This presentation introduces an x-ray scattering tensor tomography (XSTT) approach tailored to rapidly explore embedded micro-scale structures within composite materials on a centimeter scale. Thanks to advancements in rapid data acquisition and sophisticated reconstruction algorithm, this technique is extremely efficient for centimeter-scale studies of industrially significant fiber-reinforced composites (FRC). The integration of finite element method (FEM) simulations with XSTT data showcases its potential as an efficient tool for computer-aided engineering of FRCs. In addition to the time-steady characterization of FRCs, our pioneering work in tracking time-resolved deformations within viscous fluids containing micro-scale fibers also creates new opportunities for advancing rheological studies. These methodological advancements significantly impact material characterization, offering new perspectives and expanding possibilities in material science, engineering, and practical industrial applications.
Breast cancer is the most common malignancy in women. Unfortunately, even though screening programs have helped to increase survival rates, the number of false positives and false negatives remains high. Phase-contrast X-ray CT is a promising imaging technique which could improve breast cancer diagnosis by combining the high three-dimensional resolution of conventional CT with higher soft-tissue contrast. Grating Interferometry CT (GI-CT) arguably has the highest chance to make the transition to clinical practice. Unfortunately though, obtaining high-quality images is challenging. Grating fabrication defects and photon starvation lead to high noise amplitudes in the measured data. Moreover, the highly ill-conditioned differential nature of the GI-CT forward operator renders the inversion from corrupted data even more cumbersome. In this article we report on a novel regularized iterative reconstruction algorithm with a powerful data-driven regularization strategy to tackle this challenging inverse problem. In particular, we present an algorithm that combines the L-BFGS optimization scheme with a Plug-and-Play denoiser parameterized by a deep neural network and empirically show that the proposed method achieves high quality images, both on simulated data as well as on real measurements.
Transmission microscopes have become a valuable tool for hard X-ray imaging. They allow even complex in situ and operando setups to be realized. However, the objective lens, typically a Fresnel zone plate with a high numerical aperture, is commonly a limiting factor. The small working distance as well as the low efficiency of Fresnel zone plates with high numerical apertures restrict setups either to accommodate specific sample environments or to provide high resolution. Lensless imaging techniques, e.g. ptychography, do not suffer from such adverse effects of Fresnel zone plates. Consequently, they are frequently used for high-resolution X-ray imaging. A recently developed method, X-ray Fourier ptychography aims to combine the benefits of both techniques. It has been shown to provide quantitative high-resolution imaging whilst keeping large working distances for in situ and operando setups. This is achieved by acquiring multiple images with a full-field transmission microscope, each at a different lateral position of the Fresnel zone plate. Moving the objective off the optical axis varies the frequency content for the acquisitions. The resulting dataset is numerically combined using well-established phase retrieval algorithms to recover a complex-valued representation of the sample. Here, we demonstrate how Fourier ptychographic phase retrieval can further be used to mitigate artifacts caused by samples that were placed out of focus, as well as misaligned optical elements. Employing a similar approach to increase the contrast in case of weakly absorbing specimens is also envisioned.
Grating-based phase contrast mammography can help facilitate breast cancer diagnosis, as several research works have demonstrated. To translate this technique to the clinics, it has to be adapted to cover a large field of view within a limited exposure time and with a clinically acceptable radiation dose. This indicates that a straightforward approach would be to install a grating interferometer (GI) into a commercial mammography device. We developed a wave propagation based optimization method to select the most convenient GI designs in terms of phase and dark-field sensitivities for the Philips Microdose Mammography (PMM) setup. The phase sensitivity was defined as the minimum detectable breast tissue electron density gradient, whereas the dark-field sensitivity was defined as its corresponding signal-to-noise Ratio (SNR). To be able to derive sample-dependent sensitivity metrics, a visibility reduction model for breast tissue was formulated, based on previous research works on the dark-field signal and utilizing available Ultra-Small-Angle X-ray Scattering (USAXS) data and the outcomes of measurements on formalin-fixed breast tissue specimens carried out in tube-based grating interferometers. The results of this optimization indicate the optimal scenarios for each metric are different and fundamentally depend on the noise behavior of the signals and the visibility reduction trend with respect to the system autocorrelation length. In addition, since the inter-grating distance is constrained by the space available between the breast support and the detector, the best way we have to improve sensitivity is to count on a small G2 pitch.
Despite the fact that the resolution of conventional contact/proximity lithography can reach feature sizes down to ~0.5- 0.6 micrometers, the accurate control of the linewidth and uniformity becomes already very challenging for gratings with periods in the range of 1-2 μm. This is particularly relevant for the exposure of large areas and wafers thinner than 300 μm. If the wafer or mask surface is not fully flat due to any kind of defects, such as bowing/warpage or remaining topography of the surface in case of overlay exposures, noticeable linewidth variations or complete failure of lithography step will occur. We utilized the newly developed Displacement Talbot lithography to pattern gratings with equal lines and spaces and periods in the range of 1.0 to 2.4 μm. The exposures in this lithography process do not require contact between the mask and the wafer, which makes it essentially insensitive to surface planarity and enables exposures with very high linewidth uniformity on thin and even slightly deformed wafers. We demonstrated pattern transfer of such exposures into Si substrates by reactive ion etching using the Bosch process. An etching depth of 30 μm or more for the whole range of periods was achieved, which corresponds to very high aspect ratios up to 60:1. The application of the fabricated gratings in phase contrast x-ray imaging is presented.
A theoretical description of the performance of a Talbot and Talbot-Lau type interferometers is developed,
providing a framework for the optimization of the geometry for monochromatic and polychromatic beams.
Analytical formulas for the smallest detectable refraction angle and the visibility of the setup are derived.
The polychromatic visibility of the interference fringes is particularly relevant for the design of setups with
conventional X-ray tubes, and it is described in terms of the spectrum of the source and the type of beamsplitter
grating. We show the practical realization of such a design by imaging a metallic screw at 100 keV.
KEYWORDS: Absorption, Sensors, X-ray imaging, Monte Carlo methods, X-rays, Signal to noise ratio, Positron emission tomography, Breast, Tissues, Wave propagation
X-ray phase-contrast imaging has been developed as an alternative to conventional absorption imaging, partly for its
dose advantage over absorption imaging at high resolution. Grating-based imaging (GBI) and propagation-based
imaging (PBI) are two phase-contrast techniques used with polychromatic laboratory sources. We compare the two
methods by experiments and simulations with respect to required dose. A simulation method based on the projection
approximation is designed and verified with experiments. A comparison based on simulations of the doses required for
detection of an object with respect to its diameter is presented, showing that for monochromatic radiation, there is a dose
advantage for PBI for small features but an advantage for GBI at larger features. However, GBI suffers more from the
introduction of polychromatic radiation, in this case so much that PBI gives lower dose for all investigated feature sizes.
Furthermore, we present and compare experimental images of biomedical samples. While those support the dose
advantage of PBI, they also highlight the GBI advantage of quantitative reconstruction of multimaterial samples. For all
experiments a liquid-metal-jet source was used. Liquid-metal-jet sources are a promising option for laboratory-based
phase-contrast imaging due to the relatively high brightness and small spot size.
Today’s commercial X-ray micro computed tomography (CT) specimen systems are based on microfocus sources,
2D pixel array cameras and short source-to-detector distances (i.e. cone-beam configurations). High resolution
is achieved by means of geometric magnification. The further development of such devices to acquire phase and
scattering contrast images can dramatically enhance their range of applications. Due to the compact geometries,
which imply a highly diverging beam, the gratings must be curved to maintain highest imaging performance
over a large field of view. We report about the implementation of extremely compact Talbot and Talbot-
Lau type grating interferometers which are compatible to the geometry of typical micro CT systems. For the
analytical description of the imaging system, formulas are presented describing the dependency of the sensitivity
on geometric parameters, camera and source parameters. Further, the imaging pipeline consisting of the data
acquisition protocol, radiographic phase retrieval and tomographic image reconstruction is illustrated. The
reported methods open the way for an immediate integration of phase and scattering contrast imaging on table
top X-ray micro CT scanners.
Dark-field imaging has the potential to overcome limitations in computed tomography (CT) investigating relatively
weakly absorbing material. However, an object-position dependence of the visibility loss in dark-field
imaging is observed. This effect might be negligible for small objects, but, for acquisition geometries using fanangle
apertures and field of views as those in human CT scanners, the object-position dependence of visibility
loss has to be taken into consideration if the scattering structure within the object is in the range of the grating
periods, i.e. micrometer. This work examines the effect of object-position dependent visibility loss in dark-field
imaging experimentally, investigates its consequences and presents an algorithm which solves the corresponding
reconstruction problem.
X-ray phase contrast imaging (PCI) can provide high sensitivity of weakly absorbing low-Z objects in medical and biological fields, especially in mammography. Grating-based differential phase contrast (DPC) method is the most potential PCI method for clinic applications because it can works well with conventional X-ray tube and it can retrieve attenuation, DPC and dark-field information of the samples in a single scanning. Three kinds of information have different details and contrast which represent different physical characteristics of X-rays with matters. Hence, image fusion can show the most desirable characteristics of each image. In this paper, we proposed a multi-scale image fusion for X-ray grating-based DPC mammography. Firstly, non-local means method is adopted for denoising due to the strong noise, especially for DPC and dark-field images. Then, Laplacian pyramid is used for multi-scale image fusion. The principal component analysis (PCA) method is used on the high frequency part and the spatial frequency method is used on the low frequency part. Finally, the fused image is obtained by inverse Laplacian pyramid transform. Our algorithm is validated by experiments. The experiments were performed on mammoDPC instrumentation at the Paul Scherrer Institut in Villigen, Switzerland. The results show that our algorithm can significantly show the advantages of three kinds of information in the fused image, which is very helpful for the breast cancer diagnosis.
Differential phase-contrast imaging in the x-ray domain provides three physically complementary signals:1, 2 the
attenuation, the differential phase-contrast, related to the refractive index, and the dark-field signal, strongly
influenced by the total amount of radiation scattered into very small angles. In medical applications, it is of
the utmost importance to present to the radiologist all clinically relevant information in as compact a way as
possible. Hence, the need arises for a method to combine two or more of the above mentioned signals into
one image containing all information relevant for diagnosis. We present an image composition algorithm that
fuses the attenuation image and the differential phase contrast image into a composite, final image based on the
assumption that the real and imaginary part of the complex refractive index of the sample can be related by a
constant scaling factor. The merging is performed in such a way that the composite image is characterized by
minimal noise-power at each frequency component.
A new imaging setup, aimed to perform differential X-ray phase contrast (DPC) imaging with a Talbot interferometer
on a microfocus X-ray tube, is demonstrated. The main features compared to recently proposed setups
are an extremely short source to detector distance, high spatial resolution and a large field of view. The setup
is designed for an immediate integration into a industrial micro CT scanner. In this paper, technical challenges
of a compact setup, namely the critical source coherence and divergence, are discussed. A theoretical analysis
using wave optics based computer simulations is performed to estimate the DPC signal visibility and the size
of the field of view for a given setup geometry. The maximization of the signal visibility as a function of the
inter-grating distance yields the optimal grating parameters. Imaging results using the optimized grating parameters
are presented. The reduction of the field of view, being a consequence of the high beam divergence,
was solved by fabricating new, cylindrically bent diffraction gratings. The fabrication process of these gratings
required a change of the currently used wafer materials and an adaption of the manufacturing techniques. The
implementation of the new setup represents a major step forward for the industrial application of the DPC
technique.
In this manuscript, we present the design and realization of a Fourier-Domain Spectroscopic-OCT system with a
simple spectrometer, based on off-the-shelf parts and a low-cost, state-of-the-art broadband S-LED light source
with three spectrally shifted S-LED modules. Depth resolved spectral absorption measurements in the wavelength
range from 750 nm to 850 nm are demonstrated using an expansion of OCT called spectroscopic OCT
(SOCT). The realized setup was tested and evaluated towards its ability to measure physical parameters such
as blood oxygen saturation quantitatively in vivo. Different sample configurations including multilayer setups
and scattering layers were used. Additionally, we present the theoretical model and experimental verification of
interferences between autocorrelation terms and the signal carrying crosscorrelation terms, strongly affecting the
absorption measurements. A simple background subtraction, minimizing the artifacts caused by the interferences
of autocorrelation and crosscorrelation terms is presented and verified.
Nowadays, thanks to the high brilliance available at modern, third generation synchrotron facilities and recent
developments in detector technology, it is possible to record volumetric information at the micrometer scale within few
minutes. High signal-to-noise ratio, quantitative information on very complex structures like the brain micro vessel
architecture, lung airways or fuel cells can be obtained thanks to the combination of dedicated sample preparation
protocols, in-situ acquisition schemes and cutting-edge imaging analysis instruments. In this work we report on recent
experiments carried out at the TOMCAT beamline of the Swiss Light Source [1] where synchrotron-based tomographic
microscopy has been successfully used to obtain fundamental information on preliminary models for cerebral fluid flow
[2], to provide an accurate mesh for 3D finite-element simulation of the alveolar structure of the pulmonary acinus [3]
and to investigate the complex functional mechanism of fuel cells [4]. Further, we introduce preliminary results on the
combination of absorption and phase contrast microscopy for the visualization of high-Z nanoparticles in soft tissues, a
fundamental information when designing modern drug delivery systems [5]. As an outlook we briefly discuss the new
possibilities offered by high sensitivity, high resolution grating interferomtery as well as Zernike Phase contrast
nanotomography [6].
Highly brilliant X-rays delivered by third generation synchrotron facilities coupled with modern detector technology
permit routinely acquisition of high resolution tomograms in few minutes, making high throughput experiments a reality
and bringing real-time tomography closer. New solutions for fast post-processing of such large amount of data are
mandatory to fully exploit advantages provided by the high acquisition speed enabling new experiments until recently
even unimaginable.
The TOMCAT beamline1 is well equipped for fast and high throughput experiments2, 3. Here, we will focus on our
solutions regarding the reconstruction process and discuss a fast reconstruction algorithm4, based on the Fourier
Transform method as opposed to slower standard Filtered Back-Projection routines. We perform the critical step of such
method, the polar-to-Cartesian mapping in the Fourier space, by convolution with the Fourier transform of functions with
particular characteristics. This convolution approach combines speed with accuracy, making real-time data postprocessing
closer to reality.
This fast reconstruction algorithm implemented at TOMCAT also features several plug-ins, aimed at taming
reconstruction artifacts. Here, we will discuss a new approach for removing rings from reconstructed datasets arising
from defective detector pixels and/or damaged scintillator screens. This new method is based on a combined wavelet-
FFT decomposition5. Another important feature of the presented reconstruction algorithm deals with local tomographic
datasets, characterized by incomplete data. We show here that ad-hoc padding of the sinograms prior to reconstruction
significantly reduces typical artifacts related to data incompleteness, making local tomography a valuable acquisition
mode when small volumes in relatively large samples are of interest.
Synchrotron-based X-ray Tomographic Microscopy is a powerful technique for fast, non-destructive, high resolution quantitative volumetric investigations on diverse samples. At the TOMCAT (TOmographic Microscopy and Coherent radiology experimenTs) beamline at the Swiss Light Source (SLS), synchrotron light is delivered by a 2.9 T superbend. The main optical component, a Double Crystal Multilayer Monochromator, covers an energy range between 8 and 45
keV. The standard TOMCAT detector offers field of views ranging from 0.75x0.75 mm2 up to 12.1x12.1mm2 with a theoretical resolution of 0.37 μm and 5.92 μm, respectively. The beamline design and flexible endstation setup make a large range of investigations possible. In addition to routine measurements, which exploit the absorption contrast, the high coherence of the source also enables phase contrast tomography, implemented with two complementary techniques. Differential Phase Contrast (DPC) imaging has been fully integrated in terms of fast acquisition and data reconstruction. Scans of samples within an aqueous environment are also feasible. The second phase contrast method is a Modified Transport of Intensity approach that yields a good approximation of the 3D phase distribution of a weakly absorbing object from a single tomographic dataset. Typical acquisition times for a tomogram are in the order of few minutes, ensuring high throughput and allowing for semi-dynamical investigations and in-situ experiments. Raw data are automatically post-processed online and full reconstructed volumes are available shortly after a scan with minimal user intervention. In addition to a beamline overview, a selection of high-impact tomographic applications will be presented.
Over the last decade, synchrotron-based X-ray tomographic microscopy has established itself as a fundamental tool for non-invasive, quantitative investigations of a broad variety of samples, with application ranging from space research and materials science to biology and medicine. Thanks to the brilliance of modern third generation sources, voxel sizes in the micrometer range are routinely achieved by the major X-ray microtomography devices around the world, while the isotropic 100 nm barrier is reached and trespassed only by few instruments. The beamline for TOmographic Microscopy and Coherent rAdiology experiments (TOMCAT) of the Swiss Light Source at the Paul Scherrer Institut, operates a multimodal endstation which offers tomographic capabilities in the micrometer range in absorption contrast - of course - as well as phase contrast imaging. Recently, the beamline has been equipped with a full field, hard X-rays microscope with a theoretical pixel size down to 30 nm and a field of view of 50 microns. The nanoscope performs well at X-ray
energies between 8 and 12 keV, selected from the white beam of a 2.9 T superbend by a [Ru/C]100 fixed exit multilayer monochromator. In this work we illustrate the experimental setup dedicated to the nanoscope, in particular the ad-hoc designed X-ray optics needed to produce a homogeneous, square illumination of the sample imaging plane as well as the magnifying zone plate. Tomographic reconstructions at 60 nm voxel size will be shown and discussed.
Recent data have shown that predicting bone strength can be greatly improved by including microarchitectural
parameters in the analysis. Moreover, bone ultrastructure has been implicated as an important contributor to bone
strength. We therefore hypothesized that a better understanding of phenotypes linked to bone ultrastructure will provide
new insight in the assessment of bone quality and its contribution to bone strength and fracture risk. Therefore, we first
developed an experimental design to assess quantitatively ultrastructural murine bone tissue properties non-invasively in
three dimensions by using synchrotron radiation-based (SR) computed tomography (CT) methods with resolutions on the
order of one micrometer and below. New morphometric indices were introduced to quantify ultrastructural phenotypes of
murine cortical bone assessed by our SR CT-based setup, namely the canal network and the osteocyte lacunar system.
These ultrastructural phenotypes were then successfully studied in two genetically distinct mouse strains. Finally, we
provided strong evidence for a significant influence of the canal network on murine bone mechanics. In the long run, we
believe that the morphometric analysis of the ultrastructural phenotypes and the study of bone phenotypes at different
hierarchy levels, in conjunction with bone mechanics, will provide new insights in the assessment of bone quality.
Vascular factors associated with Alzheimer's disease (AD) have recently gained increased attention. To investigate changes in vascular, particularly microvascular architecture, we developed a hierarchical imaging framework to obtain large-volume, high-resolution 3D images from brains of transgenic mice modeling AD. In this paper, we present imaging and data analysis methods which allow compiling unique characteristics from several hundred gigabytes of image data. Image acquisition is based on desktop micro-computed tomography (µCT) and local synchrotron-radiation µCT (SRµCT) scanning with a nominal voxel size of 16 µm and 1.4 µm, respectively. Two visualization approaches were implemented: stacks of Z-buffer projections for fast data browsing, and progressive-mesh based surface rendering for detailed 3D visualization of the large datasets. In a first step, image data was assessed visually via a Java client connected to a central database. Identified characteristics of interest were subsequently quantified using global morphometry software. To obtain even deeper insight into microvascular alterations, tree analysis software was developed providing local morphometric parameters such as number of vessel segments or vessel tortuosity. In the context of ever increasing image resolution and large datasets, computer-aided analysis has proven both powerful and indispensable. The hierarchical approach maintains the context of local phenomena, while proper visualization and morphometry provide the basis for detailed analysis of the pathology related to structure. Beyond analysis of microvascular changes in AD this framework will have significant impact considering that vascular changes are involved in other neurodegenerative diseases as well as in cancer, cardiovascular disease, asthma, and arthritis.
To describe the different aspects of bone quality, we follow a hierarchical approach and assess bone tissue properties in different regimes of spatial resolution, beginning at the organ level and going down to cellular dimensions. For these purposes we developed different synchrotron radiation (SR) based computed-tomography (CT) methods to assess murine bone ultrastructure. In a first step, a tubular system and the osteocyte lacunar system within murine cortical bone have been established as novel ultrastructural quantitative traits. Results in two mouse strains showed that morphometry of these quantitative traits was dependent on strain and partially on gender, and that their scaling behavior with bone size was fundamentally different. In a second step, we explored bone competence on an ultrastructural level and related our findings to the two ultrastructural quantitative traits introduced before. We showed that SR CT imaging is a powerful tool to investigate the initiation and propagation of microcracks, which may alter bone quality and may lead to increased fracture risk by means of microdamage accumulation. In summary, investigation of ultrastructural bone tissue properties will eventually lead to a better understanding of bone quality and its relative contribution to bone competence.
M. Stampanoni, A. Groso, A. Isenegger, G. Mikuljan, Q. Chen, A. Bertrand, S. Henein, R. Betemps, U. Frommherz, P. Böhler, D. Meister, M. Lange, R. Abela
Synchrotron-based X-ray Tomographic Microscopy (SRXTM) is nowadays a powerful technique for non-destructive,
high-resolution investigations of a broad kind of materials. High-brilliance and high-coherence third generation
synchrotron radiation facilities allow micrometer and sub-micrometer, quantitative, three-dimensional
imaging within very short time and extend the traditional absorption imaging technique to edge-enhanced
and phase-sensitive measurements. At the Swiss Light Source TOMCAT, a new beamline for TOmographic Microscopy and Coherent rAdiology experimenTs, has been recently built and started regular user operation in
June 2006. The new beamline get photons from a 2.9 T superbend with a critical energy of 11.1 keV. This makes
energies above 20 keV easily accessible. To guarantee the best beam quality (stability and homogeneity), the
number of optical elements has been kept to a minimum. A Double Crystal Multilayer Monochromator (DCMM)
covers an energy range between 8 and 45 keV with a bandwidth of a few percent down to 10-4. The beamline
can also be operated in white-beam mode, providing the ideal conditions for real-time coherent radiology. This
article presents the beamline design, its optical components and the endstation. It further illustrates two recently
developed phase contrast techniques and finally gives an overview of recent research topics which make intense
use of SRXTM.
Biomechanical testing is the gold standard to determine bone competence, and has been used extensively. Direct mechanical testing provides detailed information on overall bone mechanical and material properties, but fails in revealing local properties such as local deformations and strains or quantification of fracture progression. Therefore, we incorporated several imaging methods in our mechanical setups in order to get a better insight into bone deformation and failure characteristics. Our aim was to develop an integrative approach for hierarchical investigation of bone, working at different scales of resolution ranging from the whole bone to its ultrastructure. At a macroscopic level, we used high-resolution and high-speed cameras which drastically increased the amount of information obtained from a biomechanical bone test. The new image data proved especially important when dealing with very small bones such as the murine femur. Here the feedback of the camera in the process of aligning and positioning the samples is indispensable for reproducibility. In addition, global failure behavior and fracture initiation can now be visualized with high temporal resolution. At a microscopic level, bone microstructure, i.e. trabecular architecture and cortical porosity, are known to influence bone strength and failure mechanisms significantly. For this reason, we developed an image-guided failure assessment technique, also referred to as functional microimaging, allowing direct time-lapsed 3D visualization and computation of local displacements and strains for better quantification of fracture initiation and progression at the microscopic level. While the resolution of typical desktop micro-computed tomography is around a few micrometers, highly brilliant X-rays from synchrotron radiation permit to explore the nanometer world. This allowed, for the first time, to uncover fully nondestructively the 3D ultrastructure of bone including vascular and cellular structures and to investigate their role in development of bone microcracks in an unprecedented resolution. We conclude that functional microimaging, i.e. the combination of biomechanical testing with non-destructive 3D imaging and visualization are extremely valuable in studying bone failure mechanisms. Functional investigation of microcrack initiation and propagation will lead to a better understanding of the relative contribution of bone mass and bone quality to bone competence.
A wide range of disorders are associated with alterations of the central and peripheral vascular system. Modified vascular corrosion casting using a newly developed polymer, allows for the first time hierarchical assessment of 3D vessel data in animals down to the level of capillaries. Imaging of large volumes of vasculature at intermediate resolution (16 μm) was performed using a desktop micro-computed tomography system. Subsequently regions of interest were identified for additional high resolution imaging (1.4 μm) at the X-ray Tomographic Microscopy (XTM) station of the Swiss Light Source (SLS). A framework for systematic hierarchical imaging and quantification was developed. Issues addressed included enhanced XTM data acquisition, introduction of local tomography, sample navigation, advanced post processing, and data combination. In addition to visual assessment of qualitative changes, morphometrical and architectural indices were determined using direct 3D morphometry software developed in house. Vessel specific parameters included thickness, surface, connectivity, and vessel length. Reconstructions of cerebral vasculature in mutant mice modeling Alzheimer's disease revealed significant changes in vessel architecture and morphology. In the future, a combination of these techniques may support drug discovery. Additionally, future ultra-high-resolution in vivo systems may even allow non-invasive tracking of temporal alterations in vascular morphology.
State-of-the-art synchrotron-based microtomography devices have
nowadays to fulfill very stringent requirements in term of spatial
resolution, detection efficiency and data throughput. The most
used detection system is based on collecting the light produced by
a thin scintillation screen with microscope optics and conveying
it to a high-performance charge coupled device (CCD) camera. With
the chip-size of currently available CCDs installed at high
brilliance sources like the Swiss Light Source (SLS) raw data are
produced at rate of gigabyte/minute. It is crucial therefore to
provide the necessary infrastructure to be able to post-process
the data in real time, and provide to the user 3D information
immediately after the end of the scan. The visible-light-based
detection system is intrinsically limited by scintillation
properties, optical coupling and CCD granularity to a practical
limit of about 1 micron spatial resolution and efficiency of a few
percent. A novel detector, called Bragg magnifier, is one of the
techniques recently proposed to efficiently trespass the
micrometer barrier. It exploits two-dimensional asymmetric Bragg
diffraction from flat crystals to produce X-ray images with
magnification factors up to 150x150 and pixel sizes less than
100x100 nm2. The infrastructure devoted to microtomography
at the SLS is described, as well as some very promising
experiments. The layout of a novel, tomography dedicated beamline
is also presented.
In current biological and biomedical research, quantitative endpoints have become an important factor of success. Classically, such endpoints were investigated with 2D imaging, which is usually destructive and the 3D character of tissue gets lost. 3D imaging has gained in importance as a tool for both, qualitative and quantitative assessment of biological systems. In this context synchrotron radiation based tomography has become a very effective tool for opaque 3D tissue systems. Cell cultures and adherent scaffolds are visualized in 3D in a hydrated environment, even uncovering the shape of individual cells. Advanced morphometry allows to characterize the differences between the cell cultures of two distinct phenotypes. Moreover, a new device is presented enabling the 3D investigation of trabecular bone under mechanical load in a time-lapsed fashion. Using the highly brilliant X-rays from a synchrotron radiation source, bone microcracks and an indication for un-cracked ligament bridging are uncovered. 3D microcrack analysis proves that the classification of microcracks from 2D images is ambiguous. Fatigued bone was found to fail in burst-like fashion, whereas non-fatigued bone exhibited a distinct failure band. Additionally, a higher increase in microcrack volume was detected in fatigued in comparison to non-fatigued bone. The developed technologies prove to be very effective tools for advanced 3D imaging of both hard and soft tissue.
We have developed a two-grating interferometer for hard X rays that
can be used for phase imaging and tomography. A silicon phase
grating positioned just downstream of the object under study splits
the distorted wavefront into essentially a positive and a negative
first-order beam. At a given distance from this beam-splitter grating, where the two beams still mostly overlap, they form a
pattern of interference fringes that is distorted according to the
wavefront distortions. The fringes may be finer than the resolution
of an area detector used to record the signal, but an absorption
grating with suitable pitch, put in front of the detection plane,
allows the detection of intensity variations that correspond to the
derivative of the wavefront phase taken along the direction perpendicular to the grating lines. A combination of this technique
with the phase-stepping method, in which several exposures are made
which differ in the phase of the fringe pattern, allows to eliminate
effects of non-uniform intensity due to inhomogeneous illumination
and edge-enhancing inline phase contrast. Several examples of
tomograms taken under different experimental conditions are shown,
including a polychromatic "pink-beam" setup.
We derive mathematical relations for hard X-ray moire wavefront analysis with a grating interferometer. In particular, the first derivative of the wavefront phase profile and the local radius of curvature of the wavefront are related to the position and inclination of the observed moiré fringes.
Recent results show that bone vasculature is a major contributor to local tissue porosity, and therefore can be directly linked to the mechanical properties of bone tissue. With the advent of third generation synchrotron radiation (SR) sources, micro-computed tomography (μCT) with resolutions in the order of 1 μm and better has become feasible. This technique has been employed frequently to analyze trabecular architecture and local bone tissue properties, i.e. the hard or mineralized bone tissue. Nevertheless, less is known about the soft tissues in bone, mainly due to inadequate imaging capabilities. Here, we discuss three different methods and applications to visualize soft tissues. The first approach is referred to as negative imaging. In this case the material around the soft tissue provides the absorption contrast necessary for X-ray based tomography. Bone vasculature from two different mouse strains was investigated and compared qualitatively. Differences were observed in terms of local vessel number and vessel orientation. The second technique represents corrosion casting, which is principally adapted for imaging of vascular systems. The technique of corrosion casting has already been applied successfully at the Swiss Light Source. Using the technology we were able to show that pathological features reminiscent of Alzheimer’s disease could be distinguished in the brain vasculature of APP transgenic mice. The third technique discussed here is phase contrast imaging exploiting the high degree of coherence of third generation synchrotron light sources, which provide the necessary physical conditions for phase contrast. The in-line approach followed here for phase contrast retrieval is a modification of the Gerchberg-Saxton-Fienup type. Several measurements and theoretical thoughts concerning phase contrast imaging are presented, including mathematical phase retrieval. Although up-to-now only phase images have been computed, the approach is now ready to retrieve the phase for a large number of angular positions of the specimen allowing application of holotomography, which is the three-dimensional reconstruction of phase images.
With the advent of high brilliance, third generation synchrotron
radiation sources, the spatial resolution of non-destructive X-ray
tomographic investigations can be scaled down to the micrometer or
even submicrometer range while the coherent nature of the
radiation extends the traditional absorption imaging techniques
towards edge-enhanced or phase-sensitive measurements. The
performance of the presently used detectors is limited by
scintillation properties, optical light coupling and charge
coupled device granularity which impose a practical limit of about
1 micrometer spatial resolution with efficiencies of a few
percent. We developed a detector called Bragg magnifier which
exploits double asymmetrical Bragg diffraction from flat crystals
to efficiently produce distortion- and aberrations-free X-ray
images with magnification factors up to 150x150 and pixel sizes of
less than 100x100nm2.
At the Material Science Beamline 4S of the Swiss Light Source (SLS), the X-ray Tomographic Microscopy (XTM) facility is entering its final construction phase. A high performance detector based on a scintillating screen optically coupled to a CCD camera has been developed and tested. MTF-responses of the detector system show spatial resolution down to the micrometer level. A second detector, which will provide a quantum jump in term of spatial resolution and efficiency, has been successfully simulated and will be integrated in the current device soon. A user- friendly graphical interface gives access to the main measurements parameters needed for a complete tomographic scan in absorption as well as in phase-contrast mode. The new instrumentation shall be used for the analysis of the physical structure and chemical composition of technical materials and biological samples, e.g. enabling non- destructive testing during the development of modern composite materials, or enabling pseudo-dynamic testing of bone samples to establish structure-function relationships in simulated osteoporosis.
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