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Computer simulation of radiography can be used for different purposes in NDT, such as qualification of NDT systems, optimization of radiographic parameters, feasibility analysis, model-based data interpretation, and training of NDT/NDE personnel. BAM has been working on modeling in the field of radiographic testing for many years. With the gathered theoretical background and the familiarity with practical requirements of industrial application the simulation software aRTist has been developed. This analytical simulator includes a description of the radiation source, the interaction of radiation with test pieces and flaws, and the detection process with special focus on film and digital industrial radiology. It features high processing speed with nearinteractive frame rates and a high level of realism. Here we focus on the recent developments of the simulator, notably the release of aRTist version 2. Extended functionality regarding automated virtual computed tomography now allows for arbitrary scan paths. Another program extension supports reliability investigations and provides a user interface for planning automatic simulations with varying parameters and defects.
Carrying out dimensional measurements by CT means assessing coordinates in space. CT must therefore be treated as a coordinate measuring technique similar to optical or tactile Coordinate Measuring Machines (CMMs). The well-established standards and guidelines for the acceptance- and verificationtesting of CMMs require the use of calibrated reference standards to achieve measurement machine characteristics.
Hence, transferring these concepts from coordinate metrology to CT, a dedicated CT-specific reference standard was designed, manufactured and calibrated using a tactile CMM. For comparison purposes, a CAD model was created by reverse engineering using the calibration data. The calibrated model was fed into a virtual CT and the measurement process was simulated. The reference standard was measured by micro-CT.
By comparing the characteristics of the measurement output of CT and the output gained from simulation, the influences of measurement artefacts can be judged, for the first time, in analogy to existing Guidelines of coordinate metrology.
Accurate and reliable detection of subsea Pipeline corrosion is required in order to verify the integrity of the pipeline. A laboratory trial was conducted with a representative pipe sample. The accurate measurement of the wall thickness and corrosion was performed with high energy X-rays and a digital detector array. A 7.5 MV betatron was used to penetrate a stepped pipe and a welded test pipe of 3 m length and 327 mm outer diameter, with different artificial corrosion areas in the 24 mm thick steel wall. The radiographs were taken with a 40 x 40 cm² digital detector array, which was not large enough to cover the complete pipe diameter after magnification. A C-arm based geometry was tested to evaluate the potential for automated inspection in field. The primary goal was the accurate measurement of wall thickness conforming to the standard. The same geometry was used to explore the ability of a C-arm based scanner in asymmetric mode for computed tomography (CT) measurement, taking projections covering only two thirds of the pipe diameter. The technique was optimized with the modelling Software aRTist. A full volume of the pipe was reconstructed and the CT data set was used for reverse engineering, providing a CAD file for further aRTist simulations to explore the technique for subsea inspections.
The objects of this investigation were sculptures taken from a ca. three hundred years old baroque epitaph of a church in Tonning, a town in Northern Germany. Around 1900 it was found in a disastrous state heavily damaged by wood-worm. At that time, the whole artwork was treated with the tar extract carbolineum as a remedy. Nowadays, this substance has been identified as carcinogenic, and its presence can be perceived by its stench and visually at certain spots on the surface where it has penetrated the covering paint.
A gold-painted sculpture of a massive wooden skull was interrogated with X-rays and fast neutrons to investigate the internal distribution of the carbolineum. The X-ray tomography, with its excellent spatial resolution revealed galleries left over from the worm infestation in the outer areas and cracks in the central region. The golden color coating appeared as a thick and dense layer. In comparison the tomography with fast neutrons, though being of lower resolution and yet unresolved artefacts revealed sections of slightly different densities in the bulk of the wood. These differences we attribute to the differences in the distribution of the impregnant in the wood, visible due to its higher hydrogen content making it less transparent for neutrons.
Modelling becomes more and more important in modern NDE. It is increasingly used to optimize techniques for complex applications, to support the preparation of written procedures, and for education purposes. To describe the complete chain of RT, the model includes simulating all necessary properties of X- or Gamma-ray sources, the interaction of photons with material with special attention to scattered radiation, the detection process, and the complete geometrical RT setup handling arbitrary parts or constructions. Depending on the given inspection problem and the influencing factors that should be addressed by the simulation, an appropriate physical model has to be chosen to describe the underlying interaction mechanisms. The simulator aRTist combines analytical and Monte Carlo methods to efficiently model the radiation transport such that transmission as well as scatter techniques can be modelled. In this contribution we Focus on Monte Carlo Simulation of scatter contribution within aRTist. Examples for RT/tomographic applications and back-scatter techniques are presented to demonstrate the usability of the presented simulation tool for a broad range of radiological applications.
Industrial radiography or Radiographic Testing (RT) is a method of non-destructive testing where many types of manufactured components can be examined to verify the internal structure and integrity of the specimen. The computer program aRTist can generate synthetic radiographs from a virtual RT test set-up. In the field of industrial radiology simulation is used, e.g. to optimize techniques for complex applications, to support the preparation of written procedures, and for education purposes.
The simulator aRTist combines analytical and Monte Carlo methods to efficiently model the radiation transport. The program comes with a graphical user interface written in Tcl/Tk. In combination of Tcl/Tk and the 3D capabilities of the visualization toolkit (VTK) a practical and convenient simulator has been realized. This will be illustrated by discussing application scenarios of classical radiography, X-ray computer tomography, and X-ray backscatter imaging. Additionally, some insight to the software implementation of the simulator will be given.
Simulation-Assisted Augmentation of Missing Wedge and Region-of-Interest Computed Tomography Data
(2024)
This study reports a strategy to use sophisticated, realistic X-ray Computed Tomography (CT) simulations to reduce Missing Wedge (MW) and Region-of-Interest (RoI) artifacts in FBP (Filtered Back-Projection) reconstructions. A 3D model of the object is used to simulate the projections that include the missing information inside the MW and outside the RoI. Such information augments the experimental projections, thereby drastically improving the reconstruction results. An X-ray CT dataset of a selected object is modified to mimic various degrees of RoI and MW problems. The results are evaluated in comparison to a standard FBP reconstruction of the complete dataset. In all cases, the reconstruction quality is significantly improved. Small inclusions present in the scanned object are better localized and quantified. The proposed method has the potential to improve the results of any CT reconstruction algorithm.