• Title, Summary, Keyword: 자화율

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A Study of Susceptibility Decomposition in MRI (자기 공명 영상 시스템에서 자화율 분해 영상법에 관한 연구)

  • 노용만;홍인기
    • Journal of Biomedical Engineering Research
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    • v.16 no.4
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    • pp.395-402
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    • 1995
  • The intravoxel spin phases in magnetic resonance imaging (MRI) usually vary due to susceptibility differences of materials to be imaged. The phase variation in the voxel results in a reduction of the signal intensity. This signal intensity reduction is known as the susceptibility effect in MRI and has been studied extensively. In this paper, a new spectral decomposition technique Is proposed and the signal change due to the susceptibility effect can be analyzed. A pulse sequence for the spectral decomposition of the susceptibility was developed and applied to susceptibility imaging of venous blood possessing paramagnetic properties. The computer simulations and their corresponding experimental results obtained using both a phantom and human volunteers are reported. Key words : susceptibility effect in MRI : spectral decomposition of susceptibility effect.

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Magnetic Susceptibility depending on the Thermal Degradation of HK-40 Steel (HK-40강의 열화도에 따른 자화율의 변화)

  • Kim, Jeong-Min;Son, De-Rac;Park, Jong-Seo;Nahm, Seung-Hoon;Kim, Dong-Gyun;Han, Sang-In;Choi, Song-Chun;Ryu, Dae-Hyun
    • Journal of the Korean Society for Nondestructive Testing
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    • v.24 no.1
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    • pp.22-28
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    • 2004
  • Since the used materials of furnace heater tube with different kinds of thermal degradation were not commonly available, the HK-40 steel specimens were heat-treated isothermally at elevated temperature to simulate the microstructure at the service temperature. HK-40 steel specimens with five different aging time were prepared by isothermal heat treatment at $1050^{\circ}C$. The characteristics of the magnetic susceptibility have been investigated for the degradation evaluation of HK-40 steel. The magnetic susceptibility at room temperature increases as the extent of degradation of the materials increases. The variation of magnetic susceptibility was compared with the variation of tensile properties and Vickers hardness. To investigate the effect of the microsturctural change on the characteristics of tensile properties, hardness and magnetic susceptibility, the microstructures were examined by a scanning electron microscope(SEM) and the chemical compositions were analyzed by a energy spectrometer of SEM. As a result, the magnetic susceptibility method can be suggested as one of the nondestructive evaluation methods for the degradation of the HK-40 steel.

Survivability of In Vitro Fertilized and Somatic Cell Nuclear Transfer Bovine Embryos Following Vitrification (소 체외수정란 및 체세포 복제란의 초자화 동결 후 생존성)

  • Kwon, Dae-Jin;Park, Joo-Hee;Park, Choon-Keun;Yang, Boo-Keun;Cheong, Hee-Tae
    • Reproductive and Developmental Biology
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    • v.31 no.1
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    • pp.29-33
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    • 2007
  • This study was conducted to examine the development of in vitro fertilized (IVF) and nuclear transfer (NT) embryos following vitrification IVF and NT embryos developed to the blastocyst stage were equilibrated by 3 steps, vitrified and thawed, and their survival and hatching rates were examined. In IVF embryos, higher survival (82.1%, 96/117) and hatching rates (64.1%, 75/117) were obtained respectively after thawing and culture in expanded blastocysts compared to blastocysts (p<0.05). High survival and hatching rates were also obtained by vitrification of NT blastocysts, especially in expanded and hatching blastocysts (81.1 and 78.3%, respectively). The result of this study shows that IVF and NT blastocysts, especially late stage blastocysts, are successfully cryopreserved by vitrification.

Adaptive Requantization Technique for Efficient Transcoding in MPEG Bitstreams (MPEG 비트스트림 상의 효율적인 트랜스코딩을 위한 재양자화 기법)

  • Kim Jongho;Jeong Jechang
    • Proceedings of the Korean Society of Broadcast Engineers Conference
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    • pp.47-51
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    • 2004
  • 다양한 형태의 유무선 네트워크 환경에서의 비디오 서비스를 위해 컨텐츠의 비트율을 각 환경에 맞게 조절하는 트랜스코딩 기술이 필수적인 요소로 대두되고 있다. 본 논문에서는 MPEG 비트스트림의 효율적인 트랜스코딩을 위한 적응적 재양자화 기법을 제안한다. 압축된 비트스트림 상에서 비트율 변화를 위해서는 양자화 파라미터를 변화시켜야 하는데 이 과정에서 재양자화 에러가 발생하여 화질 및 비트율 조절에 큰 문제가 되고 있다 본 논문에서는 다양한 테스트 영상에 대해서 비트율 변화에 대한 왜곡 정도를 테스트한 결과 특정 양자화 파라미터 비율 구간에 대해서 왜곡 현상이 심해지는 현상에 따라 이를 효율적으로 모델링하는 기법을 제안한다. 또한 제안한 모델에 근거하여 영상에 적응적인 재양자화 알고리즘을 제안한다. 제안한 알고리즘은 적은 비트율을 가지면서 화질을 유지하고 간단한 조건 및 연산에 기반하여 실시간 구현이 가능하다.

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A study on the reduction on magnetic susceptible artifacts through the usage of silicon (실리콘을 이용한 자화율 인공물의 감소에 관한 연구)

  • Choi, Kwan-Woo;Lee, Ho-Beom
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.13 no.12
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    • pp.5937-5942
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    • 2012
  • This study used silicon that is similar to the density of the tissue of the human body to compensate for the uneven areas that are in contact with air in order to reduce susceptible artifacts. The subjects of the study were 16 normal people and the areas of the human body in which there are a lot of uneven areas with complicated structure and a lot of susceptible artifacts were formed since the surface area that comes into contact with the air is large were the areas that were chosen to be examined. A 3.0T superconducting magnetic resonance device was used as the test equipment and SPIR images that are sensitive to magnetic differences were obtained as sagittal planes on a line that extended the metatarsal and the phalanges, including the middle of the longitudinal arc and the 5 distal phalanxes. The method of analysis was to reduce the susceptibility between the tissue and the air to discover the reduction of susceptible artifacts by comparing the SNR and CNR before and after applying silicon. A statistical analysis was utilized for the sample matching T examination. The results of the study revealed that the susceptible artifacts were reduced in the images of the uneven areas that were compensated and applied with silicon. The SNR increased in significant amount in correlation from $3.91{\pm}1.33$ before application to $21.69{\pm}4.52$ after application and the CNR decreased in significant amount in correlation from $28.97{\pm}8.20$ before application to $4.88{\pm}2.14$. In conclusion, this study did not affect the voxel but it was an innovative method of improvement that compensated for the fundamental issue of the difference in susceptibility between the air and the body. The application is simple and the study has great significance in that it proposed a method to reduce susceptible artifacts in a low cost and highly efficient manner.

Dynamic Responses in Ultra-Soft Magnetic Thin Films (초 연자성 박막에서의 동적 자화 거동)

  • 정인섭
    • Journal of the Korean Magnetics Society
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    • v.4 no.1
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    • pp.1-6
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    • 1994
  • The magnetization dynamics was investigated by solving possible origins of overdamped susceptibility observed in ultra-soft magnetic amorphous thin films. The experimental high frequency spectrum and computational spectrum calculated from Gilbert's equation of motion were compared in order to find proper damping factor $\alpha{\approx}20$ and demagnetizing coefficients $D_{x}{\approx}D_{y}{\approx}D_{z}{\approx}0$ for ultra-soft magnetic films. A magnetization vortex mode was, then, proposed to explain the origin of the reversible susceptibility and other anomalies of the ultra-soft magnetic heterogeneous thin films. In this mode it is suggested that there occur, within the nanoscale structural features of the ultra-soft films, incoherent rotational spin motions that are highly damped by the energy transfer from short wavelength spin wave modes and local defect structure mode interactions.

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Clinical Applications of Neuroimaging with Susceptibility Weighted Imaging: Review Article (SWI의 신경영상분야의 임상적 이용)

  • Roh, Keuntak;Kang, Hyunkoo;Kim, Injoong
    • Investigative Magnetic Resonance Imaging
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    • v.18 no.4
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    • pp.290-302
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    • 2014
  • Purpose : Susceptibility-weighted magnetic resonance (MR) sequence is three-dimensional (3D), spoiled gradient-echo pulse sequences that provide a high sensitivity for the detection of blood degradation products, calcifications, and iron deposits. This pictorial review is aimed at illustrating and discussing its main clinical applications. Materials and Methods: SWI is based on high-resolution, 3D, fully velocity-compensated gradient-echo sequences using both magnitude and phase images. To enhance the visibility of the venous structures, the magnitude images are multiplied with a phase mask generated from the filtered phase data, which are displayed at best after post-processing of the 3D dataset with the minimal intensity projection algorithm. A total of 200 patients underwent MR examinations that included SWI on a 3 tesla MR imager were enrolled. Results: SWI is very useful in detecting multiple brain disorders. Among the 200 patients, 80 showed developmental venous anomaly, 22 showed cavernous malformation, 12 showed calcifications in various conditions, 21 showed cerebrovascular accident with susceptibility vessel sign or microbleeds, 52 showed brain tumors, 2 showed diffuse axonal injury, 3 showed arteriovenous malformation, 5 showed dural arteriovenous fistula, 1 showed moyamoya disease, and 2 showed Parkinson's disease. Conclusion: SWI is useful in detecting occult low flow vascular lesions, calcification and microbleed and characterising diverse brain disorders.

Magnetic Field Dependence of Brownian Motion in Iron-oxide Nanoparticles (산화철 나노입자의 브라운 운동에 대한 자기장 의존성 연구)

  • Jung, Eun Kyung;Yoon, Seok Soo;Kim, Dong Young
    • Journal of the Korean Magnetics Society
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    • v.26 no.1
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    • pp.13-18
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    • 2016
  • The ac magnetic susceptibility was measured in iron-oxide nanoparticles with average size of 26 nm, which were uniformly dispersed in organic solvent. The ac magnetic susceptibility measured under zero magnetic fields was well fitted with Debye relaxation model and the relaxation frequency was 370 Hz. The relaxation frequency of the nanoparticles coincided with relaxation time of the Brownian motion, which is due to the viscosity of the liquid medium in which magnetic nanoparticles dwell. The Brown relaxation frequencies were linearly increased with magnetic field.

Magnetization characteristics of melt-textured Y-Ba-Cu-O with BaCe$O_{3}$ addition (용융공정으로 제조한 Y-Ba-Cu-O/BaCe$O_{3}$ 초전도체의 자화특성)

  • Kim, Chan-Jung;Park, Hae-Ung;Kim, Gi-Baek;Hong, Gye-Won
    • Korean Journal of Materials Research
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    • v.5 no.4
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    • pp.433-444
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    • 1995
  • BaCe$O_{3}$를 첨가하여 용융공정으로 제조한 단결정형 Y$Ba_{2}$$Cu_{3}$$O_{x}$(1-2-3) 초전도체의 온도에 대한 자화특성을 연구하였다. 고상반응법과 용융공정으로 0에서 30wt% BaCe$O_{3}$를 1-2-3 결정내에 미세 분산시켰다. 초전도체의 자화특성은 VSM(vibrating sample magnetometer)을 사용하여 77K, 60K, 40K와 20K, 2 Tesla 자장범위에서 측정하였다. BaCe$O_{3}$를 첨가하지 않은 겨우나 5wt% BaCe$O_{3}$를 첨가한 1-2-3 결정의 경우, 77K, 외부자장이 증가시 자화율 차이가 증가하는 비정상 자화특성이 관찰된다. 측정온도가 60K에서는 제2차 최대점이 나타나는 자장값이 고자장쪽으로 이동한다. 20K와 40K의 저온에서는 비정상자화특성이 2 T의 자장범위까지 관찰되지 않았다. 15wt%와 20wt% BaCe$O_{3}$첨가한 시편에서는 자장이 증가하면 자화율차이가 단순히 감소한다. Y-Ba-Cu-O의 flux pinning 기구를 BaCe$O_{3}$첨가에 의한 미세조직변화로 설명하였다.

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