Source Spot Size Research Articles

High-energy high-dose microfocus X-ray computed tomography driven by high-average-current photo-injector.

High-energy, high-dose, microfocus X-ray computed tomography (HHM CT) is one of the most effective methods for high-resolution X-ray radiography inspection of high-density samples with fine structures. Minimizing the effective focal spot size of the X-ray source can significantly improve the spatial resolution and the quality of the sample images, which is critical and important for the performance of HHM CT. The objective of this study is to present a 9 MeV HHM CT prototype based on a high-average-current photo-injector in which X-rays with about 70μm focal spot size are produced via using tightly focused electron beams with 65/66μm beam size to hit an optimized tungsten target. In digital radiography (DR) experiment using this HHM CT, clear imaging of a standard 0.1 mm lead DR resolution phantom reveals a resolution of 6 lp/mm (line pairs per mm), while a 5 lp/mm resolution is obtained in CT mode using another resolution phantom made of 10 mm ferrum. Moreover, comparing with the common CT systems, a better turbine blade prototype image was obtained with this HHM CT system, which also indicates the promising application potentials of HHM CT in non-destructive inspection or testing for high-density fine-structure samples.

Laser beam guiding in partially stripped magnetized quantum plasma

Relativistic and ponderomotive nonlinearities arising by the passage of a linearly polarized laser beam through a partially stripped magnetized quantum plasma are analyzed. The interaction formalism has been developed using the recently developed quantum hydrodynamic model. The effects associated with the Fermi pressure, quantum Bohm potential and electron spin have been incorporated. A nonparaxial, non-linear wave equation has been obtained by the use of source dependent expansion technique and spot size has been evaluated. The nonlinear relativistic self-focusing tends to focus the beam while the ponderomotive nonlinearity tends to defocus. The effect of magnetization and quantum effects on the spot size and the beam power have been studied.

Design and performance of a pulsed power-driven x-ray source for flash radiography

The design and test results of a pulsed power-driven X-ray source which is named Hawkeye-I are described. The Hawkeye-I is developed to execute flash X-ray radiography. It is a six-stage induction voltage adder and terminated by a positive polarity rod-pinch diode. The six stages are identical and the prime energy of each stage is provided by a tesla transformer elevating the output voltage from a discharge brick which consists of two $4\text{ }\text{ }\ensuremath{\mu}\mathrm{F}$ capacitors and a three-electrode gas switch. Comparing to the induction voltage adders driven by Marx generators, the numbers of gas switches and capacitors in the energy storage sections of Hawkeye-I decrease significantly. The Hawkeye-I can produce a maximum output voltage of about 4.2 MV. The corresponding X-ray source spot size and dose at 1 m are 1.4 mm and 17.9 rad, respectively. Fifty consecutive shots have been conducted to evaluate the reliability of the machine and 98% of the shots are successful. Furthermore, as the energy propagating in the accelerator is mainly determined by seven laser-triggered gas switches, the Hawkeye-I is capable of controlling the timing of the X-ray pulse accurately.

Modularized data-driven reconstruction framework for nonideal focal spot effect elimination in computed tomography.

High-performance computed tomography (CT) plays a vital role in clinical decision-making. However, the performance of CT imaging is adversely affected by the nonideal focal spot size of the x-ray source or degraded by an enlarged focal spot size due to aging. In this work, we aim to develop a deep learning-based strategy to mitigate the problem so that high spatial resolution CT images can be obtained even in the case of a nonideal x-ray source. To reconstruct high-quality CT images from blurred sinograms via joint image and sinogram learning, a cross-domain hybrid model is formulated via deep learning into a modularized data-driven reconstruction (MDR) framework. The proposed MDR framework comprises several blocks, and all the blocks share the same network architecture and network parameters. In essence, each block utilizes two sub-models to generate an estimated blur kernel and a high-quality CT image simultaneously. In this way, our framework generates not only a final high-quality CT image but also a series of intermediate images with gradually improved anatomical details, enhancing the visual perception for clinicians through the dynamic process. We used simulated training datasets to train our model in an end-to-end manner and tested our model on both simulated and realistic experimental datasets. On the simulated testing datasets, our approach increases the information fidelity criterion (IFC) by up to 34.2%, the universal quality index (UQI) by up to 20.3%, the signal-to-noise (SNR) by up to 6.7%, and reduces the root mean square error (RMSE) by up to 10.5% as compared with FBP. Compared with the iterative deconvolution method (NSM), MDR increases IFC by up to 24.7%, UQI by up to 16.7%, SNR by up to 6.0%, and reduces RMSE by up to 9.4%. In the modulation transfer function (MTF) experiment, our method improves the MTF50% by 34.5% and MTF10% by 18.7% as compared with FBP, Similarly remarkably, our method improves MTF50% by 14.3% and MTF10% by 0.9% as compared with NSM. Also, our method shows better imaging results in the edge of bony structures and other tiny structures in the experiments using phantom consisting of ham and a bottle of peanuts. A modularized data-driven CT reconstruction framework is established to mitigate the blurring effect caused by a nonideal x-ray source with relatively large focal spot. The proposed method enables us to obtain high-resolution images with less ideal x-ray source.

Kα X-ray Emission from Nanowire Cu Targets Driven by Femtosecond Laser Pulses for X-ray Conversion and Backlight Imaging.

A high-quality X-ray source was proposed by modifying the target material structure characteristics driven by ultrahigh laser energy. The experiments were performed on the Ti:sapphire femtosecond laser beam device (4.3–6 J, 30 fs), one of the three XG-III lasers in Laser Fusion Research Center of China Academy of Engineering Physics. The femtosecond laser beam drove the nanowire copper material with an average length of 18–50 μm and a diameter of about 260 nm. A single-photon counting charge-coupled device was employed to measure the copper Kα X-ray emission of the nanowire and foil targets. A clear maximum photon yield of the nanowire target was calculated to be 3.6 × 108 photons sr–1 s–1, the conversion efficiency was up to 0.0087%, and the average yield was 2.5 times that of the copper foil targets. In addition, by using a pinhole imaging method of φ10 μm, the minimum full width at half maximum spot size of the X-ray source was calculated in the range of 85–240 μm, which was similar to that of the copper foil material with a long radius of 170 μm and a short radius of 63 μm. The experimental data illustrate that the nanowire has the potential to enhance the energy absorption of femtosecond laser for X-ray conversion and backlight imaging.

Determination of focal spot size of high-energy microfocal X-ray source based on HfO2-coated single-bounce ellipsoidal glass monocapillary X-ray condenser

A method based on the single-bounce ellipsoidal monocapillary X-ray condenser (SEGMXC) was improved for determining the focal spot size of the high-energy microfocal X-ray source. HfO2 was selected as the high-density material (∼9.68g/cm3) and coated on the inner surface of the SEGMXC by the atomic layer deposition method. The focal spot size of a microfocal spot X-ray source was obtained as 33.14 ± 0.02 μm and the relative deviation of the effective size given by the manufacturer was 5.3%.

A detector system for a high-energy phase-contrast human computed tomography experimental device

Abstract A detector system is designed for a high-energy phase-contrast computed tomography (CT) experimental device with an X-ray tube voltage of 80 kV. The spot size of the X-ray tube is 0.4 mm*0.7 mm. The Gd2O2S scintillator detector is adopted in our design, which is characterized by a high detection efficiency and high light yield. This system contains 2304 channels and the corresponding high-density read-out electronics. Considering the influence of the large spot size of the X-ray tube source, a detector pixel size of 0.75 mm*1 mm is adopted to obtain sufficient spatial resolution. Because the light intensity fluctuation caused by the phase shift is very weak, a 20bit ADC is used to achieve sufficient efficient resolution (ER). The electronics test shows that the SNR can reach 72. Compared to a commercial detector board, the detector system has better resolution for the sample used in the phase-contrast imaging experiment.

Augmenting Soft Tissue Contrast Using Edge-Enhancing Phase-Imaging Techniques in X-Ray Microtomography.

Conventional X-ray imaging is based on the attenuation of X-rays and the technique provides sufficient contrast when the difference between attenuation coefficients of neighboring structures is sufficient. A promising imaging possibility on a μCT is the use of phase information of an X-ray beam to generate an image of the sample. This is known as phase-contrast imaging. Propagation-based phase imaging sets the least amount of requirements on the imaging setup - lateral coherence for the X-ray source and a movable detector and source. The Zeiss Xradia MicroXCT-400 at our laboratory provides this possibility. Therefore, the phase-contrast imaging protocol, which provides an edge-enhancement effect, on the μCT device was optimized using thin polylactic acid fibers in order to enhance the visibility of low density samples. The optimization consisted of source and detector distance variation measurements. To demonstrate the contrast enhancement results, the optimization was applied to two types of collagen samples embedded in air, ethanol, and water.The results showed enhanced contrast for the edge-enhanced phase-contrast images compared to absorption images. Most importantly, the results indicated that the source does not need to placed at the negative limit to obtain useful phase information. Additionally, the visibility increases with increasing sample-to-detector distance. Finally, significantly enhanced contrast was obtained for the collagen sample embedded in water using phase-imaging techniques. The technique is limited due to the focal spot size and voltage of the X-ray source. The phase-imaging technique has the possibility to enhance contrast of low density samples and to reveal structures that cannot be seen using other imaging techniques.

Experimental Study of the Effect of Light Source Spot Size on Measure Error of PSD

The energy distribution of the incident light spot on position-sensitive detector (PSD) screen is uneven and the output coordinate value is the energy centre of the light spot. Measurement error caused by the deviation between the geometric and gravity centre of the light spot will occur. The deviation will increase with the increase of the diameter of the light spot. There is no quantitative research on the position error caused by the changes of the light spot diameter and the distance from the light spot to the PSD. To evaluate the magnitude of the error, the infrared spotlight is selected as the target light. The changing pattern that the spot diameter varies with the distance between the light source and lens is studied. Additionally, the effect of the spot size on the PSD measure error is studied. The research provides reference for error evaluation of the distance and position detection of PSD. [Submitted 5 July 2017; Accepted 24 December 2017]

Experimental study of the effect of light source spot size on measure error of PSD

Experimental study of the effect of light source spot size on measure error of PSD

Preliminary Experimentation of Fast Neutron Radiography with D-T Neutron Generator at BARC

An experimental study on fast neutron radiography (FNR) has been carried out using a laboratory based D-T neutron generator facility at Bhabha Atomic Research Centre (BARC) and initial results are presented. The aim was to develop an FNR system with a moderate intensity neutron source for imaging of specimen containing mixed low-Z and high-Z materials. The experimental set-up consists of a D-T neutron generator, collimator and an EMCCD camera based imaging system. Experiments were carried out with the neutron generator having a source strength of about 2 × 109 n/s and source spot size of 20 mm. To obtain optimum image quality with such a moderate neutron yield, a collimator has been designed having an inlet aperture of 10 mm and an L/D of 43. The imaging system was kept at an optimum distance from the collimator and various test samples of materials ranging from low Z to high Z were imaged. Thick samples in step wedge form, hole features in step wedge of polyethylene, mild steel and lead were imaged and analysed. Also a test sample of a low Z material (HDPE) with a hole placed behind a thick Pb was imaged to study the effect of thickness of high Z material on image quality with fast neutrons. The initial results emphasizes that a moderate yield D-T neutron generator based fast neutron radiography system with EMCCD camera could be deployed for field applications yielding moderate image quality to obtain first hand information of the investigated samples.

Fast High-Energy X-Ray Imaging for Severe Accidents Experiments on the Future PLINIUS-2 Platform

The future PLINIUS-2 platform of the Commissariat a l’Energie Atomique (CEA) of Cadarache will be dedicated to the study of corium interactions in severe nuclear accidents, and will host innovative large-scale experiments. The nuclear measurement laboratory of CEA Cadarache is in charge of real-time high-energy X-ray imaging setups, for the study of the corium–water and corium–sodium interaction, and of the corium stratification process. Imaging such large and high-density objects requires a 15 MeV linear electron accelerator coupled to a tungsten target creating a high-energy bremsstrahlung X-ray flux, with corresponding dose rate about 100 Gy/min at 1 m. The signal is detected by phosphor screens coupled to high-framerate scientific CMOS cameras. The imaging setup is established using an experimentally validated home-made simulation software High-Energy MODeling for RAdiography and TOmography (MODHERATO). The code computes quantitative radiographic signals from the description of the source, object geometry and composition, detector, and geometrical configuration (magnification factor, etc.). It accounts for several noise sources (photonic and electronic noises, and swank and readout noise), and for image blur due to the source spot-size and to the detector unsharpness. In a view to PLINIUS-2, the simulation has been improved to account for the scattered flux, which is expected to be significant. This paper presents the scattered flux calculation using the Monte-Carlo N-particle transport code, and its integration into the MODHERATO simulation. Then, the validation of the improved simulation is presented, through confrontation to real measurement images taken on a small-scale equivalent setup on the PLINIUS platform. Excellent agreement is achieved. This improved simulation is therefore being used to design the PLINIUS-2 imaging setups (source, detectors, and cameras). Simulation will be presented for different configurations, as well as preliminary tests of alternative detectors considered for PLINIUS-2.

High conversion efficiency and small spot size of Kα X-ray generated from nano-foam Cu targets irradiated by femtosecond laser pulses

Developing high-quality X-ray source to diagnose shock wave and changing the material and structure features of the target were presented to enhance its absorbability to ultra-intense laser energy. Experiments were carried out on the XingGuang-III Ti: sapphire laser facility (2.1– 6 J, 30 fs) at Laser Fusion Research Center, China Academy of Engineering Physics. The minimum intensity was 1.6 × 1018 W/cm2 on a nano-foam Cu target with the thickness of 100 µm, the porosity of 70% and the density ratio of 30% solids of Cu. The emission of Kα X-rays from the target was measured using a single-photon counting CCD device. This nano-foam target had generated a Kα peak photon rate of 2.9 × 108 photons sr−1 s−1 and the maximum conversion efficiency (CE) value was 0.0084%. The average CE of the nano-foam Cu was 1.8 times greater than that of foil Cu target. The minimum spot size of the X-ray source was measured to be about 40 µm at full width at half maximum, smaller than 47–86 µm of the foil Cu target using 0.1-mm thick knife-edge method. The nano-foam structure showed the potential of enhancing the CE of the femtosecond laser for X-ray conversion.

X-ray source with quasi-monochromatic parallel beam

In inertial confined fusion experiments, an excellent-performance and high-efficiency X-ray source plays an important role in X-ray radiography schemes. Indeed, it can be used in a variety of X-ray experimental techniques. The mono-chromaticity, flux intensity, degree of collimation (the radiation can be transported long distances without loss), and spot size of the X-ray source affect the quality of imaging. Ray-tracing simulations, which are validated by experimental results, demonstrate that high-intensity collimated X-ray beams can be produced from an isotropic X-ray source. Therefore, a method of improving the performance of an X-ray source from a laser-produced plasma is presented. A spherically bent crystal is used to collimate mono-chromatic X-rays emitted from a laser-produced plasma. Here we design a spherically bent crystal spectrometer system for collimating the laser-produced X-rays. The system performance is experimentally tested at the Shenguang Ⅱ (SGⅡ) laser facility located in Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences. The beam divergence is measured by using a metal grid placed downstream from the crystal, the metal grid that possesses wires with 60 μm in diameter and 127 μm in period. An imaging plate (IP) is placed at various distances downstream from grid. The quality of the generated beam is monitored by measuring the dimensions of the grid image formed by the beam on IP. While the narrow range of wavelength is measured with a spherically bent crystal spectrometer. Experimental results show that the spherically bent crystal spectrometer system can produce quasi-monochromatic (10<sup>-3</sup> < △ <i>λ/λ</i> <10<sup>-2</sup>) X-ray beams with a high degree of collimation (less than 2 mrad divergence), uniform spot size (~500 μm), and a relative tenability in the wide spectral range. The influences of various experimental parameters on the quality of beam collimation are evaluated in two ways. They can be investigated in test experiments by representing the beam divergence distribution as a function of Bragg angle. In another study of the effect of the aberrations, when the incident beam on the spherically bent crystal is not normal, the beam is less collimated in the tangential plane, and out of collimation in the sagittal plane. Following the ray-tracing method, we analyze the diffracted beam divergence produced by the astigmatic aberration. The qualitative conclusion is that the good agreement with the experimental results is obtained. By fully utilizing limited Bragg angle range, the spherically bent crystal spectrometer system can realize collimated diffracted X-ray beams with divergence of less than 1 mrad by using a laser-produced plasma X-ray source under the appropriately experimental parameters.

Fast high-energy X-ray imaging for Severe Accidents experiments on the future PLINIUS-2 platform

The future PLINIUS-2 platform of CEA Cadarache will be dedicated to the study of corium interactions in severe nuclear accidents, and will host innovative large-scale experiments. The Nuclear Measurement Laboratory of CEA Cadarache is in charge of real-time high-energy X-ray imaging set-ups, for the study of the corium-water and corium-sodium interaction, and of the corium stratification process. Imaging such large and high-density objects requires a 15 MeV linear electron accelerator coupled to a tungsten target creating a high-energy Bremsstrahlung X-ray flux, with corresponding dose rate about 100 Gy/min at 1 m. The signal is detected by phosphor screens coupled to high-framerate scientific CMOS cameras. The imaging set-up is established using an experimentally-validated home-made simulation software (MODHERATO). The code computes quantitative radiographic signals from the description of the source, object geometry and composition, detector, and geometrical configuration (magnification factor, etc.). It accounts for several noise sources (photonic and electronic noises, swank and readout noise), and for image blur due to the source spot-size and to the detector unsharpness. In a view to PLINIUS-2, the simulation has been improved to account for the scattered flux, which is expected to be significant. The paper presents the scattered flux calculation using the MCNP transport code, and its integration into the MODHERATO simulation. Then the validation of the improved simulation is presented, through confrontation to real measurement images taken on a small-scale equivalent set-up on the PLINIUS platform. Excellent agreement is achieved. This improved simulation is therefore being used to design the PLINIUS-2 imaging set-ups (source, detectors, cameras, etc.).

Image system analysis of human eye wave-front aberration on the basis of HSS

Hartmann–Shack sensor (HSS) has been used in objective measurement of human eye wave-front aberration, but the research on the effects of sampling point size on the accuracy of the result has not been reported. In this paper, point spread function (PSF) of the whole system mathematical model was obtained via measuring the optical imaging system structure of human eye wave-front aberration measurement. The impact of Airy spot size on the accuracy of system was analyzed. Statistics study show that the geometry of Airy spot size of the ideal light source sent from eye retina formed on the surface of HSS is far smaller than the size of the HSS sample point image used in the experiment. Therefore, the effect of Airy spot on the precision of the system can be ignored. This study theoretically and experimentally justifies the reliability and accuracy of human eye wave-front aberration measurement based on HSS.

Feasibility Study for Improving the Image Characteristics in Digital Tomosynthesis (DTS) Using a Compressed-Sensing (Cs)-Based Pre-Deblurring Scheme

ABSTRACTDigital tomosynthesis (DTS) has been widely used in both industrial nondestructive testing and medical x-ray imaging as a popular multiplanar imaging modality. However, although it provides some of the tomographic benefits of computed tomography (CT) at reduced dose and imaging time, the image characteristics are relatively poor due to blur artifacts originated from incomplete data sampling for a limited angular range and also aspects inherent to imaging system, including finite focal spot size of the x-ray source, detector resolution, etc. In this work, in order to overcome these difficulties, we propose an intuitive method in which a compressed-sensing (CS)-based deblurring scheme is applied to the projection images before common DTS reconstruction. We implemented the proposed deblurring algorithm and performed a systematic experiment to demonstrate its viability for improving the image characteristics in DTS. According to our results, the proposed method appears to be effective for the blurring problems in DTS and seems to be promising to our ongoing application to x-ray nondestructive testing.

Improvement of image characteristics in high-voltage computed tomography (CT) by applying a compressed-sensing (CS)-based image deblurring scheme

We have established a high-voltage computed tomography (CT) system with a 1–3MV LINAC x-ray generator for industrial nondestructive testing. However, reconstructed CT images are typically blurred, limiting its image performance, mainly due to the finite focal spot size of the x-ray source, aspects inherent to detector such as the detector pixel size and the detector resolution, and the reconstruction procedure as well. Thus the recovery of the reconstructed CT images from their degraded version is essential for improving the image characteristics. In this work, we investigated the compressed-sensing (CS)-based deconvolution scheme for more accurate image deblurring in CT. We implemented the proposed image deblurring algorithm for CT and performed a systematic simulation and experiment to demonstrate its viability. Our results indicate that the proposed deblurring scheme appears to be effective for the blurring problems in CT and is applicable to improve its present image characteristics.

Spot size measurement of a flash-radiography source using the pinhole imaging method

The spot size of the X-ray source is a key parameter of a flash-radiography facility, and is usually quoted as an evaluation of the resolving power. The pinhole imaging technique is applied to measure the spot size of the Dragon-I linear induction accelerator, by which a two-dimensional spatial distribution of the source spot is obtained. Experimental measurements are performed to measure the spot image when the transportation and focusing of the electron beam are tuned by adjusting the currents of solenoids in the downstream section. The spot size of full-width at half maximum and that defined from the spatial frequency at half peak value of the modulation transfer function are calculated and discussed.

Compact and cost effective lab-based edge-illumination x-ray phase contrast imaging with a structured focal spot

We present a different implementation of the Edge Illumination (EI) X-ray Phase Contrast imaging method based on the use of multiple focal spots created through an additional x-ray mask. While this resembles directly inspired by the Talbot-Lau implementation of grating interferometry, the aim of the source mask and its effect on the acquired images are different. The individual “sourcelets” are much larger than in grating methods, and then still spatially incoherent; however, their use allows (a) exploiting cheap and large focal spot sources and (b) reducing the source spot size from the usual 70–100 μm typically used in EI to few tens of μm, which enables the realisation of more compact setups. However, in EI, multiple sources create images shifted by one detector pixel with respect to the other, imposing the use of an image restoration algorithm. Here, we show that the approach is feasible by deconvolving differential phase-contrast image profiles acquired with three separate sources, and comparing results with simulation predictions for equivalent profiles generated by a single source. We also show that this enables reducing the system length from the 2 m used so far to 1 m.