Quasi-monochromatic X-ray Source Research Articles

Time-resolved X-ray diffraction diagnostic development for the National Ignition Facility.

We present the development of an experimental platform that can collect four frames of x-ray diffraction data along a single line of sight during laser-driven, dynamic-compression experiments at the National Ignition Facility. The platform is comprised of a diagnostic imager built around ultrafast sensors with a 2-ns integration time, a custom target assembly that serves also to shield the imager, and a 10-ns duration, quasi-monochromatic x-ray source produced by laser-generated plasma. We demonstrate the performance with diffraction data for Pb ramp compressed to 150GPa and illuminated by a Ge x-ray source that produces ∼7 × 1011, 10.25-keV photons/ns at the 400μm diameter sample.

Spectral shape of quasi-monochromatic radiation from electron colliding with tightly focused laser pulses

We theoretically investigate spectra of emitted light in nonlinear Thomson backscattering, which is generated during the head-on collision of the electron and the tightly focused circularly polarized laser pulse. With numerical analysis, a novel approach of generating quasi-monochromatic x-rays is obtained. By properly setting the electron–laser interaction point, limiting the laser intensity, and increasing pulse duration, the emission spectral bandwidth would be effectively narrowed without reducing the radiant energy of the electrons. In the end, the optimal situations for obtaining the quasi-monochromatic x-ray source are presented.

Long duration x-ray source development for x-ray diffraction at the National Ignition Facility.

We present the results of experiments to produce a 10 ns-long, quasi-monochromatic x-ray source. This effort is needed to support time-resolved x-ray diffraction (XRDt) measurements of phase transitions during laser-driven dynamic compression experiments at the National Ignition Facility. To record XRDt of phase transitions as they occur, we use high-speed (∼1ns) gated hybrid CMOS detectors, which record multiple frames of data over a timescale of a few to tens of ns. Consequently, to make effective use of these imagers, XRDt needs the x-ray source to be narrow in energy and uniform in time as long as the sensors are active. The x-ray source is produced by a laser irradiated Ge foil. Our results indicate that the x-ray source lasts during the whole duration of the main laser pulse. Both time-resolved and time-integrated spectral data indicate that the line emission is dominated by the He-α complex over higher energy emission lines. Time-integrated spectra agree well with a one-dimensional Cartesian simulation using HYDRA that predicts a conversion efficiency of 0.56% when the incident intensity is 2 × 1015 W/cm2 on a Ge backlighter.

A Study of Quasi-Monochromatic X-Ray Sources for Breast Cancer Early Detection

Objectives: Early detection and treatment provide the opportunity to decrease the mortality rate from breast cancer. Quasi-monochromatic technique can enhance low contrast lesion detection by eliminating beam-hardening artifacts. We hypothesized that this technique would be feasible and can be used to assist in breast cancer early detection. Methods: The performance of stationary Digital Breast Tomosynthesis with quasi-monochromatic X-ray sources was evaluated using both simulated and physical phantoms. Normalized spectra in the fraction of total photons vs. photon energy were generated. Results: As expected, the peaked energies from sources, from smallest to largest, are Mo/Mo, W/Ag-1000, and W/Ce-10, W/Ce-100. For contrast vs. noise standard deviation on the simulated CIRS phantom, W/Ce-100 and W/Ce-10 have similar performance on both low and high contrast objects. For low contrast object, W/Ce-100 is barely noticeably better than W/Ce-10, and they are better than both W/Ag-1000 and Mo/Mo. For high contrast objects W/Ce-10 is slightly better than W/Ce-100. The spectra of the implemented W/Ce-10 X-ray source were measured, which matched the simulation well. The contrast noise ratios of reconstructed objects in American College of Radiology mammographic phantom with and without using W/Ce-10 combination are 7.1 and 5.4, respectively. Conclusions: The combination of stationary digital breast tomosynthesis and quasi-monochromatic technique can compensate the loss of X-ray flux due to heavy K-edge filtering. This technique can enable the stationary DBT scanners to operate at acceptable scanning times with better low contrast lesion detectability. Advances in Knowledge: The stationary digital breast tomosynthesis can provide high quality images within short scanning time by using X-ray source array, which makes quasi-monochromatic technique feasible.

Broadband, monochromatic and quasi-monochromatic x-ray propagation in multi-Z media for imaging and diagnostics

With the advent of monochromatic and quasi-monochromatic x-ray sources, we explore their potential with computational and experimental studies on propagation through a combination of low and high-Z (atomic number) media for applications to imaging and detection. The multi-purpose code GEANT4 and a new code PHOTX are employed in numerical simulations, and a variety of x-ray sources are considered: conventional broadband devices with well-known spectra, quasi-monochromatic laser driven sources, and monochromatic synchrotron x-rays. Phantom samples consisting of layers of low-Z and high-Z material are utilized, with atomic-molecular species ranging from H2O to gold. Differential and total attenuation of x-ray fluxes from the different x-ray sources are illustrated through simulated x-ray images. Main conclusions of this study are: I. It is shown that a 65 keV Gaussian quasi-monochromatic source is capable of better contrast with less radiation exposure than a common 120 kV broadband simulator. II. A quantitative measure is defined and computed as a metric to compare the efficacy of any two x-ray sources, as a function of concentration of high-Z moieties in predominantly low-Z environment and depth of penetration. III. Characteristic spectral features of , fluorescent emission and Compton scattering indicate pathways for accelerating x-ray photoexcitation and absorption; in particular, we model the tungsten at 59 keV alongside experimental measurements at the European synchrotron research facility to search for the signature of induced resonance fluorescence. The present study should contribute to the understanding of diagnostic potential of new x-ray sources under development, as well as the underlying fundamental physical processes and features for biomedical applications.

Early Detection of Breast Cancer Using Stationary Digital Breast Tomosynthesis with Quasimonochromatic X-ray Sources

Early Detection of Breast Cancer Using Stationary Digital Breast Tomosynthesis with Quasimonochromatic X-ray Sources

Tunable All-Optical Quasimonochromatic Thomson X-Ray Source in the Nonlinear Regime

We present an all-laser-driven, energy-tunable, and quasimonochromatic x-ray source based on Thomson scattering from laser-wakefield-accelerated electrons. One part of the laser beam was used to drive a few-fs bunch of quasimonoenergetic electrons, while the remainder was backscattered off the bunch at weakly relativistic intensity. When the electron energy was tuned from 17-50 MeV, narrow x-ray spectra peaking at 5-42 keV were recorded with high resolution, revealing nonlinear features. We present a large set of measurements showing the stability and practicality of our source.

K-edge imaging with quasi-monochromatic LCS X-ray source on the basis of S-band compact electron linac

A quasi-monochromatic hard X-ray source via laser Compton scattering (LCS) was developed on the basis of an S-band compact electron linac at AIST. The total number of photons generated and the maximum X-ray energy were ∼107photons/s and 41keV, respectively, when a 42-MeV electron beam was collided with an 800-nm Ti:sapphire laser at a 15° collision angle. We successfully demonstrated K-edge imaging using these LCS X-rays for the high-contrast observation of a human phantom with barium sulfate-concentrated blood vessels. In this paper, we describe the results of the K-edge imaging and analytical estimates of the contrast enhancement effect for the energy range ∼37keV, which corresponds to the K-edge energy of barium.

TH-A-141-06: Optimization of Incident X-Ray Source Spectrum Through Filtration for a Benchtop X-Ray Fluorescence Computed Tomography (XFCT) System

Purpose: To optimize acquisition of fluorescence photon signal from gold nanoparticles (GNPs) and reduce the effect of Compton scatter in benchtop x-ray fluorescence computed tomography (XFCT). Methods: In polychromatic XFCT, fluorescence signal is obscured by Compton scatter of source photons, and thus the choice of source spectrum is crucial. An experimental XFCT system for irradiation of a GNP-containing small animal-sized phantom was accurately modeled using the MCNP5 code for Monte Carlo simulations. The model used either a lead (Pb) or tin (Sn) filter to harden the 105 kVp source spectrum, and was validated with fluorescence/scatter profile measurements. Spectra (Pb: 1, 2, and 3 mm; Sn: 0.9, 1, 2, and 3 mm) were input into the model and their effect on fluorescence production/detection was investigated. Simulations were also run with hypothetical quasi-monochromatic x-ray sources (81, 85, 90, 95, and 100 keV) to determine the ideal energy for discriminating gold K-shell fluorescence peaks from Compton scatter background. Fluorescence signal-to-dose ratio (FSDR) and relative scan time (RST) were used to assess the degree of optimization during simulations. Results: For both materials, increasing filtration hardened source spectra and significantly decreased fluence available for producing fluorescence photons, while increasing FSDR. The RST increased at a much higher rate for a given increase in FSDR. Compared to Pb, Sn produced generally higher overall fluence, more prominent fluorescence peaks, favorably harder scatter profiles, increased FSDR, and shorter RST. Simulations using hypothetical quasi-monochromatic spectra showed that increasing source energy, between 81 and 100 keV, increased signal-to-background ratio and FSDR. Conclusion: Judicious choice of filter material/thickness to tailor polychromatic x-ray spectrum, considering trade-offs between FSDR and RST, can dramatically improve the performance of benchtop XFCT. This work will foster the further development of a benchtop XFCT system for routine pre-clinical imaging applications with GNPs.Supported by NIH/NCI grant R01CA155446; NIH/NCI grant R01CA155446

Is SPECT or CT Based Attenuation Correction More Quantitatively Accurate for Dedicated Breast SPECT Acquired with Non-Traditional Trajectories?

Attenuation correction is necessary for SPECT quantification. There are a variety of methods to create attenuation maps. For dedicated breast SPECT imaging, it is unclear if either SPECT- or CT-based attenuation map would provide the most accurate quantification and whether or not segmenting the different tissue types will have an effect on the qunatification. For these experiments, 99mTc diluted in methanol and water was filled into geometric and anthropomorphic breast phantoms and was imaged with a dedicated dual-modality SPECT-CT scanner. SPECT images were collected using a compact CZT camera with various 3D acquisitions including vertical and 30° tilted parallel beam, and complex sinusoidal trajectories. CT images were acquired using a quasi-monochromatic x-ray source and CsI(T1) flat panel digital detector in a half-cone beam geometry. Measured scatter correction for SPECT and CT were implemented. To compare photon attenuation correction in the reconstructed SPECT images, various volumetric attenuation matrices were derived from 1) uniform SPECT, 2) uniform CT, and 3) segmented CT, populated with different attenuation coefficient values. Comparisons between attenuation masks using phantoms consisting of materials with different attenuation values show that at 140 keV the differences in the attenuation between materials do not affect the quantification as much as the size and alignment of the attenuation map. The CT-based attenuation maps give quantitative values 30% below the actual value, but are consistent. While the SPECT-based attenuation maps can provide within 10% accurate quantitative values, but are less consistent.

Quasi-monochromatic hard X-ray source via laser Compton scattering and its application

We have developed a quasi-monochromatic hard X-ray source via laser Compton scattering (LCS) based on an S-band compact electron linac at AIST. The number of total photons and the maximum X-ray energy was 10 7 photons/sec and about 40 keV, respectively, in 15-degree crossing angle between a 42 MeV electron beam and a 800 nm Ti:Sa laser. The biological observation of the human bone with fractures has been successfully demonstrated using the LCS X-ray of 26.4 keV with the in-line phase contrast scheme. Good contrast enhancement is clearly observed between the absorption and the phase contrast images.

Compact x‐ray sources for mammographic applications: Monte Carlo simulations of image quality

Thomson scattering x-ray sources can provide spectral distributions that are ideally suited for mammography with sufficient fluence rates. In this article, the authors investigate the effects of different spectral distributions on the image quality in simulated images of a breast mammographic phantom containing details of different compositions and thicknesses. They simulated monochromatic, quasimonochromatic, and polychromatic x-ray sources in order to define the energy for maximum figure of merit (signal-difference-to-noise ratio squared/mean glandular dose), the effect of an energy spread, and the effect of the presence of higher-order harmonics. The advantages of these sources with respect to conventional polychromatic sources as a function of phantom and detail thickness were also investigated. The results show that the energy for the figure of merit peak is between 16 and 27.4 keV, depending on the phantom thickness and detail composition and thickness. An energy spread of about 1 keV standard deviation, easily achievable with compact x-ray sources, does not appreciably affect the image quality.

Visibility of tumor-like details in inline phase contrast mammography using quasimonochromatic X-ray sources

A new generation of quasimonochromatic high-flux X-ray sources, based on the X-ray radiation produced through Compton scattering between an electron beam and a laser beam, is under development. One of the possible applications of this source is inline phase contrast mammography, based on the observation of the edge-enhancement effect that can be observed at the border of structures inside the breast in images produced using a partially or totally coherent X-ray beam. In this work we present the results of a set of simulations of inline phase contrast mammography using typical inverse Compton scattering sources parameters. The simulated sample was a tumour-like mass having spherical shape, diameter between 200 μm and 5 mm, placed inside a breast-like matrix, 4 cm thick, and a standard composition of 50% glandular tissue and 50% adipose tissue. We discuss the minimum requirements for mammography using inverse Compton scattering sources and we discuss how the working parameters of the experimental setup (focal spot size, source–object distance, object–detector distance, detector point spread function, mean energy, energy bandwidth) affect the image quality, and specifically the edge-enhancement visibility. In particular, we show that the energy bandwidth does not significantly affect the visibility up to several keV. On the other hand, the edge-enhancement visibility depends substantially on other parameters such as source–object distance and detector point spread function.

Advantages of quasi-monochromatic X-ray sources in absorption mammography

Mammography is a challenging field of medical imaging. Early detection of breast cancer requires identifying small contrast details. The choice of the appropriate monochromatic energy enhances the visibility of such details. Thomson scattering source can provide tunable quasi-monochromatic X-ray beams. In this work, we investigate by Monte Carlo simulations the optimal monochromatic energy to image mammographic phantoms. In order to mimic a Thomson scattering source, we consider the effect on image quality of the presence of an energy spread and of the presence of higher-order harmonics.

Image quality simulations in X-ray mammography

The application of tunable monochromatic X-rays to mammography can improve the image quality and reduce the radiation dose to the patient. A new generation of quasi-monochromatic, high-flux X-ray sources is currently under development, based on Thomson scattering of photons produced by a laser on a highly focused electron beam. In this paper we investigate the effect of different spectral distributions on the image contrast on 2 cm, 4 cm, 6 cm, 8 cm breast mammographic phantoms containing details of different composition (tumor mass and calcification details) and thickness. In the simulations we assume a homogeneous breast composition and three compositions (25%; 50% and 75% glandular) are investigated. We simulate monochromatic, quasi-monochromatic and polychromatic X-ray sources in order to define the optimal energies that maximize the image quality parameter. In particular we compare the simulations of the Gaussian quasi-monochromatic spectra. having different energy standard deviations (1, 2, 3, 4, 5 keV) with traditional X-ray tubes spectra. Results show that Gaussian spectra having an energy spread of about 1 keV standard deviation call improve the image quality of about 30% with respect to traditional X-ray tube ones.

Development of a Multi-Energy CT for Small Animals: Characterization of the Quasi-Monochromatic X-Ray Source

A new multi-energy CT for small animals is operative (now only in scanning mode) at the Physics Department of the University of Bologna. The system makes use of a set of quasi-monochromatic X-ray beams produced by means of an Highly-Oriented Pyrolytic Graphite Bragg monochromator. This source is able to provide beams with energy tunable in a range from 20 to 70 keV. Here we present a complete characterization of the source. A theoretical model of the source has been analyzed, according to the known Zachariasen's theory for diffracting crystals. The beams have also been characterized in resolution and intensity, over the accessible range, and we present here some measured spectra. The monochromator system demonstrated an energy spread of about 3 keV (Full Width at Half Maximum-FWHM) at a beam energy of 26 keV. At the same energy, the intensity of the output beam is about 6% of the primary beam.

Phase contrast imaging simulation and measurements using polychromatic sources with small source-object distances

Phase contrast imaging is a technique widely used in synchrotron facilities for nondestructive analysis. Such technique can also be implemented through microfocus x-ray tube systems. Recently, a relatively new type of compact, quasimonochromatic x-ray sources based on Compton backscattering has been proposed for phase contrast imaging applications. In order to plan a phase contrast imaging system setup, to evaluate the system performance and to choose the experimental parameters that optimize the image quality, it is important to have reliable software for phase contrast imaging simulation. Several software tools have been developed and tested against experimental measurements at synchrotron facilities devoted to phase contrast imaging. However, many approximations that are valid in such conditions (e.g., large source-object distance, small transverse size of the object, plane wave approximation, monochromatic beam, and Gaussian-shaped source focal spot) are not generally suitable for x-ray tubes and other compact systems. In this work we describe a general method for the simulation of phase contrast imaging using polychromatic sources based on a spherical wave description of the beam and on a double-Gaussian model of the source focal spot, we discuss the validity of some possible approximations, and we test the simulations against experimental measurements using a microfocus x-ray tube on three types of polymers (nylon, poly-ethylene-terephthalate, and poly-methyl-methacrylate) at varying source-object distance. It will be shown that, as long as all experimental conditions are described accurately in the simulations, the described method yields results that are in good agreement with experimental measurements.

Phase-contrast x-ray imaging with intense ArKα radiation from femtosecond-laser-driven gas target

Intense ArKα x ray with very little continuum background has been generated using a dense Ar gas irradiated with an intense femtosecond laser, with the measured flux of 1.2×103photons∕mrad2/pulse. This compact quasimonochromatic x-ray source, with a source size of only 12μm, has been applied to x-ray radiographic imaging of a biological specimen, resulting in high-resolution, high quality phase-contrast images. Correlation between this intense Kα emission with the laser channeling in the Ar gas is discussed.

High power laser pulse circulation experiment for compact quasi-monochromatic tunable X-ray source

Laser electron Compton scattering monochromatic tunable X-ray source using X-band (11.424GHz) electron linear accelerator and Q-switch Nd:YAG laser is under construction at Nuclear Professional School, the University of Tokyo. To enhance the X-ray intensity, we installed a laser circulation system. Now, we are performing the circulation experiment by using a high power laser (1.4J, 532nm). We confirmed the laser pulse circulated in the optical circuit more than 15 times and the laser intensity is enhanced about 3.5 times.

A Compton X-ray source based on a SC linac at KAERI

A quasi-monochromatic X-ray source based on a KAERI SC linac system has been designed and is being manufactured now. 10 MeV 10 mA electron beam together with 20 W 1.06 μm laser beam will be used for 1.8 keV Compton X-ray generation with a few percentage of energy spread and 10 7 photons /s flux. A simple straight beamline was designed to deliver the electron beam with no degradation of its emittance and energy spread and to focus it to a proper size to produce the desired X-rays. We expect the first demonstration of 1.8 keV Compton X-ray generation in autumn 2006.