• Nuclear Medicine and Molecular Imaging
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• 제42권2호
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• pp.118-126
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• 2008

Statistical image reconstruction methods have played an important role in emission computed tomography (ECT) since they accurately model the statistical noise associated with gamma-ray projection data. Although the use of statistical methods in clinical practice in early days was of a difficult problem due to high per-iteration costs and large numbers of iterations, with the development of fast algorithms and dramatically improved speed of computers, it is now inevitably becoming more practical. Some statistical methods are indeed commonly available from nuclear medicine equipment suppliers. In this paper, we first describe a mathematical background for statistical reconstruction methods, which includes assumptions underlying the Poisson statistical model, maximum likelihood and maximum a posteriori approaches, and prior models in the context of a Bayesian framework. We then review a recent progress in developing fast iterative algorithms.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.472-472
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• 2010

The tomography has played a key role in tokamak plasma diagnostics for image reconstruction. The Phillips-Tikhonov (P-T) regularization method was attempted in this work to reconstruct cross-sectional phantom images of the plasma by minimizing the gradient between adjacent pixel data. Recent studies about the comparison of the several tomographic reconstruction methods showed that the P-T method produced more accurate results. We have studied existing Laplacian matrix used in Phillips-Tikhonov regularization method and developed modified Laplacian matrix (Modified L). The comparison of the reconstruction result by the modified L and existing L showed that modified L produced more accurate result. The difference was significantly pronounced when a portion of plasma was reconstructed. These results can be utilized in the Edge Plasma diagnostics; especially in divertor diagnostics on tokamak a large impact is expected. In addition, accurate reconstruction results from received data in only one direction were confirmed through phantom test by using P-T method with modified L. These results can be applied to the tangentially viewing pin-hole camera diagnostics on tokamak.

• 한국음향학회지
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• 제16권1호
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• pp.33-38
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• 1997

본 논문에서는 음향-광 효과를 이용한 STAM 시스템으로부터 얻을 수 있는 토모그라픽 영상의 분해능을 해석하였다. 이를 위하여 BFP 토모그라픽 복원 알고리즘을 이용하여 초음파변환기 회전장치와 시료 회전장치에 대한 측방향과 축방향 분해능을 해석하였다. Matlab을 이용한 분석결과, 축방향 분해능은 두 회전장치 모두 약 1.5 파장정도로 좋은 분해능을 나타내었다. 측방향 분해능은 시료 회전장치인 경우 x와 yqkdgid에서 0.53 파장의 동일한 분해능을 보였으며 초음파변환기 회전장치인 경우에는 x와 yqkdgid에서 각각 0.56 및 0.70 파장의 분해능을 나타내었다. 결과적으로 STAM 시스템은 시료회전장치를 사용할 때 더 좋은 분해능을 얻을 수 있음을 보였다.

• 대한전자공학회논문지
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• 제16권6호
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• pp.16-21
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• 1979

단순역투사에 의하여 얻어진 선명치 않은 영상에서 단층영상을 재구성할 수 있는 이차원 필터들을 주파수영역에서 고찰하고 이의 성능을 비교하였다 이 필터 함수들은 단층영상시스템의 전달함수로부터 구하였으며 그 모양은 ramp 함수에 window 함수를 곱한 형태로 되어 있다. 이 window 함수는 영상 재구성에서의 불필요한 잡음화상을 줄이는 역할을 하는 것이 모의영상 데이터를 이용한 computer simulation에서 밝혀졌다. 또한 simulation의 결과로 이차원 영상 재구성 방법이 일차원 convolution mehod에 의한 영상 재구성에 비해서 화질은 나쁘지만 계산시간은 십배 이상 단축됨을 발견하였다. 이차원 영상 재구성에서는 window 함수가 변함에 따라 재구성된 영상의 화질도 달라진다. 즉 영상의 해상도를 높일 수록 잡음이 많이 섞인 화상을 얻게 되는 것을 재구성한 영상들을 통하여 고찰하였다.

• 대한전자공학회논문지
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• 제27권2호
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• pp.16-30
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• 1990

지금까지 마이크로웨이브 영상은 주로 파수영역의 해석에 의해 2차원 푸리에 역변환으로 물체의 영상을 재현하였다. 본 논문에서는 공간영역에서 코히어런트 단층촬영 방법으로 영상을 제한할 수 있는 새로운 식을 유도하고 X-ray 단층촬영에 널리 이용되고 있는 filtered-backprojection 알고리듬을 적용하여 line 및 원통 도체에 대한 영상을 수치계산에 의해 재현하였다. 제시된 공간영역의 해석은 기존의 파수영역의 문제점인 interpolation 및 원점에 대칭인 도체의 영상재현시 나타나는 영상의 artifact을 완전히 해결할 수 있음은 물론, 보다 좋은 영상의 질을 얻을 수 있었다. 또한 파수영역의 해석과는 달리, 모멘트 방법을 적용하여 좁은 주파수 대역폭으로도 초고해상도를 얻을 수 있는 가능성을 line 물체의 영상을 통해 보였다.

• Applied Microscopy
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• 제38권3호
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• pp.275-278
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• 2008

Electron tomography (ET) is an electron microscopic technique for obtaining a 3-D image from any electron microscopy specimen and its application in biomedical science has been increased thanks to development of electron microscopy and related technologies during the last decade. There are few researches on ET in Korea during this period. Although the importance of ET has been recognized recently by many researchers, initial approach to electron tomographic research is not easy for beginners. The 4th International Congress on Electron Tomography (4 ICET) was held on Nov $5{\sim}8$, 2006, at San Diego. The program dealt instrumentation, reconstruction algorithm, visualization/quantitative analysis and electron tomographic presentation of biological specimen and nano particles. 1 have summarized oral presentations and analyzed the posters presented on the meeting. Cryo-electron microscopic system was popular system for ET and followed conventional transmission electron microscopic system. Cultured cell line and tissue were most popular specimens analyzed and microorganisms including bacteria and virus also constituted important specimens. This analysis provides a current state of art in ET research and a guide line for practical application of ET and further research strategies.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.1301-1302
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• 2008

In this study, the fracture strength for fracture mechanism porous calcium phosphate made from sintered with ${\beta}$-tricalcium phosphate obtained by wet precipitation procedure is analyzed using finite element method and experiment measurement. First, three $3{\times}3{\times}3mm^3$ and $5{\times}5{\times}5mm^3$ specimens are prepared and tomographic images of one $5{\times}5{\times}5mm^3$ specimen are obtained by micro focus X-ray CT. The compression tests using the specimens are carried out to measure the elastic modulus and fracture strength to analyze the fracture mechanism of porous calcium phosphate specimen. The tomographic images are reconstructed by 3D reconstruction program. The finite elements are directly built up in the reconstructed specimen. The numerical simulation for the compression tests is performed using the element. The mechanism of calcium phosphate of simulation are obtained by the compression tests using there cylindric specimen of height 19.5 mm and diameter 10 mm. From the results, the applicability of porous calcium phosphate is evaluated to care fracture and vacant bone of a patient as the reinforcement material.

• 한국안전학회지
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• 제18권4호
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• pp.98-104
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• 2003

Various nondestructive evaluation (NDE) techniques have been studied to locate steel rebars of dowel, and to detect invisible damage such as voids and cracks inside concrete and debonding between rebars and concrete caused by corrosions and earthquakes. In this study, the aurhors developed 3-dimensional (3D) electromagnetic (EM) imaging technology to detect such damage and to identify exact location of steel rebars of dowel. The authors have developed sub-surface two-dimensional (2D) imaging technique using tomographic antenna array in previous works. In this study, extending the earlier analytical and experimental works on 2D image reconstruction, a 3D microwave imaging system using tomographic antenna array was developed, and multi-frequency technique was applied to improve quality of the reconstructed image and to reduce background noises. This paper presents the analytical expressions of numerical focusing procedures for 3D image reconstruction and numerical simulation to study the resolution of the system and the effectiveness of multi-frequency technique. Also, the design of 4?4 antenna array with switching devices is introduced as a preliminary study for the final design of whole array.

• Nuclear Engineering and Technology
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• 제53권3호
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• pp.888-893
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• 2021

The International Atomic Energy Agency has developed a tomographic imaging system for accomplishing the total fuel rod-by-rod verification time of fuel assemblies within the order of 1-2 h, however, there are still limitations for some fuel types. The aim of this study is to develop a deep learning-based denoising process resulting in increasing the tomographic image acquisition speed of fuel assembly compared to the conventional techniques. Convolutional AutoEncoder (CAE) was employed for denoising the low-quality images reconstructed by filtered back-projection (FBP) algorithm. The image data set was constructed by the Monte Carlo method with the FBP and ground truth (GT) images for 511 patterns of missing fuel rods. The de-noising performance of the CAE model was evaluated by comparing the pixel-by-pixel subtracted images between the GT and FBP images and the GT and CAE images; the average differences of the pixel values for the sample image 1, 2, and 3 were 7.7%, 28.0% and 44.7% for the FBP images, and 0.5%, 1.4% and 1.9% for the predicted image, respectively. Even for the FBP images not discriminable the source patterns, the CAE model could successfully estimate the patterns similarly with the GT image.

• Journal of Mechanical Science and Technology
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• 제14권1호
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• pp.1-10
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• 2000

This work shows that it is possible to obtain information about more than one parameter from acoustic field information. A variety of ultrasonic Lamb wave modes were utilized to reconstruct thickness and density of an isotropic plate. An image reconstruction of one parameter (thickness of a plate) was carried out for four cases, i.e., the lowest symmetrical and anti symmetrical modes, and the fastest symmetrical and anti symmetrical Lamb waves among multiple modes. For two parameter reconstructions (thickness and density), the image processing was performed using the lowest symmetrical and antisymmetrical modes simultaneously. In this work, a modified version of algebraic reconstruction technique (ART), which is a form of finite-series expansion method, was employed to reconstruct the ultrasonically computed tomographic images. Results from several sample geometries are presented.