ELETTRA Synchrotron Radiation Facility Research Articles

Edge-illumination spectral phase-contrast tomography

Following the rapid, but independent, diffusion of x-ray spectral and phase-contrast systems, this work demonstrates the first combination of spectral and phase-contrast computed tomography (CT) obtained by using the edge-illumination technique and a CdTe small-pixel (62 μm) spectral detector. A theoretical model is introduced, starting from a standard attenuation-based spectral decomposition and leading to spectral phase-contrast material decomposition. Each step of the model is followed by quantification of accuracy and sensitivity on experimental data of a test phantom containing different solutions with known concentrations. An example of a micro CT application (20 μm voxel size) on an iodine-perfused ex vivo murine model is reported. The work demonstrates that spectral-phase contrast combines the advantages of spectral imaging, i.e. high-Z material discrimination capability, and phase-contrast imaging, i.e. soft tissue sensitivity, yielding simultaneously mass density maps of water, calcium, and iodine with an accuracy of 1.1%, 3.5%, and 1.9% (root mean square errors), respectively. Results also show a 9-fold increase in the signal-to-noise ratio of the water channel when compared to standard spectral decomposition. The application to the murine model revealed the potential of the technique in the simultaneous 3D visualization of soft tissue, bone, and vasculature. While being implemented by using a broad spectrum (pink beam) at a synchrotron radiation facility (Elettra, Trieste, Italy), the proposed experimental setup can be readily translated to compact laboratory systems including conventional x-ray tubes.

Bending Magnet Photon Absorber Design and Calculations for the Elettra 2.0 Storage Ring

To harness the major advances that have been done in the field of synchrotron light research, Elettra synchrotron radiation facility is being updated. Presently in its design phase, the Elettra 2.0 project will allow new and better research to be performed at the facility. In the upgrade of the storage ring, the new 6BA lattice brings challenges in terms of available space and radiated power. This paper presents the bending magnet photon absorber designed to cope with the new requirements. The absorber concept created for ESRF-EBS has been revised and re-engineered to make it suitable for the specific features of Elettra’s sources. To reduce the high-power densities induced by the short source-absorber distance, the one-jawed, toothed profile was obtained via a robust optimization, considering possible misalignments or beam miss-steering. Novelty of the approach is the absorber insertion in the vacuum chamber from the inside of the ring. Finally, presented are the thermo-mechanical and computational fluid dynamics simulations (ANSYS) performed to validate the design, comprehensive of a Monte-Carlo, ray-traced simulation to evaluate photon reflections (SYNRAD) and their effects.

Versatile procedure for the correction of non-isochromatism in XPEEM spectroscopic imaging

Non-isochromatism in X-ray PhotoEmission Electron Microscopy (XPEEM) may result in unwanted artifacts especially when working with large field of views. The lack of isochromatism of XPEEM images may result from multiple factors, for instance the energy dispersion of the X-rays on the sample or the effect of one or more dispersive elements in the electron optics of the microscope, or the combination of both. In practice, the photon energy or the electron kinetic energy may vary across the image, complicating image interpretation and analysis. The effect becomes severe when imaging at low magnification upon irradiation with high energy photons. Such imaging demands for a large X-ray illuminating spot size usually achieved by opening the exit slit of the X-ray monochromator while reducing the monochromaticity of the irradiating light. However, we show that the effect is linear and can be fully removed. A versatile correction procedure is presented which leads to true monochromatic photoelectron images at improved signal-to-noise ratio. XPEEM data recorded at the nanospectroscopy beamline of the Elettra synchrotron radiation facility illustrate the working principle of the procedure. Also, reciprocal space XPEEM data such as angle-resolved photoelectron spectroscopy (ARPES) momentum plots suffer from linear energy dispersion artifacts which can be corrected in a similar way. Representative data acquired from graphene synthesized on copper by chemical vapor deposition prove the benefits of the correction procedure.

Dual pulsed laser deposition system for the growth of complex materials and heterostructures.

Here, we present an integrated ultra-high-vacuum (UHV) apparatus for the growth of complex materials and heterostructures. The specific growth technique is the Pulsed Laser Deposition (PLD) by means of a dual-laser source based on an excimer KrF ultraviolet and solid-state Nd:YAG infra-red lasers. By taking advantage of the two laser sources-both lasers can be independently used within the deposition chambers-a large number of different materials-ranging from oxides to metals, to selenides, and others-can be successfully grown in the form of thin films and heterostructures. All of the samples can be in situ transferred between the deposition chambers and the analysis chambers by using vessels and holders' manipulators. The apparatus also offers the possibility to transfer samples to remote instrumentation under UHV conditions by means of commercially available UHV-suitcases. The dual-PLD operates for in-house research as well as user facility in combination with the Advanced Photo-electric Effect beamline at the Elettra synchrotron radiation facility in Trieste and allows synchrotron-based photo-emission as well as x-ray absorption experiments on pristine films and heterostructures.

Attenuation coefficient in the energy range 14–36 keV of 3D printing materials for physical breast phantoms

Objective. To measure the monoenergetic x-ray linear attenuation coefficient, μ, of fused deposition modeling (FDM) colored 3D printing materials (ABS, PLAwhite, PLAorange, PET and NYLON), used as adipose, glandular or skin tissue substitutes for manufacturing physical breast phantoms. Approach. Attenuation data (at 14, 18, 20, 24, 28, 30 and 36 keV) were acquired at Elettra synchrotron radiation facility, with step-wedge objects, using the Lambert–Beer law and a CCD imaging detector. Test objects were 3D printed using the Ultimaker 3 FDM printer. PMMA, Nylon-6 and high-density polyethylene step objects were also investigated for the validation of the proposed methodology. Printing uniformity was assessed via monoenergetic and polyenergetic imaging (32 kV, W/Rh). Main results. Maximum absolute deviation of μ for PMMA, Nylon-6 and HD-PE was 5.0%, with reference to literature data. For ABS and NYLON, μ differed by less than 6.1% and 7.1% from that of adipose tissue, respectively; for PET and PLAorange the difference was less than 11.3% and 6.3% from glandular tissue, respectively. PLAorange is a good substitute of skin (differences from −9.4% to +1.2%). Hence, ABS and NYLON filaments are suitable adipose tissue substitutes, while PET and PLAorange mimick the glandular tissue. PLAwhite could be printed at less than 100% infill density for matching the attenuation of glandular tissue, using the measured density calibration curve. The printing mesh was observed for sample thicknesses less than 60 mm, imaged in the direction normal to the printing layers. Printing dimensional repeatability and reproducibility was less 1%. Significance. For the first time an experimental determination was provided of the linear attenuation coefficient of common 3D printing filament materials with estimates of μ at all energies in the range 14–36 keV, for their use in mammography, breast tomosynthesis and breast computed tomography investigations.

Motion artifacts assessment and correction using optical tracking in synchrotron radiation breast CT.

PurposeThe SYRMA‐3D collaboration is setting up a breast computed tomography (bCT) clinical program at the Elettra synchrotron radiation facility in Trieste, Italy. Unlike the few dedicated scanners available at hospitals, synchrotron radiation bCT requires the patient's rotation, which in turn implies a long scan duration (from tens of seconds to few minutes). At the same time, it allows the achievement of high spatial resolution. These features make synchrotron radiation bCT prone to motion artifacts. This article aims at assessing and compensating for motion artifacts through an optical tracking approach.MethodsIn this study, patients’ movements due to breathing have been first assessed on seven volunteers and then simulated during the CT scans of a breast phantom and a surgical specimen, by adding a periodic oscillatory motion (constant speed, 1 mm amplitude, 12 cycles/minute). CT scans were carried out at 28 keV with a mean glandular dose of 5 mGy. Motion artifacts were evaluated and a correction algorithm based on the optical tracking of fiducial marks was introduced. A quantitative analysis based on the structural similarity (SSIM) index and the normalized mean square error (nMSE) was performed on the reconstructed CT images.ResultsCT images reconstructed through the optical tracking procedure were found to be as good as the motionless reference image. Moreover, the analysis of SSIM and nMSE demonstrated that an uncorrected motion of the order of the system's point spread function (around 0.1 mm in the present case) can be tolerated.ConclusionsResults suggest that a motion correction procedure based on an optical tracking system would be beneficial in synchrotron radiation bCT.

Effects of angiotensin II receptor blockers in the coronary arteries of hypertensive rats: Analysis of elemental distribution using LEXRF

Hypertension is one of the major public health problems worldwide. It can cause severely alterations in artery structure and function such as vascular remodeling. Angiotensin II (Ang II) has been linked to vascular dysfunction. It has been shown that blockade of the Ang II type 1 receptor with an Ang II receptor blocker (ARBs) may reverse vascular pathology independently of blood pressure lowering. There is therefore a special interest in establishing whether antihypertensive treatment may correct in part or completely the structural and functional alterations of arteries. Several studies have shown regression of structural remodeling or of functional alterations of small arteries in spontaneously hypertensive rats (SHR) treated with ARBs agents. However, its efficiency was not verified at elemental level in the literature. Knowledge of the elemental distribution in tissues has a great importance in the study of diseases, because chemical imbalance can alter biological functions. Elemental semiquantitative microanalysis in the coronary artery of normotensive, SHRs, and SHRs rats treated with ARBs (losartan and olmesartan) was performed using low energy X‐ray fluorescence maps acquired on TwinMic X‐ray spectromicroscopy station, located at the Elettra synchrotron radiation facility. Morphological changes in coronary samples were also investigated. The results demonstrate that despite the antihypertensive agents used belong to the same class, their capacities to revert chemical and structural changes in the coronary arteries caused by hypertension are different.

Large-area single-photon-counting CdTe detector for synchrotron radiation computed tomography: adedicated pre-processing procedure.

Large-area CdTe single-photon-counting detectors are becoming more and more attractive in view of low-dose imaging applications due to their high efficiency, low intrinsic noise and absence of a scintillating screen which affects spatial resolution. At present, however, since the dimensions of a single sensor are small (typically a few cm2), multi-module architectures are needed to obtain a large field of view. This requires coping with inter-module gaps and with close-to-edge pixels, which generally show a non-optimal behavior. Moreover, high-Z detectors often show gain variations in time due to charge trapping: this effect is detrimental especially in computed tomography (CT) applications where a single tomographic image requires hundreds of projections continuously acquired in several seconds. This work has been carried out at the SYRMEP beamline of the Elettra synchrotron radiation facility (Trieste, Italy), in the framework of the SYRMA-3D project, which aims to perform the world's first breast-CT clinical study with synchrotron radiation. An ad hoc data pre-processing procedure has been developed for the PIXIRAD-8 CdTe single-photon-counting detector, comprising an array of eight 30.7 mm × 24.8 mm modules tiling a 246 mm × 25 mm sensitive area, which covers the full synchrotron radiation beam. The procedure consists of five building blocks, namely dynamic flat-fielding, gap seaming, dynamic ring removal, projection despeckling and around-gap equalization. Each block is discussed and compared, when existing, with conventional approaches. The effectiveness of the pre-processing is demonstrated for phase-contrast CT images of a human breast specimen. The dynamic nature of the proposed procedure, which provides corrections dependent upon the projection index, allows the effective removal of time-dependent artifacts, preserving the main image features including phase effects.

The Indo–Italian cooperation at the Elettra synchrotron radiation facility

The Indo–Italian cooperation at the Elettra synchrotron radiation facility

A Framework for Iterative Reconstruction in Phase-Contrast Computed Tomography Dedicated to the Breast

We present the implementation of a computed tomography (CT) iterative reconstruction strategy developed within the SYRMA-CT project for in vivo phase-contrast CT of uncompressed breast, ongoing at the ELETTRA synchrotron radiation facility (Trieste, Italy). Propagation-based phase-contrast imaging exploits the high spatial coherence of the monoenergetic laminar X-ray beam, as well as the large object-to-detector distance and the use of a Pixirad-8 high-resolution photon-counting CdTe detector. The signal in projection views depends on the X-ray absorption as well as on the phase shift introduced by the breast tissue in the beam path. A phase retrieval algorithm allowed recovering the projected 2-D phase information of the irradiated tissue layer, which was input to the CT reconstruction; then, the breast slices were reconstructed via a simultaneous algebraic reconstruction technique algorithm. Our iterative reconstruction—coupled with a filtering process for reducing the noise level and ring artifacts while preserving edges sharpness—showed better image quality than conventional filtered back projection (FBP) reconstruction. This phantom study showed that our iterative reconstruction produced images with higher contrast-to-noise ratio and spatial resolution than those obtained with FBP. Finally, the developed algorithm removed ring-like artifacts, without worsening the image quality.

Design and fabrication of a preamplifier to be used with a MWPC at the ILSF

The Iranian Light Source Facility (ILSF) is a new 3 GeV third generation synchrotron radiation facility in Middle East, which at the time being is in its design stage. For day one operation of the ILSF a custom made two-dimensional multiwire position sensitive detector with delay line readout will be used in small/wide angle scattering and diffraction experiments with synchrotron radiation. For many years such X-ray detectors have played an important role in these synchrotron radiation experiments and owing to their robustness they are still in use in many places. Paired with state of the art read-out electronics they are serious low cost competitors to other solutions based on solid-state hybrid pixel detectors. To achieve minimum dead time and high global count rates these detectors will require preamplifiers with certain characteristics, which involve low noise, good signal/noise ratio (better than 20 dB), high gain, short rise time (lower than 10 ns) and pulse duration shorter than 120 ns. In this paper, we present the design and first results of the evaluation of a voltage preamplifier developed at ILSF within a collaboration agreement between ILSF, Iran and the Italian Synchrotron Radiation Facility (Elettra), Italy. The application of this preamplifier in an in-house multiwire detector is discussed and results are presented.

Imaging performance of phase-contrast breast computed tomography with synchrotron radiation and a CdTe photon-counting detector

PurposeWithin the SYRMA-CT collaboration based at the ELETTRA synchrotron radiation (SR) facility the authors investigated the imaging performance of the phase-contrast computed tomography (CT) system dedicated to monochromatic in vivo 3D imaging of the female breast, for breast cancer diagnosis. MethodsTest objects were imaged at 38keV using monochromatic SR and a high-resolution CdTe photon-counting detector. Signal and noise performance were evaluated using modulation transfer function (MTF) and noise power spectrum. The analysis was performed on the images obtained with the application of a phase retrieval algorithm as well as on those obtained without phase retrieval. The contrast to noise ratio (CNR) and the capability of detecting test microcalcification clusters and soft masses were investigated. ResultsFor a voxel size of (60μm)3, images without phase retrieval showed higher spatial resolution (6.7mm−1 at 10% MTF) than corresponding images with phase retrieval (2.5mm−1). Phase retrieval produced a reduction of the noise level and an increase of the CNR by more than one order of magnitude, compared to raw phase-contrast images. Microcalcifications with a diameter down to 130μm could be detected in both types of images. ConclusionsThe investigation on test objects indicates that breast CT with a monochromatic SR source is technically feasible in terms of spatial resolution, image noise and contrast, for in vivo 3D imaging with a dose comparable to that of two-view mammography. Images obtained with the phase retrieval algorithm showed the best performance in the trade-off between spatial resolution and image noise.

Energy dependent calibration of XR-QA2 radiochromic film with monochromatic and polychromatic x-ray beams.

This work investigates the energy response and dose-response curve determinations for XR-QA2 radiochromic film dosimetry system used for synchrotron radiation work and for quality assurance in diagnostic radiology, in the range of effective energies 18-46.5 keV. Pieces of XR-QA2 films were irradiated, in a plane transverse to the beam axis, with a monochromatic beam of energy in the range 18-40 keV at the ELETTRA synchrotron radiation facility (Trieste, Italy) and with a polychromatic beam from a laboratory x-ray tube operated at 80, 100, and 120 kV. The film calibration curve was expressed as air kerma (measured free-in-air with an ionization chamber) versus the net optical reflectance change (netΔR) derived from the red channel of the RGB scanned film image. Four functional relationships (rational, linear exponential, power, and logarithm) were tested to evaluate the best curve for fitting the calibration data. The adequacy of the various fitting functions was tested by using the uncertainty analysis and by assessing the average of the absolute air kerma error calculated as the difference between calculated and delivered air kerma. The sensitivity of the film was evaluated as the ratio of the change in net reflectance to the corresponding air kerma. The sensitivity of XR-QA2 films increased in the energy range 18-39 keV, with a maximum variation of about 170%, and decreased in the energy range 38-46.5 keV. The present results confirmed and extended previous findings by this and other groups, as regards the dose response of the radiochromic film XR-QA2 to monochromatic and polychromatic x-ray beams, respectively. The XR-QA2 radiochromic film response showed a strong dependence on beam energy for both monochromatic and polychromatic beams in the range of half value layer values from 0.55 to 6.1 mm Al and corresponding effective energies from 18 to 46.5 keV. In this range, the film response varied by 170%, from a minimum sensitivity of 0.0127 to a maximum sensitivity of 0.0219 at 10 mGy air kerma in air. The more suitable function for air kerma calibration of the XR-QA2 radiochromic film was the power function. A significant batch-to-batch variation, up to 55%, in film response at 120 kV (46.5 keV effective energy) was observed in comparison with published data.

Enhanced and Flexible Software Tools for X-ray Computed Tomography at the Italian Synchrotron Radiation Facility Elettra

X-ray computed tomography (CT) experiments performed at synchrotron radiation fa- cilities require adequate computing and storage resources due to the large amount of acquired and reconstructed data produced. To satisfy the heterogeneous needs of beamline users, flexible solu- tions are also required. Moreover, the growing demand of quantitative image analysis impose an easy integration between the CT reconstruction process and the subsequent feature extraction step. This paper presents some of the software solutions adopted by the SYRMEP beamline of the Italian synchrotron radiation facility Elettra. By using the enhanced version of the reconstruction software here presented as well as data reduction and data analysis tools, beamline users can easily imple- ment an integrated and comprehensive approach to the digital image processing and image analysis required by a tomography-oriented scientific workflow.

Objective measurements of image quality in synchrotron radiation phase-contrast imaging versus digital mammography.

Phase-contrast mammography with synchrotron radiation is an innovative X-ray imaging practice that improves the identification of breast lesions. Previous studies have proven the superiority of the mammography images taken in the phase-contrast modality using synchrotron radiation beams as compared with images taken in conventional mammography by subjective analyses. However, to our knowledge, no previous study has compared different acquisition systems in order to quantify this improvement by means of objective robust indicators. In this research, we intend to quantify the superiority of phase-contrast imaging by means of objective metrics of image quality. Images from the American College of Radiology Mammographic Accreditation Phantom were obtained at hospitals, in two digital mammography equipment and at the Elettra synchrotron radiation facility (Trieste, Italy), using free space propagation phase-contrast modality. Regions of interest were selected to analyze image quality at the fibers (phase object) and masses (area object) simulated on the phantom by means of the signal-to-noise ratio, the figure of merit, the contrast and the edge visibility. The image contrast and edge visibility were significantly higher at the phase-contrast modality as compared with digital mammography equipment. The figure of merit using phase-contrast modality was higher for the fibers and comparable for the masses. The results showed an improvement of the contrast and edge visibility in phase-contrast images. These improvements may be important in the detection of small lesions and details.

Use of XR-QA2 radiochromic films for quantitative imaging of a synchrotron radiation beam

In the framework of an ongoing project, promoted by INFN, at the SYRMEP beamline of the ELETTRA synchrotron radiation facility (Trieste, Italy) for phase-contrast breast X-ray computed tomography, the assessment of the dose to the breast is one of the issues, requiring the determination of the distribution of X-ray incident photon fluence. This work investigates the use of XR-QA2 radiochromic films for quantitative imaging of the synchrotron radiation (SR) beam. XR-QA2 films were irradiated in a plane transverse to the beam axis, with a monochromatic beam of energy of 28, 35, 38 or 40 keV. The response of the radiochromic film was calibrated in terms of average air kerma measured with an ionization chamber. The net reflectance of the exposed film was then converted to photon fluence per unit air kerma (mm−2mGy−1). The SR beam profile was acquired also with a scintillator (GOS) based, fiber optic coupled CCD camera as well as with a scintillator based flat panel detector. Horizontal and vertical line profiles acquired with the radiochromic films show the 2D distribution of the beam intensity, with variations in the order of 15–20% in the horizontal direction. The response of the radiochromic film is comparable to that of the other imaging detectors, within less than 5% variation.

Energy response of GR-200A thermoluminescence dosemeters to 60Co and to monoenergetic synchrotron radiation in the energy range 28-40 keV.

The response of LiF:Mg,Cu,P thermoluminescence dosemeters (type GR-200A) to monoenergetic radiation of energy 28, 35, 38 and 40 keV was evaluated with respect to irradiation with a calibrated (60)Co gamma-ray source. High-precision measurements of the relative air kerma response performed at the SYRMEP beamline of the ELETTRA synchrotron radiation facility (Trieste, Italy) showed a significant deviation of the average response to low-energy X-rays from that to (60)Co, with an over-response from 6 % (at 28 keV) to 22 % (at 40 keV). These data are not consistent with literature data for these dosemeters, where model predictions gave deviation from unity of the relative air kerma response of about 10 %. The authors conclude for the need of additional determinations of the low-energy relative response of GR-200A dosemeters, covering a wider range of monoenergetic energies sampled at a fine energy step, as planned in future experiments by their group at the ELETTRA facility.

A simplified edge illumination set-up for quantitative phase contrast mammography with synchrotron radiation at clinical doses

This work presents the first study of x-ray phase contrast imaging based on a simple implementation of the edge illumination method (EIXPCi) in the field of mammography with synchrotron radiation. A simplified EIXPCi set-up was utilized to study a possible application in mammography at clinical doses. Moreover, through a novel algorithm capable of separating and quantifying absorption and phase perturbations of images acquired in EIXPCi modality, it is possible to extract quantitative information on breast images, allowing an accurate tissue identification. The study was carried out at the SYRMEP beamline of Elettra synchrotron radiation facility (Trieste, Italy), where a mastectomy specimen was investigated with the EIXPCi technique. The sample was exposed at three different energies suitable for mammography with synchrotron radiation in order to test the validity of the novel algorithm in extracting values of linear attenuation coefficients integrated over the sample thickness. It is demonstrated that the quantitative data are in good agreement with the theoretical values of linear attenuation coefficients calculated on the hypothesis of the breast with a given composition. The results are promising and encourage the current efforts to apply the method in mammography with synchrotron radiation.

High temperature structural study of Gd-doped ceria by synchrotron X-ray diffraction (673 K ≤ T ≤ 1073 K).

The crystallographic features of Gd-doped ceria were investigated at the operating temperature of solid oxides fuel cells, where these materials are used as solid electrolytes. (Ce(1-x)Gd(x))O(2-x/2) samples (x = 0.1, 0.3, 0.5, 0.7) were prepared by coprecipitation of mixed oxalates, treated at 1473 K in air, and analyzed by synchrotron X-ray diffraction in the temperature range 673 K ≤ T ≤ 1073 K at the Elettra synchrotron radiation facility located in Trieste, Italy. In the whole temperature span a boundary was found at x ∼ 0.2 between a CeO2-based solid solution (for x ≤ 0.2) and a structure where Gd2O3 microdomains grow within the CeO2 matrix, taking advantage of the similarity between Gd(3+) and Ce(4+) sizes; the existence of the boundary at x ∼ 0.2 was confirmed also by measurements of ionic conductivity performed by impedance spectroscopy. Similar to what observed at room temperature, the trend of the cell parameter shows the presence of a maximum; with increasing temperature, the composition corresponding to the maximum moves toward lower Gd content. This evidence can be explained by analyzing the behavior of the coefficient of thermal expansion as a function of composition.

Elemental Clustering and Structure of Liquid LBE

Liquid Pb–Bi eutectic (LBE) alloy is of great interest as coolant and neutron spallation source for the accelerator driven systems (ADS). Scanning Photoemission Microscopy (SPEM) at the ELETTRA synchrotron radiation facility of Trieste was carried out on samples quenched from melt at different temperatures. SPEM analyses show that the two components (Pb and Bi) are not homogeneously distributed in the range of temperature from melting up to 518 °C, in particular they form clusters enriched in Pb and Bi. The cluster size decreases as temperature increases hence diffusion occurs between clusters and matrix leading to the progressive disgregation of clusters that is almost completed at 518 °C. Such micro-chemical evolution is accompanied by a structural change of the liquid evidenced by the results of High-temperature X-ray Diffraction (HT-XRD). In particular, radial distribution function (RDF) curves show a progressive change of the ratio between the shell radii of 1st and 2nd nearest neighbours.