X-ray Computed Micro Tomography

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.

Industrial X-ray computed tomography (CT) systems have the ability to map internal and external structures simultaneously in a non-destructive way with high imaging resolution. Recently, there has been an increase of surveys in the field of dimensional metrology referring to CT as a tool for nondestructive dimensional quality control (i.e., traceable measurement and geometrical tolerance verification of industrial components). This increase in surveys runs parallel to the growth of commercial markets for industrial X-ray CT technologies and research institutes as well as metrology-governing bodies' growing interest in creating standarization. Currently, there is a lack of international standards that provide comprehensive procedures and guidelines for dealing with the verification of CT systems' dimensional metrology performance and developing task-specific measurement uncertainty budgets in compliance with the Guide to the Expression of Uncertainty in Measurement (GUM). To overcome this, some CT manufactures have opted to design their own calibration methods so that they can provide an estimate of maximum permissible error (MPE) for the measurements obtained with systems dedicated to metrology tasks. Essentially, the traceability of the instrument to the meter is provided with an expanded uncertainty upper-bounded by the MPE. In an effort to clarify some of these concepts, this paper gives a brief review of the use of X-ray CT for dimensional metrology with an update on the international attempt to create standards for metrological testing and uncertainty assessment with this technique. An example of in-house calibration is presented, which found deviations in the range-4.4 m to 3.5 m between CT measurements and calibrated references obtained at the National Institute of Standards and Technology (NIST), and this is contrasted to the MPE limits pre-established for CT measurement. A particular emphasis is made in the understanding of the terms " trueness " , " precision " , " accuracy " , and " uncertainty " , so the main metrology-related terminology is revisited with reference to international standards and other guidelines. It is concluded that while in-house calibrations might suffice, international standards are still needed, not only to reach homogeneity in the commercial market but also to avoid misinterpretations. In addition, users and manufacturers from the industry of measuring equipment need to better understand the terms " accuracy " and " uncertainty " , which are often misused and interchanged.

Obtaining the mesostructure of concrete from X-ray computed tomography (CT) requires segmentation of the data into distinct phases, a process complicated by the limited contrast between aggregates and mortar matrix. This paper explores the possibility to add baryte or hematite into the concrete mixture to enhance the contrast between cement paste and aggregates in CT, thus allowing for a semi-automatic segmentation. Raw and segmented CT images of plain and modified concrete mixtures are obtained and compared to assess the validity of the proposed approach. Characterization tests are also performed in order to ensure that the concrete characteristics are not appreciably affected by the presence of the enhancers.

Amplitude-wavelength (AW) maps or "Stedman diagrams" are often used to provide a graphical representation of the limitations and capabilities of surface measuring instruments. This paper presents an approach for setting the parameter constraints of X-ray computed tomography (CT) in terms of resolution and measuring range for the purpose of representing the performance of industrial CT systems on an AW map. Such AW map will allow instrument users to quickly compare the CT instrument performance to other measuring systems. Examples of the construction of AW maps for different working capabilities of X-ray CT systems, and based on experimental data, are provided. Polypropylene, aluminum, and steel are three workpiece materials considered for determining some of the limitations of measuring capability for the maps developed in this paper. Although the limiting boundaries of the AW plots presented in this paper set a generalized measure of performance for comparisons with other measuring instruments, they may evolve with more comprehensive models of the limiting factors in X-ray CT.

Please see a more thorough and updated version of this research in https://www.researchgate.net/publication/350354479_Assessing_the_effect_of_sample_orientation_on_dimensional_X-ray_computed_tomography_through_experimental_and_simulated_data

About 20 Late Copper Age bowls with cross-shaped foots from Deschmann’s pile dwellings (Ljubljansko barje, central Slovenia) and Trieste Karst (North-Eastern Italy) have been investigated using X-ray computed microtomography (microCT) in order to study the vessel-forming technique, to characterise their pastes and to test the hypothesis that some Karst bowls could have been imported from nowadays central Slovenia or even more distant regions. In three selected virtual slices per sample, clay, lithic inclusions and pores have been segmented and quantified. In addition, the area, maximum length and width of each lithic inclusion have been calculated. Then, the microCT-derived results have been statistically analysed by principal component analysis (PCA). The orientation of pores and disjunctions in microCT volumes show that the basins of the bowls were built using mainly the coiling technique, while the base was shaped starting from a central piece, to which a layer of clay was added and then reshaped in order to produce the foots. The Slovenian bowls include both medium/coarse-grained and very fine- or fine-grained vessels mainly tempered with carbonate inclusions. The pastes of the Karst bowls are considerably heterogeneous. One bowl was most likely imported to the Karst but not from central Slovenia as it shows peculiar components, shape and decoration. The other two imported vessels show a very fine-grained paste comparable to the one of several samples from Deschmann’s pile dwellings. Such technological similarity is confirmed by PCA of microCT data and petrographic observations. Our study confirms the existence of strong cultural connections between central Slovenia and the northernmost Adriatic coast during the Late Copper Age.

A promising bone graft substitute is porous titanium. Porous titanium, produced by selective laser melting (SLM), can be made as a completely open porous and load-bearing scaffold that facilitates bone regeneration through osteoconduction. In this study, the bone regenerative capacity of porous titanium is improved with a coating of osteostatin, an osteoinductive peptide that consists of the 107-111 domain of the parathyroid hormone (PTH)-related protein (PTHrP), and the effects of this osteostatin coating on bone regeneration were evaluated in vitro and in vivo. SLM-produced porous titanium received an alkali-acid-heat treatment and was coated with osteostatin through soaking in a 100 nM solution for 24 h or left uncoated. Osteostatin-coated scaffolds contained similar to 0.1 mu g peptide/g titanium, and in vitro 81% was released within 24 h. Human periosteum-derived osteoprogenitor cells cultured on osteostatin-coated scaffolds did not induce significant changes in osteogenic (alkaline phosphatase [ALP], collagen type 1 [Col1], osteocalcin [OCN], runt-related transcription factor 2 [Runx2]), or angiogenic (vascular endothelial growth factor [VEGF]) gene expression; however, it resulted in an upregulation of osteoprotegerin (OPG) gene expression after 24 h and a lower receptor activator of nuclear factor kappa-B ligand (RankL):OPG mRNA ratio. In vivo, osteostatin-coated, porous titanium implants increased bone regeneration in critical-sized cortical bone defects (p=0.005). Bone regeneration proceeded until 12 weeks, and femurs grafted with osteostatin-coated implants and uncoated implants recovered, respectively, 66% and 53% of the original femur torque strength (97 +/- 31 and 77 +/- 53 N center dot mm, not significant). In conclusion, the osteostatin coating improved bone regeneration of porous titanium. This effect was initiated after a short burst release and might be related to the observed in vitro upregulation of OPG gene expression by osteostatin in osteoprogenitor cells. Long-term beneficial effects of osteostatin-coated, porous titanium implants on bone regeneration or mechanical strength were not established here and may require optimization of the pace and dose of osteostatin release.

Link to Full-Text Articles :
http://www.ncbi.nlm.nih.gov/pubmed/25627039

The objective of this study was to investigate the sensitivity of the nonlinear elastic properties of cortical bone to the presence of a single submillimetric crack. Nonlinear elasticity was measured by nonlinear resonant ultrasound spectroscopy (NRUS) in 14 human cortical bone specimens. The specimens were parallelepiped beams (50×2×2mm(3)). A central notch of 500µm was made to control crack initiation and propagation during four-point bending. The nonlinear hysteretic elastic and dissipative parameters αf and αQ, and Young׳s modulus Eus were measured in dry condition for undamaged (control) specimens and in dry and wet conditions for damaged specimens. The length of the crack was assessed using synchrotron radiation micro-computed tomography (SR-μCT) with a voxel size of 1.4μm. The initial values of αf, measured on the intact specimens, were remarkably similar for all the specimens (αf =-5.5±1.5). After crack propagation, the nonlinear elastic coefficient αf increased significantl...

For a more thorough and updated version of this research please see: (1) https://www.researchgate.net/publication/319377742_Title_Dimensional_metrology_with_X-ray_CT_a_comparison_with_CMM_measurements_on_internal_features_and_compliant_structures and (2) https://www.researchgate.net/publication/330857072_Uncertainty_for_uncorrected_measurement_results_in_X-ray_computed_tomography