Evaluation of Ultra-Low Dose CT in the Diagnosis of Pediatric-Like Fractures Using an Experimental Animal Study

Joerg D Moritz,Beata Hoffmann,Dirk Sehr,Katrin Keil,Juliane Eggerking,Godo Groth,Amke Caliebe,Jens Dischinger,Martin Heller,Hendrik Bolte 대한영상의학회 2012 Korean Journal of Radiology Vol.13 No.2

Objective: The aim of this prospective study was to evaluate the performance of ultra-low dose CT for the diagnosis of pediatric-like fractures and ascertain the lowest dose level sufficient for diagnostics. Materials and Methods: Fifty-one bones of young pig cadavers were artificially fractured and subsequently examined by using a 64 multi-detector CT with 36 various dose levels down to a dose comparable with that of X-rays. Two pediatric radiologists analysed the CT scans according to the presence or absence of a fracture, determination of the fracture type and the displacement as well as the diagnostic certainty. For each dose protocol, a success rate for the correct determination of the above-mentioned CT analyses was calculated. A success rate of at least 95% was considered sufficient for diagnostics. Results: All but the lowest dose levels were sufficient to identify the fracture. Only the two lowest dose levels were insufficient to detect the fracture type. All dose levels were adequate for the identification of the displacement. The lowest dose level sufficient for diagnostics was 120 kVp, 11 mAs, and pitch 1.5, with a CTDIvol of 10% of a standard dose and an effective dose three times as large as that of X-rays. Conclusion: Ultra-low dose CT provides the feasibility of a significant dose reduction, still allowing sufficient diagnostics of pediatric-like fractures. Objective: The aim of this prospective study was to evaluate the performance of ultra-low dose CT for the diagnosis of pediatric-like fractures and ascertain the lowest dose level sufficient for diagnostics. Materials and Methods: Fifty-one bones of young pig cadavers were artificially fractured and subsequently examined by using a 64 multi-detector CT with 36 various dose levels down to a dose comparable with that of X-rays. Two pediatric radiologists analysed the CT scans according to the presence or absence of a fracture, determination of the fracture type and the displacement as well as the diagnostic certainty. For each dose protocol, a success rate for the correct determination of the above-mentioned CT analyses was calculated. A success rate of at least 95% was considered sufficient for diagnostics. Results: All but the lowest dose levels were sufficient to identify the fracture. Only the two lowest dose levels were insufficient to detect the fracture type. All dose levels were adequate for the identification of the displacement. The lowest dose level sufficient for diagnostics was 120 kVp, 11 mAs, and pitch 1.5, with a CTDIvol of 10% of a standard dose and an effective dose three times as large as that of X-rays. Conclusion: Ultra-low dose CT provides the feasibility of a significant dose reduction, still allowing sufficient diagnostics of pediatric-like fractures.

Time Dependent Process-Zone Growth in Polycarbonate

Amkee Kim,Sam Hong Song 대한기계학회 1995 KSME International Journal Vol.9 No.4

MOLECULAR DYNAMICS SIMULATION OF INDENTATION ON SILVER COATED COPPER NANOSTRUCTURE

Amkee Kim,Long Trandinh,Ilhyun Kim 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.11

The effect of misfit on the indentation behaviour of silver coated copper multilayer was studied by molecular dynamics simulation. It was found that the misfit bands on interface formed by the mismatch of lattice structure between copper and silver in slip direction [110] and the dislocation band width depended on the mismatched lattice constants of materials. More dislocations were created and glided by indentation, which created a “four-wing flower” structure consisting of pile?up of dislocation at the interface. The size of “flower” depended on the thickness of silver layer. The critical thickness for “flower” was approximately 4nm above which the “flower” disappeared. As the result, deformation mechanisms such as dislocation pile-up, dislocation cross-slip and movement of misfit dislocation were revealed. Only silver atoms in the dislocation pile-up were involved in the creation of the “flower” while the dislocations in copper were glided in slip direction on interface.

Study on Compressive Behavior of Heterogeneous Al-alloy Foam by Cruciform-Hemisphere Model

Amkee Kim(김엄기),Kazi Tunvir(카지 턴비르),Sung-Jun Park(박성준),Gil-Do Jeong(정길도),Hasan(하산),Seong-Sik Cheon(전성식) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5

Compressive behavior of closed cell aluminum (Al) alloy (Al-Si-Ca and Al-Si-Cu-Mg) foams having an isotropic material property was investigated by finite element (FE) analysis of a multiple lattice finite element model composed of cruciform and hemispherical sections. Different wall thickness for the hemisphere and the cruciform sections were considered in the model on the basis of micro structural examination of real foam. The simulation for Al-Si-Ca foam being ductile showed a good agreement with the experiment in the entire deformation range. However Al-Si-Ca-Mg foam being brittle in nature showed less resistance to the large deformation compared to the simulation.

Study of Al-Alloy Foam Compressive Behavior Based on Instrumented Sharp Indentation Technology

Amkee Kim,Kazi Tunvir 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.6

The stress-strain relation of aluminum (Al) alloy foam cell wall was evaluated by the instrumented sharp indentation method. The indentation in a few micron ranges was performed on the cell wall of Al-alloy foam having a composition of Al-3wt.%Si-2wt.%Cu-2wt.%Mg as well as its precursor (material prior to foaming). To extract the stress-strain relation in terms of yield stress σy, strain hardening exponent n and elastic modulus E, the closed-form dimensionless relationships between load-indentation depth curve and elasto-plastic property were used. The tensile properties of precursor material of Al-alloy foam were also measured independently by uni-axial tensile test. In order to verify the validity of the extracted stress-strain relation, it was compared with the results of tensile test and finite element (FE) analysis. A modified cubic-spherical lattice model was proposed to analyze the compressive behavior of the Al-alloy foam. The material parameters extracted by the instrumented nanoindentation method allowed the model to predict the compressive behavior of the Al-alloy foam accurately.

다공성 알루미늄 합금이 충진된 스테인레스 강 원통 Shell의 제조 및 굽힘거동

김엄기(Amkee Kim),이효진(Hyo-Jin Lee),조성식(Seong-Seock Cho) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4

Potential applications of foam-filled section are the automotive structures. A foam-filled section can be used for the front rail and firewall structures to absorb impact energy during frontal or side collision. In the case of side collision where bending is involved in the crushing mechanics, the foam filler will be significant in maintaining progressive crushing of the thin-walled structures so that more impact energy can be absorbed. In this study, the manufacturing process of closed cell aluminum alloy foam filled stainless steel tube was studied, and the various foam filled specimens including piecewise fillers were prepared, tested and discussed about the bending behaviors.

Polycarbonate의 소성역(Process Zone) 크기 예측을 위한 모델

김엄기 公州大學校工科大學生産技術硏究所 1994 論文集 Vol.2 No.-

Polycarbonate 내에 발생하는 프로세스 존은 불균일한 전단대(shear band)로 구성되어 있다. 따라서 Chudnovsky 모델을 이용한 polycarbonate 프로세스 존 크기 예측은 이 모델이 갖고 있는 한계성(이 모델은 프로세스 존을 균일한 제 2 상으로 취급한다) 때문에 샐제값과 큰 차이를 나타낸다. 본 연구에서는 Chudnovsky 모델의 일반화를 통하여 불균일한 polycarbonate 프로세스 존에 적용 가능한 크기 예측 모델을 개발하였다. 실험결과 새롭게 개발된 모델에 의한 예측값이 실험값과 일치하는 좋은 결과를 보였다. 또한 모델 사용에 부수되는 계산식의 풀이 방법을 제시하여 새 모델을 이용할 때 오는 어려움을 제거했다. Since the process zone in polycarbonate consists of inhomogeneous shear bands, the application of Chudnovsky Model based on the homogeneous process zone to ploycarbonate is not suitable. In fact, there is significant difference between the size predicted by the model and the experemental result. A generalization of Chudnovsky Model for the polycarbonate process zone is attempted in this paper. The newly generalized model shows good prediction in terms of process zone size. In addition, the numerical method to solve the equations involved in the model is described.

A Study on Fracture Surface of Aged Turbine by Fractal Dimension

Kim, Amkee,Nahm, Seung-Hoon The Korean Society of Mechanical Engineers 2001 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.15 No.10

Since fracture surface presents clear evidence to describe the circumstances of material failure event, analysis of fracture surface should provide plenty of useful information for failure prevention. Thus if we extract proper information from the fracture surface, the safety evaluation, for plant component could be more accurate. In general, the chaotic morphology of fracture surface is determined by the degree of material degradation as well as by other factors such as type of load, geometry of specimen, notch condition, microstructure of material and environment. In this research, we developed a fractal analysis technology for the fracture surface of aged turbine rotor steel based on the slit-island technique using an image analyzer. Moreover the correlation between the fractal dimension and the aging time was studied.

Evaluation of Mechanical Properties of Al-Si-Cu-Mg Alloy Foams Using Electrical Conductivity

Kim, Amkee,Lee, Chang-Hun,Hasan, Md Anwarul,Nahm, Seung-Hoon,Lee, Hyo-Jin,Cho, Seong-Seock,Ahn, Byung-Wook 한밭대학교 생산융합기술연구소 2004 생산기반기술연구소 논문집 Vol.4 No.1

Closed cell Al-Si-Cu-Mg alloy foams of two different compositions (Al-5%Si-4%Cu-4%Mg alloy, Al-3%Si-2%Cu-2%Mg alloy) were produced using the powder metallurgy method. The electrical conductivity of the foams was measured. Uni-axial compression test was also performed on foams with different composition and different density. It is already well established that mechanical properties of Al-foam depend on its relative density while the power law equation for electrical conductivity of metal foam given by Ashby suggests that electrical conductivity of aluminium foam is a function of its relative density. Since the mechanical properties of Al-foam and its electrical conductivity are both function of relative density, so they can be expressed as a function of each other. In this paper mathematical relations have been derived to establish direct link between electrical conductivity and compressive properties of Al-Si-Cu-Mg alloy foams.

열화된 HK40강의 마식특성에 관한 연구

김엄기(Amkee Kim),전용두(Yong-Du Chun),이금배(Kum-Bae Lee),김창훈(Chang-Hoon Kim),남승훈(Seung-Hoon Nahm) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4

The erosion behavior of artificically aged HK40 steel was investigated. Erosion tests were conducted at room temperature, 200℃ and 400℃ using Al₂O₃particles. Erosion rates increased with increment of temperature. The maximum erosion rate appeared with the impingement angle of 30 degree. The erosion rate increased, reached the maximum at 1000 hours, and after that, decreased with heat treatment time. The mechanism of erosion seems to be the cutting wear which is very much associated with the strength of material. As results, the erosion rates were rather affected by the tensile strength and the strain hardening coefficient than the hardness and the yield strength. such changes of material properties would be caused by the change of micro-structure to the precipitation of carbide and the dissolution of solid element within matrix during the heat treatment.