Irene Zanette

Quantitative X-ray phase-contrast computed tomography at 82 keV

Potential applications of grating-based X-ray phase-contrast imaging are investigated in various fields due to its compatibility with laboratory X-ray sources. So far the method was mainly restricted to X-ray energies below 40 keV, which is too low to examine dense or thick objects, but a routine operation at higher energies is on the brink of realisation. In this study, imaging results obtained at 82 keV are presented. These comprise a test object consisting of well-defined materials for a quantitative analysis and a tooth to translate the findings to a biomedical sample. Measured linear attenuation coefficients ? and electron densities ?e are in good agreement with theoretical values. Improved contrast-to-noise ratios were found in phase contrast compared to attenuation contrast. The combination of both contrast modalities further enables to simultaneously assess information on density and composition of materials with effective atomic numbers Z? > 8. In our biomedical example, we demonstrate the possibility to detect differences in mass density and calcium concentration within teeth.

Quantitative breast tissue characterization using grating-based x-ray phase-contrast imaging

X-ray phase-contrast imaging has received growing interest in recent years due to its high capability in visualizing soft tissue. Breast imaging became the focus of particular attention as it is considered the most promising candidate for a first clinical application of this contrast modality. In this study, we investigate quantitative breast tissue characterization using grating-based phase-contrast computed tomography (CT) at conventional polychromatic x-ray sources. Different breast specimens have been scanned at a laboratory phase-contrast imaging setup and were correlated to histopathology. Ascertained tumor types include phylloides tumor, fibroadenoma and infiltrating lobular carcinoma. Identified tissue types comprising adipose, fibroglandular and tumor tissue have been analyzed in terms of phase-contrast Hounsfield units and are compared to high-quality, high-resolution data obtained with monochromatic synchrotron radiation, as well as calculated values based on tabulated tissue properties. The results give a good impression of the methods prospects and limitations for potential tumor detection and the associated demands on such a phase-contrast breast CT system. Furthermore, the evaluated quantitative tissue values serve as a reference for simulations and the design of dedicated phantoms for phase-contrast mammography.

Assessment of grating-based X-ray phase-contrast CT for differentiation of invasive ductal carcinoma and ductal carcinoma in situ in an experimental ex vivo set-up.

ObjectiveLimited contrast between healthy and tumour tissue is a limiting factor in mammography and CT of the breast. Phase-contrast computed tomography (PC-CT) provides improved soft-tissue contrast compared with absorption-based techniques. In this study, we assessed the technical feasibility of grating-based PC-CT imaging of the breast for characterisation of ductal carcinoma in situ (DCIS).MethodsGrating-based PC-CT was performed on one breast specimen containing an invasive ductal carcinoma and DCIS using monochromatic radiation of 23xa0keV. Phase-contrast and absorption-based images were compared qualitatively and quantitatively with histopathology in a blinded fashion.ResultsGrating-based PC-CT showed improved differentiation of soft-tissue components. Circular structures of high phase-shift contrast corresponding to the walls of the dilated ductuli of the DCIS were visualised with a contrast-to-noise ratio (CNR) of 9.6 using PC-CT but were not detectable on absorption-based images (CNRu2009=u20090.27). The high phase-shift structures of the dilated ductuli were identifiable in the PC-CT volume data set allowing for 3D characterisation of DCIS.ConclusionsOur results indicate that unlike conventional CT, grating-based PC-CT may allow the differentiation between invasive carcinoma and intraductal carcinoma and healthy breast tissue and provide 3D visualisation of DCIS.Key Points• Phase-contrast computed tomography (CT) yields improved soft-tissue contrast.• The method can resolve the fine structure of a breast tumour.• Invasive and intraductal carcinoma can be differentiated.• Differentiation is possible by visual inspection and quantification.• The method could improve early breast cancer diagnosis.

Experimental comparison of grating- and propagation-based hard X-ray phase tomography of soft tissue

When imaging soft tissues with hard X-rays, phase contrast is often preferred over conventional attenuation contrast due its superior sensitivity. However, it is unclear which of the numerous phase tomography methods yields the optimized results at given experimental conditions. Therefore, we quantitatively compared the three phase tomography methods implemented at the beamline ID19 of the European Synchrotron Radiation Facility: X-ray grating interferometry (XGI), and propagation-based phase tomography, i.e., single-distance phase retrieval (SDPR) and holotomography (HT), using cancerous tissue from a mouse model and an entire heart of a rat. We show that for both specimens, the spatial resolution derived from the characteristic morphological features is about a factor of two better for HT and SDPR compared to XGI, whereas the XGI data generally exhibit much better contrast-to-noise ratios for the anatomical features. Moreover, XGI excels in fidelity of the density measurements, and is also more robust against low-frequency artifacts than HT, but it might suffer from phase-wrapping artifacts. Thus, we can regard the three phase tomography methods discussed as complementary. The application will decide which spatial and density resolutions are desired, for the imaging task and dose requirements, and, in addition, the applicant must choose between the complexity of the experimental setup and the one of data processing.

Three-dimensional quantification of capillary networks in healthy and cancerous tissues of two mice

A key issue in developing strategies against diseases such as cancer is the analysis of the vessel tree in comparison to the healthy one. In the search for parameters that might be characteristic for tumor capillaries we study the vascularization in mice for cancerous and healthy tissues using synchrotron radiation-based micro computed tomography in absorption and phase contrast modes. Our investigations are based on absorption tomograms of casted healthy and cancerous tissues as well as a phase tomogram of a fixated tumor. We demonstrate how the voxel-based tomography data can be vectorized to assess the capillary networks quantitatively. The processing includes segmentation, skeletonization, and vectorization to finally extract the vessel parameters. The mean diameter of capillaries in healthy and cancerous tissues corresponds to (8.0±1.1) μm and (3.9±1.1) μm, respectively. Further evaluated parameters show marginal or no differences between capillaries in healthy and cancerous tissues, namely fractal dimension 2.3±0.3 vs. 2.3±0.2, tortuosity (SOAM) 0.18 rad/μm vs. 0.24 rad/μm and vessel length 20 μm vs. 17 μm. The bifurcation angles exhibit a narrow distribution around 115°. Furthermore, we show that phase tomography is a powerful alternative to absorption tomography of casts for the vessel visualization omitting any invasive specimen preparation procedure.

Grating-based X-ray phase-contrast tomography of atherosclerotic plaque at high photon energies

BACKGROUNDnTissue characterization of atherosclerosis by absorption-based imaging methods is limited due to low soft-tissue contrast. Grating-based phase-contrast computed tomography (PC-CT) may become an alternative for plaque assessment if the phase signal can be retrieved at clinically applicable photon energies. The aims of this feasibility study were (i) to characterize arterial vessels at low and high photon energies, (ii) to extract qualitative features and (iii) quantitative phase-contrast Hounsfield units (HU-phase) of plaque components at 53 keV using histopathology as gold standard.nnnMATERIALS AND METHODSnFive human carotid artery specimens underwent grating-based PC-CT using synchrotron radiation of either 23 keV or 53 keV and histological work-up. Specimens without advanced atherosclerosis were used to extract signal criteria of vessel layers. Diseased specimens were screened for important plaque components including fibrous tissue (FT), lipid (LIP), necrotic core (NEC), intraplaque hemorrhage (IPH), inflammatory cell infiltration (INF) and calcifications (CA). Qualitative features as well as quantitative HU-phase were analyzed.nnnRESULTSnThirty-three regions in 6 corresponding PC-CT scans and histology sections were identified. Healthy samples had the same signal characteristics at 23 keV and 53 keV with bright tunica intima and adventitia and dark media. Plaque components showed differences in signal intensity and texture at 53 keV. Quantitative analysis demonstrated the highest HU-phase of soft plaque in dense FT. Less organized LIP, NEC and INF were associated with lower HU-phase values. The highest HU-phase were measured in CA.nnnCONCLUSIONnPC-CT of atherosclerosis is feasible at high, clinically relevant photon energies and provides detailed information about plaque structure including features of high risk vulnerable plaques.

X-Ray Phase-Contrast CT of a Pancreatic Ductal Adenocarcinoma Mouse Model

To explore the potential of grating-based x-ray phase-contrast computed tomography (CT) for preclinical research, a genetically engineered mouse model of pancreatic ductal adenocarcinoma (PDAC) was investigated. One ex-vivo mouse specimen was scanned with different grating-based phase-contrast CT imaging setups covering two different settings: i) high-resolution synchrotron radiation (SR) imaging and ii) dose-reduced imaging using either synchrotron radiation or a conventional x-ray tube source. These experimental settings were chosen to assess the potential of phase-contrast imaging for two different types of application: i) high-performance imaging for virtual microscopy applications and ii) biomedical imaging with increased soft-tissue contrast for in-vivo applications. For validation and as a reference, histological slicing and magnetic resonance imaging (MRI) were performed on the same mouse specimen. For each x-ray imaging setup, attenuation and phase-contrast images were compared visually with regard to contrast in general, and specifically concerning the recognizability of lesions and cancerous tissue. To quantitatively assess contrast, the contrast-to-noise ratios (CNR) of selected regions of interest (ROI) in the attenuation images and the phase images were analyzed and compared. It was found that both for virtual microscopy and for in-vivo applications, there is great potential for phase-contrast imaging: in the SR-based benchmarking data, fine details about tissue composition are accessible in the phase images and the visibility of solid tumor tissue under dose-reduced conditions is markedly superior in the phase images. The present study hence demonstrates improved diagnostic value with phase-contrast CT in a mouse model of a complex endogenous cancer, promoting the use and further development of grating-based phase-contrast CT for biomedical imaging applications.

Speckle-based x-ray phase-contrast imaging with a laboratory source and the scanning technique

The speckle-based scanning method for x-ray phase-contrast imaging is implemented with a liquid-metal-jet source. Using the two-dimensional scanning technique, the phase shift introduced by the object is retrieved in both transverse orientations, and the limitations on spatial resolution inherent to the speckle-tracking technique are avoided. This method opens up possibilities of new high-resolution multimodal applications for lab-based phase-contrast x-ray imaging.

X-ray nanotomography using near-field ptychography.

Propagation-based imaging or inline holography in combination with computed tomography (holotomography) is a versatile tool to access a samples three-dimensional (3D) micro or nano structure. However, the phase retrieval step needed prior to tomographic reconstruction can be challenging especially for strongly absorbing and refracting samples. Near-field ptychography is a recently developed phase imaging method that has been proven to overcome this hurdle in projection data. In this work we extend near-field ptychography to three dimensions and we show that, in combination with tomography, it can access the nano structure of a solid oxide fuel cell (SOFC). The quality of the resulting tomographic data and the structural properties of the anode extracted from this volume were compared to previous results obtained with holotomography. This work highlights the potential of 3D near-field ptychography for reliable and detailed investigations of samples at the nanometer scale, with important applications in materials and life sciences among others.

Multi-contrast 3D X-ray imaging of porous and composite materials

Grating-based X-ray computed tomography allows for simultaneous and nondestructive determination of the full X-ray complex index of refraction and the scattering coefficient distribution inside an object in three dimensions. Its multi-contrast capabilities combined with a high resolution of a few micrometers make it a suitable tool for assessing multiple phases inside porous and composite materials such as concrete. Here, we present quantitative results of a proof-of-principle experiment performed on a concrete sample. Thanks to the complementarity of the contrast channels, more concrete phases could be distinguished than in conventional attenuation-based imaging. The phase-contrast reconstruction shows high contrast between the hardened cement paste and the aggregates and thus allows easy 3D segmentation. Thanks to the dark-field image, micro-cracks inside the coarse aggregates are visible. We believe that these results are extremely interesting in the field of porous and composite materials studies beca...