• Proceedings of the Korean Information Science Society Conference
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• 2002.04b
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• pp.601-603
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• 2002

MRI 스캔중 촬상 대상물의 화강평면내에서의 회전은 MRI 신호에 위상오차와 불균일 표본화를 일으킨다. 따라서, 아티팩트가 포함된 MR 화상의 화질열화를 개선하기 위하여 다음과 같은 방법들을 제안한다. 우선, 미리 주어진 회전파라메타써 쌍일처 보간과 중첩 특성을 이용해서 k 공간 불균일 표본화 데이터를 수정하는 알고리즘과, 2차원 회전운동의 회전각은 이미 알려져 있고, 회전중심 위치가 미지인 경우에 대해 위상보정에 기초한 아티팩트를 보정하는 알고리즘 및 회전중심과 각도가 모두 미지인 2차원 회전운동에 대해 아티팩느를 보정하는 알고리즘을 제안한다. 이 때, 미지운동 파라메타를 예측하기 위해 찰상대상물의 경계바깥쪽에서 이상적인 MR 화상의 에너지는 최소가 되고, 활상 대상물의 회전이 존재할 때 측정된 에너지가 증가한다는 성질을 이용했다. 이러만 성질을 이용해서 시뮬레이션 화상에 적용한 결과 제안한 방법에 대한 유효성을 확인하였다.

• Proceedings of the Korea Information Processing Society Conference
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• 2012.04a
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• pp.414-416
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• 2012

본 논문에서는 X-선 혈관 조영 영상 내 심혈관의 추출 방법을 제안한다. 본 방법은 불균일 조명 보정 필터를 사용함으로써 X-선 영상 내에서 나타나는 일정하지 않은 contrast, 낮은 명암도 및 불균일 조명 문제를 해결한다. 또한 영상의 지역적인 밝기 값의 변화의 특징을 고려하면서 분할 대상영역의 각 픽셀들의 2 차 미분((second partial derivation)을 행렬의 요소(element)로 갖는 Hessian 행렬의 고유치 (eigenvalue)를 영역확장의 문턱치 결정에 이용하여 전역적인 밝기값(intensity)만을 사용하는 분할의 단점을보완하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.4
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• pp.269-275
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• 2022

In ideal configuration, elapsed-time method can measure the exact reaction wheel speed. But in real configuration, the speed measurement error exists due to tacho pulse non-uniformity. In this research, we study the method which overcome the non-uniformity effects. First, we introduce the method which spin the wheel at the specific speed and measure the non-uniformity. Then, we propose the real-time measurement error correction method which uses the obtained non-uniformity information. This method calculate the speed candidates from the elapsed-time method's counts and non-uniformity information, and choose the closest speed to the real speed. Through simulation, we show that proposed method measure the exact speed regardless of non-uniformity, and fast wheel speed control is possible.

• Investigative Magnetic Resonance Imaging
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• v.16 no.1
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• pp.6-15
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• 2012

Purpose : The objective of this study was to develop background gradient correction method using excitation pulse profile compensation for accurate fat and $T_2{^*}$ quantification in the liver. Materials and Methods: In liver imaging using gradient echo, signal decay induced by linear background gradient is weighted by an excitation pulse profile and therefore hinders accurate quantification of $T_2{^*}$and fat. To correct this, a linear background gradient in the slice-selection direction was estimated from a $B_0$ field map and signal decays were corrected using the excitation pulse profile. Improved estimation of fat fraction and $T_2{^*}$ from the corrected data were demonstrated by phantom and in vivo experiments at 3 Tesla magnetic field. Results: After correction, in the phantom experiments, the estimated $T_2{^*}$ and fat fractions were changed close to that of a well-shimmed condition while, for in vivo experiments, the background gradients were estimated to be up to approximately 120 ${\mu}T/m$ with increased homogeneity in $T_2{^*}$ and fat fractions obtained. Conclusion: The background gradient correction method using excitation pulse profile can reduce the effect of macroscopic field inhomogeneity in signal decay and can be applied for simultaneous fat and iron quantification in 2D gradient echo liver imaging.

• Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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• 2008.10a
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• pp.137-140
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• 2008

실내조명으로서의 LED는 휘도의 분포특성이 기존의 조명기구와는 판이하게 다르며, 이에 따라 불쾌감을 느끼는 정도에서도 변화가 일어날 수 있다. 본 연구에서는 현재 가장 일반적으로 사용되어지는 글레어 평가지수인 UGR을 간단히 보정하여 LED 조명기구에 대한 값으로 사용할 수 있도록 주관평가 실험을 통해 보정식을 산출해내고 LED 조명기구별 증가계수 k를 구하였다.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.49 no.2
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• pp.35-44
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• 2012

Most recent infrared (IR) sensors have a focal-plane array (FPA) structure. Spatial non-uniformity of a FPA structure, however, introduces unwanted fixed pattern noise (FPN) to images. This non-uniformity correction (NUC) of a FPA can be categorized into target-based and scene-based approaches. In a target-based approach, FPN can be separated by using a uniform target such as a black body. Since the detector response randomly drifts along the time axis, however, several scene-based algorithms on the basis of a video sequence have been proposed. Among those algorithms, the state-of-the-art one based on Kalman filter uses one-directional warping for motion compensation and only compensates for offset non-uniformity of IR camera detectors. The system model using one-directional warping cannot correct the boundary region where a new scene is being introduced in the next video frame. Furthermore, offset-only correction approaches may not completely remove the FPN in images if it is considerably affected by gain non-uniformity. Therefore, for FPN reduction in IR videos, we propose a joint correction algorithm of gain and offset based on bi-directional warping. Experiment results using simulated and real IR videos show that the proposed scheme can provide better performance compared with the state-of-the art in FPN reduction.

• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.135-141
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• 2007

This paper describes the design technology for a third generation thermal imaging system, which is more compact than before, using a $320\times240$ mid-IR focal plane detector. The third generation non-scanning thermal imaging system was constructed as a compact thermal imaging module as a reconnaissance, surveillance and navigation sensor for helicopter and infantry vehicles in the $1980's\sim1990's$ and now, we designed a new compact infrared camera and studied a new type of non-uniformity correction lens fer this camera.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.1
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• pp.52-60
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• 2008

Purpose: To establish the methods for sinogram formation and correction in order to appropriately apply the filtered backprojection (FBP) reconstruction algorithm to the data acquired using PET scanner with multiple scintillation crystal layers. Materials and Methods: Formation for raw PET data storage and conversion methods from listmode data to histogram and sinogram were optimized. To solve the various problems occurred while the raw histogram was converted into sinogram, optimal sampling strategy and sampling efficiency correction method were investigated. Gap compensation methods that is unique in this system were also investigated. All the sinogram data were reconstructed using 20 filtered backprojection algorithm and compared to estimate the improvements by the correction algorithms. Results: Optimal radial sampling interval and number of angular samples in terms of the sampling theorem and sampling efficiency correction algorithm were pitch/2 and 120, respectively. By applying the sampling efficiency correction and gap compensation, artifacts and background noise on the reconstructed image could be reduced. Conclusion: Conversion method from the histogram to sinogram was investigated for the FBP reconstruction of data acquired using multiple scintillation crystal layers. This method will be useful for the fast 20 reconstruction of multiple crystal layer PET data.

• Korean Journal of Optics and Photonics
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• v.30 no.6
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• pp.219-225
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• 2019

In an infrared optical system, using a cooled detector generates a phenomenon called a narcissus, in which the focal-plane array cooled to very low temperatures is reflected at the lens surface and detected. The narcissus can be removed by non-uniformity correction of the detector pixel, so narcissus is generally ignored in infrared optics. However, non-uniformity correction reduces the sensitivity of the system. Also, as the housing temperature varies due to an environmental temperature change, or a lens is moved for focusing or athermalization purposes, a narcissus may occur even after non-uniformity correction. To minimize such a narcissus, the amount of the effect must be controlled in the lens-design stage. In this paper we designed a midinfrared optical system and analyzed the narcissus by setting the lens surface reflectance to 1%. In addition, the design was divided into stages of an initial design, an improved design, and a minimum design, and the narcissus was improved to about 56% of that in the initial design.

• Journal of the Korean Society of Radiology
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• v.7 no.3
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• pp.227-232
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• 2013

The pixels used in a digital X-ray detector have different sensitivities and offset values. A non-uniform image is consequently obtained. Flat-field correction was introduced to resolve this problem and carried out image preprocessing in a digital imaging system. Nevertheless, the non-uniform images caused by several reasons have been being occasionally acquired. In this study, the non-uniform images acquired in digital imaging systems were applied to flat-field correction, and NPSs were calculated and analyzed with those images before and after correction. It was confirmed that low frequency noise were effectively eliminated.