arXiv subjects

Alessandro Olivo

Publications and source records attributed to Alessandro Olivo.

17 recordsLinked to original sources

arXiv2026

Matching Trace Element Distribution to Mineralogical Phases in Ancient Biotechnology-Derived Metallic Salts: a Multimodal Analysis

Conventional X-ray fluorescence (XRF) and X-ray diffraction (XRD) analysis applied to the investigation of ancient metal salts used as pigments and/or therapeutics provide bulk average compositions in two stand-alone data sets; however, major elements aside, these two sets cannot inform on the spatial distribution of one with respect to the other. To address this issue, we present here a multimodal approach incorporating spatially resolved XRF, XRD and nanoscale X-ray imaging applied to the analysis of archaeological and experimental samples of synthetic lead carbonate (PbCO3 - Greek psimythion); psimythion was used in antiquity as a cosmetic and/or a therapeutic for external applications. The experimental sample was produced according to a well-documented recipe dated to the 4th century BCE. In this paper we demonstrate that by using a multimodal approach we can confidently assign trace elements to individual crystalline or to infer the existence of non-crystalline phases. Although the assignment of an element to a phase (i.e. the location) is now possible, the origin underlying it (i.e. the mechanism) is not always clear. Trace elements do not 'control' chemical/mineralogical composition, but they can influence it. Our approach is particularly suited to following changes in the artefact's chemical/mineralogical profile, from its manufacture, to use and burial, to excavation and conservation.

physics.app-ph↗

arXiv2026

Universal Phase Contrast in Micro-CT Systems

Conventional high-resolution micro-CT systems are regarded as attenuation-based unless visible Fresnel fringes reveal the presence of propagation-based phase contrast. Here we show that this interpretation is incomplete. When propagation-induced phase transfer is non-negligible relative to the system blur, micro-CT operates in a phase-transfer regime in which propagation improves spatial resolution relative to that expected from source and detector blur alone, irrespective of whether Fresnel fringes remain visible. Because micro-CT systems possess finite source and detector blur, this phase transfer is accompanied by a degree of hardware-induced phase retrieval (HIPR), ranging from under-HIPR to matched-HIPR and over-HIPR. We further identify detector-induced phase retrieval (DIPR) as the optimal case in which the detector provides all of the filtering required for phase retrieval, thereby preserving the phase-induced resolution enhancement while introducing spatial correlations between detected photons that reduce high-spatial-frequency noise. We derive analytical conditions for HIPR and DIPR, introduce frequency-domain metrics quantifying preserved phase transfer and detector compatibility, and validate the framework numerically with simulations and experimentally using custom and commercial micro-CT systems. Our results demonstrate that phase-induced resolution enhancement can occur in conventional micro-CT systems even in the absence of visible Fresnel fringes, changing how image formation, spatial resolution, and optimization should be interpreted.

physics.optics↗

arXiv2026

Material identification using laboratory X-ray beam tracking: quantitativeness and signal-to-noise ratio requirements

Simultaneous structural and elemental characterisation of a specimen in a non-destructive manner is an instrumental approach with applications in a variety of fields including energy materials, cultural heritage and life sciences. This is routinely performed at synchrotron facilities, e.g. by combining X-ray imaging and X-ray fluorescence. In this work we describe an approach based on a monochromatic implementation of X-ray beam tracking (XBT), a multimodal imaging technique compatible with standard laboratory sources. Monochromatic XBT gives simultaneous access to quantitative absorption and phase properties of the sample, which are related to the atomic number and the electron density respectively: their combination allows for material discrimination. Here we focus on investigating the effect of the signal-to noise ratio on the quantitativeness of the results, hence on the elemental identification. We present an XBT experiment performed using a standard X-ray laboratory source to identify the composition of three different test samples made out of Ag, Fe and Cu. These specific materials were selected as relevant to archaeological studies e.g. when specimen buried for centuries are in contact with the surrounding soil containing traces of these metals. We review the results, current limitations and provide guidance for future developments for structural and elemental characterisation in a laboratory setting.

physics.app-ph↗

arXiv2026

Retrieval of multiple fibre orientations using X-ray dark-field signal modelling

Dark-field imaging is widely used to infer fibre orientation from signal modulation as a function of sample orientation. However, current X-ray dark-field retrieval methods are restricted to single orientations and require tomography to resolve overlapping structures. This approach is time-consuming and not suitable for thin materials, which are common in materials science. Here we present a dark-field model capable of retrieving multiple fibre orientations within a single pixel. The model, based on a geometrical description of fibre scattering, was validated through Monte Carlo simulations and experiments using beam-tracking setups with 1D and 2D masks. Results demonstrate reliable orientation retrieval for up to two fibres per pixel, with the 2D mask providing multi-directional sensitivity in a single acquisition and enabling faster and simplified data collection.

physics.med-ph↗

arXiv2025

Quantitative phase nano-imaging with a laboratory source

Investigating the structure of matter at the nanoscale non destructively is a key capability enabled by X-ray imaging. One of the most powerful nano-imaging methods is X-ray ptychography, a coherent diffraction imaging technique that has become the go-to method at synchrotron facilities for applications ranging from brain imaging to battery materials. However, the requirements in terms of X-ray beam quality have limited its use to large synchrotron facilities and, to date, only one attempt has been made to translate the technique to a small-scale laboratory. To unleash the power of this technique to the broad user community of laboratory X-ray sources, there are outstanding questions to answer including whether the quantitativeness of the information is preserved in a laboratory despite the drastic decrease in X-ray flux of several orders of magnitude, with respect to synchrotron instruments. In this study not only we demonstrate that the quantitativeness of X-ray ptychography is preserved in a laboratory setting, but we also apply the method to the imaging of a brain tissue phantom. Finally, we describe the current challenges and limitations, and we set the basis for further development and future directions of quantitative nano-imaging with laboratory X-ray sources.

physics.comp-ph↗

arXiv2025

Microfluidic gratings for X-ray Phase Contrast Imaging

Fabrication of X-ray gratings has surged in the last two decades thanks to their vast employment in X-ray Phase Contrast Imaging, an imaging technique able to boost X-ray sensitivity to detect otherwise invisible details. These high aspect ratio devices are usually fabricated by complex, costly, multi-step processes that limit their size and volume scaling. These steps commonly involve UV or X-ray lithography, semiconductor selective etching and high-Z metal plating, usually Au, which require expensive tools and materials. Here we present a proof-of-concept fabrication via soft lithography and Hg infusion of microfluidic X-ray absorption gratings and their performance in biomedical imaging. Such fabrication technique requires fewer, less expensive, and more scalable processes using alternative and more sustainable materials, while showing comparable visibility with their conventional Au-based, solid equivalent. Our results constitute a promising shift in X-ray optics fabrication that could significantly lower barriers to commercialization and accelerate the practical deployment of X-ray Phase Contrast Imaging.

physics.optics↗

arXiv2025

Laboratory-based x-ray microtomography with directional dark-field sensitivity

We demonstrate dark-field x-ray microtomography in a compact, laboratory-based system capable of resolving attenuation, phase, and anisotropic scattering signals with micrometer-scale resolution across centimetre-scale samples. The method is based on two-directional beam tracking (2DBT), which requires only a single optical element and is compatible with standard x-ray sources and detectors. We validate the system's capabilities through imaging of a custom-built phantom, a fibre-reinforced composite and ex-vivo biological tissues, including a bovine intervertebral disc, a rat heart, and a porcine meniscus. The results show that dark-field tomography provides complementary information to attenuation as well as to phase tomography, by revealing sub-resolution features such as fibre orientation and microstructural heterogeneity at length scales that are well below the voxel size. A key element of our system is its sensitivity to scattering along two orthogonal directions in the image plane, enabling the measurement of scattering anisotropy with a single exposure. As well as simple and robust, our approach is sensitive and precise. These findings demonstrate the potential of 2DBT for non-destructive and three-dimensional structural characterisation of samples and materials in engineering, materials science and biomedical applications.

physics.optics↗

arXiv2025

Electron volt energy resolution with ptychography using a broadband continuum spectrum

Ptychography is a scanning coherent diffraction imaging technique successfully applied in the electron, visible and x-ray regimes. One of the distinct features of ptychography with respect to other coherent diffraction techniques is its capability of dealing with partial spatial and temporal coherence via the reconstruction algorithm. Here we focus on the temporal and clarify theoretically and with simulations the constraints which affect the energy resolution limits of the ptychographic algorithms. Based on this, we design and perform simulations for a broadband ptychography in the hard x-ray regime, which enables an energy resolution down to 1 eV. We benchmark the simulations against experimental ptychographic data from a nickel test sample, by extracting the x-ray absorption near edge spectrum with energy resolution of 5 eV using a continuum spectrum of 20 eV bandwidth. We review the results, discuss the limitations, and provide guidelines for future broadband ptychography experiments, its prospective applications and potential impact on achieving diffraction limited resolutions.

physics.app-ph↗

arXiv2023

A laboratory-based X-ray phase contrast microscopy system for targeting in unstained soft-tissue samples

We propose an imaging system and methodology for mapping soft-tissue samples in three dimensions, with micron-scale and isotropic spatial resolution, with low-concentrations as well as in the absence of heavy metal staining. We used hard X-ray phase-contrast imaging for the X-ray ability to non-destructively probe the internal structure of opaque specimens and for enhanced contrast obtained by exploiting phase effects, even in cases with reduced or absent staining agents. To demonstrate its applicability to soft-tissue specimens, we built a compact system that is easily deployable in a laboratory setting. The imaging system is based on a conventional rotating anode X-ray tube and a state-of-the-art custom-made radiation detector. The system's performance is quantitatively assessed on a calibration standard. Its potential for soft-tissue microscopy is demonstrated on two biological specimens and benchmarked against gold-standard synchrotron data. We believe that the approach proposed here can be valuable as a bridging imaging modality for intravital correlative light electron microscopy and be applied across disciplines where the three-dimensional morphology of pristine-condition soft tissues is a key element of the investigation.

physics.ins-det↗

arXiv2023

High angular sensitivity X-ray phase-contrast microtomography of soft-tissue through a two-directional beam-tracking synchrotron set-up

Two-directional beam-tracking (2DBT) is a method for phase-contrast imaging and tomography that uses an intensity modulator to structure the X-ray beam into an array of independent circular beamlets that are resolved by a high-resolution detector. It features isotropic spatial resolution, provides two-dimensional phase sensitivity, and enables the three-dimensional reconstructions of the refractive index decrement, $δ$, and the attenuation coefficient, $μ$. In this work, we report on the angular sensitivity and the spatial resolution of 2DBT images in a synchrotron-based implementation. In its best configuration, we obtained angular sensitivities of $\sim$20 $n$rad and spatial resolution of at least 6.25 $μ$m in phase-contrast images. We also demonstrate exemplar application to the three-dimensional imaging of soft tissue samples, including a mouse liver and a decellularised porcine dermis.

physics.ins-det↗

arXiv2023

Multi-contrast x-ray identification of inhomogeneous materials and their discrimination through deep learning approaches

Recent innovations in x-ray technology (namely phase-based and energy-resolved imaging) offer unprecedented opportunities for material discrimination, however they are often used in isolation or in limited combinations. Here we show that the optimized combination of contrast channels (attenuation at three x-ray energies, ultra-small angle scattering at two, standard deviation of refraction) significantly enhances material identification abilities compared to dual-energy x-ray imaging alone, and that a combination of off-the-shelf machine learning approaches can effectively discriminate e.g., threat materials in complex datasets. The methodology is validated on a range of materials and image dataset that are both an order of magnitude larger than those used in previous studies. Our results can provide an effective methodology to discriminate, and in some cases identify, different materials in complex imaging scenarios, with prospective applications across the life and physical sciences. While the detection of threat materials is used as a demonstrator here, the methodology could be equally applied to e.g., the distinction between diseased and healthy tissues or degraded vs. pristine materials.

physics.app-ph↗

arXiv2023

Single-shot X-ray Dark-field Tomography

X-ray dark-field imaging creates a representation of the sample where contrast is generated by subresolution features within the volume under inspection. These are detected by a local measurement of the radiation field's angular distribution, and how it is affected by the interaction with matter. X-ray dark-field imaging typically requires taking multiple exposures for separating the contributions to the detected X-ray intensity arising from scattering, refraction and attenuation; a procedure often called phase retrieval. We propose an approach to retrieve an X-ray dark-field image from a single X-ray shot. We demonstrate the method using a laboratory-based, rotating anode X-ray tube system without the need for coherent radiation or a high-resolution detector. This reduces the complexity of data acquisition, enabling faster scanning and increasing dose efficiency. Moreover, our approach reduces the problem dimensionality by one, with substantial implications for data-intensive applications like tomography. The model assumes a homogeneous material, and we show this is a valid hypothesis for soft biological tissues by reconstructing dark-field tomography images from data sets containing a single shot per view. We believe our method to be broadly applicable and relevant for many X-ray dark-field imaging implementations, including fast radiography, directional dark-field and for use with pulsed X-ray sources.

physics.med-ph↗

arXiv2023

Direct x-ray scattering signal measurements in edge-illumination/beam-tracking imaging and their interplay with the variance of the refraction signals

X-ray dark-field or ultra-small angle scatter imaging has become increasingly important since the introduction of phase-based x-ray imaging and is having transformative impact in fields such as in vivo lung imaging and explosives detection. Here we show that dark-field images acquired with the edge-illumination method (either in its traditional double mask or simplified single mask implementation) provide a direct measurement of the scattering function, which is unaffected by system-specific parameters such as the autocorrelation length. We show that this is a consequence both of the specific measurement setup and of the mathematical approach followed to retrieve the dark-field images. We show agreement with theoretical models for datasets acquired both with synchrotron and laboratory x-ray sources. We also introduce a new contrast mechanism, the variance of refraction, which is extracted from the same dataset and provides a direct link with the size of the scattering centres. We show that this can also be described by the same theoretical models. We study the behaviour of both signals vs. key parameters such as x-ray energy and scatterer radius. We find this allows quantitative, direct, multi-scale scattering measurements during imaging, with implications in all fields where dark-field imaging is used.

physics.optics↗

arXiv2022

X-ray phase-contrast micro tomography of soft tissues using a compact laboratory system with two-directional sensitivity

X-ray micro tomography is a non-destructive, three-dimensional inspection technique applied across a vast range of fields and disciplines, ranging from research to industrial, encompassing engineering, biology and medical research. Phase-contrast imaging extends the domain of application of X-ray micro tomography to classes of samples that exhibit weak attenuation, thus appear with poor contrast in standard X-ray imaging. Notable examples are low-atomic-number materials, like carbon-fibre composites, soft matter and biological soft tissues. We report on a compact and cost effective system for X-ray phase-contrast micro tomography. The system features high sensitivity to phase gradients and high resolution, requires a low-power sealed X-ray tube, a single optical element, and fits in a small footprint. It is compatible with standard X-ray detector technologies: single-photon-counting offers higher sensitivity whereas flat-panels are preferred for a larger field of view. The system is benchmarked against known-material phantoms and its potential for soft-tissue three-dimensional imaging is demonstrated on small-animal organs: a piglet oesophagus and a rat heart.

physics.ins-det↗

arXiv2022

Fabrication of High-Aspect Ratio Nanogratings for Phase-based X-ray Imaging

Diffractive optical elements such as periodic gratings are fundamental devices in X-ray imaging - a technique that medical, material science and security scans rely upon. Fabrication of such structures with high aspect ratios at the nanoscale creates opportunities to further advance such applications, especially in terms of relaxing X-ray source coherence requirements. This is because typical grating-based X-ray phase imaging techniques (e.g., Talbot self-imaging) require a coherence length of at least one grating period and ideally longer. In this paper, the fabrication challenges in achieving high aspect-ratio nanogratings filled with gold are addressed by a combination of laser interference and nanoimprint lithography, physical vapor deposition, metal assisted chemical etching (MACE), and electroplating. This relatively simple and cost-efficient approach is unlocked by an innovative post-MACE drying step with hexamethyldisilazane, which effectively minimizes the stiction of the nanostructures. The theoretical limits of the approach are discussed and, experimentally, X-ray nanogratings with aspect ratios >40 demonstrated. Finally, their excellent diffractive abilities are shown when exposed to a hard (12.2 keV) monochromatic x-ray beam at a synchrotron facility, and thus potential applicability in phase-based X-ray imaging.

physics.app-ph↗

arXiv2022

Accelerated iterative tomographic reconstruction with x-ray edge illumination

Compared to standard tomographic reconstruction, iterative approaches offer the possibility to account for extraneous experimental influences, which allows for a suppression of related artifacts. However, the inclusion of corresponding parameters in the iterative forward model typically leads to longer computation times. Here, we demonstrate experimentally for phase sensitive X-ray imaging based on the edge illumination principle that inadequately sampled illumination curves result in ring artifacts in tomographic reconstructions. We take advantage of appropriately sampled illumination curves instead, which enables us to eliminate the corresponding parameter from the forward model and substantially increase computational speed. In addition, we demonstrate a 30\% improvement in spatial resolution of the iterative approach compared with the standard non-iterative single shot approach. Further, we report on several significant improvements in our numerical implementation of the iterative approach, which we make available online with this publication. Finally, we show that the combination of both experimental and algorithmic advancement lead to a total speed increase by one order of magnitude and an improved contrast to noise ratio in the reconstructions.

eess.IV↗

arXiv2020

Neutron Dark-Field Imaging with Edge Illumination

We report on an Edge Illumination setup enabling neutron dark-field imaging where two amplitude modulators are used to structure and subsequently analyze the neutron beam. The modulator and analyzer are manufactured by laser ablation of readily available thin metal foils. The sample representation in terms of transmission and dark-field contrast is extracted by numerically inverting a convolution model for the intensity modulation function which had a visibility exceeding 80\%. Two test samples are presented to show how dark-field contrast can complement the more conventional neutron radiography, in particular to investigate the micro-structure of materials. Thanks to the simplicity of the setup, the negligible coherence requirements and the robustness of the method, this approach may find application in multi-contrast neutron radiography and tomography.

physics.ins-det↗