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Eingeladener Vortrag
- nein (44)
The reliability investigations are dedicated to throw light on the performance of the NDE system with
respect to the required aim. This is especially of interest when digitized and processed signals are
involved where it becomes hard to assess whether the quality of the system has raised or not. Three
different ways to investigate reliability of NDE signals will be described. The first way of investigation,
the performance demonstration, is preferred e.g. in the US American nuclear power industry. This is an
integral consideration of the non destructive test as a system where the whole NDE system is packed in a
black box and only the input in terms of the real existing flaws in the component is considered and
compared to the output in terms of the indications of the human inspector or of the automated system.
The second the European tradition relies on a standardized description of physical/technical
parameters of the NDE system which are preconditions for successful system performance. An example
for such a standardized set of performance parameters is given in the recently released standard about Xray
film digitization CEN EN 14096. The third approach the modular conception is a marriage of
both: The signal chain is cut into main modules. Each module is assessed in a most appropriate
individual way e.g. via modeling calculations. The single results are joint together according to the
reliability of the subsystems. Separating criteria for the system were proposed through a reliability
formula developed during a series of European-American workshops on NDE reliability. Examples of
all three approaches will be given.
The last 25 years have seen an explosion in the number of new x-ray based imaging methods and applications. In reviewing these new capabilities we see that the ability to generate improved data quality underlies a number of the major advances. Improvement in the quality of x-ray sources, in detector resolution and dynamic range, in data analysis methods both in image processing and in reconstruction techniques have yielded significant advances in image quality. In addition to the improved imaging hardware, the use of computers play a key role in extending capabilities in high speed computed tomography, in real time image enhancement, in automated defect recognition and in the development of accurate x-ray inspection simulations. The ability to generate information and to analyze the complexities introduced by typical inspection demands can quickly outstrip even today's computational resources. Developments in parallel computing and computer memory are beginning to managing the huge data volumes now routinely produced and open up a number of new applications. Some examples include high-resolution 3D-image generation with the capability to probe micron length scales, dual energy computed tomography providing improved airport security, materials characterization techniques providing new tool for process development, and x-ray image formation modeling. The ability to model the details of the generation of bremsstrahlung radiation and its interaction with the complex geometry of the object under consideration provide for the first time a means to determine and quantify the optimal parameters for an inspection. These advances over the last 25 years represent exciting time in x-ray imaging, the impact of which will be played out in the next decade. ©2001 American Institute of Physics.
Standard radiography simulators are based on the attenuation law complemented by built-up-factors (BUF) to describe the interaction of radiation with material. The assumption of BUF implies that scattered radiation reduces only the contrast in radiographic images but does not image object structures itself. This simplification holds for a wide range of applications like weld inspection as known from practical experience. But only a detailed description of the different underlying interaction mechanisms is capable to explain effects like mottling or others that every radiographer has experienced in practice. The application of the N-Particle Monte Carlo code MCNP is capable to handle primary and secondary interaction mechanisms contributing to the image formation process like photon interactions (absorption, incoherent and coherent scattering including electron-binding effects, pair production) and electron interactions (electron tracing including X-Ray fluorescence and Bremsstrahlung production). Additionally it opens up possibilities like the separation of influencing factors and the understanding of the functioning of intensifying screen used in film radiography. The paper intends to discuss the opportunities in applying the Monte Carlo method to investigate special features in radiography in terms of selected examples. It is important to note that the use of Monte Carlo methods is a laboratory type of technique for basic investigations because of the enormous computing power that is needed. For in-field applications such as for inspection planing simplified models are of much greater importance and increasingly in use. ©2003 American Institute of Physics
The paper presents a special reconstruction algorithm that is capable to monitor density differences in multi-phase flows. The flow cross section is represented as discrete dynamic random field. A fixed gray value is assigned to each flow phase characterizing the material property of the phase. The image model is given by a set of non-linear stochastic difference equations. The corresponding inversion task is not accessible by common tomographic techniques applying reconstruction algorithms like filtered backprojection or algebraic reconstruction technique (ART). The developed algorithm is based on the Kalman filter technique adapted to non-linear phenomena. The average velocity distribution together with the corresponding covariance matrix of the liquid flow through a pipe serves as prior information in statistical sense. To overcome the non-linearity in the process model as well as in the measurement model the statistical linearization technique is applied. Moreover the Riccati equation, giving the error covariance matrix, and the equation for the optimal gain coefficients can be solved in advance and later used in the filter equation. It turns out that the resulting reconstruction or filter algorithm is recursive, i.e. yielding the quasi-optimal solution to the formulated inverse problem at every reconstruction step by successively counting for the new information collected in the projections. The applicability of the developed algorithm is discussed in terms of characterizing or monitoring a multi-phase flow in a pipe. ©2003 American Institute of Physics
Numerical Simulation of X-Ray Scattering Processes during Radiographic Inspection of Materials
(2006)
Abstract A technique for numerical simulation of the processes of forming X-ray radiography images of complex multicomponent objects with allowance for the penetrating-radiation absorption and scattering processes is proposed. The technique proposed is based on an efficient description of complex 3D objects with piecewise-homogeneous structures and uses precisely specified shells separating homogeneous components of an object. Being combined with a developed version of the Monte Carlo method, this approach yields an efficient computational apparatus for analyzing the regularities of the formation of radiographic images of objects internal structures. This apparatus is intended for state-of-the-art multiprocessor computing systems. Having been obtained via the technique developed, the results of the numerical analysis of the effect of different mechanisms of interaction between photons and matter (including coherent and incoherent scattering with allowance for bonds of electrons in atoms) on the formed radiographic image of the objects internal structure are discussed. The advantage of the described technique over the known MCNP program complex is shown.
Measurement sciences
(2006)
The computer simulation of radiography is applicable for different purposes in NDT such as for the qualification of NDT systems, the optimization of system parameters, feasibility analysis, model-based data interpretation, education and training of NDT/NDE personnel, and others. Within the framework of the European project PICASSO simulators will be adapted to support reliability assessments of NDT tasks. The radiographic simulator aRTist developed by BAM is well suited for this task. It combines analytical modelling of the RT inspection process with the CAD-orientated object description applicable to various industrial sectors such as power generation, aerospace, railways and others. The analytic model includes the description of the radiation source, the interaction of Radiation
with the material of the part, and the detection process with special focus to DIR. To support reliability estimations the simulation tool is completed by a tool for probability of detection (POD) estimation. It consists of a user interface for planning automatic simulation runs with varying parameters, specifically defect variations.
Further, an automatic image analysis procedure is included to evaluate the defect visibility and calculate the POD therefrom.
X-ray computed tomography (CT) is a volumetric (3D) Imaging diagnostic method, well established in the medical field, and in industrial NDE as well. Developments in industrial CT aim to extent the applicability to complex structures, which do not allow the access of all directions. This are e.g. limited view, data and angle CT applications. New reconstruction algorithms are required on one
side, and the accuracy has to be improved on the other side. Numerical Simulation can support such developments by providing well defined data sets for the testing of reconstruction algorithms. This approach of virtual CT is realized within the radiographic simulator aRTist, developed by BAM. The poster shows the possibilities of this tool to consider complex scan paths. Simulated data sets have been reconstructed by an versatile backprojection algorithm.
An approach is presented to construct operators for transforming the characteristics of incident radiation to transmitted radiation, as well as operators for transforming the transmitted radiation to measured values. Simu-lating the radiation transport is based on Monte Carlo modeling of the interaction of X-ray photons and electrons with matter. The proposed method permits to construct, for instance, the operator connecting the initial radiation spectrum with the absorbed photon energy penetrating a given object. The elaborated approach provides the possibility of effective mathematical modeling of radiation techniques such as radiography, treating complex multi-component objects. Moreover, the method can be used to construct the operator equation for solving in-verse problems, e.g. the reconstruction of the initial radiation spectrum using simple experimental measure-ments. Comparison with some experimental measurements is presented.
Statistical algorithms are presented for modeling the interaction processes between electrons and matter. A software
implementation has been developed for hybrid supercomputers making use of NVIDIA© CUDA©
technology. Standard Monte Carlo schemes are modified for effectively exploiting the parallel computing capabilities
of graphical processors. The model of individual collisions (MIC) is used to describe the interaction of
electrons with atoms. This model does not include the approximations assumed in multiple collision theory or
the continuous slow down approach with the Landau theory for energy-loss fluctuations. The distributions of
electron characteristics are obtained from tabulated electron cross section data. The examples discussed in this
paper demonstrate the applicability of the algorithms to investigating the interaction of electrons with X-ray tube
targets producing Bremsstrahlung. The proposed technique can be used for mathematical modeling in radiography.
X-Ray imaging and modeling
(2008)
Simulation of X-ray spectra
(2008)
Die radiografische Bildqualität in ihrer klassischen Definition hängt von Kontrast, Rauschen und Unschärfe ab. Diese Parameter werden normalerweise mit Bildgüteprüfkörpern (BPK) bestimmt. Die Streustrahlung reduziert im Allgemeinen immer die Bildqualität in der Radiografie. Verschiedene Einflussgrößen werden unter Berücksichtigung von Techniken, wie Film-Radiografie, Computer-Radiografie mit Speicherfolien und digitale Radiographie mit Matrixdetektoren, analysiert. In Lehrbüchern und Standards werden das Streuverhältnis k und verschiedene Kontraste definiert. Für digitale Medien werden zusätzliche Parameter wie das Signal-Rausch-Verhältnis SNR und das Kontrast-Rausch-Verhältnis CNR eingeführt. In diesem Zusammenhang wird der Einfluss der Streustrahlung aus dem Messobjekt und dem Detektor bestehend aus Kassette bzw. Gehäuse und sensitiver Detektorschicht auf die Bildqualität ermittelt. Die numerische Modellierung wird eingesetzt, um die Streustrahlung und die Primärstrahlung aus dem Objekt separat zu bestimmen. Die Streustrahlung aus dem Objekt und Detektor erzeugen eine Abbildung des Objektes, die dem Primärstrahlungsbild überlagert ist, wobei das Streubild eine höhere Unschärfe aufweist. Dieser Effekt hängt von der Fehlergröße, dem Abstand zwischen Detektor und Objekt und der Zwischenfilterung ab.