지 사실을 알 수 있었다. 1. 시스템에서 발생된 (인가전압이 0[V]) 노이즈라 볼 수 가있는 렌덤노이즈(Random Noise)를 디지털필터인 FIR(Finite Impulse Response)필터를 통하여 상당한 노이즈를 억제할 수가 있었다. 2. 이산 웨이블렛 변환 시 레벨 1~4까지 변환한 결과 최적의 변환상태 Level-3을 기준으로 하였다. 3. 특정추출 파라메터는 음향방출신호의 최대값, 평균값, 분산, 왜도, 첨쇄도를 특정추출파라메터로 이용하였다. 4. 특정추출 결과를 이용하여 전체 열화시간 중 대표적 음향방출신호 중 초기열화신호, 중기열화신호, 말기열화신호를 얻을 수 있었다. 이런 특정추출을 통하여 변압기열화상태를 진단할 수 있는 가능성을 확인 할 수가 있었다.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.5
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• pp.74-82
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• 2015

As the complexity of an electronic device and the reduction of its operating voltage is progressing, susceptibility test of the chip and module for internal or external noises is essential. Although the immunity compliance of the chip was served with IEC 62132-4 Direct Power Injection method as an industry standard, in fact, EM immunity of the chip is influenced by their Power Domain Network (PDN). This paper evaluates the EM noise tolerance of a PLL and compares their noise transfer characteristics to the PLL on various PCB boards. To make differences of the PDNs of PCBs, various PCBs with or without LDO and with several types of capacitors are tested. For evaluation of discrepancies between EM characteristics of an IC only and the IC on real boards, the analysis of the noise transfer characteristics according to the PDNs shows that it gives important information for the design having robust EM characteristics. DPI measurement results show that greatly improved immunity of the PLL in the low-frequency region according to using the LDO and a frequency change of the PLL according to the DPI could also check with TEM cell measurement spectrum.

• Journal of the Korean Society of Radiology
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• v.17 no.6
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• pp.911-917
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• 2023

The method of observing nodular changes on the liver surface using clinical ultrasonography is useful for diagnosing cirrhosis. However, the speckle noise that inevitably occurs in ultrasound images makes it difficult to identify changes in the liver surface and echo patterns, which has a negative impact on the diagnosis of cirrhosis. The purpose of this study is to model the median modified Wiener filter (MMWF), which can efficiently reduce noise in cirrhotic ultrasound images, and confirm its applicability. Ultrasound images were acquired using an ACR phantom and an actual cirrhotic patient, and the proposed MMWF algorithm and conventional noise reduction algorithm were applied to each image. Coefficient of variation (COV) and edge rise distance (ERD) were used as quantitative image quality evaluation factors for the acquired ultrasound images. We confirmed that the MMWF algorithm improved both COV and ERD values compared to the conventional noise reduction algorithm in both ACR phantom and real ultrasound images of cirrhotic patients. In conclusion, the proposed MMWF algorithm is expected to contribute to improving the diagnosis rate of cirrhosis patients by reducing the noise level and improving spatial resolution at the same time.

• Journal of radiological science and technology
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• v.47 no.3
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• pp.175-182
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• 2024

Advanced modeled iterative reconstruction (ADMIRE) represents a repetitive reconstruction method that can adjust strength and kernel, each of which are known to affect computed tomography (CT) image quality. The aim of this study was to quantitatively analyze the noise and spatial resolution of CT images according to ADMIRE control factors. Patient images were obtained by applying ADMIRE strength 2 and 3, and kernel B40 and B59. For quantitative evaluations, the noise level, spatial resolution, and overall image quality were measured using coefficient of variation (COV), edge rise distance (ERD), and natural image quality evaluation (NIQE). The superior values for the average COV, ERD, and NIQE results were obtained for the ADMIRE reconstruction conditions of ADMIRE 2 + B40, ADMIRE 3 + B59, and ADMIRE3 + B59. NIQE, which represents the overall image quality based on no-reference, was about 6.04 when using ADMIRE 3 + B59, showing the best result among the reconstructed image acquisition conditions. The results of this study indicate that the ADMIRE strength and kernel chosen for use in ADMIRE reconstruction have a significant impact on CT image quality. This highlights the importance of adjusting to the control factors in consideration of the clinical environment.

• Proceedings of the Korea Water Resources Association Conference
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• 2023.05a
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• pp.225-225
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• 2023

하상 측정은 하천 유지관리, 수공구조물 설계 및 보수, 수생태 조사의 필수적인 자료이다. 최근 4대강 대규모 사업 이후 자연적 안정화로 인해 침식 및 재퇴적이 진행되어 정밀 하상 모니터링이 요구되고 있다. 통상적인 하상 조사 기법은 레벨측량 및 RTK-GPS 등을 활용하여 점단위로 직접 계측하는 기법과 수심이 깊을 경우 ADCP와 같은 음향측심기법을 통해 하상변동을 계측하고 있다. 하지만 점단위 직접 측정은 사구와 사련과 같은 하상 구조 교란 및 계측 시 위험을 동반하고 수심자료의 측정오차가 크게 발생하는 한계점이 존재한다. 또한 초음파 방식의 경우 막음길이와 바닥면 노이즈 등의 한계점으로 50 cm 미만의 저수심부 하상 측정이 불가능한 실정이다. 이러한 한계점을 극복하기 위해 최근 드론의 보급으로 수심라이다(Bathymetry LiDAR), SFM, 드론 탑재 초분광 영상을 활용한 초분광수심법과 같은 저고도, 고해상도의 비접촉식 면단위 하상 측정 기법이 대안으로 각광받고 있고 최근 관심은 해당 최신 기술의 성능 점검 및 적용성 평가에 있다. 따라서 본 연구에서는 초분광수심법 중 보편적으로 적용할 수 있는 최적밴드비분석(OBRA)의 성능 점검과 실무 적용성을 국내 하천을 대상으로 검토하였다. 해당 기술의 실무 적용성 평가항목 중 수심 적용 범위가 경제적이고 효율적인 성능 평가의 주된 항목이다. 선행 연구에 따르면 감천을 대상으로 저수심부의 성능 평가를 진행한 결과 상세한 하상계측이 가능하다고 제시하였다. 따라서 본 연구는 낙동강-황강 합류부를 대상으로 전형적인 평수기 탁도 조건에서 초분광수심법을 적용할 경우 최대측정가능수심의 범위를 결정하는 방법 및 결과를 제시하려고 한다. 또한 현장실험 당시 합천댐 방류로 인하여 황강의 탁도가 높아진 상태에 기인하여 고탁도 조건에서 초분광수심법의 적용성 평가도 추가 검토하였다. 해당 연구는 수심과 밴드비의 비선형성을 통해 최적 밴드비 분석의 결과로 도출될 수 있는 상관계수와 평균 제곱근 오차(RMSE)의 동향을 보아 다양한 시나리오의 배제수심을 통해 최대측정가능수심을 산정하였으며 그 이상의 범위는 수심맵 산정에서 제외하였다. 그 결과로 낙동강 본류에서 2.5 m 이하, 황강 지류에서 1.25 m 이하의 최대측정가능수심이 나타났고 해당 범위 이하에서는 상세한 하상이 나타났다. 또한 고탁도 조건인 황강에서는 낙동강에 비해 절반 수준의 최대측정가능수심 범위가 나타나 탁도 조건에 따른 초분광수심법의 한계가 있는 것을 확인하였다.