• Journal of the Korean School Mathematics Society
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• v.26 no.1
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• pp.21-47
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• 2023

This study examines the activity system of teaching and learning about informal statistical inference using sampling simulation, based on cultural-historical activity theory. The research explores what contradictions arise in the activity system and how the system changes as a result of these contradictions. The participants were 20 elementary school students in the 5th to 6th grades who received classes on informal statistical inference using sampling simulations. Thematic analysis was used to analyze the data. The findings show that a contradiction emerged between the rule and the object, as well as between the mediating artifact and the object. It was confirmed that visualization of empirical sampling distribution was introduced as a new artifact while resolving these contradictions. In addition, contradictions arose between the subject and the rule and between the rule and the mediating artifact. It was confirmed that an algorithm to calculate the mean of the sample means was introduced as a new rule while resolving these contradictions.

• Journal of Magnetics
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• v.21 no.3
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• pp.421-424
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• 2016

The purpose of this study is to evaluate an effectiveness of switching turbo direction to improve motion artifacts of small bowels and aorta. From June to October 2015, 60 patients suspected of having Crohn's disease were enrolled. The MR Enterography scans were performed using same protocol other than the turbo direction: with the Z phase encoding (group A) and with Y phase encoding (group B). Qualitative analysis of each group was performed to evaluate the effectiveness of switching turbo direction from Z to Y. As a result, the 5-point Likert scale for paired observers were $2.33{\pm}0.88$ for group A and $3.80{\pm}0.85$ for group B on dynamic contrast enhanced coronal images. In conclusion, group B is proved to be superior to group A and can lessen the motion artifacts derived from phase shifts.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.2
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• pp.112-117
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• 2008

Artifact corrections including normalization and attenuation correction were important for quantitative analysis in Nuclear Medicine Imaging. Normalization is the process of ensuring that all lines of response joining detectors in coincidence have the same effective sensitivity. Failure to account for variations in LOR sensitivity leads to bias and high-frequency artifacts in the reconstructed images. Attenuation correction is the process of the correction of attenuation phenomenon lies in the natural property that photons emitted by the radiopharmaceutical will interact with tissue and other materials as they pass through the body. In this paper, we will review the several approaches for normalization and attenuation correction strategies.

• Proceedings of the KIEE Conference
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• 2002.07d
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• pp.2777-2779
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• 2002

본 논문에서는 영상안에서의 노이즈를 제거하기 위한 방법과 영상을 압축하기 위한 방법을 제안하였다. 영상을 필터링하기 위한 방법으로 해상도의 손상 없이 영상의 신호대잡음비(SNR)를 개선시킬 수 있는 국부 형태 적응 필터링을 제안하였다. 제안한 알고리즘에서는 템플릿 형태가 고정되어 있는 기존의 필터링 방법 대신에 다중 템플릿들을 정의하였다. 적응 템플릿 필터링을 자기공명영상에 적용할 때 기존의 필터링 방법들에 비하여 향상된 결과를 얻을 수 있으나. $T_1$ 영상과 같이 비교적 작은 동적 범위를 가진 영상에서는 에지에서 계단모양의 artifact가 발견되곤 한다. 본 논문에서는 다중 성분을 갖는 복셀들을 선별하여 이들에 대해서는 가장 큰 크기의 템플릿을 할당함으로써 artifact를 제거하는 방법을 제안하였다. 영상 압축에 있어서는 두 가지 모델이 제안되었다. 첫 번째로, 향상된 정수 기반 웨이블렛 변환을 사용한 무손실에 가까운 압축을 제안하였으며, 두 번째로, 완전 복원이 가능한 정수 기반 웨이블렛 변환을 사용한 통합된 유/무손실 압축을 제안하였다. 모의 실험에서, 제안된 알고리즘에 의해 재구성된 영상들은 부동 소수점 기반 웨이블렛 변환과 JPEG에 의해 재구성된 영상들에 비해 높은 신호대잡음비를 보였다.

• Proceedings of the Korea Institute of Convergence Signal Processing
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• 2000.08a
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• pp.309-312
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• 2000

In this work, a new algorithm for canceling MRI artifact due to translational motion in image plane is described. In the previous approach, the motions in the x direction and the y direction are estimated simultaneously. By analyzing their features, each x and y directional motion is canceled by different algorithms in two steps. First, it is noticed that the x directional motion corresponds to a shift of the x directional spectrum of the MRI signal. Next, the y directional motion is canceled by using a new constraint condition. This algorithm is shown to be effective by using a phantom image with simulated motion.

• Journal of radiological science and technology
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• v.40 no.1
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• pp.19-25
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• 2017

The aim of this study was to evaluate Magnetic Resonance Imaging safety by measuring the translational attraction, torque and susceptibility artifact for Bone-Anchored Hearing Aid (BAHA) implant at 1.5 T and 3.0 T MRI by standard criteria. In vitro assessment tools were made of acrylic-resin by American Society for Testing and Materials (ASTM) F2052-06 and F2119-07 standard. Translational attraction of BAHA implant was measured by the maximum deflection angle at 96 cm position, where the magnetically induced deflection was the greatest. The torque was assessed by the qualitative criteria of evaluating the alignment and rotation pattern, when the BAHA implant was positioned on a line with $45^{\circ}$ intervals inside the circular container in the center of the bore. The susceptibility artifact images were obtained using the hanged test tool, which was filled with $CuSO_4$ solution. And then the artifact size was measured using Susceptibility A rtifact Measurement (SA M) software. In results, the translational attraction was 0 mm at both 1.5 T and 3.0 T and the torque was 0(no torque) at 1.5 T, and +1(mild torque) at 3.0 T. The size of susceptibility artifacts was between 13.20 mm and 38.91 mm. Therefore, The BAHA implant was safe for the patient in clinical MR environment.

• Journal of the Korean Society of Radiology
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• v.13 no.1
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• pp.31-37
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• 2019

The study analyzes Non SEMAC and SEMAC to reduce susceptibility artifacts that may occur when performing magnetic resonance imaging(MRI) of metal patients. The Foot and Ankle Phantom was used as the experimental tool and the 3.8 cm general screw was used to make the magnetic susceptibility artifact. The experimental equipment was used 3.0T Magnetom Skyra and the area was measured with the 17th image where the signal off is the most noticeable in the obtained image. Statistical analysis was performed using the SPSS(Ver.25) program and the significance was assessed by the Wilcoxon Signed Rank Test. As a result, the area of Non SEMAC which is the lowest signal was $289.53{\pm}23.07197mm$. When the Turbo Factor was changed to 3, 4, and 5 after SEMAC use, it decreased to $125.02{\pm}7.45875mm$, $120.96{\pm}12.01704mm$ and $108.79{\pm}16.53498mm$, respectively. In conclusion, this study demonstrates that Using SEMAC with Turbo Factor effectively reduces the susceptibility artifacts.

• Archives of Pharmacal Research
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• v.10 no.3
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• pp.200-201
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• 1987

Frangufoline (sanjoinine-A) (1) was transformed into its epimer, sanjoinine-$Ah_1$(2) on heat treatment. Absolute configuration of (1) and (2) was determined.

• The Journal of Korea Assosiation for Disability and Oral Health
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• v.15 no.1
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• pp.74-78
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• 2019

Atypical teratoid rhabdoidal tumor(AT/RT) is a rare and fast-growing tumor usually diagnosed in childhood. Routine magnetic resonance imaging(MRI) assessment of AT/RT patients is done to detect metastatic tumors and recurrent lesions. The purpose of this case report is to present a case about caries treatment of a 3-year-8-month old female patient with AT/RT under general anesthesia. A 3-year-8-month old patient with AT/RT visited Seoul National University Dental Hospital for caries treatment. At the first dental visit, she was receiving chemotherapy. Multiple caries were observed from clinical and radiographic examination. The dental procedure was successfully performed under general anesthesia. Patients with brain tumor may take routine MRI to detect metastatic tumors and recurrent lesions. Dentists should take into consideration of possible dislodgement of restoration by ferromagnetic properties and artifact formation on MRI image. Ready-made zirconia crowns can be a good restoration option for such patients.

• Journal of Conservation Science
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• v.24
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• pp.43-56
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• 2008

When we consolidate the iron artifacts, only we used VM&P Naphtha as solvent of paraloid NAD10. After consolidating the iron artifacts using paraloid NAD10, artifacts were too glossy to exhibit and see. We choose the solvent YK-VMP as solvent of paraloid NAD10 for complementing this defect and examined characterizations of paraloid NAD10 films in each solvent. As a result of evaluation by several surface analysis such as optical microscope, measuring film thickness, adhesive strength, gloss of surface, contact angle, yellowing test and EIS, it is possible to use YK-VMP instead of VM&P Naphtha as solvent of paraloid NAD10, because YK-VMP lowered surface gloss and did not change the effect of consolidation.