Wave Propagation Simulation Based on the Fourier Diffraction Integral for X-Ray Refraction Contrast Imaging-Computed Tomography

Won-Seok Chang,Jong-Ki Kim,Jin-Ho Cho,Jae-Hong Lim 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.69 No.6

With the advent of coherent X-ray sources, X-ray refraction has begun to be utilized for X-ray imaging of unprecedented sensitivity. The aim of this study was to develop a wave propagation simulator that provides a map of X-ray refraction after passing through an object. We applied the Fresnel diffraction integral for calculating the propagated wave and then obtained the refraction map by differentiating the phase in the refraction-analyzing direction. The simulation was validated by comparing the computed tomography (CT) reconstruction of a virtual phantom with its map of refractive index: the deviations were below 0.7% for soft tissues under our test condition. The simulator can be used for testing and developing highly-sensitive X-ray imaging techniques based on X-ray refraction analysis prior to experimentation.

지질불연속면에 대한 탄성파 굴절법탐사 자료처리 고찰 -GRM, GLI, Tomography()

김지수 ( Ji Soo Kim ),김수현 ( Su Hyun Kim ),이준호 ( Jun Ho Lee ),김원기 ( Won Ki Kim ),이용재 ( Yong Jae Lee ) 대한지질공학회 2006 지질공학 Vol.16 No.4

지하 불연속면의 탐지를 위한 굴절법 탄성파 자료에 대하여 3가지의 중요한 자료처리기법을 속도와 심도의 관점에서 비교 관찰하였다. 즉 수치모델링으로 생성된 수평 3층, 경사 3층, 수직단층, 매몰 수직 파쇄대 구조에 대한 발파점 자료들을 일반화된 역행 주시법(GRM), 일반화된 선형 역산법(GLI), 토모그래피를 적용하여 그 자료처리 결과들을 서로 비교·분석하였다. 토모그래피는 수직단층, 매몰 파쇄대등의 복잡한 지형기복에서 보다 정확한 지하속도구조를 파악할 수 있는 반면에 일반화된 역행 주시법(GRM)과 일반화된 선형 역산법(GLI)은 수평구조와 경사 경계면 등의 평면 불연속면에 효과적으로 나타나는데 이것은 이들 방법이 주시곡선의 초동 분석위주로 수행되기 때문인 것으로 해석된다. Three processing strategies of seismic refraction data are tested in terms of velocity and depth profiles or structures for mapping of geological discontinuities: GRM(generalized reciprocal method), GLI(generalized linear inversion), Tomography. The test data used in this study are the shot gathers reconstructed by numerical modeling for the structures of 3 planar layers(horizontal, inclined), the buried vertical fracture zones, and vertical fault zones. Tomography is shown to be very efficient for mapping of more complicated zone such as vertical fault and buried fracture zones, whereas GRM and GLI can be useful for horizontal and/or inclined layers, probably on their bases of analysis of first arrivals in travel time curves.

지질불연속면에 대한 탄성파 굴절법탐사 자료처리 고찰 -GRM, GLI, Tomography

김지수 ( Ji Soo Kim ),김수현 ( Su Hyun Kim ),이준호 ( Jun Ho Lee ),김원기 ( Won Ki Kim ),이용재 ( Yong Jae Lee ) 대한지질공학회 2006 지질공학 Vol.16 No.3

지하 불연속면의 탐지를 위한 굴절법 탄성파 자료에 대하여 3가지의 중요한 자료처리기법을 속도와 심도의 관점에서 비교 관찰하였다. 즉 수치모델링으로 생성된 수평 3층, 경사 3층, 수직단층, 매몰 수직 파쇄대 구조에 대한 발파점 자료들을 일반화된 역행 주시법(GRM), 일반화된 선형 역산법(GLI), 토모그래피를 적용하여 그 자료처리 결과들을 서로 비교·분석하였다. 토모그래피는 수직단층, 매몰 파쇄대등의 복잡한 지형기복에서 보다 정확한 지하속도구조를 파악할 수 있는 반면에 일반화된 역행 주시법(GRM)과 일반화된 선형 역산법(GLI)은 수평구조와 경사 경계면 등의 평면 불연속면에 효과적으로 나타나는데 이것은 이들 방법이 주시곡선의 초동 분석위주로 수행되기 때문인 것으로 해석된다. Three processing strategies of seismic refraction data are tested in terms of velocity and depth profiles or structures for mapping of geological discontinuities: GRM(generalized reciprocal method), GLI(generalized linear inversion), Tomography. The test data used in this study are the shot gathers reconstructed by numerical modeling for the structures of 3 planar layers(horizontal, inclined), the buried vertical fracture zones, and vertical fault zones. Tomography is shown to be very efficient for mapping of more complicated zone such as vertical fault and buried fracture zones, whereas GRM and GLI can be useful for horizontal and/or inclined layers, probably on their bases of analysis of first arrivals in travel time curves.

Holographic tomography: hardware and software solutions for 3D quantitative biomedical imaging (Invited paper)

Arkadiusz Kuś,Wojciech Krauze,Piotr L. Makowski,Małgorzata Kujawińska 한국전자통신연구원 2019 ETRI Journal Vol.41 No.1

In this paper, we demonstrate the current concepts in holographic tomography (HT) realized within limited angular range with illumination scanning. The presented solutions are based on the work performed at Warsaw University of Technology in Poland and put in context with the state of the art in HT. Along with the theoretical framework for HT, the optimum reconstruction process and data visualization are described in detail. The paper is concluded with the description of hardware configuration and the visualization of tomographic reconstruction, which is calculated using a provided processing path.

Refraction traveltime tomography based on damped wave equation for irregular topographic model

Park, Yunhui,Pyun, Sukjoon Elsevier 2018 Journal of applied geophysics Vol.150 No.-

<P><B>Abstract</B></P> <P>Land seismic data generally have time-static issues due to irregular topography and weathered layers at shallow depths. Unless the time static is handled appropriately, interpretation of the subsurface structures can be easily distorted. Therefore, static corrections are commonly applied to land seismic data. The near-surface velocity, which is required for static corrections, can be inferred from first-arrival traveltime tomography, which must consider the irregular topography, as the land seismic data are generally obtained in irregular topography.</P> <P>This paper proposes a refraction traveltime tomography technique that is applicable to an irregular topographic model. This technique uses unstructured meshes to express an irregular topography, and traveltimes calculated from the frequency-domain damped wavefields using the finite element method. The diagonal elements of the approximate Hessian matrix were adopted for preconditioning, and the principle of reciprocity was introduced to efficiently calculate the Fréchet derivative. We also included regularization to resolve the ill-posed inverse problem, and used the nonlinear conjugate gradient method to solve the inverse problem.</P> <P>As the damped wavefields were used, there were no issues associated with artificial reflections caused by unstructured meshes. In addition, the shadow zone problem could be circumvented because this method is based on the exact wave equation, which does not require a high-frequency assumption. Furthermore, the proposed method was both robust to an initial velocity model and efficient compared to full wavefield inversions. Through synthetic and field data examples, our method was shown to successfully reconstruct shallow velocity structures. To verify our method, static corrections were roughly applied to the field data using the estimated near-surface velocity. By comparing common shot gathers and stack sections with and without static corrections, we confirmed that the proposed tomography algorithm can be used to correct the statics of land seismic data.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A refraction traveltime tomography is developed to invert near-surface velocity. </LI> <LI> The finite-element method using unstructured mesh is used to handle irregular topography. </LI> <LI> Traveltimes and Fréchet derivatives are calculated using frequency-domain damped wavefield. </LI> <LI> The proposed algorithm is proved to be applicable to real seismic data. </LI> </UL> </P>

Water Bottom Seismic Refraction Survey for Engineering Applications

Cha, Young-Ho,Jo, Churl-Hyun,Suh, Jung-Hee 한국암반공학회 2003 Geosystem engineering Vol.6 No.2

The accurate mapping of the basement is one of the most crucial factors in construction of harbour facilities and bridges in the coastal areas. In shallow waters, the seismic reflection method often fails to image the basement geometry beneath the sediment due to reverberation. We present the result of a shallow marine seismic refraction survey using two ships, 12-channel hydrophone arrays deployed on the bottom and a bore-hole sparker or percussion powder as sources. Velocity structure could be computed by tomography algorithm since more than 6 different source points had been applied for one spread. The comparison of the results of the refraction survey with drilling logs demonstrates remarkable consistency in basement geometry. It thus appears that the refraction method in this study is an efficient and cost-effective way to investigate the basement structure in coastal area, river, and lake.

경사 2층 구조를 위한 3차원 굴절탄성파 주시 토모그래피

조동행 ( Dong Heng Cho ),조광호 ( Kwang Ho Cho ) 한국지구물리·물리탐사학회 1998 지구물리와 물리탐사 Vol.1 No.1

Feasibility of Using a One-temperature Model for Determining Plasma’s Temperature by Measuring Its Refractive Index

Yun-yun Chen,Fen-ping Cui,Fang Gu,Ying-ying Zhang 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.11

In this paper, the feasibility of using a one-temperature model to determine plasma’s temperatureby measuring its refractive index is studied based on the consideration that many plasma flow fieldsare not in local thermodynamic equilibrium (LTE). We compare the refractive indices between theone- and the two-temperature models of an arc plasma, in order to discuss the applicability ofthe one-temperature model in optical diagnosis. We found that the applicability is determined bythe pressure, the temperature ratio between electrons and heavy particles, the probe wavelength,and the chosen optical method’s refractive index measurement precision. Consequently, a commonmodel is deduced to describe the refractive index of plasma whether it be in LTE or not. In a word,this study is crucial to better apply optical methods based on measurements of the refractive indexto diagnose plasma flow fields.

Relations between Age, Weight, Refractive Error and Eye Shape by Computerized Tomography in Children

( Ha Tae Song ),( Young Jun Kim ),( Soo Jung Lee ),( Yeon Sung Moon ) 대한안과학회 2007 Korean Journal of Ophthalmology Vol.21 No.3

Purpose: To investigate relationships between age, weight, refractive error, and morphologic changes in children`s eyes by computerized tomography (CT). Methods: Of the 772 eyes of 386 patients under the age of 20 years, who visited our Department of Ophthalmology between January 2005 to August 2006 and underwent CT of the orbit, 406 eyes of 354 patients with clear CT images and normal eyeball contour were enrolled in the present retrospective study. The axial lengths, widths, horizontal and vertical lengths, refractive errors, and body weight of eyes were measured, and relationship between these parameters were investigated. Results: Axial length was found to correlate significantly with eye width (r=0.914), and in emmetropic eyes and myopic eyes, axial lengths and widths were found to increase as age and body weight increased. Axial lengths increased rapidly until age 10, and then increased slowly. In emmetropic eyes, widths / axial lengths increased with age, but in myopic eyes these decreased as age or severity of myopia increased. Moreover, as age increased, the myopic population and severity also increased. Conclusions: The axial length was longer in case of myopia compared to emmetropia in all age groups and there was almost no difference in the increase rate of axial length by the age of myopia and emmetropia. However, the width was wider in case of myopia compared to emmetropia in all age groups and the increase rate of width in myopia by age was smaller than that of emmetropia. Myopia showed decreasing rate of width/axial length with increase of age, from 1.004 in 5 years to 0.971 in 20 years. However, emmetropia showed increasing rate of width/axial length with increase of age, from 0.990 in 5 years to 1.006 in 20 years. Korean Journal of Ophthalmology 21(3):163-168, 2007

RGP콘택트렌즈와 각막사이에 생성된 누액렌즈의 두께와 굴절력과의 상관관계

정예린,김기홍,추병선 대한시과학회 2023 대한시과학회지 Vol.25 No.3

목적 : 본 연구는 RGP 렌즈 착용 상태에서 렌즈후면과 각막전면에 존재하는 눈물층의 두께와 눈물의 굴절력을측정하였다. 방법 : 본 연구의 대상자는 20명(평균연령 23.02±1.89세)이 참여하였다. 각 참여자는 각막곡률의 측정값에 따라 피팅상태가 flat fit, alignment fit, steep fit이 되도록 3개의 다른 BC의 RGP를 피팅하였다. RGP렌즈를 착용한 상태에서 OCT로 눈물층 두께 측정, 자동굴절계를 이용하여 눈물렌즈의 굴절력을 측정하였다. 결과 : 측정결과 베이스 커브에 따라 발생한 렌즈 후면과 각막 간의 눈물층 높이의 평균값은 플랫한 피팅 상태에서는 6.20±1.06 μm, 정렬된 피팅상태에서는 9.10±1.55 μm, 스팁한 피팅상태에서는 12.5±1.50 μm으로 통계적으로 유의한 차이가 나타났다(F(2, 57)=103.05, p<0.010). 피팅상태에 따라 생성된 눈물렌즈의 굴절력은 플랫 피팅인 경우 –0.85±0.75 D, 정렬된 경우 –0.48±0.85 D, 스팁 피팅인 경우 +1.56±0.77 D로 통계적으로 유의하게 나타났다(F(2, 57)=53.71,p<0.010). 3가지 피팅에 따라서 RPG 렌즈 후면과 각막전면의 있는 눈물 렌즈의 두께와 눈물 렌즈로 생성된 굴절력과의 상관관계 분석에서 r=0.58로 다소 높은 상관관계를 보였다. 결론 : 본 연구에서는 정렬된 피팅이 된 경우, 최소의 굴절력 조정이 요구되며, 반면 스팁한 피팅인 경우 더 많은 조정이 필요하다. Purpose : This study aimed to measure the post-Rigid Gas Permeable lens (RGP) tear film thickness and its refractive power. Methods : Twenty participants (23.02±1.89 years old) were enrolled. Each participant was prescribed three different Base Curves (BC) of RGP to induce different fitting patterns (alignment fit, flat fit, and steep fit). The tear film thickness using OCT and refractive power was measured. Results : The average tear film thickness between post lens and cornea were 6.20±1.06 μm with the flat fit, 9.10±1.55 μm with the alignment fit, and 12.5±1.50 μm with the steep fit (F(2, 57)=103.05, p<0.010). The refractive power of the tear film was –0.85±0.75 D with the flat fit, -0.48±0.85 D with the alignment fit, and +1.56±0.77 D with the steep fit (F(2, 57)= 53.71, p<0.010). According to the three fittings, there was a high correlation of r=0.58 between the thickness of the tear lens on the rear of the RGP lens and the cornea and the refractive power generated by the tear lens. Conclusion : This study showed that alignment fitting requires minimum refractive power adjustment while steep fitting requires a more careful approach.