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

Development of a novel single absorption grating based versatile multi-contrast imaging facility at the X-ray Imaging beamline, Indus-2

A multi-contrast x-ray imaging facility with a single x-ray absorption grating is developed at the X-ray Imaging beamline (BL-04), Indus-2 synchrotron radiation source, India, and implemented in both monochromatic and white beam operation modes of the beamline for versatile utilization of this technique in structural characterization of a wide range of samples from soft biological to metallic, dense, and thick materials. The developed facility is characterized by resolution, visibility, and signal-to-noise ratio and tested for static and dynamic morphological analysis under different experimental conditions. The qualitative and quantitative analysis of extracted multi-contrast x-ray images of different samples demonstrates the relative merits of various experimental conditions. This unique multi-contrast facility with a single x-ray absorption grating that operates in dual modes of the X-ray Imaging beamline enables the study of both static and transient phenomena across a wide range of applications at the beamline.

Insights into γ-irradiation effect on hole structure and conductivity of doped ethylene-propylene-diene rubber with different wheat husk fibers lengths

In this paper, three samples of ethylene-propylene-diene monomer rubber (EPDM)/wheat husk fibers (WHF) with short (SW30), medium (EW30), and long (HW30) lengths of WHF were investigated as a function of γ-irradiation dose up to 300 kGy. The swelling coefficient Q of the toluene, benzene, and chloroform solvents was performed, and the Q reflects the ability of the polymer composites to absorb and retain a solvent within their structure. The conductivity of the examined composites has been computed, and their dielectric characteristics have been calculated. It was found that the dielectric constant exhibited frequency-dependent behavior indicating enhanced charge carrier mobility. The conduction mechanisms in the composites were found to be quantum mechanical tunneling and correlated barrier hopping, depending on the composite and irradiation dose. The γ-irradiation dose dependence of the free volume size, deduced from positron annihilation lifetime spectroscopy, is increasing for the SW30 composite while it decreases for both EW30 and HW30 composites. Increasing the free volume hole size is connected to the degradation effect on the SW30 samples. For EW30 and HW30, there is shrinkage of free volume in the composites due to crosslinking induced by γ-irradiation. Additionally, the nanoscopic properties derived from PAL spectroscopy are correlated with the macroscopic properties of the composites.

Robust quantitative X-ray phase diagnostic for carbon composite characterisation in the context of lightning induced risk

Getting complementary physical information from a single image acquisition is particularly valuable for materials analysis. Grating based X-ray Phase Contrast Imaging (XPCI) methods allow decoupling attenuation, phase and scattering information. However, the phase and scattering extraction processes can easily suffer from artefacts, which is detrimental to implement this imaging technique in societal applications. In this paper, we demonstrate that grating based XPCI can provide a robust phase measurement in complex materials such as damaged composites. The technique allows the phase to be analysed using a self-assessment method that first identifies the artefacts from the imaging setup, and then can be used as an indicator to interpret the signal from a material. We focus on carbon fibre reinforced polymers which we subjected to laboratory-controlled lightning strikes. We evidence that the combined information from phase and attenuation allow identifying the type of defect induced by the lightning current. The phase information is converted into relative mass density variation within the sample and depicts areas with a loss in density up to 40%. We ensure that these results are valid by comparing them with an X-ray attenuation contrast tomographic reconstruction.

Towards clinical-dose grating interferometry breast CT with fused intensity-based iterative reconstruction

X-ray grating interferometry CT (GI-CT) is an emerging imaging modality which provides three complementary contrasts that could increase the diagnostic content of clinical breast CT: absorption, phase, and dark-field. Yet, reconstructing the three image channels under clinically compatible conditions is challenging because of severe ill-conditioning of the tomographic reconstruction problem. In this work we propose to solve this problem with a novel reconstruction algorithm that assumes a fixed relation between the absorption and the phase-contrast channel to reconstruct a single image by automatically fusing the absorption and phase channels. The results on both simulations and real data show that, enabled by the proposed algorithm, GI-CT outperforms conventional CT at a clinical dose.

Five material tissue decomposition by dual energy computed tomography

The separation of mixtures of substances into their individual components plays an important role in many areas of science. In medical imaging, one method is the established analysis using dual-energy computed tomography. However, when analyzing mixtures consisting of more than three individual basis materials, a physical limit is reached that no longer allows this standard analysis. In addition, the X-ray attenuation coefficients of chemically complicated basis materials may not be known and also cannot be determined by other or previous analyses. To address these issues, we developed a novel theoretical approach and algorithm and tested it on samples prepared in the laboratory as well as on ex-vivo medical samples. This method allowed both five-material decomposition and determination or optimization of the X-ray attenuation coefficients of the sample base materials via optimizations of objective functions. After implementation, this new multimodal method was successfully tested on self-mixed samples consisting of the aqueous base solutions iomeprol, eosin Y disodiumsalt, sodium chloride, and pure water. As a first proof of concept of this technique for detailed material decomposition in medicine we analyzed exact percentage composition of ex vivo clots from patients with acute ischemic stroke, using histological analysis as a reference standard.

Quantitative X-ray phase contrast computed tomography with grating interferometry : Biomedical applications of quantitative X-ray grating-based phase contrast computed tomography

The ability of biomedical imaging data to be of quantitative nature is getting increasingly important with the ongoing developments in data science. In contrast to conventional attenuation-based X-ray imaging, grating-based phase contrast computed tomography (GBPC-CT) is a phase contrast micro-CT imaging technique that can provide high soft tissue contrast at high spatial resolution. While there is a variety of different phase contrast imaging techniques, GBPC-CT can be applied with laboratory X-ray sources and enables quantitative determination of electron density and effective atomic number. In this review article, we present quantitative GBPC-CT with the focus on biomedical applications.

Dual Energy Differential Phase Contrast CT (DE-DPC-CT) Imaging

When more than two elemental materials are present in a given object, material quantification may not be robust and accurate when the routine two-material decomposition scheme in current dual energy CT imaging is employed. In this work, we present an innovative scheme to accomplish accurate three-material decomposition with measurements from a dual energy differential phase contrast CT (DE-DPC-CT) acquisition. A DE-DPC-CT system was constructed using a grating interferometer and a photon counting CT imaging system with two energy bins. The DE-DPC-CT system can simultaneously measure both the imaginary and the real part of the complex refractive index to enable a three-material decomposition. Physical phantom with 21 material inserts were constructed and measured using DE-DPC-CT system. Results demonstrated excellent accuracy in elemental material quantification. For example, relative root-mean-square errors of 4.5% for calcium and 5.2% for iodine were achieved using the proposed three-material decomposition scheme. Biological tissues with iodine inserts were used to demonstrate the potential utility of the proposed spectral CT imaging method. Experimental results showed that the proposed method correctly differentiates the bony structure, iodine, and the soft tissue in the biological specimen samples. A triple spectra CT scan was also performed to benchmark the performance of the DE-DPC-CT scan. Results demonstrated that the material decomposition from the DE-DPC-CT has a much lower quantification noise than that from the triple spectra CT scan.

Single spectrum three-material decomposition with grating-based x-ray phase-contrast CT

Grating-based x-ray phase-contrast imaging provides three simultaneous image channels originating from a single image acquisition. While the phase signal provides direct access to the electron density in tomography, there is additional information on sub-resolutional structural information which is called dark-field signal in analogy to optical microscopy. The additional availability of the conventional attenuation image qualifies the method for implementation into existing diagnostic routines. The simultaneous access to the attenuation coefficient and the electron density allows for quantitative two-material discrimination as demonstrated lately for measurements at a quasi-monochromatic compact synchrotron source. Here, we investigate the transfer of the method to conventional polychromatic x-ray sources and the additional inclusion of the dark-field signal for three-material decomposition. We evaluate the future potential of grating-based x-ray phase-contrast CT for quantitative three-material discrimination for the specific case of early stroke diagnosis at conventional polychromatic x-ray sources. Compared to conventional CT, the method has the potential to discriminate coagulated blood directly from contrast agent extravasation within a single CT acquisition. Additionally, the dark-field information allows for the clear identification of hydroxyapatite clusters due to their micro-structure despite a similar attenuation as the applied contrast agent. This information on materials with sub-resolutional microstructures is considered to comprise advantages relevant for various pathologies.

X-ray nano-tomography of complete scales from the ultra-white beetles Lepidiota stigma and Cyphochilus

High resolution X-ray nano-tomography experiments are often limited to a few tens of micrometer size volumes due to detector size. It is possible, through the use of multiple overlapping tomography scans, to produce a large area scan which can encompass a sample in its entirety. Mounting and positioning regions to be scanned is highly challenging and normally requires focused ion beam approaches. In this work we have imaged intact beetle scale cells mounted on the tip of a needle using a micromanipulator stage. Here we show X-ray holotomography data for single ultra-white scales from the beetles Lepidiota stigma (L. stigma) and Cyphochilus which exhibit the most effective scattering of white light in the literature. The final thresholded matrices represent a scan area of 25 × 70 × 362.5 µm and 25 × 67.5 × 235µm while maintaining a pixel resolution of 25 nm. This tomographic approach allowed the internal structure of the scales to be captured completely intact and undistorted by the sectioning required for traditional microscopy techniques.

Measurement(s)	chitin • scale
Technology Type(s)	computed tomography • x-ray holotomography
Sample Characteristic - Organism	Lepidiota • Cyphochilus

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12251450

Direct quantitative material decomposition employing grating-based X-ray phase-contrast CT

Dual-energy CT has opened up a new level of quantitative X-ray imaging for many diagnostic applications. The energy dependence of the X-ray attenuation is the key to quantitative material decomposition of the volume under investigation. This material decomposition allows the calculation of virtual native images in contrast enhanced angiography, virtual monoenergetic images for beam-hardening artifact reduction and quantitative material maps, among others. These visualizations have been proven beneficial for various diagnostic questions. Here, we demonstrate a new method of 'virtual dual-energy CT' employing grating-based phase-contrast for quantitative material decomposition. Analogue to the measurement at two different energies, the applied phase-contrast measurement approach yields dual information in form of a phase-shift and an attenuation image. Based on these two image channels, all known dual-energy applications can be demonstrated with our technique. While still in a preclinical state, the method features the important advantages of direct access to the electron density via the phase image, simultaneous availability of the conventional attenuation image at the full energy spectrum and therefore inherently registered image channels. The transfer of this signal extraction approach to phase-contrast data multiplies the diagnostic information gained within a single CT acquisition. The method is demonstrated with a phantom consisting of exemplary solid and fluid materials as well as a chicken heart with an iodine filled tube simulating a vessel. For this first demonstration all measurements have been conducted at a compact laser-undulator synchrotron X-ray source with a tunable X-ray energy and a narrow spectral bandwidth, to validate the quantitativeness of the processing approach.

X-ray phase-contrast imaging with engineered porous materials over 50 keV

X-ray phase-contrast imaging can substantially enhance image contrast for weakly absorbing samples. The fabrication of dedicated optics remains a major barrier, especially in high-energy regions (i.e. over 50 keV). Here, the authors perform X-ray phase-contrast imaging by using engineered porous materials as random absorption masks, which provides an alternative solution to extend X-ray phase-contrast imaging into previously challenging higher energy regions. The authors have measured various samples to demonstrate the feasibility of the proposed engineering materials. This technique could potentially be useful for studying samples across a wide range of applications and disciplines.

Accurate effective atomic number determination with polychromatic grating-based phase-contrast computed tomography

The demand for quantitative medical imaging is increasing in the ongoing digitalization. Conventional computed tomography (CT) is energy-dependent and therefore of limited comparability. In contrast, dual-energy CT (DECT) allows for the determination of absolute image contrast quantities, namely the electron density and the effective atomic number, and is already established in clinical radiology and radiation therapy. Grating-based phase-contrast computed tomography (GBPC-CT) is an experimental X-ray technique that also allows for the measurement of the electron density and the effective atomic number. However, the determination of both quantities is challenging when dealing with polychromatic GBPC-CT setups. In this paper, we present how to calculate the effective atomic numbers with a polychromatic, laboratory GBPC-CT setup operating between 35 and 50\,kVp. First, we investigated the accuracy of the measurement of the attenuation coefficients and electron densities. For this, we performed a calibration using the concept of effective energy. With the reliable experimental quantitative values, we were able to evaluate the effective atomic numbers of the investigated materials using a method previously shown with monochromatic X-ray radiation. In detail, we first calculated the ratio of the electron density and attenuation coefficient, which were experimentally determined with our polychromatic GBPC-CT setup. Second, we compared this ratio with tabulated total attenuation cross sections from literature values to determine the effective atomic numbers. Thus, we were able to calculate two physical absolute quantities -- the electron density and effective atomic number -- that are in general independent of the specific experimental conditions like the X-ray beam spectrum or the setup design.

Development of an X-ray imaging system to prevent scintillator degradation for white synchrotron radiation

The high flux of the white X-ray beams from third-generation synchrotron light sources can significantly benefit the development of high-speed X-ray imaging, but can also bring technical challenges to existing X-ray imaging systems. One prevalent problem is that the image quality deteriorates because of dust particles accumulating on the scintillator screen during exposure to intense X-ray radiation. Here, this problem has been solved by embedding the scintillator in a flowing inert-gas environment. It is also shown that the detector maintains the quality of the captured images even after days of X-ray exposure. This modification is cost-efficient and easy to implement. Representative examples of applications using the X-ray imaging system are also provided, including fast tomography and multimodal phase-contrast imaging for biomedical and geological samples.

In-vivo X-ray Dark-Field Chest Radiography of a Pig

X-ray chest radiography is an inexpensive and broadly available tool for initial assessment of the lung in clinical routine, but typically lacks diagnostic sensitivity for detection of pulmonary diseases in their early stages. Recent X-ray dark-field (XDF) imaging studies on mice have shown significant improvements in imaging-based lung diagnostics. Especially in the case of early diagnosis of chronic obstructive pulmonary disease (COPD), XDF imaging clearly outperforms conventional radiography. However, a translation of this technique towards the investigation of larger mammals and finally humans has not yet been achieved. In this letter, we present the first in-vivo XDF full-field chest radiographs (32 × 35 cm²) of a living pig, acquired with clinically compatible parameters (40 s scan time, approx. 80 µSv dose). For imaging, we developed a novel high-energy XDF system that overcomes the limitations of currently established setups. Our XDF radiographs yield sufficiently high image quality to enable radiographic evaluation of the lungs. We consider this a milestone in the bench-to-bedside translation of XDF imaging and expect XDF imaging to become an invaluable tool in clinical practice, both as a general chest X-ray modality and as a dedicated tool for high-risk patients affected by smoking, industrial work and indoor cooking.

Non-iterative Directional Dark-field Tomography

Dark-field imaging is a scattering-based X-ray imaging method that can be performed with laboratory X-ray tubes. The possibility to obtain information about unresolvable structures has already seen a lot of interest for both medical and material science applications. Unlike conventional X-ray attenuation, orientation dependent changes of the dark-field signal can be used to reveal microscopic structural orientation. To date, reconstruction of the three-dimensional dark-field signal requires dedicated, highly complex algorithms and specialized acquisition hardware. This severely hinders the possible application of orientation-dependent dark-field tomography. In this paper, we show that it is possible to perform this kind of dark-field tomography with common Talbot-Lau interferometer setups by reducing the reconstruction to several smaller independent problems. This allows for the reconstruction to be performed with commercially available software and our findings will therefore help pave the way for a straightforward implementation of orientation-dependent dark-field tomography.

Qualitative and Quantitative Imaging Evaluation of Renal Cell Carcinoma Subtypes with Grating-based X-ray Phase-contrast CT

Current clinical imaging methods face limitations in the detection and correct characterization of different subtypes of renal cell carcinoma (RCC), while these are important for therapy and prognosis. The present study evaluates the potential of grating-based X-ray phase-contrast computed tomography (gbPC-CT) for visualization and characterization of human RCC subtypes. The imaging results for 23 ex vivo formalin-fixed human kidney specimens obtained with phase-contrast CT were compared to the results of the absorption-based CT (gbCT), clinical CT and a 3T MRI and validated using histology. Regions of interest were placed on each specimen for quantitative evaluation. Qualitative and quantitative gbPC-CT imaging could significantly discriminate between normal kidney cortex (54 ± 4 HUp) and clear cell (42 ± 10), papillary (43 ± 6) and chromophobe RCCs (39 ± 7), p < 0.05 respectively. The sensitivity for detection of tumor areas was 100%, 50% and 40% for gbPC-CT, gbCT and clinical CT, respectively. RCC architecture like fibrous strands, pseudocapsules, necrosis or hyalinization was depicted clearly in gbPC-CT and was not equally well visualized in gbCT, clinical CT and MRI. The results show that gbPC-CT enables improved discrimination of normal kidney parenchyma and tumorous tissues as well as different soft-tissue components of RCCs without the use of contrast media.

Mass Density Measurement of Mineralized Tissue with Grating-Based X-Ray Phase Tomography

Establishing the mineral content distribution in highly mineralized tissues, such as bones and teeth, is fundamental in understanding a variety of structural questions ranging from studies of the mechanical properties to improved pathological investigations. However, non-destructive, volumetric and quantitative density measurements of mineralized samples, some of which may extend several mm in size, remain challenging. Here, we demonstrate the potential of grating-based x-ray phase tomography to gain insight into the three-dimensional mass density distribution of tooth tissues in a non-destructive way and with a sensitivity of 85 mg/cm³. Density gradients of 13 − 19% over 1 − 2 mm within typical samples are detected, and local variations in density of 0.4 g/cm³ on a length scale of 0.1 mm are revealed. This method proves to be an excellent quantitative tool for investigations of subtle differences in mineral content of mineralized tissues that can change following treatment or during ageing and healing.

Hard X-ray index of refraction tomography of a whole rabbit knee joint: A feasibility study

We report results of the computed tomography reconstruction of the index of refraction in a whole rabbit knee joint examined at the photon energy of 51keV. Refraction based images make it possible to delineate the bone, cartilage, and soft tissues without adjusting the contrast window width and level. Density variations, which are related to tissue composition and are not visible in absorption X-ray images, are detected in the obtained refraction based images. We discuss why refraction-based images provide better detectability of low contrast features than absorption images.

A Novel and Sensitive Approach for the Evaluation of Liver Ischemia-Reperfusion Injury After Liver Transplantation

OBJECTIVES

The purpose of our study was to evaluate the potential of x-ray propagation-based phase-contrast imaging (PCI) computed tomography (CT) for the detection and characterization of early changes after ischemia-reperfusion (IR) in a standardized rat liver transplantation (LTx) model.

MATERIALS AND METHODS

Syngeneic orthotopic liver transplantation was performed in male Lewis rats. Ischemia-reperfusion injury (IRI)-induced changes of liver parenchyma were investigated in a time-dependent manner (2, 16, 24, and 32 hours). X-ray phase-contrast images of formalin-fixated liver specimens were acquired in CT mode by using a voxel size of 8 × 8 × 8 μm. Necrapoptotic cell death was visualized with the TdT-mediated dUTP-biotin nick end labeling technique, and alterations of liver graft microhemodynamics, that is, acinar and sinusoidal perfusion failure, were evaluated by in vivo fluorescence microscopy.

RESULTS

Acquired and reconstructed PCI-CT images showed an increase in necrotic liver parenchyma dependent on cold storage time, measuring 5.7% ± 1.6% after 2 hours (comparable to 2.6% ± 0.4% for sham livers), 11.5% ± 2.1% (16 hours; P < 0.05 vs control), 23.0% ± 0.5% (24 hours; P < 0.001 vs control), and 31.3% ± 2.2% (32 hours; P < 0.001 vs control). There were a significant lower number of perfused acini in dependence on increasing cold storage time. The acinar perfusion index reached 0.970 ± 0.006 after 2 hours of cold ischemia (comparable to 0.960 ± 0.009 for sham livers) and declined continuously after 16, 24, and 32 hours cold ischemia (0.58 ± 0.03, 0.49 ± 0.02, 0.41 ± 0.03, each P < 0.0001 vs controls). Comparable results were found for sinusoidal perfusion, reaching 1.8% ± 0.4% of nonperfused sinusoids for 2 hours of cold ischemia and 8.2% ± 0.8% after 16 hours, 18.8% ± 1.4% after 24 hours, and 39.0% ± 2.4% after 32 hours (each P < 0.0001 vs controls). Prolonged cold ischemia was associated with an increasing number of TdT-mediated dUTP-biotin nick end labeling-positive cells (hepatocytes and sinusoidal lining cells), reaching 0.4 ± 0.1 (sham), 0.7 ± 0.4 (2 hours), 6.4 ± 1.1 (16 hours), 2.1 ± 0.3 (24 hours), and 14.7 ± 3.5 (32 hours; P = 0.002) for hepatocytes.

CONCLUSIONS

X-ray PCI of histological liver specimens can detect IR-induced tissue necrosis and can provide detailed complementary 3-dimensional information to standard histopathologic findings.

High energy X-ray phase and dark-field imaging using a random absorption mask

High energy X-ray imaging has unique advantage over conventional X-ray imaging, since it enables higher penetration into materials with significantly reduced radiation damage. However, the absorption contrast in high energy region is considerably low due to the reduced X-ray absorption cross section for most materials. Even though the X-ray phase and dark-field imaging techniques can provide substantially increased contrast and complementary information, fabricating dedicated optics for high energies still remain a challenge. To address this issue, we present an alternative X-ray imaging approach to produce transmission, phase and scattering signals at high X-ray energies by using a random absorption mask. Importantly, in addition to the synchrotron radiation source, this approach has been demonstrated for practical imaging application with a laboratory-based microfocus X-ray source. This new imaging method could be potentially useful for studying thick samples or heavy materials for advanced research in materials science.

X-ray phase-contrast computed tomography of human coronary arteries

OBJECTIVE

The objective of this study was to assess the potential of grating-based phase-contrast computed tomography (gb-PCCT) for the detection and characterization of human coronary artery disease in an experimental ex vivo validation study.

MATERIALS AND METHODS

The study was approved by the institutional review board, and informed consent was obtained from all patients. Specimens were examined using a conventional low-coherence x-ray tube (40 kV) and a Talbot-Lau grating interferometer. Histopathologic assessment was used as the standard of reference. Signal characteristics of calcified, fibrous (FIB), and lipid-rich (LIP) tissue were visually and quantitatively assessed by phase-contrast Hounsfield units (HU). Conventional absorption-based HU values were also measured. Conservative measurements of diagnostic accuracy for the detection and differentiation of plaque components as well as quantitative measurements of vessel dimensions were obtained, and receiver operating characteristic curve analysis for plaque differentiation was performed.

RESULTS

A total of 15 coronary arteries from 5 subjects were available for analysis (386 sections). Calcified, FIB, and LIP displayed distinct gb-PCCT signal criteria. The diagnostic accuracy of gb-PCCT was high with sensitivity, specificity, and negative and positive predictive values of 0.89 or greater for all plaque components with good interrater agreement (к ≥ 0.88). In addition, quantitative measurements of vessel dimensions in gb-PCCT were strongly correlated with measurements obtained from histopathology (Pearson R ≥ 0.86). Finally, phase-contrast Hounsfield units were superior to conventional HU in differentiating FIB and LIP (receiver operating characteristic analysis, 0.86 vs. 0.77, respectively; P < 0.05).

CONCLUSIONS

In an ex vivo setting, gb-PCCT provides improved differentiation and quantification of coronary atherosclerotic plaque and may thus serve as a tool for nondestructive histopathology.

Quantitative Three-Dimensional Imaging of Lipid, Protein, and Water Contents via X-Ray Phase-Contrast Tomography

X-ray phase-contrast computed tomography is an emerging imaging technology with powerful capabilities for three-dimensional (3D) visualization of weakly absorbing objects such as biological soft tissues. This technique is an extension of existing X-ray applications because conventional attenuation-contrast images are simultaneously acquired. The complementary information provided by both the contrast modalities suggests that enhanced material characterization is possible when performing combined data analysis. In this study, we describe how protein, lipid, and water concentrations in each 3D voxel can be quantified by vector decomposition. Experimental results of dairy products, porcine fat and rind, and different human soft tissue types are presented. The results demonstrate the potential of phase-contrast imaging as a new analysis tool. The 3D representations of protein, lipid, and water contents open up new opportunities in the fields of biology, medicine, and food science.

Visualization of microvasculature and thrombi by X-ray phase-contrast computed tomography in hepatocellular carcinoma

Visualization of the microvascular network and thrombi in the microvasculature is a key step to evaluating the development of tumor growth and metastasis, and influences treatment selection. X-ray phase-contrast computed tomography (PCCT) is a new imaging technique that can detect minute changes of density and reveal soft tissues discrimination at micrometer-scale resolution. In this study, six human resected hepatocellular carcinoma (HCC) tissues were investigated with PCCT. A histological stain was added to estimate the accuracy of PCCT. The results showed that the fine structures of the microvasculature (measuring 30-100 µm) and thrombi in tiny blood vessels were displayed clearly on imaging the HCC tissues by PCCT. Moreover, density distributions of the thrombi were obtained, which could be reliably used to distinguish malignant from benign thrombi in HCC. In conclusion, PCCT can clearly show the three-dimensional subtle structures of HCC that cannot be detected by conventional absorption-based computed tomography and provides a new method for the imageology of HCC.

In Vivo Dark-Field Radiography for Early Diagnosis and Staging of Pulmonary Emphysema

OBJECTIVES

The aim of this study was to evaluate the suitability of in vivo x-ray dark-field radiography for early-stage diagnosis of pulmonary emphysema in mice. Furthermore, we aimed to analyze how the dark-field signal correlates with morphological changes of lung architecture at distinct stages of emphysema.

MATERIALS AND METHODS

Female 8- to 10-week-old C57Bl/6N mice were used throughout all experiments. Pulmonary emphysema was induced by orotracheal injection of porcine pancreatic elastase (80-U/kg body weight) (n = 30). Control mice (n = 11) received orotracheal injection of phosphate-buffered saline. To monitor the temporal patterns of emphysema development over time, the mice were imaged 7, 14, or 21 days after the application of elastase or phosphate-buffered saline. X-ray transmission and dark-field images were acquired with a prototype grating-based small-animal scanner. In vivo pulmonary function tests were performed before killing the animals. In addition, lungs were obtained for detailed histopathological analysis, including mean cord length (MCL) quantification as a parameter for the assessment of emphysema. Three blinded readers, all of them experienced radiologists and familiar with dark-field imaging, were asked to grade the severity of emphysema for both dark-field and transmission images.

RESULTS

Histopathology and MCL quantification confirmed the introduction of different stages of emphysema, which could be clearly visualized and differentiated on the dark-field radiograms, whereas early stages were not detected on transmission images. The correlation between MCL and dark-field signal intensities (r = 0.85) was significantly higher than the correlation between MCL and transmission signal intensities (r = 0.37). The readers' visual ratings for dark-field images correlated significantly better with MCL (r = 0.85) than visual ratings for transmission images (r = 0.36). Interreader agreement and the diagnostic accuracy of both quantitative and visual assessment were significantly higher for dark-field imaging than those for conventional transmission images.

CONCLUSIONS

X-ray dark-field radiography can reliably visualize different stages of emphysema in vivo and demonstrates significantly higher diagnostic accuracy for early stages of emphysema than conventional attenuation-based radiography.

AHA classification of coronary and carotid atherosclerotic plaques by grating-based phase-contrast computed tomography

OBJECTIVES

To evaluate the potential of grating-based phase-contrast computed-tomography (gb-PCCT) to classify human carotid and coronary atherosclerotic plaques according to modified American Heart Association (AHA) criteria.

METHODS

Experiments were carried out at a laboratory-based set-up consisting of X-ray tube (40 kVp), grating-interferometer and detector. Eighteen human carotid and coronary artery specimens were examined. Histopathology served as the standard of reference. Vessel cross-sections were classified as AHA lesion type I/II, III, IV/V, VI, VII or VIII plaques by two independent reviewers blinded to histopathology. Conservative measurements of diagnostic accuracies for the detection and differentiation of plaque types were evaluated.

RESULTS

A total of 127 corresponding gb-PCCT/histopathology sections were analyzed. Based on histopathology, lesion type I/II was present in 12 (9.5 %), III in 18 (14.2 %), IV/V in 38 (29.9 %), VI in 16 (12.6 %), VII in 34 (26.8 %) and VIII in 9 (7.0 %) cross-sections. Sensitivity, specificity and positive and negative predictive value were ≥0.88 for most analyzed plaque types with a good level of agreement (Cohen's kappa = 0.90). Overall, results were better in carotid (kappa = 0.97) than in coronary arteries (kappa = 0.85). Inter-observer agreement was high with kappa = 0.85, p < 0.0001.

CONCLUSIONS

These results indicate that gb-PCCT can reliably classify atherosclerotic plaques according to modified AHA criteria with excellent agreement to histopathology.

KEY POINTS

• Different atherosclerotic plaque types display distinct morphological features in phase-contrast CT. • Phase-contrast CT can detect and differentiate AHA plaque types. • Calcifications caused streak artefacts and reduced sensitivity in type VI lesions. • Overall agreement was higher in carotid than in coronary arteries.

Grating-based X-ray Dark-field Computed Tomography of Living Mice

Changes in x-ray attenuating tissue caused by lung disorders like emphysema or fibrosis are subtle and thus only resolved by high-resolution computed tomography (CT). The structural reorganization, however, is of strong influence for lung function. Dark-field CT (DFCT), based on small-angle scattering of x-rays, reveals such structural changes even at resolutions coarser than the pulmonary network and thus provides access to their anatomical distribution. In this proof-of-concept study we present x-ray in vivo DFCTs of lungs of a healthy, an emphysematous and a fibrotic mouse. The tomographies show excellent depiction of the distribution of structural – and thus indirectly functional – changes in lung parenchyma, on single-modality slices in dark field as well as on multimodal fusion images. Therefore, we anticipate numerous applications of DFCT in diagnostic lung imaging. We introduce a scatter-based Hounsfield Unit (sHU) scale to facilitate comparability of scans. In this newly defined sHU scale, the pathophysiological changes by emphysema and fibrosis cause a shift towards lower numbers, compared to healthy lung tissue.

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We present so far unreported x-ray scatter dark-field CT scans of living mice performed with a Talbot–Lau interferometer.

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Dark field gives access to structural information not provided by attenuation CT at scales below the detector pixel size.

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Changes of lung alveoli structure are clearly visualized by dark-field CT for emphysema and fibrosis.

Lung diseases pose one of the leading causes of death worldwide. They are often difficult to diagnose at an early stage due to low sensitivity of conventional medical imaging systems towards structural changes of the lung tissue. With dark-field imaging based on scattering of x-rays such structural changes can be visualized even at imaging system resolutions coarser than the lung alveoli, as opposed to conventional x-ray imaging based on attenuation. By overcoming experimental scan time and dose issues, we report the first dark-field computed tomography scans on living mice, demonstrating excellent depiction of the anatomical distribution of pathological lung changes.

Ex Vivo Perfusion-Simulation Measurements of Microbubbles as a Scattering Contrast Agent for Grating-Based X-Ray Dark-Field Imaging

The investigation of dedicated contrast agents for x-ray dark-field imaging, which exploits small-angle scattering at microstructures for contrast generation, is of strong interest in analogy to the common clinical use of high-atomic number contrast media in conventional attenuation-based imaging, since dark-field imaging has proven to provide complementary information. Therefore, agents consisting of gas bubbles, as used in ultrasound imaging for example, are of particular interest. In this work, we investigate an experimental contrast agent based on microbubbles consisting of a polyvinyl-alcohol shell with an iron oxide coating, which was originally developed for multimodal imaging and drug delivery. Its performance as a possible contrast medium for small-animal angiography was examined using a mouse carcass to realistically consider attenuating and scattering background signal. Subtraction images of dark field, phase contrast and attenuation were acquired for a concentration series of 100%, 10% and 1.3% to mimic different stages of dilution in the contrast agent in the blood vessel system. The images were compared to the gold-standard iodine-based contrast agent Solutrast, showing a good contrast improvement by microbubbles in dark-field imaging. This study proves the feasibility of microbubble-based dark-field contrast-enhancement in presence of scattering and attenuating mouse body structures like bone and fur. Therefore, it suggests a strong potential of the use of polymer-based microbubbles for small-animal dark-field angiography.

Statistical iterative reconstruction algorithm for X-ray phase-contrast CT

Grating-based phase-contrast computed tomography (PCCT) is a promising imaging tool on the horizon for pre-clinical and clinical applications. Until now PCCT has been plagued by strong artifacts when dense materials like bones are present. In this paper, we present a new statistical iterative reconstruction algorithm which overcomes this limitation. It makes use of the fact that an X-ray interferometer provides a conventional absorption as well as a dark-field signal in addition to the phase-contrast signal. The method is based on a statistical iterative reconstruction algorithm utilizing maximum-a-posteriori principles and integrating the statistical properties of the raw data as well as information of dense objects gained from the absorption signal. Reconstruction of a pre-clinical mouse scan illustrates that artifacts caused by bones are significantly reduced and image quality is improved when employing our approach. Especially small structures, which are usually lost because of streaks, are recovered in our results. In comparison with the current state-of-the-art algorithms our approach provides significantly improved image quality with respect to quantitative and qualitative results. In summary, we expect that our new statistical iterative reconstruction method to increase the general usability of PCCT imaging for medical diagnosis apart from applications focused solely on soft tissue visualization.

Image optimization in digital dental radiography

Presented is a method for establishing the appropriate balance of image quality and radiation dose for dental imaging. Using the Monte Carlo N-Particle Extended (MCNPX) radiation transport code, the DC Planmeca radiographic unit and a dental bitewing phantom were modeled. The Carestream 6100 RVG sensor signal response, noise response, dose rate dependence, and reproducibility were determined experimentally, including uncertainties and inter/intraunit variabilities. The computationally varied parameters were peak kilovoltage and tube filtration. The entrance air kerma for the current clinical technique was used to establish reference image quality. Four figures of merit (FOM) were chosen to encompass parameter variation. With equal weighting of FOMs and no equipment limitations, the optimal parameters were 90 kVp with 0.1 mm added copper filtration. The optimal technique in the radiographic units' operating range was 70 kVp and 0.1 mm added copper filtration, resulting in a ∼50% (±17%) entrance dose and ∼40% effective dose savings.

Improved diagnosis of pulmonary emphysema using in vivo dark-field radiography

OBJECTIVES

The purpose of this study was to assess whether the recently developed method of grating-based x-ray dark-field radiography can improve the diagnosis of pulmonary emphysema in vivo.

MATERIALS AND METHODS

Pulmonary emphysema was induced in female C57BL/6N mice using endotracheal instillation of porcine pancreatic elastase and confirmed by in vivo pulmonary function tests, histopathology, and quantitative morphometry. The mice were anesthetized but breathing freely during imaging. Experiments were performed using a prototype small-animal x-ray dark-field scanner that was operated at 35 kilovolt (peak) with an exposure time of 5 seconds for each of the 10 grating steps. Images were compared visually. For quantitative comparison of signal characteristics, regions of interest were placed in the upper, middle, and lower zones of each lung. Receiver-operating-characteristic statistics were performed to compare the effectiveness of transmission and dark-field signal intensities and the combined parameter "normalized scatter" to differentiate between healthy and emphysematous lungs.

RESULTS

A clear visual difference between healthy and emphysematous mice was found for the dark-field images. Quantitative measurements of x-ray dark-field signal and normalized scatter were significantly different between the mice with pulmonary emphysema and the control mice and showed good agreement with pulmonary function tests and quantitative histology. The normalized scatter showed a significantly higher discriminatory power (area under the receiver-operating-characteristic curve [AUC], 0.99) than dark-field (AUC, 0.90; P = 0.01) or transmission signal (AUC, 0.69; P < 0.001) alone did, allowing for an excellent discrimination of healthy and emphysematous lung regions.

CONCLUSIONS

In a murine model, x-ray dark-field radiography is technically feasible in vivo and represents a substantial improvement over conventional transmission-based x-ray imaging for the diagnosis of pulmonary emphysema.

Single-shot Z(eff) dense plasma diagnostic through simultaneous refraction and attenuation measurements with a Talbot-Lau x-ray moiré deflectometer

The Talbot-Lau x-ray moiré deflectometer is a powerful plasma diagnostic capable of delivering simultaneous refraction and attenuation information through the accurate detection of x-ray phase shift and intensity. The diagnostic can provide the index of refraction n=1-δ+iβ of an object (dense plasma, for example) placed in the x-ray beam by independently measuring both δ and β, which are directly related to the electron density n(e) and the attenuation coefficient μ, respectively. Since δ and β depend on the effective atomic number Z(eff), a map can be obtained from the ratio between phase and absorption images acquired in a single shot. The Talbot-Lau x-ray moiré deflectometer and its corresponding data acquisition and processing are briefly described to illustrate how the above is achieved; Z(eff) values of test objects within the 4-12 range were obtained experimentally through simultaneous refraction and attenuation measurements. We show that Z(eff) mapping of objects does not require previous knowledge of sample length or shape. The determination of Z(eff) from refraction and attenuation measurements with moiré deflectometry could be of high interest to various domains of high energy density research, such as shocked materials and inertial confinement fusion experiments, as well as material science and nondestructive testing.

Quantitative imaging using high-energy X-ray phase-contrast CT with a 70 kVp polychromatic X-ray spectrum

Imaging of large and dense objects with grating-based X-ray phase-contrast computed tomography requires high X-ray photon energy and large fields of view. It has become increasingly possible due to the improvements in the grating manufacturing processes. Using a high-energy X-ray phase-contrast CT setup with a large (10 cm in diameter) analyzer grating and operated at an acceleration tube voltage of 70 kVp, we investigate the complementarity of both attenuation and phase contrast modalities with materials of various atomic numbers (Z). We confirm experimentally that for low-Z materials, phase contrast yields no additional information content over attenuation images, yet it provides increased contrast-to-noise ratios (CNRs). The complementarity of both signals can be seen again with increasing Z of the materials and a more comprehensive material characterization is thus possible. Imaging of a part of a human cervical spine with intervertebral discs surrounded by bones and various soft tissue types showcases the benefit of high-energy X-ray phase-contrast system. Phase-contrast reconstruction reveals the internal structure of the discs and makes the boundary between the disc annulus and nucleus pulposus visible. Despite the fact that it still remains challenging to develop a high-energy grating interferometer with a broad polychromatic source with satisfactory optical performance, improved image quality for phase contrast as compared to attenuation contrast can be obtained and new exciting applications foreseen.

Large-angle x-ray scatter in Talbot-Lau interferometry for breast imaging

Monte Carlo simulations were used to investigate large-angle x-ray scatter at design energy of 25 keV during small field of view (9.6 cm × 5 cm) differential phase contrast imaging of the breast using Talbot-Lau interferometry. Homogenous, adipose and fibroglandular breasts of uniform thickness ranging from 2 to 8 cm encompassing the field of view were modeled. Theoretically determined transmission efficiencies of the gratings were used to validate the Monte Carlo simulations, followed by simulations to determine the x-ray scatter reaching the detector. The recorded x-ray scatter was classified into x-ray photons that underwent at least one Compton interaction (incoherent scatter) and Rayleigh interaction alone (coherent scatter) for further analysis. Monte Carlo based estimates of transmission efficiencies showed good correspondence [Formula: see text] with theoretical estimates. Scatter-to-primary ratio increased with increasing breast thickness, ranging from 0.11 to 0.22 for 2-8 cm thick adipose breasts and from 0.12 to 0.28 for 2-8 cm thick fibroglandular breasts. The analyzer grating reduced incoherent scatter by ~18% for 2 cm thick adipose breast and by ~35% for 8 cm thick fibroglandular breast. Coherent scatter was the dominant contributor to the total scatter. Coherent-to-incoherent scatter ratio ranged from 2.2 to 3.1 for 2-8 cm thick adipose breasts and from 2.7 to 3.4 for 2-8 cm thick fibroglandular breasts.

Complex dark-field contrast and its retrieval in x-ray phase contrast imaging implemented with Talbot interferometry

PURPOSE

Under the existing theoretical framework of x-ray phase contrast imaging methods implemented with Talbot interferometry, the dark-field contrast refers to the reduction in interference fringe visibility due to small-angle x-ray scattering of the subpixel microstructures of an object to be imaged. This study investigates how an object's subpixel microstructures can also affect the phase of the intensity oscillations.

METHODS

Instead of assuming that the object's subpixel microstructures distribute in space randomly, the authors' theoretical derivation starts by assuming that an object's attenuation projection and phase shift vary at a characteristic size that is not smaller than the period of analyzer grating G₂ and a characteristic length dc. Based on the paraxial Fresnel-Kirchhoff theory, the analytic formulae to characterize the zeroth- and first-order Fourier coefficients of the x-ray irradiance recorded at each detector cell are derived. Then the concept of complex dark-field contrast is introduced to quantify the influence of the object's microstructures on both the interference fringe visibility and the phase of intensity oscillations. A method based on the phase-attenuation duality that holds for soft tissues and high x-ray energies is proposed to retrieve the imaginary part of the complex dark-field contrast for imaging. Through computer simulation study with a specially designed numerical phantom, they evaluate and validate the derived analytic formulae and the proposed retrieval method.

RESULTS

Both theoretical analysis and computer simulation study show that the effect of an object's subpixel microstructures on x-ray phase contrast imaging method implemented with Talbot interferometry can be fully characterized by a complex dark-field contrast. The imaginary part of complex dark-field contrast quantifies the influence of the object's subpixel microstructures on the phase of intensity oscillations. Furthermore, at relatively high energies, for soft tissues it can be retrieved for imaging with a method based on the phase-attenuation duality.

CONCLUSIONS

The analytic formulae derived in this work to characterize the complex dark-field contrast in x-ray phase contrast imaging method implemented with Talbot interferometry are of significance, which may initiate more activities in the research and development of x-ray differential phase contrast imaging for extensive biomedical applications.

FMT-PCCT: hybrid fluorescence molecular tomography-x-ray phase-contrast CT imaging of mouse models

The implementation of hybrid fluorescence molecular tomography (FMT) and X-ray computed tomography (CT) has been shown to be a necessary development, not only for combining anatomical with functional and molecular contrast, but also for generating optical images of high accuracy. FMT affords highly sensitive 3-D imaging of fluorescence bio-distribution, but in stand-alone form it offers images of low resolution. It was shown that FMT accuracy significantly improves by considering anatomical priors from CT. Conversely, CT generally suffers from low soft tissue contrast. Therefore utilization of CT data as prior information in FMT inversion is challenging when different internal organs are not clearly differentiated. Instead, we combined herein FMT with emerging X-ray phase-contrast CT (PCCT). PCCT relies on phase shift differences in tissue to achieve soft tissue contrast superior to conventional CT. We demonstrate for the first time FMT-PCCT imaging of different animal models, where FMT and PCCT scans were performed in vivo and ex vivo, respectively. The results show that FMT-PCCT expands the potential of FMT in imaging lesions with otherwise low or no CT contrast, while retaining the cost benefits of CT and simplicity of hybrid device realizations. The results point to the most accurate FMT performance to date.

X-ray phase-contrast imaging at 100 keV on a conventional source

X-ray grating interferometry is a promising imaging technique sensitive to attenuation, refraction and scattering of the radiation. Applications of this technique in the energy range between 80 and 150 keV pose severe technical challenges, and are still mostly unexplored. Phase-contrast X-ray imaging at such high energies is of relevant scientific and industrial interest, in particular for the investigation of strongly absorbing or thick materials as well as for medical imaging. Here we show the successful implementation of a Talbot-Lau interferometer operated at 100 keV using a conventional X-ray tube and a compact geometry, with a total length of 54 cm. We present the edge-on illumination of the gratings in order to overcome the current fabrication limits. Finally, the curved structures match the beam divergence and allow a large field of view on a short and efficient setup.

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 method's 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.

Phase-contrast CT: qualitative and quantitative evaluation of atherosclerotic carotid artery plaque

PURPOSE

To evaluate the potential of phase-contrast computed tomography (CT) for atherosclerotic plaque imaging in human carotid arteries in an experimental ex vivo study.

MATERIALS AND METHODS

The study was approved by the institutional review board, and informed consent was obtained from the patients' relatives. Seven postmortem human carotid artery specimens were imaged at a laboratory setup by using a conventional x-ray tube and grating interferometer. After histologic processing, phase-contrast imaging and histopathologic data were matched. Characteristics of the necrotic core (NC) covered by a fibrous cap (FC), intraplaque hemorrhage (IPH), and calcifications (CAs) were established, and sensitivity, specificity, and accuracy of phase-contrast CT for plaque detection and the potential for accurate quantification were assessed. The Cohen κ and Pearson correlation coefficient R were used to determine the agreement between phase-contrast imaging and histopathologic findings for plaque characterization and correlation of quantitative plaque measurements, respectively. A difference with a P value of less than .05 was considered significant.

RESULTS

Characteristic criteria were found in all analyzed plaque components. Applying these criteria, phase-contrast CT had a good sensitivity for the detection of the FC and NC, IPH, and CAs (all, >80%) and excellent specificity and accuracy (all, >90%), with good interreader agreement (κ ≥ 0.72, P < .0001). There were excellent correlations for quantitative measurements of FC, NC, and CAs between phase-contrast imaging and histopathologic findings (R ≥ 0.92). Interreader reproducibility was excellent, with an intraclass correlation coefficient of 0.98 or higher for all measurements.

CONCLUSION

The results of this study indicate that ex vivo phase-contrast CT can help identify and quantify atherosclerotic plaque components, with excellent correlation to histopathologic findings. Although not yet applicable in vivo, phase-contrast CT may become a valuable tool to monitor atherosclerotic disease process noninvasively.

Imaging liver lesions using grating-based phase-contrast computed tomography with bi-lateral filter post-processing

X-ray phase-contrast imaging shows improved soft-tissue contrast compared to standard absorption-based X-ray imaging. Especially the grating-based method seems to be one promising candidate for clinical implementation due to its extendibility to standard laboratory X-ray sources. Therefore the purpose of our study was to evaluate the potential of grating-based phase-contrast computed tomography in combination with a novel bi-lateral denoising method for imaging of focal liver lesions in an ex vivo feasibility study. Our study shows that grating-based phase-contrast CT (PCCT) significantly increases the soft-tissue contrast in the ex vivo liver specimens. Combining the information of both signals – absorption and phase-contrast – the bi-lateral filtering leads to an improvement of lesion detectability and higher contrast-to-noise ratios. The normal and the pathological tissue can be clearly delineated and even internal structures of the pathological tissue can be visualized, being invisible in the absorption-based CT alone. Histopathology confirmed the presence of the corresponding findings in the analyzed tissue. The results give strong evidence for a sufficiently high contrast for different liver lesions using non-contrast-enhanced PCCT. Thus, ex vivo imaging of liver lesions is possible with a polychromatic X-ray source and at a spatial resolution of ∼100 µm. The post-processing with the novel bi-lateral denoising method improves the image quality by combining the information from the absorption and the phase-contrast images.

Evaluation of phase-contrast CT of breast tissue at conventional X-ray sources - presentation of selected findings

BACKGROUND

Grating-based phase contrast computed tomography (PC-CT) at synchrotron radiation sources has been shown to provide improved visualization of breast tumors. However, broad clinical application of phase-contrast imaging will likely depend on transferring the technology to standard polychromatic X-ray sources. On the basis of selected findings, we demonstrate the potential of grating-based PC-CT using a conventional X-ray source.

MATERIALS AND METHODS

Grating-based PC-CT of two ex-vivo formalin fixed breast specimens containing lobular carcinoma was conducted using a Talbot Lau interferometer run at a polychromatic X-ray source of 40kVp. Phase-contrast and absorption-based 3D-datasets of both specimens were simultaneously recorded. Radiological images were manually matched with corresponding histological sections. The visualization of selected histological findings in phase contrast was compared to absorption contrast.

RESULTS

Grating-based PC-CT was able to depict the 3-dimensional structure of dilated ducts and high phase contrast was found as a correlate to thickened fibrous ductal walls. Differences in contrast between fibrous and less fibrous breast tissue were observed in phase- but not in absorption-contrast images. Furthermore, regions of low phase contrast correlated with the extension of compact tumor components.

CONCLUSIONS

On the basis of selected findings, we show that grating-based PC-CT at a polychromatic X-ray source provides complementary information to conventional absorption contrast; albeit at lower spatial resolution than synchrotron-based imaging.