Biomedical X-ray Imaging Enabled by Carbon Nanotube X-ray Sources

Although discovered more than 100 years ago, X-ray source technology has evolved rather slowly. The recent invention of the carbon nanotube （CNT） X-ray source technology holds great promise to revolutionize the field of biomedical X-ray imaging. CNT X-ray sources have been successfully adapted to several biomedical imaging applications including dynamic rnicro-CT of small animals and stationary breast tomosynthesis of breast cancers. Yet their more irnportant biomedical imaging applications still lie ahead in the future, with the devel- oprnent of stationary rnulti-source CT as a noteworthy exarnple.

Two Monte Carlo-based simulators for imaging-system modeling and projection simulation of flat-panel X-ray source

The advantages of a flat-panel X-ray source(FPXS)make it a promising candidate for imaging applications.Accurate imaging-system modeling and projection simulation are critical for analyzing imaging performance and resolving overlapping projection issues in FPXS.The conventional analytical ray-tracing approach is limited by the number of patterns and is not applicable to FPXS-projection calculations.However,the computation time of Monte Carlo(MC)simulation is independent of the size of the patterned arrays in FPXS.This study proposes two high-efficiency MC projection simulators for FPXS:a graphics processing unit(GPU)-based phase-space sampling MC(gPSMC)simulator and GPU-based fluence sampling MC(gFSMC)simulator.The two simulators comprise three components:imaging-system modeling,photon initialization,and physical-interaction simulations in the phantom.Imaging-system modeling was performed by modeling the FPXS,imaging geometry,and detector.The gPSMC simulator samples the initial photons from the phase space,whereas the gFSMC simulator performs photon initialization from the calculated energy spectrum and fluence map.The entire process of photon interaction with the geometry and arrival at the detector was simulated in parallel using multiple GPU kernels,and projections based on the two simulators were calculated.The accuracies of the two simulators were evaluated by comparing them with the conventional analytical ray-tracing approach and acquired projections,and the efficiencies were evaluated by comparing the computation time.The results of simulated and realistic experiments illustrate the accuracy and efficiency of the proposed gPSMC and gFSMC simulators in the projection calculation of various phantoms.

Beam and image experiment of beam deflection electron gun for distributed X-ray sources

Distributed X-ray sources comprise a single vacuum chamber containing multiple X-ray sources that are triggered and emit X-rays at a specific time and location. This process facilitates an application for innovative system concepts in X-ray and computer tomography. This paper proposes a novel electron beam focusing, shaping,and deflection electron gun for distributed X-ray sources.The electron gun uses a dispenser cathode as an electron emitter, a mesh grid to control emission current, and two electrostatic lenses for beam shaping, focusing, and deflection. Novel focusing and deflecting electrodes were designed to increase the number of focal spots in the distributed source. Two identical half-rectangle opening electrodes are controlled by adjusting the potential of the two electrodes to control the electron beam trajectory, and then, multifocal spots are obtained on the anode target. The electron gun can increase the spatial density of the distributed X-ray sources, thereby improving the image quality. The beam experimental results show that the focal spot sizes of the deflected(deflected amplitude 10.5 mm)and non-deflected electron beams at full width at half maximum are 0.80 mm 90.50 mm and 0.55 mm 90.40 mm, respectively(anode voltage 160 kV; beam current 30 mA). The imaging experimental results demonstrate the excellent spatial resolution and time resolution of an imaging system built with the sources, which has an excellent imaging effect on a field-programmable gate array chip and a rotating metal disk.

Laser-produced plasma helium-like titanium Kα x-ray source and its application to Rayleigh-Taylor instability study

Several experiments are performed on the ShenGuang-Ⅱ laser facility to investigate an x-ray source and test radiography concepts. X-ray lines emitted from laser-produced plasmas are the most practical means of generating these high intensity sources. By using a time-integrated space-resolved keV spectroscope and pinhole camera, potential helium-like titanium Kα x-ray backlighting （radiography） line source is studied as a function of laser wavelength, ratio of pre-pulse intensity to main pulse intensity, and laser intensity （from 7.25 to ～ 11.3 × 10^15 W/cm2）. One-dimensional radiography using a grid consisting of 5 #m Au wires on 16 μm period and the pinhole-assisted point projection is tested. The measurements show that the size of the helium-like titanium Ka source from a simple foil target is larger than 100 ~m, and relative x-ray line emission conversion efficiency ~x from the incident laser light energy to helium- like titanium K-shell spectrum increases significantly with pre-pulse intensity increasing, increases rapidly with laser wavelength decreasing, and increases moderately with main laser intensity increasing. It is also found that a gold gird foils can reach an imaging resolution better than 5-μm featured with high contrast. It is further demonstrated that the pinhole-assisted point projection at such a level will be a novel two-dimensional imaging diagnostic technique for inertial confinement fusion experiments.

Optimization of 4.7-keV X-ray titanium sources driven by 100-ps laser pulses

An experiment with thin titanium foils irradiated by two pulses delayed in time is conducted on the bnenguang-Il laser facility. A prepulse induces an underdense plasma, 2-ns later a main pulse （λL ≈ 0.35 μm, EL ≈120 J, τL ≈100 ps） is injected into the underdense plasma and produces strong line emission from the titanium K shell （i.e., Hea at 4.7 keV）. Data show that the intensity of 4.7-keV X-ray emission with the prepulse is approximately twice more than without the prepulse, and can be used as a backlighting source satisfying the diagnostic requirements for dense plasma probing. High- quality plasma images are obtained with the backlighfing 4.7-keV X-rays in a Rayleigh-Taylor hydrodynamic instability experiment.

Development of a seven-cell S-band standing-wave RF-deflecting cavity for Tsinghua Thomson scattering X-ray source

A 2856-MHz,π-mode,seven-cell standingwave deflecting cavity was designed and fabricated for bunch length measurement in Tsinghua Thomson scattering X-ray source(TTX)facility.This cavity was installed in the TTX and provided a deflecting voltage of 4.2 MV with an input power of 2.5 MW.Bunch length diagnoses of electron beams with energies up to 39 MeV have been performed.In this article,the RF design of the cavity using HFSS,fabrication,and RF test processes are reviewed.High-power operation with accelerated beams and calibration of the deflecting voltage are also presented.

Experimental Study of the X-Ray Radiation Source at Approximately Constant Radiation Temperature

An X-ray radiation source with approximately constant radiation temperature is realized by irradiating golden hohlraum with a shaped laser pulse. A simple theoretical model based on power balance is used to design the shape of the drive laser pulse. Experiments are carried out on the Shenguang III prototype laser facility, and the experimentM results are presented for radiation sources with the flat-top lasting about 2.5 ns at two different peak temperatures of about 150 eV and 170 eV, respectively, including the the drive laser pulses and the time integrated possible improvements are discussed. time histories of the temperatures, the shapes of radiation spectra. The validity of the model and

Energy loss caused by shielding effect of steel cage outside source tube

The energy loss, produced by shielding effect of steel cage outside the source tube, is quite considerable. With PENELOPE software package, MC results have been obtained based on the simulation of different source con- formations. The result illustrates that the naked source tubes can improve the utilization ratio of the cobalt facilities. It demonstrates the applied value of the naked source tube in engineering.

Numerical simulation for all-optical Thomson scattering X-ray source

Energy spectra, angular distributions, and temporal profiles of the photons produced by an all-optical Thomson scat- tering X-ray source are explored through numerical simulations based on the parameters of the SILEX-I laser system （800 nm, 30 fs, 300 TW） and the previous wakefield acceleration experimental results. The simulation results show that X-ray pulses with a duration of 30 fs and an emission angle of 50 mrad can be produced from such a source. Using the optimized electron parameters, X-ray pulses with better directivity and narrower energy spectra can be obtained. Besides the electron parameters, the laser parameters such as the wavelength, pulse duration, and spot size also affect the X-ray yield, the angular distribution, and the maximum photon energy, except the X-ray pulse duration which is slightly changed for the case of ultrafast laser-electron interaction.

Low Energy Plasma Focus as an Intense X-ray Source for Radiography

Study on X-ray emission from a low energy (1.8 kJ) plasma focus devicepowered by a 9 μF capacitor bank, charged at 20 kV and giving peak discharge current of about 175kA by using a lead-inserted copper-tapered anode is reported. The X-ray yield in different energywindows is measured as a function of hydrogen filling pressure. The maximum yield in 4π-geometry isfound to be (27.3+-1.1) J and corresponding wall plug efficiency for X-ray generation is 1.52+-0.06%. X-ray emission, presumably due to bombarding activity of electrons in current sheath at theanode tip was dominant, which is confirmed by the pinhole images. The feasibility of the device asan intense X-ray source for radiography is demonstrated.

Studying a kind of portable ultra-bright microfocus x-ray source

This paper studies the properties of a kind of portable ultra-bright microfocus x-ray source with the Monte-Carlo method in detail. The new x-ray source consists of an electron-emission system, an electrostatic focusing system and a metal target. A crystal Lanthanum Hexaboride cathode, a Wehnelt grid and an extracted electrode compose the triode electrode electron-gun system. Two equal radius cylinder electrodes form the focusing system. The key factors determining the focus properties of the electron beam such as the ratio Dw/H, grid bias Vg, and the properties of the extracted electrode arc numerically studied. The calculated results reveal that when Dw/H, Vg, the length of the extracted electrode, and the distance between the grid and the extracted electrode equals 5, q）.6 kV, 10 mm, and 8 mm respectively, the electron beam focal spot can be concentrated down to 9 μm in radius and a reasonable focal length about 72.5 mm can be achieved, at the same time, the cathode emission currents can be as high as 30 mA.

Phase Imaging Using Laser-produced X-ray Sources

A possible novel application of hard x-ray emitted during laser-plasma interaction was discussed. We established an Optical Transform Function to study the joint effect of the spectral distribution and temporal profile of the laser-produced x-ray on x-ray phase imaging. Though the laser-produced x-ray pulse duration is short and incoherent, the analysis confirms that the current x-ray phase imaging theory still holds for laser-produced x-ray phase imaging.

Self Consistent Calibration of Detectors and Sources for Hard and Soft X-Ray Diagnostics

X-Ray sources, detectors and optical components are now used in a wide range of applications. What is crucial is the absolute calibration of such devices to permit a quantitative assessment of the system under study. A new X-ray laboratory has been built in Frascati (ENEA) to develop diagnostics for nuclear fusion experiments and study applications of these X-ray techniques in other domains, like new material science, non destructive tests and so on. An in-house developed selfconsistent calibration procedure is described that permits the absolute calibration of sources (X-ray emitted fluxes) and detectors (detection efficiencies) as function of the X-ray photon energy, in the range 2 - 120 keV. The calibration procedure involves the use of an in-house developed code that also predicts the spectral response of any detector in any experimental condition that can be setup in the laboratory. The procedure has been then applied for the calibration and characterisation of gas and solid state imaging detectors, such as Medipix-2, GEM gas detector, CCD camera, Cd-Te C-MOS imager, demonstrating the versatility of the method developed here.

Research on the Influence of X-ray Phase Contrast Imaging Parameters with Micro-focus Source

X-ray in-line phase contrast imaging enables weakly to absorb specimens to be imaged successfully with high resolution and definition. In this paper we use computer simulation method to analyze how each parameter influences the quality of the image. It can avoid wasting unnecessary time and materials in the course of experiment to get ideal images.

Improvements to conventional X-ray tube-based cone-beam computed tomography system

Conventional X-ray tube-based cone-beam computed tomography(CX-CBCT) systems have great potential in industrial applications. Such systems can rapidly obtain a three-dimensional(3D) image of an object.Conventional X-ray tubes fulfill the requirements for industrial applications, because of their high tube voltage and power. Continuous improvements have been made to CX-CBCT systems, such as imaging time shortening,acquisition strategy optimization, and imaging software development, etc. In this study, a CX-CBCT system is developed. Additionally, some improvements to the CX-CBCT system are proposed based on the hardware conditions of the X-ray tube and detector. A near-detector(ND)geometry condition is employed to obtain a sharper image and larger detection area. An improved acquisition strategy is proposed to simplify operations and reduce total imaging time. In the ND geometry condition, a simplified method called FBP slice stacking(SS-FBP) is proposed, which can be applied to 3D image reconstruction. SS-FBP is timesaving relative to traditional methods. Furthermore, imaging software for the CX-CBCT system is developed in the MATLAB environment. Several imaging experiments were performed. The results suggest that the CX-CBCT system works properly, and that the above improvements are feasible and practical.

Experimental research on the feature of an x-ray Talbot–Lau interferometer versus tube accelerating voltage

X-ray Talbot-Lau interferometer has been used most widely to perform x-ray phase-contrast imaging with a con- ventional low-brilliance x-ray source, and it yields high-sensitivity phase and dark-field images of samples producing low absorption contrast, thus beating tremendous potential for future clinical diagnosis. In this work, by changing the accel- erating voltage of the x-ray tube from 35 kV to 45 kV, x-ray phase-contrast imaging of a test sample is performed at each integer value of the accelerating voltage to investigate the characteristic of an x-ray Talbot-Lau interferometer （located in the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Japan） versus tube voltage. Ex- perimental results and data analysis show that within a range this x-ray Talbot-Lau interferometer is not sensitive to the accelerating voltage of the tube with a constant fringe visibility of ~ 44%. This x-ray Talbot-Lau interferometer research demonstrates the feasibility of a new dual energy phase-contrast x-ray imaging strategy and the possibility to collect a refraction spectrum.

A Reflectron Time-of-Flight Mass Spectrometer with a Nano-Electrospray Ionization Source for Study of Metal Cluster Compounds

An experiment facility has been set up for the study of metal cluster compounds in our laboratory, which consists of a nano-electrospray ionization source, an ion transmission and focus system, and a reflectron time-of-fight mass spectrometer. Taking advantage of the nano-electrospray ionization source, polyvalent ions are usually produced in the ＂ionization＂ process and the obtained mass resolution of the equipment is over 8000. The molecular ion peaks of metal cluster compounds [Au20（PPhpy2）10Cl2]（SbF6）4, where PPhpy2=bis（2- pyridyl）phenylphosphine, and [AuaAg2（C）L6]（BF4）4, where L=2-（diphenylphosphino）-5- methylpyridine, are distinguished in the respective mass spectrum, accompanied by some fragment ion peaks. In addition, the mass-to-charge ratios of the parent ions are determi- nated. Preliminary results suggest that the device is a powerful tool for the study of metal cluster compounds. It turns out that the information obtained by the instrumentation serves as an essential supplement to single crystal X-ray diffraction for structure characterization of metal cluster compounds.

Mineralogical study of surface sediments in the western Arctic Ocean and their implications for material sources

Mineralogical analysis was performed on bulk sediments of 79 surface samples using X-ray diffraction. The analytical results, combined with data on ocean currents and the regional geological background, were used to investigate the mineral sources. Mineral assemblages in sediments and their distribution in the study area indicate that the material sources are complex. （1） Feldspar is abundant in the sediments of the middle Chukchi Sea near the Bering Strait, originating from sediments in the Anadyr River carried by the Anadyr Current. Sediments deposited on the western side of the Chukchi Sea are rich in feldspar. Compared with other areas, sediments in this region are rich in hornblende transported from volcanic and sedimentary rocks in Siberia by the Anadyr Stream and the Siberian Coastal Current. Sediments in the eastern Chukchi Sea are rich in quartz sourced from sediments of the Yukon and Kuskokwim rivers carried by the Alaska Coastal Current. Sediments in the northern Chukchi Sea are rich in quartz and carbonates from the Mackenzie River sediments. （2） Sediments of the southern and central Canada Basin contain little calcite and dolomite, mainly due to the small impact of the Beaufort Gyre carrying carbonates from the Canadian Arctic Islands. Compared with other areas, the mica content in the region is high, implying that the Laptev Sea is the main sediment source for the southern and central Canada Basin. In the other deep sea areas, calcite and dolomite levels are high caused by the input of large amounts of sediment carried by the Beaufort Gyre from the Canadian Arctic Islands （Banks and Victoria）. The Siberian Laptev Sea also provides small amounts of sediment for this region. Furthermore, the Atlantic mid-water contributes some fine-grained material to the entire deep western Arctic Ocean.

Light-controlled pulsed x-ray tube with photocathode

Unstable mechanical structure,low energy efficiency,and cooling requirements limit the application of conventional x-ray tubes based on filament as cathode in several academic areas.In this paper,we demonstrate a light-controlled pulsed x-ray tube using multialkali cathode as electron generator.The photocathode active area of the light controlled x-ray tube is 13.2 cm^(2)(41 mm in diameter),which provides high photoelectron-emitting efficiency up to 0.288 mA/lm in 460-nm LED and 2.37-mA maximum tube current.Furthermore,the modulation ability from 1 kHz to 100 kHz of the x-ray tube is tested.The results suggest that the light-controlled pulsed x-ray tube has easy modulation and short x-ray pulse properties and is promising to be the next generation x-ray tube with wide applications in medical radiation therapy as well as the calibration for detectors and scintillators.

X－Ray from Laser Produced Plasma as an Excitation Source in Spectroscopy Study

Spectral and temporal characteristics of soft X-ray from the laser-produced plasma (LPX)were studied under different conditions.The obtained LPX spectrum showed a little different from the black-body distribution in some other references,which is analysed theoretically.It is shown that LPX can be used as a convenient exciting method in spectroscopy study.