X-ray Tomography

X-ray computed tomography (CT)—more commonly known as CAT scan—has recently evolved from the world of medical imaging and nondestructive evaluation to the field of dimensional metrology; the CT technique can now be used to measure a specimen’s geometrical dimensions (of both internal and external features). As a result, CT presently contributes to the areas of dimensional inspection and geometric analysis for technology companies that produce manufactured parts for a variety of industries such as automotive, aerospace, medical devices, electronics, metalworking, injection molding plastics, composite materials, ceramics, and 3D printing or additive manufacturing. While dimensional accuracy is not crucial for medical diagnoses or other qualitative analyses, accurate dimensional quantification is the essence of X-ray CT metrology. Despite increasing advances in this technology, the current state of the art of CT metrology still confronts challenges when trying to estimate measurement uncertainties, mainly due to the plethora of influencing factors contributing to the CT measurement process. Gradual progress has occurred over the last decade toward a better understanding of some of these influencing factors that were illuminated by a series of collaborative research initiatives between a collective of several universities and institutions (predominantly located in the European Union) committed to the advancement and development of industrial CT scanning as a measuring technology. In an effort to further understand phenomenologically the role of variables affecting the precision and accuracy of CT dimensional measurements, this dissertation presents a series of experimental studies that evaluate the performance of cone-beam CT measurements, and their uncertainty estimates, in comparison with reference measurements generally obtained from tactile coordinate measurement machines (CMMs). In some cases, the results are contrasted against simulations performed in Matlab software (to compute fan-beam projection data) and an additional simulation tool called “Dreamcaster” (for ray casting and Radon-space analysis). The main CT variables investigated were: temperature in the X-ray CT enclosure, number of projections for a CT scan, workpiece tilt orientation, sample image magnification, material thickness influences, software post-filtration, threshold determination, and measurement strategies. For dimensions of geometric features ranging from 0.5 mm to 65 mm, a comparison between dimensional CT and CMM measurements, performed at optimized conditions, typically resulted in differences of approximately 5 µm or less for data associated with dimensional lengths (length, width, height, and diameters) and around 5 to 50 µm for data associated with measurements of form, while expanded uncertainties computed for the CT measurements ranged from 1 to over 50 µm. Methods for estimating measurement uncertainty of CT scanning are also assessed in this work. Special attention is paid to the current state of measurement comparisons (in the field of dimensional X-ray CT) by presenting a comprehensive study of metrics used for proficiency testing, including rigorous tests of statistical consistency (null-hypothesis testing) performed with Monte Carlo simulation, and particularly applied to results from two recent CT interlaboratory comparisons. This latter study contributes to the knowledge of methods for performance assessment in measurement comparisons. In particular, it is shown that the use of the En-metric in the current state of CT interlaboratory comparisons could be difficult to interpret when used to evaluate performance and/or statistical consistency of CT measurement sets.

The ability of Minkowski Functionals to characterize local structure in different biological tissue types has been demonstrated in a variety of medical image processing tasks. We introduce anisotropic Minkowski Functionals (AMFs) as a novel variant that captures the inherent anisotropy of the underlying gray-level structures. To quantify the anisotropy characterized by our approach, we further introduce a method to compute a quantitative measure motivated by a technique utilized in MR diffusion tensor imaging, namely fractional anisotropy. We showcase the applicability of our method in the research context of characterizing the local structure properties of trabecular bone micro-architecture in the proximal femur as visualized on multi-detector CT. To this end, AMFs were computed locally for each pixel of ROIs extracted from the head, neck and trochanter regions. Fractional anisotropy was then used to quantify the local anisotropy of the trabecular structures found in these ROIs and to compare its distribution in different anatomical regions. Our results suggest a significantly greater concentration of anisotropic trabecular structures in the head and neck regions when compared to the trochanter region (p < 10-4). We also evaluated the ability of such AMFs to predict bone strength in the femoral head of proximal femur specimens obtained from 50 donors. Our results suggest that such AMFs, when used in conjunction with multi-regression models, can outperform more conventional features such as BMD in predicting failure load. We conclude that such anisotropic Minkowski Functionals can capture valuable information regarding directional attributes of local structure, which may be useful in a wide scope of biomedical imaging applications.

Computed tomography is still being intensively studied and widely used to solve a number of industrial and medical applications. The simultaneous algebraic reconstruction technique (SART) and Bayesian inference reconstruction (BIR) are considered as advantageous iteration methods that are most suitable for improving the quality of the reconstructed 3D-images. The paper deals with the parallel iterative algorithms to ensure the reconstruction of three-dimensional images of the breast, recovered from a limited set of noisy X-ray projections. Algebraic method of reconstruction with simultaneous iterations – SART and iterative method for statistical reconstruction of BIR are deemed to be the most preferred iterative methods. We believe that these methods are particularly useful for improving the quality of breast reconstructed image. We use the graphics processor (GPU) to accelerate the process of reconstruction. Preliminary results show that all investigated methods are useful in breast reconstruction layered images. However, it was found that the method of classical tomosynthesis SAA is less efficient than iterative methods SART and BIR as the worst suppress the anatomical noise. Despite the fact that the estimated ratio of the contrast / noise ratio in the presence of internal structures with low contrast is higher for classical tomosynthesis method the SAA, its effectiveness in the presence of highly structured background is low. In our opinion the best results can be achieved using statistical iterative reconstruction BIR.

The strength of rock strongly depends on the water content especially when the rocks contain clay materials. The interaction between soft rock and water always threaten the soft rock engineering projects. For this problem, new sets of laboratory experiment systems are developed to simulate the interaction between soft rock and water or vapor. In this paper, the principles of experiment systems are introduced with particular reference to the application on soft rock in Mogao Grottoes, one of the world famous ancient sites in China. Two kinds of rock samples, the sandstone and muddy sandstone, are obtained by in-situ sampling system. Then the laboratory experiments are performed under different environment conditions. By the specific boundary conditions design, the physical-chemical effect and mechanic effect on water absorption of rock samples are separated for further mechanism study by the experiment system, and the different hydrological actions of water and vapor under variable experiment environment are obtained. The interaction mechanism is discussed with assistant methods, such as SEM (Scanning Electron Microscope), mercury injection test, X-ray diffraction analysis and etc. With the relation between water content and soft rock strength, the study may provide guidance and basis for the soft rock engineering in the future.

This paper addresses reducing the number of radiographs taken for X-ray computed tomography (CT) to optimize the scanning time while maintaining accuracy of dimensional measurements. Reduced image numbers correspond to under-sampling of signal data in the Fourier domain. The goal is to reduce the costs of measurement processes particularly in production lines. The study was performed by experimental measurements on two objects: a (cheese-like) hole-cube made in both aluminium and nylon; and also by theoretical simulations with Matlab™ using the standard test image 'Shepp-Logan phantom'. Image quality is assessed using three metrics: the root mean square error (RMSE), the peak signal-to-noise ratio, and the mean structural similarity Index; in all of these metrics degradation of image quality by diminishing the number of radiographs í µí± í µí± collected during the CT scans was observed. Particularly, the experimental results showed the proportionality RMSE with 1/ √ í µí± í µí± as predicted from the theory of imaging with X-ray photons, and the signal-to-noise ratio (SNR) of a reconstructed CT image holds the proportionality SNR~ √ í µí± í µí±. This is contrasted by observations of dimensional measurements; the accuracy of measurements of dimension with the CT technique remained about the same when collecting anything from 2000 to 400 radiographs for CT reconstruction of the aluminium and nylon hole-cubes, with deviations |∆| = |í µí±¥̅ í µí° ¶í µí±‡ − í µí±¥̅ í µí° ¶í µí±€í µí±€ | mostly in the range 2 to 20 µm despite noticeable variation on image quality. This is an important result for optimizing CT measurement. Effectively, for dimensional metrology, a loss in image quality can be tolerated as a trade-off for time reduction, particularly with added uncertainties of only a few micrometers and measurement time reduction of several minutes with current technology. If less than 400 or 360 radiographs are used,|∆|-deviations of greater than 50 µm were found.

In the field of restoration of ancient handworks, X-ray tomography is a powerful method to reconstruct the internal structure of the object in non-invasive way. In some cases, such as small objects fully realized with hard metals and completely hidden by clay or products of oxidation, the tomography, although necessary to obtain the 3D appearance of the object, does not give any additional information on its internal monolithic structure. We present here the application of the shape-from-silhouette technique on X-ray images to reconstruct the 3D profile of handworks. The acquisition technique is similar to tomography, since several X-ray images are taken while the object is rotated. Some reference points are placed on a structure co-rotating with the object and are acquired on the images for calibration and registration. The shape-from-silhouette algorithm gives finally the 3D appearance of the handwork. We present the analysis of a tin pendant of VI-VIII century b.C. (Venetian area) completely hidden by solid ground. The D reconstruction shows surprisingly that the pendant is a very elaborated piece, with two embraced figures that were completely invisible before restoration.

In AREVA Nuclear Power&amp;#39;s High Temperature Reactor (HTR) design called ANTARES, fuel consists of compacts composed of few thousands millimetric quasi-spherical particles dispersed in a graphite matrix. Compact homogeneity, defined as the homogeneous particles spatial distribution in the matrix, as well as the possibility of obtaining particles in contact, need to be assessed since they condition the thermo-mechanical behavior of

The authors compared the autopsy and tomographic findings of meatus acusticus int. In addition to the dimensions of meatus acusticus int. the authors also evaluated its shape and measured the distance between fossa jugularis and lower wall of fundus. The mean values of six parameters observed and measured on the cadavers and the tomograms differed in the following way: three parameters up to 0.5 mm and three by 0.8 mm, 1.1 mm and 1.2 mm, respectively. In eight patients the tomograms were evaluated as pathological; these were described in detail and put into relation to CT, CT-cisternomeatographic or the operation finding.