• Proceedings of the KSMRM Conference
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• 1999.04a
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• pp.34-42
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• 1999

의료영상에서 인공물(Artifacts) 이라 함은 영상이 얻어지는 신체부위와 아무런 관련이 없으나 얻어진 영상에는 마치 영상의 일부분으로 나타나는 모든 것을 가리킨다. 따라서 영상에서 이들 인공물들은 실제 조직의 해부학적인 구조를 나타내지 않으므로 영상 판독에 영향을 주어 잘못된 진단을 초래할 수도 있다. 그러나 MR 영상이 가능한 이래로 새로운 여러 종류의 MR 인공물들이 많이 발견 되었으나 다행스럽게도 거의 모든 MR 인공물들은 쉽게 설명이 가능하며, 따라서 이들 인공물들에 의한 진단 오류의 가능성은 매우 희박한 실정이다. 그러나 새로운 영상방법이나 혹은 새로운 펄스대열이 계속 고안됨에 따라 새로운 종류의 인 공물들이 생겨날 가능성은 항상 존재하고 있다. 지금까지 알려진 여러 MR 인공물들은 그 생겨난 원인에 따라 다음과 같이 크게 세 가지로 분류가 가능하다. I. Motion Artifacts 1. Voluntary motion 2. Involuntary motion 1) Bowel Peristalsis 2) Respiration 3) Cardiac and vessel pulsation 4) Swallowing 3. Fluid motion 1) Blood flow 2) Cerebrospinal fluid flow II. Reconstruction Artifacts 1. Aliasing 2. Partial volume averaging 3. Truncation (Ringing) 4. Central point III. Magnetic and RF Field Related Artifacts 1. Chemical shift 1) First kind 2) Second kind 2. Susceptibility 1) Dental 2) Metal 3. Magic angle 4. Zipper 5. Bad data point 6. RF field inhomogeneity 7. Magnetic field inhomogeneity 8. Eddy current 9. slice overlapping 10. Zebra 11. RF overflow

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.6
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• pp.761-767
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• 2007

In centralized control system, complicated control systems including sensors, power supply and dampers should be required to satisfy the target response of large-scale structures. The practical applications of the centralized control system, however, is very difficult due to high order finite element model of structures, uncertainty of models, and limitations of the excitation system. In this study, the decentralized response-dependent MR damper of which magnetic field is automatically modulated according to the displacement or velocity transferred to the damper without any sensing and computing systems. this decentralized response-dependent MR damper are investigated according to the ranges of relative magnitude between the control force of MR damper and the story shear force of structures by nonlinear time history analysis. Finally, its performance is compared with centralized LQR algorithm which is used in general centralized control theory for a three story building structure.

• Design & Manufacturing
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• v.13 no.3
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• pp.12-18
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• 2019

Fluid jet polishing is a method of jetting a fluid to polish a concave or free-form surface. However, the fluid jet method is difficult to form a stable polishing spot because of the lack of concentration. In order to solve this problem, MR fluid jet polishing system using an abrasive mixed with an MR fluid whose viscosity changes according to the intensity of a magnetic field is under study. MR fluid jet polishing is not easy to formulate for precise optimal conditions and material removal due to numerous fluid compositions and process conditions. Therefore, in this paper, quantitative data on the factors that have significant influence on the machining conditions are presented using various simulations and the correlation studies are conducted. In order to verify applicability of the fabricated MR fluid jet polishing system by nozzle diameter, the flow pattern and velocity distribution of MR fluid and polishing slurry of MR fluid jet polishing were analyzed by flow analysis and shear stress due to magnetic field changes was analyzed. The MR fluid of the MR fluid jet polishing and the flow pattern and velocity distribution of the polishing slurry were analyzed according to the nozzle diameter and the effects of nozzle diameter on the polishing effect were discussed. The analysis showed that the maximum shear stress was 0.45 mm at the diameter of 0.5 mm, 0.73 mm at 1.0 mm, and 1.24 mm at 1.5 mm. The cross-sectional shape is symmetrical and smooth W-shape is generated, which is consistent with typical fluid spray polishing result. Therefore, it was confirmed that the high-quality surface polishing process can be stably performed using the developed system.

• Smart Structures and Systems
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• v.3 no.3
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• pp.385-403
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• 2007

The effectiveness of the newly developed smart passive control system employing a magnetorheological (MR) damper and an electromagnetic induction (EMI) part for seismic protection of base isolated structures is numerically investigated. An EMI part in the system consists of a permanent magnet and a coil, which changes the kinetic energy of the deformation of an MR damper into the electric energy (i.e. the induced current) according to the Faraday's law of electromagnetic induction. In the smart passive control system, the damping characteristics of an MR damper are varied with the current input generated from an EMI part. Hence, it does not need any control system consisting of sensors, a controller and an external power source. This makes the system much simpler as well as more economic. To verify the efficacy of the smart passive control system, a series of numerical simulations are carried out by considering the benchmark base isolated structure control problems. The numerical simulation results show that the smart passive control system has the comparable control performance to the conventional MR damper-based semiactive control system. Therefore, the smart passive control system could be considered as one of the promising control devices for seismic protection of seismically excited base isolated structures.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2002.09a
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• pp.429-431
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• 2002

Metabolic analysis of biological tissues, the interventional radiology in MRT (Magnetic Resonance Treatment) and for clinical diagnoses, representation of 4-Dimensional (4D) structural information (x,y,z,t) of biological tissues is required. This paper discusses image representation techniques for those 4D MR Images. We have proposed an image reconstruction method for ultra-fast 3D MRI. It is based on image interpolation and prediction of un-acquired pictorial data in both of the real and the k-space (the acquisition domain in MRI). A 4D MR image is reconstructed from only two 3D MR images and acquired a few echo signals that are optimized by prediction of the tissue motion. This prediction can be done by the phase of acquired echo signal is proportioned to the tissue motion. On the other hand, reconstructed 4D MR images are represented as a 3D-movie by using computer graphics techniques. Rendered tissue surfaces and/or ROIs are displayed on a CRT monitor. It is represented in an arbitrary plane and/or rendered surface with their motion. As examples of the proposed representation techniques, the finger and the lung motion of healthy volunteers are demonstrated.

• Investigative Magnetic Resonance Imaging
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• v.22 no.3
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• pp.141-149
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• 2018

Purpose: The purpose of this study is to develop a simple method to measure magnetic susceptibility of arbitrarily shaped materials through MR imaging and numerical modeling. Materials and Methods: Our 3D printed phantom consists of a lower compartment filled with a gel (gel part) and an upper compartment for placing a susceptibility object (object part). The $B_0$ maps of the gel with and without the object were reconstructed from phase images obtained in a 3T MRI scanner. Then, their difference was compared with a numerically modeled $B_0$ map based on the geometry of the object, obtained by a separate MRI scan of the object possibly immersed in an MR-visible liquid. The susceptibility of the object was determined by a least-squares fit. Results: A total of 18 solid and liquid samples were tested, with measured susceptibility values in the range of -12.6 to 28.28 ppm. To confirm accuracy of the method, independently obtained reference values were compared with measured susceptibility when possible. The comparison revealed that our method can determine susceptibility within approximately 5%, likely limited by the object shape modeling error. Conclusion: The proposed gel-phantom-based susceptibility measurement may be used to effectively measure magnetic susceptibility of MR-compatible samples with an arbitrary shape, and can enable development of various MR engineering parts as well as test biological tissue specimens.

• Korean Journal of Poultry Science
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• v.38 no.4
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• pp.315-322
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• 2011

This study was carried out to determine the effect of dietary supplementation of resveratrol and methoxylated resveratrol extracted from branch of Morus alba L. on the quality of chicken thigh meat during cold storage. For 35 days, 1-day-old 320 broiler chicks (Ross) were divided into 8 groups and supplemented the diet; basal diet only (BD), BD with antibiotics (AB), vitamin E 20 IU (VE 20), vitamin E 200 IU (VE 200), resveratrol 20 ppm (RV 20), resveratrol 200 ppm (RV 200), methoxylated resveratrol 20 ppm (MR 20), and methoxylated resveratrol 200 ppm (MR 200). After slaughtering the broilers, thighs were collected and analyzed the quality change of the meat during storage at $4^{\circ}C$ for 5 days. The meat quality factors such as pH, color, water holding capacity, and sensory characteristics of thigh meat were determined on the experiment day 1, 3, and 5. AB, VE, and MR increased pH value of chicken thigh compare to BD (p<0.05). Lightness ($L^*$) showed no significant difference during storage day 1 and 5. VE 200 and MR 20 stabilized the redness ($a^*$) of chicken thigh as the value of day 1. Water holding capacity of chicken thigh from VE 20, RV 200, MR 20, and MR 200 on storage day 3 was higher than that of BD (p<0.05). In sensory evaluation, the panelist discriminated the tenderness and gave the higher score on the chicken from AB, VE20, RV 20, and MR 20 compare to BD (p<0.05). These results suggest that the dietary resveratrol and methoxylated resveratrol could be used as chicken meat quality enhancer in broiler industry.

• Transactions of Materials Processing
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• v.22 no.2
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• pp.80-85
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• 2013

The surface integrity of micro-machined products affects the performance of products significantly. Micro-burrs resulting from micro-cutting degrades the surface quality. Therefore it is desired to eliminate them completely and many studies have been undertaken for this purpose. In this study, micro-end-milling was carried out on nickel alloy and brass materials commercially used for light guide plate mold in 3-D optical devices. After completing this micro-machining, the burr heights were measured with a microscope. Then, deburring was done on the machined edges using the MR jet polishing method. A jet angle of $0^{\circ}$ and deburring times of 1, 3, and 5 min. were chosen. It was found that burrs were completely eliminated after 5 min of MR fluid jet polishing.

• Nuclear Engineering and Technology
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• v.55 no.1
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• pp.222-228
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• 2023

This study aimed to analyze the applicability of the improved median filter in positron emission tomography (PET)/magnetic resonance (MR) fusion images based on parallel imaging using generalized autocalibrating partially parallel acquisition (GRAPPA). In this study, a PET/MR fusion imaging system based on a 3.0T magnetic field and ¹⁸F radioisotope were used. An improved median filter that can set a mask of the median value more efficiently than before was modeled and applied to the acquired image. As quantitative evaluation parameters of the noise level, the contrast to noise ratio (CNR) and coefficient of variation (COV) were calculated. Additionally, no-reference-based evaluation parameters were used to analyze the overall image quality. We confirmed that the CNR and COV values of the PET/MR fusion images to which the improved median filter was applied improved by approximately 3.32 and 2.19 times on average, respectively, compared to the noisy image. In addition, the no-reference-based evaluation results showed a similar trend for the noise-level results. In conclusion, we demonstrated that it can be supplemented by using an improved median filter, which suggests the problem of image quality degradation of PET/MR fusion images that shortens scan time using GRAPPA.

• Investigative Magnetic Resonance Imaging
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• v.3 no.2
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• pp.167-172
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• 1999

Purpose : To evaluate the detection rate of hyperacute intracerebral hemorrhage in echo planar imaging (EPI) and other MR sequences. materials and Methods : Intracerebral hemorrhage was experimentally induced in ten rats. EPI, fast spin-echo (FSE) T2 weighted images, fluid attenuated inversion recovery (FLAIR), spin-echo (SE) T1 weighted images and gradient echo (GE) T1 weight ed images of rat's brains were obtained 2 hours after onset of intracerebral hemorrhage. EPI and FSE T2 images were additionally obtained 30 min and 1 hour after onset of hemorrhage in 3 and 6 rat, repeatedly, For objective visual assessment, discrimination between the lesion and normal brain parenchyma was evaluated on various MR sequences by three radiologists. For quantitative assessment, contrast-to-noise ratio (CNR) was calculated fro hemorrhage-normal brain parenchyma. Statistical analysis was performed usning the Wilcoxon-Ranks test. Results : EPI, FLAIR, and FSE T2 images showed high signal intensity lesions. The lesion discrimination was easier on EPI than on other sequences, and also EPI showed higher signal intensity for the subjective visual assessment. In quantitative evaluation, CNR of the hemorrhagic lesion versus normal brain parenchyma were higher on EPI and FLAIR images (p<0.01). There was no difference in CNR between EPI and FLAIR (p>0.10). On MR images obtained 30 minutes and 1 hour after the onset of intracerebral hemorrhage, the lesion detection was feasible on both EPI and FSE T2 images showing high signal intensity. Conclusion : EPI showed higher detection rate as compared with other MR sequences and could be useful in early detection and evaluation of intracerebral hemorrhage.