• Proceedings of the KSMRM Conference
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• 1999.04a
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• pp.130-136
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• 1999

척추의 MR촬영은 두부 다음으로 흔하게 시행되고 있는데, 척추의 해부학 적 구조물들은 일반적으로 널리 알려져 있고 이해하기가 쉽기 때문에 척추의 MR영상을 분석하는데 큰 어려움이 없을 수 있다. 관절부위를 포함한 근골격계 MR영상에서는 MR ar디facts가 병변을 관찰하는데 장애를 초래하여 위양성 혹은 위음성의 결과를 나타낼 수 있기 때문에 빈번히 언급되고 있다. 척추 MR영상을 판독하는 데는 다른 근골격계 영상에 비하여 artifact의 빈도 나 정도는 작지만, 의외로 많은 pitfall이나 ar디fact들이 관찰된다. 척추 MR 영상의 pitall과 artifact에 대한 정확한 인지와 이해가 필요한 이유는 MR영상에서 병변이 관찰되지 않거나 정상조직이 병변처럼 관찰될 수 있고, 또 병변의 특정을 잘못 판단할 수 있기 때문에 artifact를 교정하거나 최소화시키고, 방지할 수 있는 방법들을 사용하여 더욱 정확한 척추 MR영상의 결과를 얻는데 있다. 지면 관계상 모든 종류의 MR artifact를 언급하기 보다는 척추 MRI를 판독하면서 병변과 혼동을 주는 MR artifacts를 먼저 살펴보고, 진단적 오류를 범할 수 있는 pitfall들에 대하여 알아보도록 하겠다. 여기에서는 편의상 MR 촬영과 관계된 artifact들만을 artifact라고 하고 MR artifact와 직접적으로 연관이 없으면서 위양성이나 위음성을 초래할 수 있는 pitfall이나 variant를 pitfall로 묵어서 설명하겠다.

• Proceedings of the KSMRM Conference
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• 2001.11a
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• pp.73-83
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• 2001

영상의 좋고 나쁨을 나타낼 때는 대조도, 해상도, 잡음 그리고 Artifact 등을 정량적으로 측정하거나 기준이 되는 영상과 정성적으로 비교하게 된다. 이 중에서 Artifact는 영상의 해부학적 진단에 오류를 범하게 하여 엉뚱한 병리학적 해석을 내리게 하거나 해석이 불가능하게 하기도 하므로 적절한 규명을 하여 그 원인을 제거하는 등, 응당한 조치를 취해 최상의 화질을 유지하기 위한 노력을 기울여야한다. MR 영상에서 Artifact는 기하학적 늘림(stretch), 주름(wrinkle), 왜곡(distortion), 허상(ghost), 줄(line), 눈잡음(snow noise), 신호의 증감 등과 같은 다양한 현상으로 나타나며 이들은 영상을 해석할 때 오류를 범하는 원인이 된다. Artifact의 발생원인으로는 MR 장치의 기능장애, 부적절한 영상기법의 구사, 또는 MR 영상의 고유한 성질에 기인하기도 한다. MR Artifacts의 근본적인 이해를 위해서는 MRI의 물리적 원리와 장비에 관한 이해가 필요하다. 이렇게 MR Artifact는 여러 가지 인자들이 복합적인 관계를 가지고 나타나기 때문에 분류하기가 쉽지 않지만 전형적인 양상과 원인 그리고 그에 대한 여러 가지 대책을 살펴보고자 한다.

• Investigative Magnetic Resonance Imaging
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• v.23 no.4
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• pp.341-350
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• 2019

Purpose: To determine the MR parameters affecting India ink artifacts on opposed-phase chemical shift magnetic resonance (MR) imaging. Materials and Methods: The use of a female Sprague-Dawley rat was approved by our Institutional Animal Care and Use Committee. Using an iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) images, which is a modified Dixon method, axial opposed-phase images of the abdominal cavity were obtained with different MR parameters: series 1, different repetition times (TRs; 400, 2000, and 4000 ms); series 2, different echo times (TEs; 10, 50, and 100 ms); series 3, different field of views (FOVs; 6, 8, 16, and 24 cm); series 4, different echo train lengths (ETLs; 2, 4, and 8); series 5, different bandwidths (25, 50, and 85); and series 6, different slice thicknesses (1, 2, 4, 8, and 16 mm). Artifacts on opposed images obtained with different parameters were compared subjectively by two radiologists. For objective analysis, the thickness of the artifact was measured. Spearman's correlation between altered MR parameters and thicknesses of India ink artifact was obtained via objective analysis. Results: India ink artifact was increasingly apparent using shorter TE, larger FOV and ETL, and thicker slices upon subjective analysis. The objective analysis revealed a strong negative correlation between the thickness of the artifact and TE (r = -0.870, P < 0.01); however, strong positive correlations were found between FOV (r = 0.854, P < 0.01) and slice thickness (r = 0.971, P < 0.01). Conclusion: India ink artifact was thicker with shorter TE, larger FOV, and larger slice thickness.

• Journal of Korea Multimedia Society
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• v.19 no.2
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• pp.375-385
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• 2016

Recently, several implantable hearing aids such as cochlear implant, middle ear implant, etc., which have a module receiving power and signal from outside the body, are frequently used to treat the hearing impaired patients. Most of implantable hearing aids are adopted permanent magnet pairs to couple between internal and external devices for the enhancement of power transmission. Generally, the internal device which containing the magnet in the center of receiving coil is implanted under the skin of human temporal bone. In case of MRI scanning of a patient with the implantable hearing aid, however, homogeneous magnetic fields of the MRI might be interfered by the implanted magnet. For the above reasons, the MR image is degraded by large area of artifact, so that diagnostics are almost impossible in deteriorated region. In this paper, we proposed an external coil system that can reduce the artifact of MR image due to the internal coupling magnet. By finite element analysis estimating area of MR artifact according to varying current and shape of the external coil, optimal coil parameters were extracted. Finally, the effectiveness of the proposed external coil system was verified by confirming the artifact at real MRI scan.

• Journal of the Korean Society of Radiology
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• v.16 no.7
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• pp.835-842
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• 2022

This study is aimed to evaluate the effects of a synthetic MR technique in reducing metal artifacts. In the experiment, the in-plane and through-plane images were acquired by applying a synthetic MR technique and a high-speed spin echo technique to a phantom manufactured with screw for spinal surgery. The area of the metal artifact was compared. The metal artifacts were measured by dividing the signal-loss and the signal pile-up areas, and the area of the final artifact was calculated through the sum of the two. As a result, the metal artifacts were relatively reduced when the synthetic MR techniques were applied to both in-plane and through-plane. Comparing by sequence, the in-plane T1 images decreased by 23.45%, T2 images by 20.85%, PD images by 19.67%, and FLAIR images by 22.12%. Also, in the case of the through-plane, the T1 image decreased by 62.95%, the T2 image decreased by 73.93%, the PD image decreased by 74.68%, and the FLAIR image decreased by 66.43%. The cause of this result is that when the synthetic MR technique is applied, the distortion is due to the signal pile-up and does not occur and the size of the entire metal artifact is reduced. Therefore, synthetic MR technique can very effectively reduce metal artifacts, which can help to increase the diagnostic value of images.

• The Journal of Korean Society for Radiation Therapy
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• v.17 no.1
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• pp.45-55
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• 2005

Purpose : To evaluate the usefulness of the handmade patient immobilization device and to report the clinical results of it. Materials and methods : We made two fusion images and analyzed those images. One image is made with diagnostic MR image and CT image, the other with therapeutic planning MR image and CT image. With open head holder, we measured the skin dose and attenuation dose. Also, we made the planning CT couch plate with acrylic plate and styrofoam and compared artifact. Results : We could get more accurate fusion image when we use MR head holder(within 2mm error). The skin dose was reduced 2 times and the attenuation dose was reduced more than $20\%$ when open head holder used. The planning CT couch plate was more convenient than conventional board and reduced artifact remarkably. Conclusion : We could verify the localization point in the MR image which is taken with MR head holder. So we could fuse the image more accurately. The same method could be applied to PET and US image, if the alike immobilization device used. With open head holder, the skin dose and the attenuation dose was reduced. And those above devices could substitute for expensive foreign device, if those are manufactured adequately.

• Investigative Magnetic Resonance Imaging
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• v.22 no.4
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• pp.266-271
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• 2018

A 66-year-old woman was referred for treatment of incidental detection of two intracranial aneurysms. Time-of-flight MR angiography (TOF MRA) revealed two aneurysms at the M1 segment of the right middle cerebral artery, and clinoid segment of left internal carotid artery, respectively. On digital subtraction angiography, there was a saccular aneurysm on the left internal carotid artery, but the other aneurysm was not detected on the right middle cerebral artery. Based on comprehensive review of imaging findings, organized thrombosed aneurysm was judged as the most likely diagnosis. In the presented report, magnetization transfer (MT) pulse to TOF MRA was used, to differentiate aneurysm-mimicking lesion on TOF MRA. We report that MT technique could be effective in differentiating true aneurysm, from possible T1 high signal artifact on TOF MRA.

• Journal of Digital Contents Society
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• v.11 no.1
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• pp.73-78
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• 2010

This study attempted to examine whether the propeller diffusion weighted image method may remove magnetic susceptibility artifacts caused by metallic materials. A comparison of occurrence rates of magnetic susceptibility artifacts in the four regions, both temporal lobes, pons, and orbit, between b = 0 and b = 1,000 s/mm2 images was made after obtaining echo-planar diffusion weighted image, propeller diffusion weighted image, and ADC map images, respectively, from a total of 20 patients who had MRI shots taken of their brain and were found to be with retained metallic foreign bodies within their teeth using a 3.0T MR scanner. In the case of echo-planar diffusion weighted image technique, the presence of metallic materials may bring in some limits on accurate diagnosis due to magnetic susceptibility artifacts, while the propeller diffusion weighted image technique where magnetic susceptibility artifacts decrease is expected to be more useful in ensuring accurate diagnosis in the clinical context.

• Journal of the Institute of Electronics and Information Engineers
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• v.53 no.3
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• pp.151-159
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• 2016

In this research, we tried to suggest moderate FA(Flip Angle) for CE(Contrast Enhnaced)-Head&Neck MR Angiography with Gadoteridol. For this study, we did test MR phantom and clinical study according to FA change. After that, quantitative analysis was progressed. The results of MR phantom study were as follow: RSP(Reaction Starting Point)was recorded within 300~400 mmol. MPSI(Max Peak Signal Intensity) was 2,086, 3,705, 5,109, 6,194, 7.096, 7,192 [a.u]. MPP(Max Peak Point) was shown at 30, 50, 50, 40, 50, 40 mmol. IRMPSI(Increase Rate of MPSI) was 77.6%, 37.9%, 21.2%, 14.6%, 1.4% as increasing of FA. The results of clinical study were as follow SICB(Signal Intensity of Carotid artery Bifurcation) was recorded respectively 392.5, 4165.2, 4270, 3502.2, 3263.7, 3119.6 [a.u]. ORA(Occurence Rate of Artifact) was increased as 0, 0, 20, 40, 50, 70%. According to this research, we are not only able to assure that increase of FA can be effect on H1 spin's SI(Signal Intensity) which was combined with gadolinium agent, but also be effect on artifact rate in blood vessel. In clinical field, we expect that CE-Head&Neck MR Angiography can be performed in a practical way with this research.

• Journal of KIISE:Software and Applications
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• v.31 no.4
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• pp.411-419
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• 2004

When the imaging object rotates in image plane during MRI scan, its rotation causes phase error and non-uniform sampling to MRI signal. The model of the problem including phase error non-uniform sampling of MRI signal showed that the MRI signals corrupted by rotations about an arbitrary center and the origin in image plane are different in their phases. Therefore the following methods are presented to improve the quality of the MR image which includes the artifact. The first, assuming that the angle of 2-D rotational motion is already known and the position of 2-D rotational center is unknown, an algorithm to correct the artifact which is based on the phase correction is presented. The second, in case of 2-D rotational motion with unknown rotational center and unknown rotational angle, an algorithm is presented to correct the MRI artifact. At this case, the energy of an ideal MR image is minimum outside the boundary of the imaging object to estimate unknown motion parameters and the measured energy increases when the imaging object has an rotation. By using this property, an evaluation function is defined to estimate unknown values of rotational angle at each phase encoding step. Finally, the effectiveness of this presented techniques is shown by using a phantom image with simulated motion and a real image with 2-D translational shift and rotation.