两种微体化石三维无损成像技术的对比

近年来,各种X射线三维无损成像技术在古生物学领域的应用越来越广泛。但是,不同的X射线三维无损成像技术针对不同保存类型和尺寸的化石标本在成像效果上各有利弊。本文以埃迪卡拉纪陡山沱组磷酸盐化的动物胚胎化石为研究对象,将目前应用最广的两种X射线三维无损成像方法,即基于实验室X光源的吸收衬度显微断层成像技术和基于同步辐射光源的相位衬度显微断层成像技术进行了对比分析。通过对两种技术的原理、效率、空间分辨率和图像衬度的对比,认为基于同步辐射光源的相位衬度显微断层成像技术是目前对于均一矿化的微体化石最佳的三维无损成像解决方案。     

A single-image retrieval method for edge illumination X-ray phase-contrast imaging: Application and noise analysis

PurposeEdge illumination (EI) X-ray phase-contrast imaging (XPCI) has been under development at University College London in recent years, and has shown great potential for both laboratory and synchrotron applications. In this work, we propose a new acquisition and processing scheme. Contrary to existing retrieval methods for EI, which require as input two images acquired in different setup configurations, the proposed approach can retrieve an approximate map of the X-ray phase from a single image, thus significantly simplifying the acquisition procedure and reducing data collection times.MethodsThe retrieval method is analytically derived, based on the assumption of a quasi-homogeneous object, i.e. an object featuring a constant ratio between refractive index and absorption coefficient. The noise properties of the input and retrieved images are also theoretically analyzed under the developed formalism. The method is applied to experimental synchrotron images of a biological object.ResultsThe experimental results show that the method can provide high-quality images, where the “edge” signal typical of XPCI images is transformed to an “area” contrast that enables an easier interpretation of the sample geometry. Moreover, the retrieved images confirm that the method is highly stable against noise.ConclusionsWe anticipate that the developed approach will become the method of choice for a variety of applications of EI XPCI, thanks to its ability to simplify the acquisition procedure and reduce acquisitions time and dose to the sample. Future work will focus on the adaptation of the method to computed tomography and to polychromatic radiation from X-ray tubes.     

Ecdysis period of Rhodnius prolixus head investigated using phase contrast synchrotron microtomography

Microtomography using synchrotron sources is a useful tool in biological imaging research since the phase coherence of synchrotron beams can be exploited to obtain images with high contrast resolution. This work is part of a series of works using phase contrast synchrotron microtomography in the study of Rhodnius prolixus head, the insect vector of Chagas’ disease, responsible for about 12,000 deaths per year. The control of insect vector is the most efficient method to prevent this disease and studies have shown that the use of triflumuron, a chitin synthesis inhibitor, disrupted chitin synthesis during larval development and it’s an alternative method against insect pests.The aim of this work was to investigate the biological effects of treatments with triflumuron in the ecdysis period (the moulting of the R. prolixus cuticle) using the new imaging beamline IMX at LNLS (Brazilian Synchrotron Light Laboratory). Nymphs of R. prolixus were taken from the Laboratory of Biochemistry and Physiology of Insects, Oswaldo Cruz Foundation, Brazil. Doses of 0.05 mg of triflumuron were applied directly to the abdomen on half of the insects immediately after feeding. The insects were sacrificed 25 days after feeding (intermoulting period) and fixed with glutaraldehyde.The results obtained using phase contrast synchrotron microtomography in R. prolixus showed amazing images of the effects of triflumuron on insects in the ecdysis period, and the formation of the new cuticle on those which were not treated with triflumuron. Both formation and malformation of this insect’s cuticle have never been seen before with this technique.     

Spectroscopic imaging at compact inverse Compton X-ray sources

While K-edge subtraction (KES) imaging is a commonly applied technique at synchrotron sources, the application of this imaging method in clinical imaging is limited although results have shown its superiority to conventional clinical subtraction imaging. Over the past decades, compact synchrotron X-ray sources, based on inverse Compton scattering, have been developed to fill the gap between conventional X-ray tubes and synchrotron facilities. These so called inverse Compton sources (ICSs) provide a tunable, quasi-monochromatic X-ray beam in a laboratory setting with reduced spatial and financial requirements. This allows for the transfer of imaging techniques that have been limited to synchrotrons until now, like KES imaging, into a laboratory environment. This review article presents the first studies that have successfully performed KES at ICSs. These have shown that KES provides improved image quality in comparison to conventional X-ray imaging. The results indicate that medical imaging could benefit from monochromatic imaging and KES techniques. Currently, the clinical application of KES is limited by the low K-edge energy of available iodine contrast agents. However, several ICSs are under development or already in commissioning which will provide monochromatic X-ray beams with higher X-ray energies and will enable KES using high-Z elements as contrast media. With these developments, KES at an ICS has the ability to become an important tool in pre-clinical research and potentially advancing existing clinical imaging techniques.     

Dark-Field Imaging: Recent developments and potential clinical applications

This paper describes an X-ray phase contrast imaging technique using analyzer-based optics called X-ray Dark-Field Imaging that has been under development for the past 10 years. We describe the theory behind XDFI, the X-ray optics required for implementing it in practice, and algorithms used for 2D, 2.5D, and 3D image reconstruction. The XDFI optical chain consists of an asymmetrically cut, Bragg-type monochromator-collimator that provides a planar monochromatic X-ray beam, a positioning stage for the specimens, a Laue-case angle analyzer, and one or two cameras to capture the dark and bright field images. We demonstrate the soft-tissue discrimination capabilities of XDFI by reconstructing images with absorption and phase contrast. By using a variety of specimens such as breast tissue with cancer, joints with articular cartilage, ex-vivo human eye specimen, and others, we show that refraction-based contrast derived from XDFI is more effective in characterizing anatomical features, articular pathology, and neoplastic disease than conventional absorption-based images. For example, XDFI of breast tissue can discriminate between the normal and diseased terminal duct lobular unit, and between invasive and in-situ cancer. The final section of this paper is devoted to potential future developments to enable clinical and histo-pathological applications of this technique.     

X-ray phase imaging reaching clinical uses

X-ray phase imaging that uses the phenomena of X-ray refraction and scattering to generate image contrast has the potential to overcome the drawback of conventional X-ray radiography in observing biological soft tissues. After its dawn at synchrotron radiation facilities 30 years ago, the development of X-ray phase imaging is expanding to hospitals by grating-based phase-imaging approaches available with a conventional X-ray tube. In this review, after introducing the physical advantages and methodological details of X-ray phase imaging, recent trials of instrumentation in hospitals for diagnoses of rheumatoid arthritis and chronic obstructive pulmonary disease are introduced.     

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

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

Imaging cells and sub-cellular structures with ultrahigh resolution full-field X-ray microscopy

Our experimental results demonstrate that full-field hard-X-ray microscopy is finally able to investigate the internal structure of cells in tissues. This result was made possible by three main factors: the use of a coherent (synchrotron) source of X-rays, the exploitation of contrast mechanisms based on the real part of the refractive index and the magnification provided by high-resolution Fresnel zone-plate objectives. We specifically obtained high-quality microradiographs of human and mouse cells with 29 nm Rayleigh spatial resolution and verified that tomographic reconstruction could be implemented with a final resolution level suitable for subcellular features. We also demonstrated that a phase retrieval method based on a wave propagation algorithm could yield good subcellular images starting from a series of defocused microradiographs. The concluding discussion compares cellular and subcellular hard-X-ray microradiology with other techniques and evaluates its potential impact on biomedical research.     

多功能磁共振造影剂研究进展

磁共振成像技术因对人体无创、任意方向断层扫描三维图像且分辨率较高、提供形态与功能两方面诊断评价等突出优点,成为了临床上用于疾病诊断的重要手段之一。临床上使用磁共振造影剂可以提高成像的分辨率和灵敏度,提高图像质量,增强对比度和可读性。但是,各种成像技术由于实现原理不同,具有各自的优势和缺陷,靠传统单一的诊断模式无法提供疾病的全面信息,因而在对各种复杂疾病进行诊断时会受到一定的限制。因此,将磁共振成像与其他成像技术如CT成像、超声成像等联合起来使用,则可以达到优势互补的效果,能为疾病的临床诊断提供更快捷精确的信息,同时可将磁共振成像与各种治疗方式结合在一起,即开发基于磁共振成像的诊断治疗一体化试剂,以实现对疾病的即时治疗和实时监控。本文主要介绍了磁共振成像造影剂的原理和种类,并且综述了目前国内外在基于磁共振成像的多功能造影剂/诊疗制剂这一领域的研究进展,最后就未来可能的研究方向进行了展望。     

Focal plane array infrared imaging: a new way to analyse leaf tissue

* Here, a new approach to macromolecular imaging of leaf tissue using a multichannel focal plane array (FPA) infrared detector was compared with the proven method of infrared mapping with a synchrotron source, using transverse sections of leaves from a species of Eucalyptus. * A new histological method was developed, ideally suited to infrared spectroscopic analysis of leaf tissue. Spatial resolution and the signal-to-noise ratio of the FPA imaging and synchrotron mapping methods were compared. * An area of tissue 350 microm(2) required approx. 8 h to map using the synchrotron technique and approx. 2 min to image using the FPA. The two methods produced similar infrared images, which differentiated all tissue types in the leaves according to their macromolecular chemistry. * The synchrotron and FPA methods produced similar results, with the synchrotron method having superior signal-to-noise ratio and potentially better spatial resolution, whereas the FPA method had the advantage in terms of data acquisition time, expense and ease of use. FPA imaging offers a convenient, laboratory-based approach to microscopic chemical imaging of leaves.     

Imaging performance of phase-contrast breast computed tomography with synchrotron radiation and a CdTe photon-counting detector

PurposeWithin the SYRMA-CT collaboration based at the ELETTRA synchrotron radiation (SR) facility the authors investigated the imaging performance of the phase-contrast computed tomography (CT) system dedicated to monochromatic in vivo 3D imaging of the female breast, for breast cancer diagnosis.MethodsTest objects were imaged at 38 keV using monochromatic SR and a high-resolution CdTe photon-counting detector. Signal and noise performance were evaluated using modulation transfer function (MTF) and noise power spectrum. The analysis was performed on the images obtained with the application of a phase retrieval algorithm as well as on those obtained without phase retrieval. The contrast to noise ratio (CNR) and the capability of detecting test microcalcification clusters and soft masses were investigated.ResultsFor a voxel size of (60 μm)³, images without phase retrieval showed higher spatial resolution (6.7 mm⁻¹ at 10% MTF) than corresponding images with phase retrieval (2.5 mm⁻¹). Phase retrieval produced a reduction of the noise level and an increase of the CNR by more than one order of magnitude, compared to raw phase-contrast images. Microcalcifications with a diameter down to 130 μm could be detected in both types of images.ConclusionsThe investigation on test objects indicates that breast CT with a monochromatic SR source is technically feasible in terms of spatial resolution, image noise and contrast, for in vivo 3D imaging with a dose comparable to that of two-view mammography. Images obtained with the phase retrieval algorithm showed the best performance in the trade-off between spatial resolution and image noise.     

Monte-Carlo simulation of a slot-scanning X-ray imaging system

We present a method for simulating slot-scanning X-ray imaging using the general-purpose Monte Carlo simulation package PENELOPE and penEasy Imaging. Different phantoms can be defined with the PENGEOM package, which defines bodies as combinations of volumes limited by quadric surfaces. The source-detector geometry, the position of the object, the collimator, the X-ray tube properties, the detector material and the pixel dimensions are defined. The output of the time-delay integration detector is simulated using sequential slot outputs derived from penEasy Imaging. The simulations are validated using tungsten and aluminium test objects, which are both simulated and imaged. The simulations are compared to the X-ray images using standard image quality metrics. The MTF, NPS and DQE curves show that the real and simulated X-ray images are comparable in terms of spatial resolution, noise and frequency information. The implementation can be modified to suit alterations in the system being simulated.     

Single-shot phase contrast microscopy using polarisation-resolved differential phase contrast

We present a robust, low-cost single-shot implementation of differential phase microscopy utilising a polarisation-sensitive camera to simultaneously acquire four images from which phase contrast images can be calculated. This polarisation-resolved differential phase contrast (pDPC) microscopy technique can be easily integrated with fluorescence microscopy.     

Opportunities for biomineralization research using multiscale computed X-ray tomography as exemplified by bone imaging

Biominerals typically have complex hierarchical structures traversing many length scales. This makes their structural characterization complicated, since it requires 3D techniques that can probe full specimens at down to nanometer-resolution, a combination that is difficult – if not impossible – to achieve simultaneously. One challenging example is bone, a mineralized tissue with a highly complex architecture that is replete with a network of cells. X-ray computed tomography techniques enable multiscale structural characterization through the combination of various equipment and emerge as promising tools for characterizing biominerals. Using bone as an example, we discuss how combining different X-ray imaging instruments allow characterizing bone structures from the nano- to the organ-scale. In particular, we compare and contrast human and rodent bone, emphasize the importance of the osteocyte lacuno-canalicular network in bone, and finally illustrate how combining synchrotron X-ray imaging with laboratory instrumentation for computed tomography is especially helpful for multiscale characterization of biominerals.     

Detectability comparison of simulated tumors in digital breast tomosynthesis using high-energy X-ray inline phase sensitive and commercial imaging systems

This study compared the detectability of simulated tumors using a high-energy X-ray inline phase sensitive digital breast tomosynthesis (DBT) prototype and a commercial attenuation-based DBT system. Each system imaged a 5-cm thick modular breast phantom with 50–50 adipose-glandular percentage density containing contrast-detail (CD) test objects to simulate different tumor sizes. A commercial DBT system acquired 15 projection views over 15 degrees (15d-15p) was used to acquire the attenuation-based projection views and to reconstruct the conventional DBT slices. Attenuation-based projection views were acquired at 32 kV, 46 mAs with a mean glandular dose (D_g) of 1.6 mGy. For acquiring phase sensitive projection views, the prototype utilized two acquisition geometries: 11 projection views were acquired over 15 degrees (15d-11p), and 17 projection views were acquired over 16 degrees (16d-17p) at 120 kV, 5.27 mAs with 1.51 mGy under the magnification (M) of 2. A phase retrieval algorithm based on the phase-attenuation duality (PAD) was applied to each projection view, and a modified Feldkamp-Davis-Kress (FDK) algorithm was used to reconstruct the phase sensitive DBT slices. Simulated tumor margins were rated as more conspicuous and better visualized for both phase sensitive acquisition geometries versus conventional DBT imaging. The CD curves confirmed the improvement in both contrast and spatial resolutions with the phase sensitive DBT imaging. The superiority of the phase sensitive DBT imaging was further endorsed by higher contrast to noise ratio (CNR) and figure-of-merit (FOM) values. The CNR improvements provided by the phase sensitive DBT prototype were sufficient to offset the noise reduction provided by the attenuation-based DBT imaging.     

K-edge subtraction synchrotron X-ray imaging in bio-medical research

High contrast in X-ray medical imaging, while maintaining acceptable radiation dose levels to the patient, has long been a goal. One of the most promising methods is that of K-edge subtraction imaging. This technique, first advanced as long ago as 1953 by B. Jacobson, uses the large difference in the absorption coefficient of elements at energies above and below the K-edge. Two images, one taken above the edge and one below the edge, are subtracted leaving, ideally, only the image of the distribution of the target element. This paper reviews the development of the KES techniques and technology as applied to bio-medical imaging from the early low-power tube sources of X-rays to the latest high-power synchrotron sources. Applications to coronary angiography, functional lung imaging and bone growth are highlighted. A vision of possible imaging with new compact sources is presented.     

Near-infrared spectral imaging for quality assurance of pharmaceutical products: analysis of tablets to assess powder blend homogeneity

The objective of this study was to evaluate near-infrared (NIR) spectroscopic imaging as a tool to assess a pharmaceutical quality assurance problem—blend uniformity in the final dosage product. A system based on array detector technology was used to rapidly collect high-contrast NIR images of furosemide tablets. By varying the mixing, 5 grades of experimental tablets containing the same amount of furosemide and microcrystalline cellulose were produced, ranging from well blended to unblended. For comparison, these tablets were also analyzed by traditional NIR spectroscopy, and both approaches were used to evaluate drug product homogeneity. NIR spectral imaging was capable of clearly differentiating between each grade of blending, both qualitatively and quantitatively. The spatial distribution of the components was based on the variation or contrast in pixel intensity, which is due to the NIR spectral contribution to each pixel. The chemical nature of each pixel could be identified by the localized spectrum associated with each pixel. Both univariate and partial least squares (PLS) images were evaluated. In the suboptimal blends, the regions of heterogeneity were obvious by visual inspection of the images. A quantitative measure of blending was determined by calculating the standard deviation of the distribution of pixel intensities in the PLS score images. The percent standard deviation increased progressively from 11% to 240% from well blended to unblended tablets. The NIR spectral imaging system provides a rapid approach for acquiring spatial and spectral information on pharmaceuticals. The technique has potential for a variety of applications in product quality assurance and could affect the control of manufacturing processes.     

A GPU Simulation Tool for Training and Optimisation in 2D Digital X-Ray Imaging

Conventional radiology is performed by means of digital detectors, with various types of technology and different performance in terms of efficiency and image quality. Following the arrival of a new digital detector in a radiology department, all the staff involved should adapt the procedure parameters to the properties of the detector, in order to achieve an optimal result in terms of correct diagnostic information and minimum radiation risks for the patient. The aim of this study was to develop and validate a software capable of simulating a digital X-ray imaging system, using graphics processing unit computing. All radiological image components were implemented in this application: an X-ray tube with primary beam, a virtual patient, noise, scatter radiation, a grid and a digital detector. Three different digital detectors (two digital radiography and a computed radiography systems) were implemented. In order to validate the software, we carried out a quantitative comparison of geometrical and anthropomorphic phantom simulated images with those acquired. In terms of average pixel values, the maximum differences were below 15%, while the noise values were in agreement with a maximum difference of 20%. The relative trends of contrast to noise ratio versus beam energy and intensity were well simulated. Total calculation times were below 3 seconds for clinical images with pixel size of actual dimensions less than 0.2 mm. The application proved to be efficient and realistic. Short calculation times and the accuracy of the results obtained make this software a useful tool for training operators and dose optimisation studies.     

X-ray absorption and phase contrast imaging to study the interplay between plant roots and soil structure

Plant performance is, at least partly, linked to the location of roots with respect to soil structure features and the micro-environment surrounding roots. Measurements of root distributions from intact samples, using optical microscopy and field tracings have been partially successful but are imprecise and labour-intensive. Theoretically, X-ray computed micro-tomography represents an ideal solution for non-invasive imaging of plant roots and soil structure. However, before it becomes fast enough and affordable or easily accessible, there is still a need for a diagnostic tool to investigate root/soil interplay. Here, a method for detection of undisturbed plant roots and their immediate physical environment is presented. X-ray absorption and phase contrast imaging are combined to produce projection images of soil sections from which root distributions and soil structure can be analyzed. The clarity of roots on the X-ray film is sufficient to allow manual tracing on an acetate sheet fixed over the film. In its current version, the method suffers limitations mainly related to (i) the degree of subjectivity associated with manual tracing and (ii) the difficulty of separating live and dead roots. The method represents a simple and relatively inexpensive way to detect and quantify roots from intact samples and has scope for further improvements. In this paper, the main steps of the method, sampling, image acquisition and image processing are documented. The potential use of the method in an agronomic perspective is illustrated using surface and sub-surface soil samples from a controlled wheat trial. Quantitative characterization of root attributes, e.g. radius, length density, branching intensity and the complex interplay between roots and soil structure, is presented and discussed. This revised version was published online in June 2006 with corrections to the Cover Date.