X-ray Tube Spectrum Research Articles

An efficient Monte Carlo-based algorithm for scatter correction in keV cone-beam CT

A new method is proposed for scatter-correction of cone-beam CT images. A coarse reconstruction is used in initial iteration steps. Modelling of the x-ray tube spectra and detector response are included in the algorithm. Photon diffusion inside the imaging subject is calculated using the Monte Carlo method. Photon scoring at the detector is calculated using forced detection to a fixed set of node points. The scatter profiles are then obtained by linear interpolation. The algorithm is referred to as the coarse reconstruction and fixed detection (CRFD) technique. Scatter predictions are quantitatively validated against a widely used general-purpose Monte Carlo code: BEAMnrc/EGSnrc (NRCC, Canada). Agreement is excellent. The CRFD algorithm was applied to projection data acquired with a Synergy XVI CBCT unit (Elekta Limited, Crawley, UK), using RANDO and Catphan phantoms (The Phantom Laboratory, Salem NY, USA). The algorithm was shown to be effective in removing scatter-induced artefacts from CBCT images, and took as little as 2 min on a desktop PC. Image uniformity was greatly improved as was CT-number accuracy in reconstructions. This latter improvement was less marked where the expected CT-number of a material was very different to the background material in which it was embedded.

Radiogram enhancement and linearization using the beam hardening correction method

Traditionally, radiography is burdened by the fact that standard X-ray tube spectra are polychromatic and attenuation process in matter is energy dependent, where low-energy X-rays are preferentially absorbed. This beam hardening effect has several consequences: radiograms look noisy especially when low-energy photons are detected, empty holes look filled in computed tomography and observed object looks flatter than it should be. It will be shown it this paper that these problems can be solved using the “linearized signal to equivalent thickness” beam hardening correction method.

Study on the influence of X-ray tube spectral distribution on the analysis of bulk samples and thin films: Fundamental parameters method and theoretical coefficient algorithms

Knowledge of X-ray tube spectral distribution is necessary in theoretical methods of matrix correction, i.e. in both fundamental parameter (FP) methods and theoretical influence coefficient algorithms. Thus, the influence of X-ray tube distribution on the accuracy of the analysis of thin films and bulk samples is presented. The calculations are performed using experimental X-ray tube spectra taken from the literature and theoretical X-ray tube spectra evaluated by three different algorithms proposed by Pella et al. (X-Ray Spectrom. 14 (1985) 125–135), Ebel (X-Ray Spectrom. 28 (1999) 255–266), and Finkelshtein and Pavlova (X-Ray Spectrom. 28 (1999) 27–32). In this study, Fe–Cr–Ni system is selected as an example and the calculations are performed for X-ray tubes commonly applied in X-ray fluorescence analysis (XRF), i.e., Cr, Mo, Rh and W. The influence of X-ray tube spectra on FP analysis is evaluated when quantification is performed using various types of calibration samples. FP analysis of bulk samples is performed using pure-element bulk standards and multielement bulk standards similar to the analyzed material, whereas for FP analysis of thin films, the bulk and thin pure-element standards are used. For the evaluation of the influence of X-ray tube spectra on XRF analysis performed by theoretical influence coefficient methods, two algorithms for bulk samples are selected, i.e. Claisse–Quintin (Can. Spectrosc. 12 (1967) 129–134) and COLA algorithms (G.R. Lachance, Paper Presented at the International Conference on Industrial Inorganic Elemental Analysis, Metz, France, June 3, 1981) and two algorithms (constant and linear coefficients) for thin films recently proposed by Sitko (X-Ray Spectrom. 37 (2008) 265–272).

Influence of X-ray tube spectral distribution on uncertainty of calculated fluorescent radiation intensity

The relative radiation intensity ( R i ) defined as fluorescent radiation intensity of analyte in specimen to fluorescent radiation intensity of pure element or compound, e.g., oxide is used in calculation in both fundamental parameter methods and in theoretical influence coefficient algorithms. Accuracy of calculated R i is determined by uncertainties of atomic parameters, spectrometer geometry and also by X-ray tube spectral distribution. This paper presents the differences between R i calculated using experimental and theoretical X-ray tube spectra evaluated by three different algorithms proposed by Pella et al., Ebel, and Finkelshtein–Pavlova. The calculations are performed for the most common targets, i.e., Cr, Mo, Rh and W. In this study, R i is calculated for V, Cr, Mn, Fe, Co, Ni, Cu and Mo in steels as an example. The differences between R i calculated using different X-ray tube spectrum algorithms are presented when pure element standard, multielement standard similar to the analyzed material and one pure element standard for all analytes is used in X-ray fluorescence analysis. The differences between R i for intermediate-thickness samples (and also for thin films) and for X-ray tube, which ran for many hours, are also evaluated.

On X-ray tube spectra, the dependence on the angular and electron energy of X-rays from the targets

An algorithm was developed for the theoretical intensities of both X-ray continuum and characteristic K-radiation (K α 1 , K α 2 , K α , K β 1 , K β 2 , K β 3 , K β 13 , K β 4 and K β 5 ) of different target materials (Cr, Cu, Rh, Mo, W, Ag and Au) at different electron incidence angles (0.01° − 90°), different take-off angles of the photon emission (0.01° − 90°) and different X-ray tube voltages. It was found that the intensities of continuum and characteristic X-rays increase with increasing take-off angle and the take-off angle is inversely proportional to the absorption path of X-rays in the target. At take-off angles of 20° or more, the flux of the X-ray spectra remains practically independent of the take-off angle. Furthermore, at the optimum electron incidence angle and take-off angle of emitted X-ray photons, the dependence of X-ray tube spectra on applied voltage was also investigated.

Preliminary study of the advantages of X-ray energy selection in CT imaging

It is well known that a monochromatic X-ray source with an energy optimized for the organ thickness to be imaged could result in a better image quality in transmission radiology. In this paper we present the preliminary investigation for the implementation of this technique in computer tomography (CT) imaging. The detection system is based on a 1 mm thick silicon pixel detector bump bonded to a VLSI read-out, Medipix2. This detector ensures a good detection efficiency (46%) in the used energy range (60 kVp) with a good spatial resolution that arises from a 55 μm square pixel. The Medipix2 read-out electronics is not only a single photon counting system, but has also the capability of dual-energy threshold, that allows us to detect only photons that are in a chosen energy window. In this paper we present the results obtained in CT imaging of small samples, by selecting various energy windows within a standard X-ray tube spectrum so as to maximize the differentiation between significant attenuation coefficients. This study is preliminary for a future development of a dual-energy CT that could add functional information to the morphological information that is obtained in a CT examination.

Volume x-ray radiation of fast electrons at high-voltage nanosecond breakdown of dense gases

X-ray spectra of fast electrons injected into a gas subjected to an external electric field are simulated. For weak fields, the simulated spectra are in good agreement with the Kramers theory. For strong fields, the x-ray spectrum differs considerably from the well-known spectra of x-ray tubes with massive cathodes and the radiated energy is much higher. As the voltage applied to a given discharge gap grows, the number of emitted photons reaches a maximum, while the radiated energy tends to saturate instead of decreasing.

Feasibility of radiographic absorptiometry of the mandible as an osteoporosis screening method

We developed and evaluated single- and dual-energy radiographic absorptiometry (RA) for the measurement of mandibular bone mineral density (BMD), using standard dental equipment, that would allow for inexpensive and widespread osteoporosis screening. Accurately measured x-ray tube spectra are important for validating the simulations used in the design of the method. A constrained least-squares deconvolution technique for reducing the detector-induced blurring of the energy spectrum was developed. Application of this analytic correction to spectra acquired with a NaI-photomultiplier detector improved the measured data by 20%–60%. Implementation of the screening method is accomplished by simultaneously acquiring high- and low-energy images on a single dental radiograph by appropriate filtering of the dental x-ray tube output. Computer simulations were performed to optimize the filters with respect to error in the bone measurement. A custom-designed film holder housed the beam filters and accommodated calibration wedges that allowed the radiographs to be normalized for differences in exposure and developing conditions. Forty-six male and female subjects, ages 27 to 87 years, participated in a pilot study to assess the RA techniques. Left and right vertical periapical radiographs were taken of the premolar–molar region and, for comparison, the subjects' BMD was evaluated at the spine, left and right femur as well as total body by dual-energy x-ray absorptiometry (DXA). Mandibular BMD by either high or low single-energy RA measurements was positively correlated with skeletal BMD, as assessed by DXA, at the arms, legs, trunk, ribs, pelvis, total body, and femoral neck. ROC analysis of the single-energy techniques for identification of osteopenic and osteoporotic female subjects, as defined by DXA at the left femoral neck, yielded an area under the curve of 0.73. This is comparable to commercial devices currently used for screening and indicates that the RA method may be valuable for early diagnosis of low bone mass.

Lι, Lα1,2, Lη, Lβ1,2,3,4,5,6 and Lγ1,2,3 spectra of x‐ray tubes

AbstractInvestigations of L spectra of Mo, Rh, Ag, Sn, Gd, Er, W, Au and Bi were performed with an electron probe microanalyzer with acceleration voltages from 10 to 30 kV and typical values of the angles with respect to the plane target surface of 90° for electron incidence and 35° for x‐ray take‐off. A systematic analysis of measured intensities of 13 L lines and a comparison with literature data on relative intensities and transition probabilities led to a general description of L spectra. The production of characteristic spectra is described by Love and Scott's constant depth distribution of x‐ray excitation by electrons. The ionized levels L1, L2 and L3 corresponding to the characteristic radiation are characterized by proportionality factors Const‐L1, Const‐L2 and Const‐L3. Essential data are transition probabilities and fluorescence yields. Coster–Kronig transition probabilities are not necessary. The quality of the semi‐empirical description of L spectra is demonstrated by a comparison of measured and computed spectral responses. Copyright © 2003 John Wiley & Sons, Ltd.

Quantitative trace element analysis of individual fly ash particles by means of X-ray microfluorescence.

A new quantification procedure was developed for the evaluation of X-ray microfluorescence (XRF) data sets obtained from individual particles, based on iterative Monte Carlo (MC) simulation. Combined with the high sensitivity of synchrotron radiation-induced XRF spectroscopy, the method was used to obtain quantitative information down to trace-level concentrations from micrometer-sized particulate matter. The detailed XRF simulation model was validated by comparison of calculated and experimental XRF spectra obtained for glass microsphere standards, resulting in uncertainties in the range of 3-10% for the calculated elemental sensitivities. The simulation model was applied for the quantitative analysis of X-ray tube and synchrotron radiation-induced scanning micro-XRF spectra of individual coal and wood fly ash particles originating from different Hungarian power plants. By measuring the same particles by both methods the major, minor, and trace element compositions of the particles were determined. The uncertainty of the MC based quantitative analysis scheme is estimated to be in the range of 5-30%.

Enhancing the ratio of fluorescence to bremsstrahlung radiation in X-ray tube spectra

This paper describes techniques that can be used to improve the ratio of fluorescence to bremsstrahlung radiation ( F/ B) in X-ray tube spectra. Firstly, an extension of the EGS4 code system is used to evaluate the impact of the substrate in thin target applications, in terms of the yield of bremsstrahlung photons produced. The choice of materials to filter X-ray tube spectra, and its effect in the F/ B and the tube efficiency is discussed. The characteristics of spectra produced in transmission tubes with different target thicknesses, substrates and tube voltages are also presented.

X-ray tube spectra

X-ray tube spectra make an essential contribution to the quantitative description of experimental setups or for quantitative x-ray analysis. After an outline of the historical development of the description of tube spectra the approaches given by Wiederschwinger, Ebel et at. Schossmann et al. and Pella et at, are treated in detail. Summarizing the theoretical treatment and the applications, it can be stated that both approaches give comparable results over a certain spectral range. Pella's approach is restricted to electron incidence angles of 90° and application of Pella's spectral responses in the lower keV range should be avoided.

Measurements of discrete and continuous X-ray spectra with a photodiode at room temperature

Spectra of X- and γ-rays emitted by radioactive sources and of the radiation emitted by X-ray tubes, in the energy range 15–160 keV, have been measured with a silicon PIN photodiode at room temperature. The experimental X-ray tube spectra are compared with calculated ones on the basis of a semi-empirical model. Results indicate that the method utilized is adequate for the characterization of X-ray beams in the medical diagnostic energy region.

Calculation of x-ray tube spectral distributions

Two approaches to the calculation of x-ray tube spectral distributions for x-ray fluorescence analysis are compared. One of them is the NIST algorithm based both on Kramers' law for the continuum intensity and a semi-empirical ratio between the characteristic lines and the continuum intensity. In the other, the continuum and characteristic spectra are calculated separately just as it is done in electron microprobe analysis. Some improvements concerned with the description of the shape of the continuum spectrum at long wavelength and correction for fluorescence excited by the bremsstrahlung spectrum are proposed. The calculations of the continuum intensity and the relationship between the integral continuum and the characteristic line intensities were compared with literature experimental data for Cr, Rh, W, Cu and Mo target tubes. Some estimations of the absolute intensities of x-ray tube spectra are also shown. Copyright © 1999 John Wiley & Sons, Ltd.

Recommended specifications for new mammography equipment: report of the ACR-CDC Focus Group on mammography equipment.

The American College of Radiology has published a report that describes desirable features for new mammography x-ray units that will contribute to high-quality imaging. It encompasses all aspects of x-ray equipment performance including mechanical considerations, the x-ray tube focal spot and spectrum, generator performance, collimation, scatter rejection, and the automatic exposure control. The report is intended to provide guidance to equipment manufacturers and to purchasers of mammography systems with regard to basic performance levels that should be expected.

Comparison of Various Descriptions of X-Ray Tube Spectra

We have developed an algorithm for calculating the x-ray tube continuum based on the eqidistribution proposed by Love and Scott, extended the description of white and characteristic radiation given by Wiederschwinger et al for the energy range 10 to 50 keV to the low energy range from 5 to 30 keV, and compared the results from this algorithm to those responses obtained from algorithms using the absorption correction of Pochou and Pichoir, Philibert, Sewell and Pella. The comparison to other models showed a significandy better performance by our model.

Energy Dispersive Measurement of X-Ray Tube Spectra

A method for measuring spectral distributions of x-ray tubes directly with a solid-state detector is presented. Different anode materials (chromium, molybdenum, rhodium and tungsten) have been measured. Results for various applied voltages and take-off angles have been obtained.

Effect of X-ray Tube Window Thickness on Detection Limits for Light Elements in XRF Analysis

Abstract Widespread interest in light element analysis using XRF has stimulated the development of thin x-ray tube windows. Thinner windows enhance the soft x-ray output of the tube, which more efficiently excite the light elements in the sample. A computer program that calculates the effect of window thickness on light element sample fluorescence has been developed. The code uses an NIST algorithm to calculate the x-ray tube spectrum given various tube parameters such as beryllium window thickness, operating voyage, anode composition, and take-off angle. The interaction of the tube radiation with the sample matrix is modelled to provide the primary and secondary fluorescence from the sample. For x-rays in the energy region 30 - 1000 eV the mass attenuation coefficients were interpolated from the photo absorption data compilation of Henke, et al. The code also calculates the x-ray background due to coherent and incoherent scatter from the sample, as well as the contribution of such scatter to the sample fluorescence. Given the sample fluorescence and background the effect of tube window thickness on detection limits for light elements can be predicted.

Description of X-ray Tube Spectra by the Depth Distribution Function of Pochou and Pichoir

We have developed an algorithm for calculating the x-ray tube continuum based on the depth distribution function (DDF) proposed by Pochou and Pichoir, extended the description of white and characteristic radiation given by Wiederschwinger et al. to the low energy range from 5 to 30 keV and compared the results frorn these algorithms to the signals obtained from algorithms using the absorption correction of Philibert and of Sewell et al. Preceding calculations the measured spectra were separated into characteristic peak spectra and into the corresponding white spectra, where the background below the peak areas was numerically interpolated.

Three-dimensional differential absorption x-ray cone-beam microtomography using balanced filters and algebraic reconstruction

A new x-ray tomographic method to image a particular element is proposed and described. This method uses an x-ray tube spectrum and a pair of balanced filters with absorption edges just above and just below the edge of the desired element. The proposed system consists of a microfocus x-ray tube as an x-ray source and a 2-D detector array to collect projection data. The main advantage of this system over traditional differential tomography using two monoenergetic sources is its easy application to fan-beam or cone-beam geometry without reducing too much its intensity. ART is used to reconstruct the 3-D images from the simulated projection data generated by a Monte Carlo program. Computer experiments demonstrate the feasibility of selective imaging in cone-beam geometry.