X-ray Energy Spectrum Research Articles

An analytical X-ray CdTe detector response matrix for incomplete charge collection correction for photon energies up to 300 keV

Gamma and X-ray energy spectra measured with semiconductor detectors suffer from various distortions, one of them being so-called “tailing” caused by an incomplete charge collection. Using the Hecht equation, a response matrix of size 321 × 321 was constructed which was used to correct the effect of incomplete charge collection. The correction matrix was constructed analytically for an arbitrary energy bin and the size of the energy bin thus defines the width of the spectral window. The correction matrix can be applied separately from other possible spectral corrections or it can be incorporated into an already existing response matrix of the detector. The correction was tested and its adjustable parameters were optimized on the line spectra of 57Co measured with a cadmium telluride (CdTe) detector in a spectral range from 0 up to 160keV. The best results were obtained when the values of the free path of holes were spread over a range from 0.4 to 1.0cm and weighted by a Gauss function. The model with the optimized parameter values was then used to correct the line spectra of 152Eu in a spectral range from 0 up to 530keV. An improvement in the energy resolution at full width at half maximum from 2.40 % ± 0.28 % to 0.96 % ± 0.28 % was achieved at 344.27keV. Spectra of “narrow spectrum series” beams, N120, N150, N200, N250 and N300, generated with tube voltages of 120kV, 150kV, 200kV, 250kV and 300kV respectively, and measured with the CdTe detector, were corrected in the spectral range from 0 to 160keV (N120 and N150) and from 0 to 530keV (N200, N250, N300). All the measured spectra correspond both qualitatively and quantitatively to the available reference data after the correction. To obtain better correspondence between N150, N200, N250 and N300 spectra and the reference data, lower values of the free paths of holes (range from 0.16 to 0.65cm) were used for X-ray spectra correction, which suggests energy dependence of the phenomenon.

Multimodality Imaging, including Dual-Energy CT, in the Evaluation of Gallbladder Disease.

Imaging of the gallbladder has a key role in the examination of patients with abdominal pain-especially pain localized to the right upper quadrant. Pathologic conditions that affect the gallbladder include cholelithiasis and associated complications such as acute and chronic cholecystitis, choledocholithiasis, gallstone pancreatitis, and cancer. Modalities used to image the gallbladder include ultrasonography (US), computed tomography (CT), magnetic resonance (MR) imaging, and nuclear scintigraphy. US is the primary imaging modality used to evaluate entities suspected of being gallbladder disease, as it is both sensitive and specific for demonstrating gallstones, biliary duct dilatation, and inflammatory features. However, CT is often the first imaging examination performed in patients who present to the emergency department with acute abdominal pain. Because the CT appearance of gallstones is variable, depending on the composition of the stone, pattern of calcification, and presence of gas, gallstones and other gallbladder conditions can be difficult to detect at conventional multidetector CT, with which data are acquired by using a single x-ray energy spectrum. Dual-energy CT, with which one takes advantage of the material-dependent x-ray absorption behavior of concurrently acquired high- and low-kilovolt-peak data, can add value by increasing the conspicuity of noncalcified gallstones and improving the detection of acute cholecystitis and gallbladder malignancy. In addition, MR cholangiopancreatography can be helpful for assessing choledocholithiasis and complicated biliary duct disease. ©RSNA, 2018.

Electromagnetic radiations from laser interaction with gas-filled Hohlraum

The emission of intensive electromagnetic pulse (EMP) due to laser-target interactions at the ShenGuang-III laser facility has been evaluated by probes. EMP signals measured using the small discone antennas demonstrated two variation trends including a bilateral oscillation wave and a unilateral oscillation wave. The new trend of unilateral oscillation could be attributed to the hohlraum structure and low-Z gas in the hohlraum. The EMP waveform showed multiple peaks when the gas-filled hohlraum was shot by the high-power laser. Comparing the EMP signals with the verification of stimulated Raman scattering energy and hard x-ray energy spectrum, we found that the intensity of EMP signals decreased with the increase of the hohlraum size. The current results are expected to offer preliminary information to study physical processes on laser injecting gas-filled hohlraums in the National Ignition Facility implementation.

Discovery of Very-high-energy Emission from RGB J2243+203 and Derivation of Its Redshift Upper Limit

Very-high-energy (VHE; $>$ 100 GeV) gamma-ray emission from the blazar RGB J2243+203 was discovered with the VERITAS Cherenkov telescope array, during the period between 21 and 24 December 2014. The VERITAS energy spectrum from this source can be fit by a power law with a photon index of $4.6 \pm 0.5$, and a flux normalization at 0.15 TeV of $(6.3 \pm 1.1) \times 10^{-10} ~ \textrm{cm}^{-2} \textrm{s}^{-1} \textrm{TeV}^{-1}$. The integrated \textit{Fermi}-LAT flux from 1 GeV to 100 GeV during the VERITAS detection is $(4.1 \pm 0.8) \times 10^{\textrm{-8}} ~\textrm{cm}^{\textrm{-2}}\textrm{s}^{\textrm{-1}}$, which is an order of magnitude larger than the four-year-averaged flux in the same energy range reported in the 3FGL catalog, ($4.0 \pm 0.1 \times 10^{\textrm{-9}} ~ \textrm{cm}^{\textrm{-2}}\textrm{s}^{\textrm{-1}}$). The detection with VERITAS triggered observations in the X-ray band with the \textit{Swift}-XRT. However, due to scheduling constraints \textit{Swift}-XRT observations were performed 67 hours after the VERITAS detection, not simultaneous with the VERITAS observations. The observed X-ray energy spectrum between 2 keV and 10 keV can be fitted with a power-law with a spectral index of $2.7 \pm 0.2$, and the integrated photon flux in the same energy band is $(3.6 \pm 0.6) \times 10^{-13} ~\textrm{cm}^{-2} \textrm{s}^{-1}$. EBL model-dependent upper limits of the blazar redshift have been derived. Depending on the EBL model used, the upper limit varies in the range from z $<~0.9$ to z $<~1.1$.

X-ray-bright optically faint active galactic nuclei in the Subaru Hyper Suprime-Cam wide survey

Abstract We construct a sample of X-ray-bright optically faint active galactic nuclei by combining Subaru Hyper Suprime-Cam, XMM-Newton, and infrared source catalogs. Fifty-three X-ray sources satisfying i-band magnitude fainter than 23.5 mag and X-ray counts with the EPIC-PN detector larger than 70 are selected from 9.1 deg2, and their spectral energy distributions (SEDs) and X-ray spectra are analyzed. Forty-four objects with an X-ray to i-band flux ratio FX/Fi &amp;gt; 10 are classified as extreme X-ray-to-optical flux sources. Spectral energy distributions of 48 among 53 are represented by templates of type 2 AGNs or star-forming galaxies and show the optical signature of stellar emission from host galaxies in the source rest frame. Infrared/optical SEDs indicate a significant contribution of emission from dust to the infrared fluxes, and that the central AGN is dust obscured. The photometric redshifts determined from the SEDs are in the range of 0.6–2.5. The X-ray spectra are fitted by an absorbed power-law model, and the intrinsic absorption column densities are modest (best-fit log NH = 20.5–23.5 cm−2 in most cases). The absorption-corrected X-ray luminosities are in the range of 6 × 1042–2 × 1045 erg s−1. Twenty objects are classified as type 2 quasars based on X-ray luminsosity and NH. The optical faintness is explained by a combination of redshifts (mostly z &amp;gt; 1.0), strong dust extinction, and in part a large ratio of dust/gas.

Design of a nondestructive two-in-one instrument for measuring the polarization and energy spectrum at an X-ray FEL facility

The free electron laser (FEL), as a next-generation light source, is an attractive tool in scientific frontier research because of its advantages of full coherence, ultra-short pulse duration, and controllable polarization. Owing to the demand of real-time bunch diagnosis during FEL experiments, precise nondestructive measurements of the polarization and X-ray energy spectrum using one instrument are preferred. In this paper, such an instrument based on the electron time-of-flight technique is proposed. By considering the complexity and nonlinearity, a numerical model in the framework of Geant4 has been developed for optimization. Taking the Shanghai Soft X-ray FEL user facility as an example, its measurement performances' dependence on the critical parameters was studied systematically, and, finally, an optimal design was obtained, achieving resolutions of 0.5% for the polarization degree and 0.3 eV for the X-ray energy spectrum.

Numerical Simulation of the SGEMP Inside a Target Chamber of a Laser Inertial Confinement Facility

After X-ray irradiate a metal cavity, a large number of photoelectrons are emitted into the internal space, thereby producing a very strong system-generated electromagnetic pulse (SGEMP). The X-ray environment inside a laser inertial confinement device is very complex. Even if the diagnostic equipment working inside the target chamber has a good electromagnetic shielding capability, it would still face severe SGEMP interference. In this paper, the X-ray environments inside target chambers of National Ignition Facility, optimized method for estimated guidance accuracy (OMEGA), and Shenguang-III (SG-III) facility were obtained through a survey of the literature. In light of the survey results, the time-biased finite-difference time-domain method and the particle-in-cell method were used to numerically simulate SGEMP inside a 2-D cylindrical cavity model. Besides, the relationships between the SGEMP in the cavity and parameters such as X-ray fluence, energy spectrum, pulsewidth, and spatial size of the model were studied. The fluence and pulsewidth of the X-ray were found to have a more significant effect on the time-domain waveform of the electromagnetic field. Finally, based on the calculation results, the SGEMP of the SG-III facility in the target chamber was calculated to approximately be 0.75 MV/m.

The applicability of Dual-Energy Computed Tomography (DECT) in forensic odontology – A review

Abstract Dual energy CT (DECT) is an emerging imaging modality that combines data collected with different x-ray energy spectra. The resulting volumetric reconstructions can be utilised for material differentiation and metal artefact reduction in radiological assessments. The literature was reviewed to identify articles discussing the use of post mortem CT (PMCT) in odontology, DECT for metal artefact reduction in dental imaging, and current uses of DECT in forensic imaging. Articles written in English and published between 2004 and 2016 were selected for thematic analysis. A total of 54 articles were analysed. PMCT has been used routinely and validated for identification and age estimation due to its numerous reformatting capabilities and registration techniques. DECT-specific techniques including mono-energetic reconstructions, coupled with extended CT scale visualisation and the use of metal artefact reduction (MAR) software have been shown to overcome the limitations of metal artefact susceptibility in PMCT and enhance material differentiation in forensic odontology. Further benefits of DECT in forensic applications include improved soft-tissue visualisation, virtual bony subtraction and foreign body characterization. The literature supports the use of DECT in extending the benefits of PMCT for dental identification. Further systematic research is required to explore the use of DECT for material differentiation in forensic odontology.

Segmentation-free x-ray energy spectrum estimation for computed tomography using dual-energy material decomposition.

An x-ray energy spectrum plays an essential role in computed tomography (CT) imaging and related tasks. Because of the high photon flux of clinical CT scanners, most of the spectrum estimation methods are indirect and usually suffer from various limitations. In this study, we aim to provide a segmentation-free, indirect transmission measurement-based energy spectrum estimation method using dual-energy material decomposition. The general principle of this method is to minimize the quadratic error between the polychromatic forward projection and the raw projection to calibrate a set of unknown weights, which are used to express the unknown spectrum together with a set of model spectra. The polychromatic forward projection is performed using material-specific images, which are obtained using dual-energy material decomposition. The algorithm was evaluated using numerical simulations, experimental phantom data, and realistic patient data. The results show that the estimated spectrum matches the reference spectrum quite well and the method is robust. Extensive studies suggest that the method provides an accurate estimate of the CT spectrum without dedicated physical phantom and prolonged workflow. This paper may be attractive for CT dose calculation, artifacts reduction, polychromatic image reconstruction, and other spectrum-involved CT applications.

Corrosion of copper exposed to Zhanjiang and Zhuhai atmospheric environments

PurposeThe aim of this paper was to study the initial corrosion behavior of copper in the substations of Zhanjiang and Zhuhai.Design/methodology/approachThe copper exposed at the substation of Guangdong coastal region in southern China for up to 12 months. The rust layer formed on the copper has been examined by scanning electron microscopy, X-ray energy spectrum, X-ray diffraction and electrochemical polarization techniques.FindingsThe corrosion weight loss of copper at Zhanjiang exposure site is a little more serious than that at Zhuhai exposure site in every exposure period. The corrosion products of copper have different changes in color and composition at the two exposure sites. The tensile strength of copper has a slight decrease after one-year exposure.Originality/valueThe atmospheric exposure experiments of copper in the substations of Zhanjiang and Zhuhai have been adopted for the first time. The corrosion behavior of copper was investigated, and it can provide reference for material selection of the substation.

Effect of thermal annealing on scintillation properties of Ce:Gd2Y1Ga2.7Al2.3O12 under different atmosphere

Cerium-doped 1% Ce:Gd2Y1Ga2.7Al2.3O12(GYGAG) single crystal samples grown via Czochralski method were annealed under air, O2 and N2 atmospheres from 350 to 1400 °C. The X-ray excited luminescence spectra, energy spectra and UV as well as thermally stimulated luminescence (TSL) spectra were performed comparatively on “as-grown” and thermally annealed samples. It was found that the luminescence efficiency after annealing in air and O2 was significantly enhanced compared to the non-annealed samples and this phenomenon was suggested to be caused by the existence of some oxygen vacancies in the Ce:GYGAG crystals. And the oxygen vacancies in the as-grown GYGAG crystals can be effectively eliminated by means of annealing in O2 containing atmosphere without changing the luminescence mechanism. From the TSL curves before and after annealing, three traps within 77–650 K were found to be related to oxygen vacancies.

The qualitative f-ratio method applied to electron channelling-induced x-ray imaging with an annular silicon drift detector in a scanning electron microscope in the transmission mode

Electron channelling is known to affect the x-ray production when an accelerated electron beam is applied to a crystalline material and is highly dependent on the local crystal orientation. This effect, unless very long counting time are used, is barely noticeable on x-ray energy spectra recorded with conventional silicon drift detectors (SDD) located at a small elevation angle. However, the very high count rates provided by the new commercially available annular SDDs permit now to observe this effect routinely and may, in some circumstances, hide the true elemental x-ray variations due to the local true specimen composition. To circumvent this issue, the recently developed f-ratio method was applied to display qualitatively the true net intensity x-ray variations in a thin specimen of a Ti-6Al-4V alloy in a scanning electron microscope in transmission mode. The diffraction contrast observed in the x-ray images was successfully cancelled through the use of f-ratios and the true composition variations at the grain boundaries could be observed in relation to the dislocation alignment prior to the β-phase nucleation. The qualitative effectiveness in removing channelling effects demonstrated in this work makes the f-ratio, in its quantitative form, a possible alternative to the ZAF method in channelling conditions.

Technical Note: Insertion of digital lesions in the projection domain for dual‐source, dual‐energy CT

To compare algorithms performing material decomposition and classification in dual-energy CT, it is desirable to know the ground truth of the lesion to be analyzed in real patient data. In this work, we developed and validated a framework to insert digital lesions of arbitrary chemical composition into patient projection data acquired on a dual-source, dual-energy CT system. A model that takes into account beam-hardening effects was developed to predict the CT number of objects with known chemical composition. The model utilizes information about the x-ray energy spectra, the patient/phantom attenuation, and the x-ray detector energy response. The beam-hardening model was validated on samples of iodine (I) and calcium (Ca) for a second-generation dual-source, dual-energy CT scanner for all tube potentials available and a wide range of patient sizes. The seven most prevalent mineral components of renal stones were modeled and digital stones were created with CT numbers computed for each patient/phantom size and x-ray energy spectra using the developed beam-hardening model. Each digital stone was inserted in the dual-energy projection data of a water phantom scanned on a dual-source scanner and reconstructed with the routine algorithms in use in our practice. The geometry of the forward projection for dual-energy data was validated by comparing CT number accuracy and high-contrast resolution of simulated dual-energy CT data of the ACR phantom with experimentally acquired data. The beam-hardening model and forward projection method accurately predicted the CT number of I and Ca over a wide range of tube potentials and phantom sizes. The images reconstructed after the insertion of digital kidney stones were consistent with the images reconstructed from the scanner, and the CT number ratios for different kidney stone types were consistent with data in the literature. A sample application of the proposed tool was also demonstrated. A framework was developed and validated for the creation of digital objects of known mineral composition, and for inserting the digital objects into projection data from a commercial dual-source, dual-energy CT scanner. Among other applications, it will allow a systematic investigation of the impact of scan and reconstruction parameters on kidney stone dual-energy properties under rigorously controlled conditions.

Characterization of the ESR response of alanine dosimeters to low-energy Cu-target X-tube photons

This article describes Electron Spin Resonance (ESR) response measurements of Kodak BioMax alanine films exposed to low-energy X-rays from a Cu-target tube operating at 20 kV. Commercial alanine detectors were used to ensure maximum reproducibility of the results, while the choice of a film was due the low penetration of the soft X-rays. X-ray energy spectra and fluences were determined with an innovative digital semiconductor detector system. These data were used to quantify the irradiation of the alanine films in terms of absorbed dose to water. The alanine films were found to present a stable response, highly linear with dose. To our knowledge, these data have not been previously reported and they may be extremely relevant, e.g., when mapping the high-gradient treatment fields used in microbeam radiation therapy (MRT) with synchrotron radiation.

An analytical approach to the light transport in columnar phosphors. Detector Optical Gain, angular distribution and the CsI:Tl paradigm

PurposeAn analytical model has been developed for the light propagation in columnar phosphors, based on the optical photon propagation physical and geometrical principles. MethodsThis model accounts for the multiple reflections on the sides of the crystal column, as well as for the infinite forward and backward reflections of the propagated optical photon beams created in the crystal bulk. Additionally it considers the lateral propagated optical photon beams after multiple refractions from the neighbor columns and the optical photon attenuation inside the scintillator.The model was used to predict the Detector Optical Gain (DOG), and the angular distribution, of the columnar CsI:Tl scintillators, used in medical imaging. ResultsThe model was validated against CsI:Tl optical photon transmission published results and good agreement was observed. It was, also, found that the DOG is affected by the length of the columns, as well as the incident X-ray energy spectrum. The results of the angular distribution are in accordance with the theory that the longer crystal columns have more directional light distribution. ConclusionsThe results of DOG are in accordance with the use of short crystal columns for lower energies (mammography) and the use of long crystal columns for higher energies (general radiology). Angular distribution was found more directive for long crystal columns.

Converting computed tomography images into photon interaction coefficients by using stoichiometric calibration and parametric fit models.

X ray and γ-ray are widely applied in radiology, radiotherapy, and nuclear medicine. Linear attenuation coefficients and linear energy absorption coefficients are essential for dose calculation and image correction. In this study, a method that entails combining the stoichiometric calibration and parametric physical models was developed to convert computed tomography (CT) images into the linear attenuation coefficients and linear energy absorption coefficients. A calibration scan was performed using standard tissue-equivalent materials to obtain the characteristics of the x-ray energy spectrum. Subsequently, relationships between CT numbers and tissue parameters were established using standard soft tissue and bone tissue data adopted from the literature. The linear attenuation coefficient and linear energy absorption coefficient were calculated using the parametric fit model. The results showed a linear relationship between CT numbers and tissue parameters. The tissue-equivalent materials differed from real human tissues, leading to considerable errors in estimation of mass attenuation coefficients when the photon energy was lower than 50keV. Mass attenuation coefficients and mass energy transfer coefficients of five tissues were calculated and validated using clinical CT images. The error was less than ±5% and ±8%, compared with the values of the International Commission on Radiation Units (ICRU) 46 report. The probability of photon interaction with tissues and physical characteristics of tissues can be accurately evaluated by using the proposed method and applied in various clinical applications.

Dual-Energy Computed Tomography untuk Menentukan Komposisi Batu Urin

Urolithiasis is a common disease with a reported prevalence between 4% and 20% in the worldwide. Determination of urinary calculi composition is a key factor in preoperative evaluation, treatment, and recurrence prevention. Dual-energy computed tomography (DECT) is available methods for determining urinary stone composition were only available after stone extraction, and thereby unable to aid in optimized stone management prior to intervention. DECT utilizes the attenuation difference produced by two different x-ray energy spectra to quantify urinary calculi composition while still providing the information attained with a conventional CT. Knowledge of DECT imaging pitfalls and stone mimics is important, as the added benefit of dual-energy analysis is the determination of stone composition, which in turn affects all aspects of stone management.&#x0D; This article describes DECT principles, scanner types and acquisition protocols for the evaluation of urinary calculi as they relate to imaging pitfalls (inconsistent characterization of small stones, small DECT field of view, and mischaracterization from surrounding material) and stone mimics (drainage devices) that may adversely impact clinical decisions.

The Mathematical Model of Image, Generated by Scanning Digital Radiography System

The mathematical model of image, generated by scanning digital radiography system is present. This model takes into account the X-ray energy spectrum transformation of the test object and a noise due to the quantum nature of radiation. The calculation results confirm the importance of fluctuations of the absorbed energy of the registered photon for the small size of the scintillation detectors.

Aerogel Cherenkov detector for characterizing the intense flash x-ray source, Cygnus, spectrum.

An aerogel Cherenkov detector is proposed to measure the X-ray energy spectrum from the Cygnus-intense flash X-ray source operated at the Nevada National Security Site. An array of aerogels set at a variety of thresholds between 1 and 3 MeV will be adequate to map out the bremsstrahlung X-ray production of the Cygnus, where the maximum energy of the spectrum is normally around 2.5 MeV. In addition to the Cherenkov radiation from aerogels, one possible competing light-production mechanism is optical transition radiation (OTR), which may be significant in aerogels due to the large number of transitions from SiO2 clusters to vacuum voids. To examine whether OTR is a problem, four aerogel samples were tested using a mono-energetic electron beam (varied in the range of 1-3 MeV) at NSTec Los Alamos Operations. It was demonstrated that aerogels can be used as a Cherenkov medium, where the rate of the light production is about two orders magnitude higher when the electron beam energy is above threshold.

A Monte Carlo simulation method for reconstruction of accelerator based on verified 6 MV X-ray phase-space and energy spectrum information

Objective To establish a novel Monte Carlo simulation method for reconstruction of medical accelerator model and X-ray energy spectrum based on IAEA Varian 6 MV X-ray phase-space file and photon energy spectrum of the target accelerator. Methods The verified 6 MV X-ray phase-space files were preprocessed to elevate the energy of each particle. Particles were saved in different Phase-Space-Let (PSL) files according to their position and energy, yielding an initial photon energy spectrum for Monte Carlo simulation of accelerator under an initial target energy. The initial photon energy spectrum was fit to a photon energy spectrum of an accelerator (Elekta Precise 10 MV X-ray accelerator) under an unknown target energy to yield a fitting coefficient, which was the weight of each PSL. Finally, an accelerator model under an unknown target energy was reconstructed using the initial PSL files and the weight information. The percentage depth dose (PDD) distribution was calculated in different square open fields. The effectiveness of this method was verified using one dimensional gamma passing rate. Results The peak position and overall distribution of the reconstructed 10 MV photon energy spectrum were in accordance with those of the verified 10 MV photon energy spectrum. The PDD calculated from the reconstructed 10 MV accelerator model agreed well with the measured PDD. The one-dimensional gamma passing rate was above 96%(1%/1 mm, threshold=0%). Conclusion The Monte Carlo reconstruction method proposed in this study is reliable, accurate, and effective. Key words: X-ray energy spectrum; Linac head beamreconstruction; Phase-Space-Let files; Monte Carlo simulation