arXiv subjects

Marco Endrizzi

Publications and source records attributed to Marco Endrizzi.

13 recordsLinked to original sources

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

Spatial resolution of X-ray beam-tracking microscopy

X-ray beam-tracking is a phase-contrast imaging technique capable of simultaneously retrieving transmission, phase, and dark-field images. Although the spatial resolution in beam-tracking is largely considered to be 'aperture driven', no model yet exists to describe this in full. The dark-field channel is of particular interest, due to previous observations of anomalously high sharpness compared to transmission and phase channels. We derive a full optical transfer function model for each contrast channel using the Fokker-Planck equation for near-field imaging. Experimental validation using both synchrotron-based and laboratory-based setups, with 15 um circular and 10 um rectangular apertures, reveals a limiting resolution of at least 3 um, much smaller than the apertures themselves. Together, the model and the supporting experiments offer a full description of spatial resolution in beam-tracking, and formally confirm the greater spatial resolution in the dark-field channel. These findings open new possibilities in system design and experimental protocols to exploit these capabilities.

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

Dynamic laboratory X-ray phase-contrast microtomography with structure-based prior regularisation

X-ray microtomography is a versatile tool allowing the measurement of the 3D structure of optically thick samples. As a non-destructive technique, it is readily adapted to 4D imaging, where a sample can be monitored over time, and especially in conjunction with the application of external stimuli. To apply this technique with the limited X-ray flux available at a conventional laboratory source, we leverage the contrast enhancement of free-space propagation phase-contrast imaging, achieving an increase in contrast-to-noise ratio of 5.8x. Furthermore, we combine this with iterative reconstruction, using regularisation by a structure-based prior from a high-quality reference scan of the object. This combination of phase-contrast imaging and iterative reconstruction leads to a 29.2x improvement in contrast-to-noise ratio compared to the conventional reconstruction. This enables fully dynamic X-ray microtomography, with a temporal resolution of 9 s at a voxel size of 10.5 $\mu$m. We use this to measure the movement of a waterfront in the fine vessels of a wooden skewer, as a representative example of dynamic system evolving on the scale of tens of seconds.

physics.ins-det↗

arXiv2025

Offset geometry for extended field-of-view in multi-contrast and multi-scale X-ray microtomography of lung cancer lobectomy specimens

X-ray microtomography is a powerful non-destructive technique allowing 3D virtual histology of resected human tissue. The achievable imaging field-of-view, is however limited by the fixed number of detector elements, enforcing the requirement to sacrifice spatial resolution in order to image larger samples. In applications such as soft-tissue imaging, phase-contrast methods are often employed to enhance image contrast. Some of these methods, especially those suited to laboratory sources, rely on optical elements, the dimensions of which can impose a further limitation on the field-of-view. We describe an efficient method to double the maximum field-of-view of a cone-beam X-ray microtomography system, without sacrificing on spatial resolution, and including multi-contrast capabilities. We demonstrate an experimental realisation of the method, achieving exemplary reconstructions of a resected human lung sample, with a cubic voxel of 10.5 $\mu$m linear dimensions, across a horizontal field-of-view of 4.3 cm. The same concepts are applied to free-space propagation imaging of a 2.7 mm segment of the same sample, achieving a cubic voxel of 450 nm linear dimensions. We show that the methodology can be applied at a range of different length-scales and geometries, and that it is directly compatible with complementary implementations of X-ray phase-contrast imaging.

physics.med-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

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

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↗