• 대한의용생체공학회:의공학회지
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• 제19권1호
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• pp.91-100
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• 1998

자기 공명 영상에서 최근에 개발된 fast spin echo 영상법은 종래에 사용되었던 spin echo 영상법과 거의 같은 화질과 contrast를 제공하면서도 8-16배 이상 촬영 시간이 단축되어 임상적으로 많이 사용되는 촬영 방법 중의 하나로 자리 잡았다. 그러나 종래의 spin echo영상법과는 달리, 동시에 spin밀도 영상과T 강조 영상을 제공하는 dual echo 영상법은 fast spin echo의 경우, 촬영 시간이 2배로 늘어나기 때문에 그 중요한 장점을 잃어 버리게 되었다. 본 논문에서는 dual echo를 동시에 얻기 위한 현재의 fast spin echo 영상법의 이와 같은 단점을 해결하는 새로운 영상법을 제안한다. 새로운 영상법은 기존의 fast spin echo와 거의 같은 화질을 제공하면서도 dual echo 영상을 얻는데 추가 촬영 시간을 요구하지 않는다. 이를 입증하기 위하여 인체 실험을 수행하였고 그 결과를 기존의 방법으로 얻은 영상과 비교함으로써 그 유용성을 보인다.

• Nuclear Engineering and Technology
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• 제49권7호
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• pp.1442-1450
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• 2017

In liquid metal fast breeder reactors, postulated failures of the plant protection system may lead to serious unprotected accidental consequences. Unprotected transients are generically categorized as transient overpower accidents and transient under cooling accidents. In both cases, core meltdown may occur and this can lead to a molten fuel coolant interaction (MFCI). The understanding of MFCI phenomena is essential for study of debris coolability and characteristics during post-accident heat removal. Sodium is used as coolant in liquid metal fast breeder reactors. Viewing inside sodium at elevated temperature is impossible because of its opaqueness. In the present study, a methodology to depict MFCI phenomena using a flat panel detector based imaging system (i.e., real time radiography) is brought out using a woods metal-water experimental facility which simulates the $UO_2-Na$ interaction. The developed imaging system can capture attributes of the MFCI process like jet breakup length, jet front velocity, fragmented particle size, and a profile of the debris bed using digital image processing methods like image filtering, segmentation, and edge detection. This paper describes the MFCI process and developed imaging methodology to capture MFCI attributes which are directly related to the safe aspects of a sodium fast reactor.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1997년도 추계학술대회
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• pp.294-298
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• 1997

In the magnetic resonance imaging, the fast spin echo imaging technique is a widely used clinical imaging method, since its scanning time is much shorter than the conventional spin echo imaging and it gives the almost same image quality. However, the fast spin echo technique has two times longer imaging time or the dual echo acquisition which can obtain a spin density image and a $T_2$-weighted image simultaneously. To overcome such a drawback, this paper proposes a new fast dual echo imaging technique which can give the same quality images at the single echo imaging time. The proposed technique reduces the imaging time by overlapping most of echo train data for each image reconstruction. In order to verify its validity and usability the human head experimental results which were obtained at the 0.3T permanent MRI system are presented.

• Journal of electromagnetic engineering and science
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• 제11권1호
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• pp.56-61
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• 2011

In this paper, we consider the topological derivative concept for developing a fast imaging algorithm of thin inclusions with dielectric contrast with respect to an embedding homogeneous domain with a smooth boundary. The topological derivative is evaluated by applying asymptotic expansion formulas in the presence of small, perfectly conducting cracks. Through the careful derivation, we can design a one-iteration imaging algorithm by solving an adjoint problem. Numerical experiments verify that this algorithm is fast, effective, and stable.

• Investigative Magnetic Resonance Imaging
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• 제25권4호
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• pp.300-312
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• 2021

Compressed sensing (CS) has been investigated in magnetic resonance (MR) parametric mapping to reduce scan time. However, the relatively long reconstruction time restricts its widespread applications in the clinic. Recently, deep learning-based methods have shown great potential in accelerating reconstruction time and improving imaging quality in fast MR imaging, although their adaptation to parametric mapping is still in an early stage. In this paper, we proposed a novel deep learning-based framework DEMO for fast and robust MR parametric mapping. Different from current deep learning-based methods, DEMO trains the network in an unsupervised way, which is more practical given that it is difficult to acquire large fully sampled training data of parametric-weighted images. Specifically, a CS-based loss function is used in DEMO to avoid the necessity of using fully sampled k-space data as the label, thus making it an unsupervised learning approach. DEMO reconstructs parametric weighted images and generates a parametric map simultaneously by unrolling an interaction approach in conventional fast MR parametric mapping, which enables multi-tasking learning. Experimental results showed promising performance of the proposed DEMO framework in quantitative MR T1ρ mapping.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2000년도 하계학술대회 논문집 D
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• pp.3207-3209
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• 2000

X-ray CT(Computed Tomography) has been a good modality for non-invasive diagnosis and recently, Conventional CT has been replaced rapidly with Spiral CT in recent. In X-ray CT, spiral scanning has various advantages such as better image quality, reduced scan time (in a single breath-hold), a lower x-ray dose. But, it requires very fast and high performance image processing system to reconstruct slice images from spiral scanning. This paper describes the fast image reconstruction techniques with filtered back projection from the viewpoints of fast algorithm as well as hardware implementation for real-time imaging.

• Investigative Magnetic Resonance Imaging
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• 제1권1호
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• pp.79-85
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• 1997

Fast spin echo imaging utilizes multiple spin echoes to encode multiple k-space lines instead of multiple $T_2-weighted$ images. As results, intensities in k-space data are varying according to T2 decay, which generates Gibb's artifact in the reconstructed image. The echo time for e encoding dc block determines contrast, as is specified by the effective echo time, however, all location of other echoes to different k-space frequency blocks in fast spin echo imaging is not f fully investigated. In this study, symmetric arrangement of multiple echoes in k-space is investigated to reduce Gibb's artifact. Design of filters based on the measurement of multiple e echo intensities is also proposed in two stage manner, i.e., equalization and filtering. From s simulation and experiment, it was observed that Gibb's phenomena were substantially reduced b by the proposed methods.

• Investigative Magnetic Resonance Imaging
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• 제25권4호
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• pp.229-251
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• 2021

Arteriosclerosis is the leading cause of stroke, with a fatality rate surpassing that of ischemic heart disease. High-resolution vessel wall magnetic resonance imaging is generally recognized as a non-invasive and panoramic method for the evaluation of arterial plaque; however, this method requires improved signal-to-noise ratio and scanning speed. Recent advances in high-density head and neck coil arrays are characterized by broad coverage, multiple channels, and closefitting designs. This review analyzes fast magnetic resonance imaging from the perspective of accelerated algorithms for vessel wall imaging and demonstrates the need for effective algorithms for signal acquisition using advanced radiofrequency system. We summarize different phased-array structures under various experimental objectives and equipment conditions, introduce current research results, and propose prospective research studies in the future.

• Investigative Magnetic Resonance Imaging
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• 제26권2호
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• pp.117-124
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• 2022

Purpose: In this study, we provide a way to assess even a slight effect of exercise on trunk-muscle activity. Materials and Methods: Seven healthy male participants (mean age, 24.7 ± 3.2 years; height, 171.2 ± 9.8 cm; and weight, 63.8 ± 11.9 kg) performed 15 sets of an exercise with 20 repetitions of 90° hip and right-knee flexion while lying supine. The exercise intensity was measured using the 10-point Rating of Perceived Exertion Scale after the first and 15th sets of exercises. Although cross-sectional areas and functional T2 mapping using ultrafast imaging (fast-acquired muscle functional magnetic resonance imaging, fast-mfMRI) have been proposed for imaging to evaluate exercise-induced muscle activity in real time, no previous studies have reported on the evaluation of trunk-muscle activity using functional T2 mapping. As a method for assessing trunk-muscle activity, we compared functional T2 mapping using ultrafast imaging (fast-mfMRI) with cross-sectional areas. Results: Although the muscle cross-sectional areas were increased by the exercise, there was no significant difference at rest. On the other hand, for all sets, the changes in T2 were significant compared with those at rest (P < 0.01). These results demonstrate that T2, calculated from fast-mfMRI images can be used to detect even a small amount of muscle activity induced by acute exercise, which was impossible to do with cross-sectional areas. Conclusion: Fast-mfMRI, which can also display functional information with detailed forms, enabled non-invasive real-time imaging for identifying and evaluating the degree of deep trunk-muscle activity induced by exercise.

• Investigative Magnetic Resonance Imaging
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• 제11권1호
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• pp.1-9
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• 2007

심장의 영상화에 장애가 되는 요인은 심장 운동, 호흡, 심장 내 혈류 등에 의한 인공물(artifact) 과 심장 조직의 용적이 작음으로 인한 낮은 신호 대 잡음비 등이 있다. 심장 운동에 의한 화질 저하를 막기 위해 신속영상기법(fast imaging technique) 을 이용하여 심장 운동의 특정 위상(phase) 에서만 영상을 얻는 심장동기(cardiac gating) 방법을 이용하고 있다. MRI를 이용한 심장의 검사는 심장의 형태, 심실 기능, 심근 관류, 심근 대사, 관상동맥 영상 등을 대상으로 한다. 심장의 형태적 진단에 있어서 심근내 수분의 정도와 지방조직을 보기 위해 이중(double) 혹은 삼중역전회복기법(triple inversion recovery technique) 을 사용한다. 심근관류검사를 위해서는 조영증강신속경사에코법(contrast-enhanced fast gradient echo technique)을 사용하여 일차통과조영증강(first-pass enhancement) 을 검사한다. 또한 10-15분 지연영상을 얻어 심근내 조영제의 재분포를 검사하여 만성심근경색 등의 심근파괴부위를 확인한다. 심실기능 평가를 위해서는 신속경사에 코법을 이용한 영화영상(cine image) 이 사용되며 심실의 국소적 운동이상 및 심실기능의 정량적 검사가 가능하다. MRI는 관상동맥영상을 제외한 포괄적 심장검사에 실용성이 있다. 특히 지연영상은 다른 검사장비에선 얻을수 없는 유용한 정보이다.