X-ray Attenuation Measurements Research Articles

X-ray attenuation performance of a newly synthesized tellurium based lead-free radiation shielding glass system

The lead-free quaternary glass systems containing B2O3–CaO–ZnO–TeO2 were synthesized using the traditional melt-quenching method. XRD analysis confirmed that the TeZnCaB glass system exhibited an amorphous behaviour. The density of the glass samples was increased from 3.48 g/cc to 4.08 g/cc by increasing the TeO2 concentration from 20 to 45 mol%. From UV–visible spectroscopy, it was observed that direct and indirect energy band gaps decreased with increasing the TeO2 concentration whereas the refractive index increased. TEM analysis revealed the amorphous behaviour along with nanocrystals present in the glass sample. X-ray attenuation measurements were performed to assess the radiation shielding properties of the lead-free glass system and observed that the radiation shielding capacity was increased with the TeO2 concentration. The best lead equivalent thickness was 2.02 mm for the sample with 45% TeO2 and these glasses could be promising materials for medical diagnostic applications.

Measurement and study linear attenuation coefficient of x-ray for epoxy/titanium oxide composites

In this study, X-ray attenuation measurements for voltages (20, 25, 30, 35) KV using X-ray unit with copper X-ray tube were performed for the composites material that consist of epoxy as a matrix and titanium oxide as a reinforced at concentrations ( 4 and 6 Wt. %) which was prepared by hand- lay-up method by using mechanical mixer . The linear attenuation coefficient (μ) was obtained by linear equation of the graph representation output between the logarithm of absorption and the thickness of the samples where the slope of the graph represents the linear attenuation coefficient. The obtained results showed that the linear attenuation coefficient increased by increasing the weight percentage of titanium oxide and the highest value obtained at 6Wt .% . The inverse relation between the linear attenuation coefficients of the composite samples with the x-ray voltage was also concluded. The values of mean free path (λ), halve value layer (HVL) and tenth value layer (TVL) was calculated in this study, the results were shown that the values of λ, HVL, and TVL, for pure epoxy is greater than its values of the composite material with 4and 6 Wt. % of TiO2 at all values of voltages mentioned above. The results obtained showed the efficiency of the prepared composites in the X-ray absorption and attenuation, this efficiency is relatively variable depending on the ratio of the reinforced material TiO2 which demonstrating the great and a positive effect of it on the radiation shielding properties of the epoxy polymer.

Development of two-dimensional beam hardening correction for X-ray micro-CT.

Beam-hardening in tomography with polychromatic X-ray sources results from the nonlinear relationship between the amount of substance in the X-ray beam and attenuation. Simple linearisation curves can be derived with the use of an appropriate step wedge, however, this does not yield good results when different materials are present whose relationships between X-ray attenuation and energy are very different. To develop a more accurate method of beam-hardening correction for two-phase samples, particularly immersed or embedded biological hard tissue. Use of a two-dimensional step wedge is proposed in this study. This is not created physically but is derived from published X-ray attenuation coefficients in conjunction with a modelled X-ray spectrum, optimised from X-ray attenuation measurements of a calibration carousel. To test this method, a hydroxyapatite disk was scanned twice; first dry, and then immersed in 70% ethanol solution (commonly used to preserve biological specimens). With simple linearisation the immersed disk reconstruction exhibited considerable residual beam hardening, with edges appearing approximately 10% more attenuating. With 2-dimensional correction, the attenuation coefficient showed only around 0.5% deviation from the dry case. Two-dimensional beam-hardening correction yielded accurate results and does not require segmentation of the two phases individually.

Statistical image-based material decomposition for triple-energy computed tomography using total variation regularization.

Triple-energy computed tomography (TECT) can obtain x-ray attenuation measurements at three energy spectra, thereby allowing identification of different material compositions with same or very similar attenuation coefficients. This ability is known as material decomposition, which can decompose TECT images into different basis material image. However, the basis material image would be severely degraded when material decomposition is directly performed on the noisy TECT measurements using a matrix inversion method. To achieve high quality basis material image, we present a statistical image-based material decomposition method for TECT, which uses the penalized weighted least-squares (PWLS) criteria with total variation (TV) regularization (PWLS-TV). The weighted least-squares term involves the noise statistical properties of the material decomposition process, and the TV regularization penalizes differences between local neighboring pixels in a decomposed image, thereby contributing to improving the quality of the basis material image. Subsequently, an alternating optimization method is used to minimize the objective function. The performance of PWLS-TV is quantitatively evaluated using digital and mouse thorax phantoms. The experimental results show that PWLS-TV material decomposition method can greatly improve the quality of decomposed basis material image compared to the quality of images obtained using the competing methods in terms of suppressing noise and preserving edge and fine structure details. The PWLS-TV method can simultaneously perform noise reduction and material decomposition in one iterative step, and it results in a considerable improvement of basis material image quality.

Implementation of Talbot–Lau x-ray deflectometry in the pulsed power environment using a copper X-pinch backlighter

A Talbot–Lau x-ray deflectometer can map electron density gradients in high energy density plasmas, as well as provide information about plasma elemental composition through single-image x-ray refraction and attenuation measurements. A new adaptation to a pulsed power environment used backlighting from copper X-pinches, allowing for electron density mapping of a low-Z object. Even though the X-pinch backlighter is not properly optimized for emitting x-rays in terms of source size and photon fluence, Moire fringe patterns with contrast up to 14% and fringe shift due to refraction on a beryllium object are obtained. Due to the proximity of the deflectometer with the X-pinch (∼6 cm), it is shown that a protective filter is required to avoid damage in the closest (i.e., source) grating due to both plasma debris and mechanical shock. Regarding grating survival, these did not show any damage due to the intense magnetic field or heating induced by plasma radiation. Electron density on beryllium was measured with a difference lower than 16%. The areal electron density mapping of the sample was limited by source size characteristics, in similarity to transmission radiography. These results show the potential of plasma electron density as well as material mapping through Talbot–Lau x-ray deflectometry in a pulsed power environment.

Visualization and material-based differentiation of lodged projectiles by extended CT scale and the dual-energy index

Computed tomography (CT) scans of gunshot wounds and their high sensitivity in detecting osseous lesions has often been reported in the literature. However, studies concerning in situ examinations of lodged projectiles with CT to determine the ammunition used are lacking.Projectile visualizations are hampered in standard CT due to the presence of metal artifacts and the limited range of Hounsfield units (HU). The use of special reconstruction algorithms can overcome these limitations. For instance, using extended CT scale (ECTS) reconstruction supports detailed visualizations of metallic objects. In addition to projectile visualizations, X-ray attenuation measurements (CT numbers) of metallic objects can be used to differentiate materials in CT.This study uses real forensic cases to demonstrate that—depending on the degree of deformation—a detailed visualization of lodged projectiles using ECTS can provide useful information regarding the ammunition used and allows accurate caliber measurements. Independent from the degree of deformation, the in situ classification of bullets, even fragmented bullets, according to their metallic components is feasible by dual-energy index (DEI) calculations. The assessment of a lodged projectile with CT images provides useful information on the case; thus, a close examination of lodged projectiles or bullet fragments should be a part of the overall radiological examination for cases of penetrating gunshot wounds.

Improving iodine contrast to noise ratio using virtual monoenergetic imaging and prior-knowledge-aware iterative denoising (mono-PKAID)

Multi-energy CT acquires simultaneous multiple x-ray attenuation measurements from different energy spectra which facilitates the computation of virtual monoenergetic images (VMI) at a specific photon energy (keV). Since the contrast between iodine attenuation and the attenuation of surrounding soft tissues increases at lower x-ray energies, VMIs in the range of 40–70 keV can be used to improve iodine visualization. However, at lower energy levels, image noise in VMIs is substantially increased, which counteracts the benefits from the increased iodine contrast, resulting in a decreased iodine contrast-to-noise ratio (CNR). There exists considerable data redundancy between multi-energy CT images created from the same acquisition. Similarly, a substantial spatio-spectral data redundancy exists between multi-energy CT images and the corresponding VMIs. In this work, we develop a denoising framework that exploits this data redundancy to improve iodine CNR in the VMIs. We accomplish this by applying prior-knowledge-aware iterative denoising to low-energy VMIs; we refer to the denoised images as mono-PKAID images. The proposed framework was evaluated using phantom and in vivo data acquired on a research whole-body photon-counting-detector CT, as well as using data from a commercial dual-source dual-energy CT system. The results of phantom experiments show that the proposed framework can preserve image resolution and noise texture compared to the original VMIs, while reducing noise to improve iodine CNR. Quantitative measurements show that the iodine CNR of 50 keV VMI is improved by 1.8-fold using the proposed method, relative to the VMI produced using commercial software (Mono+). With mono-PKAID, VMIs at lower keV take full advantage of higher iodine contrast without substantially increasing image noise. These observations were confirmed using patient data sets, which demonstrated that mono-PKAID reduced image noise, improved CNR in anatomical regions with iodine perfusion by 1.8-fold, and potentially enhanced the visibility of focal liver lesions.

Attenuation Changes in ASPECTS Regions: A Surrogate for CT Perfusion-based Ischemic Core in Acute Ischemic Stroke.

Background Recent studies have proven the effectiveness of thrombectomy up to 24 hours after stroke onset for patients with specific criteria at advanced CT or MRI. Clinical implementation of treatment in this extended time window remains a challenge, as many stroke centers do not routinely use advanced imaging. Purpose To determine whether automated cerebral x-ray attenuation measurements at noncontrast CT provide information on the presence of CT perfusion-defined ischemic core as applied in late time windows for thrombectomy. Materials and Methods In this retrospective study, patients with middle cerebral artery stroke due to proximal occlusion from 2009 to 2017 were included. All patients underwent noncontrast CT and CT perfusion. Automated software was used to calculate relative Hounsfield unit (rHU) values for Alberta Stroke Program Early CT Score (ASPECTS) regions on noncontrast CT images as the ratio of x-ray attenuation between ischemic versus non-ischemic hemispheres. Sensitivity, specificity, and diagnostic performance of rHU and composite rHU-ASPECTS, a score incorporating rHU from all regions, were analyzed for the classification of regional ischemic core and late time window thrombectomy criteria at CT perfusion. Results Data in a total of 200 patients were evaluated (105 women [mean age, 74 years ± 14 {standard deviation}] and 95 men [mean age, 76 years ± 14]). There were 121 patients in the validation cohort and 79 patients in the independent test cohort. Compared among all examined regions, rHU values yielded the best classification of ischemic core for the caudate nucleus, the lentiform nucleus, and the insula (with areas under the receiver operating characteristic curve [AUCs] ranging from 0.70 to 0.77; P < .001 for each). The composite rHU-ASPECTS score allowed classification of CT perfusion imaging selection criteria of ischemic core sizes of less than 70 mL and target mismatch of greater than 1.8 with AUCs of 0.80 (P = .001; 75% sensitivity and 83% specificity) in the test cohort and 0.74 (P < .001; 58% sensitivity and 82% specificity) in the validation cohort. Conclusion Noncontrast CT x-ray attenuation measurements identify Alberta Stroke Program Early CT Score regions classified as ischemic core at CT perfusion. This approach may serve as a selection criteria surrogate for thrombectomy in late time windows. © RSNA, 2019 Online supplemental material is available for this article.

X-ray computed tomography for flame-structure analysis of laminar premixed flames

Quantitative X-ray computed tomography (XCT) diagnostics for reacting flows are developed and demonstrated in application to premixed flames in open and optically inaccessible geometries. A laboratory X-ray scanner is employed to investigate methane/air flames that were diluted with krypton as an inert radiodense tracer gas. Effects of acquisition rate and tracer gas concentration on the signal-to-noise ratio are examined. It is shown that statistically converged three-dimensional attenuation measurements can be obtained with limited impact from the tracer gas and within an acceptable acquisition time. Specific aspects of the tomographic reconstruction and the experimental procedure are examined, with particular emphasis on the quantification of experimental uncertainties. A method is developed to determine density and temperature from the X-ray attenuation measurements. These experiments are complemented by one- and multi-dimensional calculations to quantify the influence of krypton on the flame behavior. To demonstrate the merit of XCT for optically inaccessible flames, measurements of a complex flame geometry in a tubular confinement are performed. The use of a coflow to provide a uniform tracer-gas concentration is shown to improve the quantitative temperature evaluation. These measurements demonstrate the viability of XCT for flame-structure analysis and multi-dimensional temperature measurements using laboratory X-ray systems. Further opportunities for improving this diagnostic are discussed.

Measurement of breast-tissue x-ray attenuation by spectral imaging: fresh and fixed normal and malignant tissue

Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. In mammography, measurement of breast density, dose estimation, and differentiation between cysts and solid tumours are example applications requiring accurate data on tissue attenuation. Published attenuation data are, however, sparse and cover a relatively wide range. To supplement available data we have previously measured the attenuation of cyst fluid and solid lesions using photon-counting spectral mammography. The present study aims to measure the attenuation of normal adipose and glandular tissue, and to measure the effect of formalin fixation, a major uncertainty in published data. A total of 27 tumour specimens, seven fibro-glandular tissue specimens, and 15 adipose tissue specimens were included. Spectral (energy-resolved) images of the samples were acquired and the image signal was mapped to equivalent thicknesses of two known reference materials, from which x-ray attenuation as a function of energy can be derived. The spread in attenuation between samples was relatively large, partly because of natural variation. The variation of malignant and glandular tissue was similar, whereas that of adipose tissue was lower. Formalin fixation slightly altered the attenuation of malignant and glandular tissue, whereas the attenuation of adipose tissue was not significantly affected. The difference in attenuation between fresh tumour tissue and cyst fluid was smaller than has previously been measured for fixed tissue, but the difference was still significant and discrimination of these two tissue types is still possible. The difference between glandular and malignant tissue was close-to significant; it is reasonable to expect a significant difference with a larger set of samples. We believe that our studies have contributed to lower the overall uncertainty of breast tissue attenuation in the literature due to the relatively large sample sets, the novel measurement method, and by clarifying the difference between fresh and fixed tissue.

Material decomposition with prior knowledge aware iterative denoising (MD-PKAID)

Dual- or multi-energy CT, also known as spectral CT, obtains x-ray attenuation measurements at two or more energy spectra, allowing quantification of materials with different compositions. This process is known as material decomposition, which is the basis for a number of spectral CT applications. The conventional image-domain basis material decomposition is based on a least-squares fitting between the underlying material-specific images and the measured source spectral CT images (i.e. energy-bin or energy-threshold CT images), and a non-iterative solution based on matrix inversion can be derived for this process. However, due to its ill-conditioned nature, the material decomposition process is intrinsically susceptible to noise amplification. Hence, material-specific images can be contaminated by the presence of strong noise, which compromises the conspicuity of small objects, and hinders the delineation of anatomical regions of interest and associated pathology. In this work, we describe an image domain material decomposition framework with prior knowledge aware iterative denoising (MD-PKAID). The proposed framework exploits the structural redundancy between the individual material-specific images and the source spectral CT images to retain structural details in denoised material-specific images. It directly treats material decomposition as a regularized optimization problem with spectral CT images measured with different energy spectra as inputs. Phantom, in vivo animal and human data were acquired on a research whole-body photon-counting-detector-based CT system and a dual-source, dual-energy CT system to test the proposed method. The phantom results show that the proposed MD-PKAID can reduce the root-mean-square-error of basis material quantification by 75% compared to the standard material decomposition based on matrix inversion, while preserving structural details and image resolution in the material-specific images. The initial in vivo results demonstrate that the proposed method can improve delineation of small vasculature features in iodine-specific images while reducing image noise.

Moisture ingress in cracked cementitious materials

Wedge split test specimens were conditioned to a relative humidity of 50%, deformed to various damage states, and exposed to liquid water. Water ingress was monitored using x-ray attenuation measurements and compared to numerical predictions. The transport model accounts for the damage state using the cracked hinge model and a simplified approach whereby a crack is considered to consist of two distinct parts: 1) a coalesced crack behaving as a free surface for moisture ingress, and 2) an area of isolated micro cracks behaving as bulk material. Comparison of experimental and model results shows the simplified crack geometry approach applied in the transport model is capable of predicting the ingress of moisture and influence of cracks. The model was found to underestimate the vertical extent of moisture ingress in the largest CMOD samples (0.20 and 0.40 mm), which was likely due to instability of the large cracks in these samples.

Measurements using X‐ray attenuation vertical distribution of the void fraction for different flow regimes in a horizontal pipe

Abstract METERO is an experimental facility built by the French Atomic Energy Commission (CEA) aimed at studying adiabatic air-water flows in horizontal pipes. The physical insight and the experimental data provided by METERO experiments support the validation of MCFD (NEPTUNE CFD) and System (CATHARE-3) codes as a part of the NEPTUNE project developed jointly by EDF, CEA, AREVA NP and IRSN. Bottin et al. (2014) have proposed a flow map of the different regimes encountered in the METERO experiments, i.e. stratified flows, slug flows, plug flows, stratified dispersed bubbly flows and dispersed bubbly flows. Following this work, we investigate the vertical distribution of the void fraction integrated horizontally using X-ray attenuation measurements. The use of the X-ray attenuation method presents the advantage of providing integrative measurements along the X-ray path. To obtain the vertical distribution of the void fraction integrated in the horizontal direction, the X-ray apparatus is rotated to ensure a spatial resolution of about 1 mm. For METERO’s pipe of 100 mm diameter, this provides a fine discretisation of the void fraction distribution with a reasonable amount of realisations, i.e. 7 angles. After a description of the experiments and the measurements’ method, different flow regimes and their transitions (e.g. slug, plug, and bubble flow regimes) are explored by varying the water and air superficial velocities within the ranges 0.71 m/s–5.31 m/s (Reynolds number of the liquid phase varying between 71,000 and 530000) and 0.023 m/s–0.68 m/s respectively. The evolution of the vertical distribution of the void fraction in horizontal pipes is discussed. Moreover, statistics such as the ratio of the air and water phase velocities are derived from the measurements. It is shown that due to the accumulation of bubbles in the upper part of the flow (where the flow is more going slowly than in the bottom part) the air phase velocity is generally smaller than the water phase velocity for bubble and plug flows. On the contrary, the air phase velocity is generally higher than the water phase velocity for slug flows with a ratio varying like five thirds of the supplied void fraction.

Calibrated X-ray micro-tomography for mineral ore quantification

Scanning Electron Microscopy (SEM) based assessments are the most widely used and trusted imaging technique for mineral ore quantification. X-ray micro tomography (XMT) is a more recent addition to the mineralogy toolbox, but with the potential to extend the measurement capabilities into the three dimensional (3D) assessment of properties such as mineral liberation, grain size and textural characteristics. In addition, unlike SEM based assessments which require the samples to be sectioned, XMT is non-invasive and non-destructive. The disadvantage of XMT, is that the mineralogy must be inferred from the X-ray attenuation measurements, which can make it hard to distinguish from one another, whereas SEM when coupled with Energy-Dispersive X-ray Spectroscopy (EDX) provides elemental compositions and thus a more direct method for distinguishing different minerals. A new methodology that combines both methods at the mineral grain level is presented. The rock particles used to test the method were initially imaged in 3D using XMT followed by sectioning and the 2D imaging of the slices using SEM-EDX. An algorithm was developed that allowed the mineral grains in the 2D slice to be matched with their 3D equivalents in the XMT based images. As the mineralogy of the grains from the SEM images can be matched to a range of X-ray attenuations, this allows minerals which have similar attenuations to one another to be distinguished, with the level of uncertainty in the classification quantified. In addition, the methodology allowed for the estimation of the level of uncertainty in the quantification of grain size by XMT, the assessment of stereological effects in SEM 2D images and ultimately obtaining a simplified 3D mineral map from low energy XMT images. Copper sulphide ore fragments, with chalcopyrite and pyrite as the main sulphide minerals, were used to demonstrate the effectiveness of this procedure.

An investigation of internal flame structure in porous media combustion via X-ray Computed Tomography

X-ray Computed Tomography (XCT) measurements are performed to characterize the internal volumetric flame structure within a Porous Media Burner (PMB). X-ray attenuation measurements are obtained using a multi-zone silicon carbide PMB combusting a radiodense Kr/O2/N2/CH4 mixture designed to enhance X-ray contrast. Time-averaged tomographic reconstructions of the X-ray attenuation field are used to assess internal PMB flame structure. Several key internal physical phenomena are observed, including heat recirculation within the combustion region, spatial inhomogeneity within the reaction zone, and preheating of gas in the upstream porous section. Further, the theory of XCT measurements applied to combustion systems is developed and implemented to arrive at 3D implied temperature field measurements at high spatial resolution. Implied temperature results are shown to exhibit quantitative agreement with those of a known 1D volume-averaged model for porous media combustion as well as with standard thermocouple measurements. These results shed light on internal thermophysical processes within PMBs while demonstrating the significant potential of XCT in obtaining quantitative, spatially resolved field data within optically inaccessible combustion environments.

Measurement of breast-tissue x-ray attenuation by spectral mammography: solid lesions

Knowledge of x-ray attenuation is essential for developing and evaluating x-ray imaging technologies. For instance, techniques to distinguish between cysts and solid tumours at mammography screening would be highly desirable to reduce recalls, but the development requires knowledge of the x-ray attenuation for cysts and tumours. We have previously measured the attenuation of cyst fluid using photon-counting spectral mammography. Data on x-ray attenuation for solid breast lesions are available in the literature, but cover a relatively wide range, likely caused by natural spread between samples, random measurement errors, and different experimental conditions. In this study, we have adapted a previously developed spectral method to measure the linear attenuation of solid breast lesions. A total of 56 malignant and 5 benign lesions were included in the study. The samples were placed in a holder that allowed for thickness measurement. Spectral (energy-resolved) images of the samples were acquired and the image signal was mapped to equivalent thicknesses of two known reference materials, which can be used to derive the x-ray attenuation as a function of energy. The spread in equivalent material thicknesses was relatively large between samples, which is likely to be caused mainly by natural variation and only to a minor extent by random measurement errors and sample inhomogeneity. No significant difference in attenuation was found between benign and malignant solid lesions. The separation between cyst-fluid and tumour attenuation was, however, significant, which suggests it may be possible to distinguish cystic from solid breast lesions, and the results lay the groundwork for a clinical trial. In addition, the study adds a relatively large sample set to the published data and may contribute to a reduction in the overall uncertainty in the literature.

Energy spectra considerations for synchrotron radiotherapy trials on the ID17 bio-medical beamline at the European Synchrotron Radiation Facility.

The aim of this study was to validate the kilovoltage X-ray energy spectrum on the ID17 beamline at the European Synchrotron Radiation Facility (ESRF). The purpose of such validation was to provide an accurate energy spectrum as the input to a computerized treatment planning system, which will be used in synchrotron microbeam radiotherapy trials at the ESRF. Calculated and measured energy spectra on ID17 have been reported previously but recent additions and safety modifications to the beamline for veterinary trials warranted a fresh investigation. The authors used an established methodology to compare X-ray attenuation measurements in copper sheets (referred to as half value layer measurements in the radiotherapy field) with the predictions of a theoretical model. A cylindrical ionization chamber in air was used to record the relative attenuation of the X-ray beam intensity by increasing thicknesses of high-purity copper sheets. The authors measured the half value layers in copper for two beamline configurations, which corresponded to differing spectral conditions. The authors obtained good agreement between the measured and predicted half value layers for the two beamline configurations. The measured first half value layer was 1.754 ± 0.035 mm Cu and 1.962 ± 0.039 mm Cu for the two spectral conditions, compared with theoretical predictions of 1.763 ± 0.039 mm Cu and 1.984 ± 0.044 mm Cu, respectively. The calculated mean energies for the two conditions were 105 keV and 110 keV and there was not a substantial difference in the calculated percentage depth dose curves in water between the different spectral conditions. The authors observed a difference between their calculated energy spectra and the spectra previously reported by other authors, particularly at energies greater than 100 keV. The validation of the beam spectrum by the copper half value layer measurements means the authors can provide an accurate spectrum as an input to a treatment planning system for the forthcoming veterinary trials of microbeam radiotherapy to spontaneous tumours in cats and dogs.

X-ray absorptiometry and ultrasound technologies for non-destructive compositional analysis of dry-cured ham

The characterization of dry-cured ham according to salt and fat contents is of great interest to industry and consumers. In this study, the feasibility of using non-destructive technologies such as X-rays and ultrasound (US) for this purpose was evaluated in dry-cured ham portions. Predictive models for fat and salt contents were based on the measurement of X-ray attenuation at different incident energies and the US velocity when the ham was at 2 and 15°C. A semi-empirical model based on the US measurements was also developed. Salt content was better predicted by X-ray technology (RMSEV=0.43%) than US (RMSEV=0.69%) and their combination had little impact on the accuracy of the prediction. US predicted fat content slightly better (RMSEV=6.70%) than X-rays (RMSEV=7.00%), and their combination increased the accuracy of the prediction (RMSEV=5.60%). Using the best models, 81% of samples were correctly classified into three salt content categories with X-rays whereas 71% of samples were correctly classified into three fat content categories by combining X-rays and US.

Using X-ray transmission/attenuation to quantify fluid absorption in cracked concrete

Cracks can alter the rate of fluid transport in concrete. Unfortunately, however, quantitative information is lacking to provide definitive statements regarding the extent to which cracks reduce durability or long-term performance. This paper describes a study that used X-ray transmission/attenuation to determine the influence of cracking on the absorption of fluid in concrete. Specifically, an experimental method is presented which uses a wedge splitting test to pre-crack specimens. These pre-cracked specimens were dried and ponded with water. At various times after the start of water ponding, X-ray attenuation measurements were taken using a grid of points around the crack. By repeating this measurement and comparing the change in X-ray transmission/attenuation, the ingress of the fluid could be determined by locating the position of the moisture front. An approach is presented to determine the geometry of the crack by using water absorption perimeter measurements of the wetting front in the concrete.

Characterisation of materials: determining density using X-ray microtomography

The authors have previously published a method of beam hardening correction for X-ray microtomography that allows accurate determination of mineral concentration in hard tissue. This uses a multi-element calibration carousel for making experimental X-ray attenuation measurements to optimise the parameters in a model of X-ray transmission and detection. From this, a calibration curve is generated to convert the X-ray polychromatic X-ray projection data to that which would be expected with monochromatic X-rays. Furthermore, the calibration curve can be modified according to the known composition of the specimen. Here, this is tested using different materials to assess its accuracy in determining their density. Generally, errors in density of around 1–2% were obtained. When modelling the conventional use of an aluminium step wedge, much larger errors are seen. The technique can be used to measure and map density or concentration in cases where this would be difficult with other methods.