Computerised X-ray Tomography Research Articles

Use of Computerised X-ray Tomography in the Study of the Fabrication Methods and Conservation of Ceramics, Glass and Stone Building Materials

This work will review and discuss the use of computerised X-ray tomography (CXT) for analysing ancient, manufactured items, like stone building materials, glass and ceramics. It will consider particular techniques required, and/or of benefit, for CXT of heritage materials, such as special precautions during the experimentation to ensure there is no damage to the materials, special imaging methods such as elemental-specific imaging, and sample-specific image analysis requirements. This study shows how the knowledge of internal features, particularly pores, discerned from CXT can be used to reverse engineer the artefact fabrication process. CXT can be used to obtain information on both the raw materials (such as types and impurities) and fabrication techniques used. These abilities can then be used to establish technological evolution and the incidence of ancient behaviours like recycling and allow the linking of particular items to specific production sites. It will also be seen how CXT can aid the development of effective conservation techniques. This work will also consider how conclusions drawn from CXT data can be amended or augmented by the use of complementary non-destructive characterisation methods, such as gas overcondensation.

Integration of multi-scale porosimetry and multi-modal imaging in the study of structure-transport relationships in porous catalyst pellets

The forming process for heterogeneous catalyst pellets impacts on reactor performance. In order to intelligently optimise the product formulation and manufacturing procedure, the impact of fabrication options on the resultant pore structure and mass transfer properties must be fully understood. In this work, the more direct information possible from multi-modal imaging methods has been combined with the more statistically-representative, multi-scale data from porosimetry, including the rarely-used gas overcondensation technique, to characterise batches of methanol synthesis catalyst tablets made using different feed types. Despite the hierarchies of complexity of the porous pellets revealed by the computerised X-ray tomography and FIB-SEM images, the impact on mass transfer of controlled modifications to the void space, achieved through mercury porosimetry, could be modelled using a relatively simple random pore-bond network. The characteristic parameters for the model were obtained from a percolation theory-based analysis of the overcondensation data. A quantitative relationship was thereby obtained between the structural information contained within the overcondensation isotherms and the rate of mass uptake of gas into the porous pellets. This revealed the differential importance to mass transfer of particular sets of pores, associated with certain pellet structural features, and the impact on tortuosity of pellet fabrication parameters such as particle feed size.

Multi-scale pore structural change across a paleodepositional transition in Utica shale probed by gas sorption overcondensation and scanning

Pore structure and network configuration in shales greatly impacts physical processes important for hydrocarbon migration, methane extraction, gas storage, or carbon sequestration. The multi-scale nature of the porosity in shales presents significant challenges to its comprehensive and accurate characterisation. The under-used gas overcondensation technique can bridge characterisation of micropores, below the detection limit of mercury porosimetry and many imaging methods, to that of macroporosity undetected by conventional adsorption experiments. Further, gas sorption scanning curves revealed advanced condensation effects that allowed the probing of the inter-relation and juxtaposition of multi-scale porosities. It was found that the changeover period, from primarily clay to carbonaceous deposits in the Utica shale, was associated with growth in the disorder of the pore network over particular key length-scales highlighted by percolation processes in the gas overcondensation and scanning curves. Critical path theory suggests that the marked percolation knee that developed in overcondensation data at the depositional transition would identify a particular pore size that is characteristic of the wider network, and would control mass transport. The peak in pore network disorder was also associated with a peak in total organic carbon content and the accessible porosity was shown to be dominated by the organic carbon phase. Complementary mercury porosimetry combined with computerised X-ray tomography has shown substantial changes in the type, and super-micron-scale spatial distribution, of the nanoporosity down to approximately 3 nm, accessible to mercury, across the depositional transition, probably related to the amount and disposition of carbonate minerals.

Structure-transport relationships in disordered solids using integrated rate of gas sorption and mercury porosimetry

This work describes a new experimental approach that delivers novel information on structure-transport relationships in disordered porous pellets. Integrated rate of adsorption and mercury porosimetry experiments have been used to probe the relative importance of particular sub-sets of pores to mass transport rates within the network of two disordered porous solids. This was achieved by examining the relative rates of low pressure gas uptake into a network, both before, and after, a known set of pores was filled with frozen, entrapped mercury. For catalyst pellets, formed by tableting, it has been found that the compaction pressure affects the relative contribution to overall mass transport made by the subset of the largest pores. Computerised X-ray tomography (CXT) has been used to map the spatial distribution of entrapped mercury and revealed that the relative importance of the sub-sets of pores is related to their level of pervasiveness across the pellet, and whether they percolate to the centre of the pellet. It has been shown that a combination of integrated mercury porosimetry and gas sorption, together with CXT, can comprehensively reveal the impact of manufacturing process parameters on pellet structure and mass transport properties. Hence, the new method can be used in the design and optimisation of pellet manufacturing processes.

The durability of masonry mortars made with ladle furnace slag

Ladle furnace basic slag is a by-product of the steelmaking industry. This study examines the properties of masonry mortars made with ladle furnace basic slag and the other conventional components such as sand, cement, and admixtures. Eight different mixes were prepared and the main properties of the resulting mortars were analysed: density, strength, porosity, microstructure and permeability. The porosity of the hardened mixes was studied by means of two complementary techniques: mercury intrusion porosimetry and computerised X-ray tomography. Finally, tests were performed to analyse the behaviour of the mixes exposed to standard detrimental agents such as frost, moisture and sulphates, as well as other special environments, such as saline water or sulphidic atmospheres. The results show that the presence of ladle furnace slag does not damage and even contributes to increasing mortar durability. Its use also decreases or eliminates volumetric contraction during mortar ageing, thereby improving certain masonry applications.

Improving the interpretation of mercury porosimetry data using computerised X-ray tomography and mean-field DFT

Despite widespread use of the technique for a long time, the proper interpretation of mercury porosimetry data, particularly retraction curves, remains uncertain. In this work, the usefulness of two complementary techniques, mean-field density functional theory (MF-DFT) and micro-computerized X-ray tomography (micro-CXT), for aiding interpretation of ambiguous mercury porosimetry data has been explored. MF-DFT has been used to show that a specific, idiosyncratic form for the top of the mercury intrusion and extrusion curves is probably associated with a particular network structure where the smallest pores only form through connections between larger pores. CXT has been used to study the pore potential theory of hysteresis and entrapment directly using a model porous material with spatially varying pore wetting properties. CXT has also been used to directly study the percolation properties, and entrapment of mercury, within a macroporous pellet. Particular percolation pathways across the heart of the pellet have been directly mapped. The forms of entrapped mercury ganglia have been directly observed and related to retraction mechanisms. A combination of CXT and mercury porosimetry can be used to map spatial variation in pore neck sizes below the spatial resolution of imaging.

Quantification of dry matter % and liquid leakage in Atlantic cod (Gadus morhua) using computerised X-ray tomography (CT)

Farmed Atlantic cod (Gadus morhua L) were subjected to computerised X-ray tomography (CT) to evaluate CT as a non-destructive and rapid method for analysing muscle dry matter percentage (DM%) and liquid leakage in cod fillets. The study consisted of a total of 317 Atlantic cod (three batches) with gutted weights varying from 0.7 to 2.7 kg. The fish were scanned at four anatomical defined positions in the longitudinal direction. DM% in whole fillets correlated positively with average CT values over all scan positions, demonstrating that CT can be used as a non-destructive method to predict dry matter percentage in cod (r=0.6 to 0.9; SEP=0.3 to 0.7 DM%). The scan position anterior to the hind back fin gave highest prediction accuracy (r=0.63 to 0.93), and DM% in whole fillets provided better information than DM% analysed in specific anatomic positions. CT value and DM% increased from head to tail in all three batches (P<0.001), demonstrating that the CT-method can provide information also about the variation of DM% within fillets. Classification of liquid leakage during storage into low (<6%), medium (6–10%) and high (>10%) amounts also corresponded significantly with distinct CT (HU) intervals, demonstrating the potential for studying and improving liquid holding capacity in cod fillets using CT. Significant differences were detected in CT and DM% between sexes and between families (P<0.001) indicating genetic variation in these traits and a potential for improvement by selective breeding.

Family differences in dry matter content in Atlantic cod (Gadus morhua) measured by computerised X-ray tomography (CT)

Family differences in dry matter content in Atlantic cod (Gadus morhua) measured by computerised X-ray tomography (CT)

Quantification of fat deposits and fat distribution in Atlantic halibut ( Hippoglossus hippoglossus L.) using computerised X-ray tomography (CT)

Fifty adult 1–8 kg Atlantic halibut were subjected to computerised X-ray tomography (CT) to evaluate CT as a non-destructive measure of relative size of fat deposits and lean tissue, and to estimate fat content. Preliminary examinations of dissected tissues showed a clear separation and no overlap in CT values for pure fat deposits and lean tissue. The estimated proportions of fat deposits and lean tissue (area%) varied significantly between five CT-scans collected in the longitudinal direction of the halibut, and the scan across the longitudinal mid-line was considered to be the most relevant for the whole halibut fillet. Fat percentage of a cutlet determined after ethyl acetate extraction correlated well ( r 2=0.85, P<0.001) with CT measured fat deposit area (%), which shows that CT can be used as a non-destructive method to predict fat content in halibut.

Use of computerised X-ray tomography to measure density variations in compacted parts: S.F. Burch. (AEA Technology plc, Abingdon, UK.)

The Hall effect and ac susceptibility have been measured in Cu−2, 5, 10 and 25 at% Mn spin-glasses between 4.2 and 300 K and analyzed in terms of the semi-empirical relation RH = R0 + (Rs/μ0)χ. In all cases the Hall coefficient peaks at the freezing temperature. It is concluded from the analysis that, particularly in the concentrated alloys, inhomogeneities exist in the magnetic structure, a feature also confirmed in Cu-25 at% Mn by a large quadrature component in the ac susceptibility. The value of Rs in Cu-5 at% Au is about six times that in Cu-10 at% Mn, a result confirming the Dzyaloshinski-Moriya interaction as a common feature of the anisotropy and Hall effect in copper-based spin-glasses.

The true clinical significance of renography in nephro-urology.

Isotopic renography is a non-invasive technique used routinely by the clinician to provide information about kidney structure and function. Whilst there is no doubt of its value in the accurate measurement of glomerular filtration rate and in the detection of parenchymal abnormalities, its role in the diagnosis of renovascular disease (especially in patients with renal insufficiency), the exclusion of obstruction and the evaluation of the patient with either acute renal failure or renal transplant dysfunction remains unproven. In part, this reflects a failure to standardise protocols and rigorously evaluate diagnostic techniques. Recent developments in ultrasound, computerised X-ray tomography and nuclear magnetic resonance now present the clinician with rival techniques and emphasise the need for the clinical development of isotopic renography.

Principles of computerised X-ray tomography and applications to building materials

This paper reviews the physical principles of conventional X-ray radiography and computerised X-ray tomography (CT). It also mentions the various instrumentation and calibration techniques, and illustrates the power of CT with examples of applications of non-destructive research in the field of geology and material characterisation (scanning of core material, correlation of cores with well logs, measurement of compressibility and compaction, multiphase fluid or gas flow experiments, measurement of bulk density and moisture content, porosity and permeability studies, and sedimentary structures). The paper exemplifies the applicability of the CT-method for the study of building materials by characterisation of a Belgian porous calcareous sandstone of Middle Eocene (Tertiary) age, and an Italian metamorphic non-porous Carrara marble. Technical problems like sample positioning, tomographic density value error distribution and data transfer and conversion are discussed in detail.

48958 Recent advances in computerised X-ray tomography using real-time radiography equipment : British Journal of Non-Destructive Testing, Vol. 34, No. 3, pp. 129–133. (Mar. 1992)

48958 Recent advances in computerised X-ray tomography using real-time radiography equipment : British Journal of Non-Destructive Testing, Vol. 34, No. 3, pp. 129–133. (Mar. 1992)

Interictal HM-PAO SPECT: a routine investigation in patients with medically intractable complex partial seizures?

Single photon emission computed tomography (SPECT) is increasingly being used as an adiunctive technique in the localisation of epileptogenic foci prior to surgery. As yet, few studies have been undertaken to establish the clinical associations of areas of reduced cerebral perfusion. Sixty-three consecutive patients (15 male, 48 female; median age 30 years, range 14–57 years) with medically intractable complex partial seizures (median/month 8, range 1–36) were investigated as outpatients. All had normal high resolution computerised X-ray tomography (CT) of brain. Twenty-seven (47%) exhibited significant perfusion defects on SPECT scanning with a rotating gamma camera system using Tc-99 HM-PAO. There were no significant differences between patients with normal and abnormal scans in terms of age at scanning or at onset of epilepsy or number of seizures. Patients with perfusion defects did, however, have longer median histories of epilepsy than those with normal scans (normal: 10 years, abnormal: 22 years; P = 0.01). Patients with abnormal scans were no more likely to have suffered febrile convulsions in early childhood. The correlation of abnormal SPECT scans with routine surface EEG recordings was poor with only 41% of cases showing clear agreement between the site of hypoperfusion and focal epileptic activity. It is not yet possible to predict clinically those patients who will exhibit perfusion defects on interictal TC-99 HM-PAO SPECT scanning.

The application of computerised X-ray tomography to ordnance 39625 Hunt, C.A. Proceedings of the 4th European Conference on Non-Destructive Testing, London (United Kingdom), 13–17 Sep. 1987, Vol. 3, pp. 2105–2110. Pergamon Press, 3173 pp. (1988)

We describe the improvements achieved in the last three years towards the construction of a large solid angle positron camera with dense drift space MWPCs. A multiplane three-dimensional tomograph is proposed, made of six MWPC modules (active area 45 × 45 cm2 each), arranged to form the lateral surface of a hexagonal prism. Its expected performance is presented and is shown to be very competitive with the multiring scintillator positron camera.

The application of computerised X-ray tomography to ordnance: 39625 Hunt, C.A. Proceedings of the 4th European Conference on Non-Destructive Testing, London (United Kingdom), 13–17 Sep. 1987, Vol. 3, pp. 2105–2110. Pergamon Press, 3173 pp. (1988)

We describe the improvements achieved in the last three years towards the construction of a large solid angle positron camera with dense drift space MWPCs. A multiplane three-dimensional tomograph is proposed, made of six MWPC modules (active area 45 × 45 cm2 each), arranged to form the lateral surface of a hexagonal prism. Its expected performance is presented and is shown to be very competitive with the multiring scintillator positron camera.

Multielement imaging in computerised X-ray tomography

A method by which several elements can be independently imaged in a single X-ray CT scan is described. The method is based on measurements of differential absorption across absorption edges. The images produced show the distribution of element concentration. Mass attenuation coefficients for the elements comprising the matrix are not required because corrections for matrix effects are made. The method is capable of imaging elements which are consecutive in the periodic table. Detection limits, in the apparatus described, are of the order of mg/cm 3. The elements chosen for imaging were palladium, silver and cadmium.

Differential X-ray absorptiometry applied to computerised X-ray tomography

Element specific CT images can be produced by scanning the specimen with two almost monochromatic X-ray beams the energies of which straddle an absorption edge of the element. Here we produce images of palladium and caesium within a specimen using X-rays produced by electron capture or induced fluorescence from a suitable target. Corrections are made to the projection data to allow for matrix effects. By using an energy dispersive detector an uncorrected image can be produced in a single scan. Concentrations of a few mg/cm 3 can be measured in 2 mm square pixels in a water-like matrix a few centimetres in diameter with a total radiation dose of less than 1 rad.