衍射增强成像方法在计算机断层成像中的应用

衍射增强成像是X射线相位衬度成像方法之一，这种方法具有较高的衬度和空间分辨率. 利用它对由轻元素组成的生物、医学样品成像可以观察到常规吸收成像无法观察到的内部微细结构. 这种方法在生物、医学、材料科学等无损检测领域中的应用研究，已成为当前国际上X射线成像领域中的研究热点. 讨论衍射增强成像方法和该方法在计算机断层成像中的应用. 实验结果表明，使用衍射增强成像方法获得的数据源能够重建出微米级的生物组织结构，这些组织结构信息在常规X射线断层成像中是难以得到的. 关键词： 衍射增强成像 CT重建 同步辐射 微细结构     

同轴X射线相位衬度计算机X射线断层摄影术研究

基于北京同步辐射装置(BSRF)开展了同轴X射线相位衬度计算机X射线断层摄影术(CT)研究.利用北京同步辐射的14 keV单色X射线作为光源,以高分辨能力的X射线胶片作为探测器,分别开展吸收衬度和同轴相位衬度成像的比较研究以及相位衬度计算机X射线断层摄影术研究.相位衬度计算机X射线断层摄影术重建采用Bronnikov提出的算法.结果显示,与传统的吸收衬度图像相比,相位衬度图像具有更好的衬度和更高的空间分辨力;实验获得人工样品和蝗虫的相位衬度计算机X射线断层摄影术重建图像.重建图像中可见样品的一些结构细节.实验结果表明,相位衬度X射线成像更适合于研究弱吸收或吸收差异很小的材料;利用北京同步辐射开展同轴X射线相位衬度计算机X射线断层摄影术研究是可行的.     

利用荧光CT实现生物医学样品内元素分布的无损成像

荧光CT是一种可无损重建元素空间分布的发射型断层成像技术,对生物医学研究具有重要意义.同步辐射的高通量、高准直和能量可调等特性使荧光CT的生物医学应用成为可能.文章通过优化设计,在上海同步辐射光源建立了一套用于生物医学样品微量元素分析的荧光CT成像系统.通过对实验装置的优化,提高了系统的数据采集速度和空间分辨率.将极大...     

Nuclear Magnetic Resonance Imaging

Abstract

The advent of X-ray computed tomographic (CT) imaging revolutionized the evaluation of a wide range of pathological conditions by producing thin tomographic sections through the body with remarkable anatomical detail. By the early 1980s, X-ray CT was an established imaging modality, and a second computer-based form of imaging was emerging from the research laboratory into the clinic. The second wave of the imaging revolution has been the development of NMR imaging (usually referred to as magnetic resonance imaging, or MRI) and its acceptance as the preferred modality for much neurological and musculoskeletal imaging. MRI's soft-tissue contrast and resolution is superior to that of other imaging techniques, the low NMR signal from bone renders it superior to X-ray CT in many cases for images of the head and spine, it has more varied contrast possibilities than CT, and can image in any plane without repositioning the patient. In spite of the high cost of purchase and installation, MR scanners are proliferating rapidly, and techniques and clinical applications for MR imaging continue to advance at an equally rapid rate.     

Radiography registration for mosaic tomography

A hybrid method of stitching X‐ray computed tomography (CT) datasets is proposed and the feasibility to apply the scheme in a synchrotron tomography beamline with micrometre resolution is shown. The proposed method enables the field of view of the system to be extended while spatial resolution and experimental setup remain unchanged. The approach relies on taking full tomographic datasets at different positions in a mosaic array and registering the frames using Fourier phase correlation and a residue‐based correlation. To ensure correlation correctness, the limits for the shifts are determined from the experimental motor position readouts. The masked correlation image is then minimized to obtain the correct shift. The partial datasets are blended in the sinogram space to be compatible with common CT reconstructors. The feasibility to use the algorithm to blend the partial datasets in projection space is also shown, creating a new single dataset, and standard reconstruction algorithms are used to restore high‐resolution slices even with a small number of projections.     

Comparison of in vitro breast cancer visibility in analyser‐based computed tomography with histopathology,mammography, computed tomography and magnetic resonance imaging

High‐resolution analyser‐based X‐ray imaging computed tomography (HR ABI‐CT) findings on in vitro human breast cancer are compared with histopathology, mammography, computed tomography (CT) and magnetic resonance imaging. The HR ABI‐CT images provided significantly better low‐contrast visibility compared with the standard radiological images. Fine cancer structures indistinguishable and superimposed in mammograms were seen, and could be matched with the histopathological results. The mean glandular dose was less than 1 mGy in mammography and 12–13 mGy in CT and ABI‐CT. The excellent visibility of in vitro breast cancer suggests that HR ABI‐CT may have a valuable role in the future as an adjunct or even alternative to current breast diagnostics, when radiation dose is further decreased, and compact synchrotron radiation sources become available.     

X射线衍射增强成像中吸收、折射以及散射衬度的计算层析

X射线相位衬度成像是一种新型的X射线成像技术,通过记录射线穿过物体后相位的改变对物体进行成像,可以提供比传统的X射线吸收成像更高的图像衬度以及空间分辨力。衍射增强成像方法(Diffraction enhancedimaging,DEI)是X射线相位衬度成像方法之一,利用一块放置在物体和探测器之间的分析晶体提取物体的吸收、折射以及散射信息并进行成像。将衍射增强成像方法与计算机断层成像技术(Computerized Tomography)进行结合,利用吸收、散射以及折射信息,分别采用滤波反投影以及雷登(Radon)变换,对昆虫样品——蜜蜂进行计算层析重建,获得了好于X射线吸收计算层析的重建结果,验证了衍射增强成像信息分离计算层析的优越性。     

Comparison of quantitative imaging of cartilage for osteoarthritis: T2, T1ρ, dGEMRIC and contrast-enhanced computed tomography

Evaluation of glycosaminoglycan (GAG) concentration in articular cartilage is of particular interest to the study of degenerative joint diseases such as osteoarthritis (OA). Noninvasive imaging techniques such as magnetic resonance imaging (MRI) and computed tomography (CT) have demonstrated the potential to assess biochemical markers of cartilage integrity such as GAG content; however, many imaging techniques are available and the optimization of particular techniques in the diagnosis of joint disease remains an active area of research. In order to highlight the differences between these various approaches, this work compares MRI (T1, T2 and T1ρ) and contrast-enhanced CT in human articular cartilage, in both the presence and absence of gadolinium-based contrast agent. Pre- and postcontrast T2 values were found to be similar on a regional level and correlated with each other. As expected, T1 values were shortened significantly on both a global and a spatial basis in the presence of gadolinium (Gd); similar results were found for T1ρ. T2 values were found to correlate mildly with postcontrast T1, T1(Gd) and with precontrast T1ρ values. In addition, contrast-enhanced CT values correlated with both precontrast T1ρ and T1(Gd) more strongly than with precontrast T2. Finally, T1(Gd) and precontrast T1ρ were found to be moderately correlated with CT data. However, T1(Gd) and precontrast T1ρ were found to be almost completely uncorrelated. Together, these results indicate that T1ρ, T2 and contrast-enhanced techniques may provide complementary information about the molecular environment in cartilage during the evolution of OA.     

Transillumination Laser Computed Tomography System with Fiber-Optic-Based Coherent Detection Imaging Method - High Spatial-Resolution and Quantitative Tomographic Imaging of Highly Scattering Objects -

We recently proposed and developed a novel transillumination laser computed tomography (CT) imaging system using a fiber-optic method based on coherent detection imaging (CDI) for biomedical use. Use of optical fibers enables portability and robustness against environmental changes in a room, such as variable temperature, air-flow shifts, and unexpected vibrations. In addition, motion-artifact-free images can be obtained because measurements can be performed with the object fixed. In the present paper, we experimentally investigate in detail the fundamental imaging properties of the system, which has a spatial resolution of 500 μm, a dynamic range of approximately 120 dB, and a minimum-detectable-optical power of 10⁻¹⁴W as a result of the excellent properties of the heterodyne detection. Based on experimental observations, the proposed system can reconstruct tomographic images of highly scattering objects in the transillumination mode, similar to X-ray CT, at sub-millimeter spatial resolution and with quantitativeness. Finally, we demonstrate with experiments using a physical phantom that the imaging system possesses high resolution and quantitative imaging abilities for highly scattering objects.     

Quantitative quasi-local tomography using absorption and phase contrast

Possibilities are investigated for quantitative computed tomography (CT) reconstruction of the spatial distribution of refractive index in a region of interest (ROI) inside an object which is larger than the field of view. The analysis is presented for the case of conventional (absorption) CT, as well as diffraction (phase-contrast) CT. It is shown that in both cases an accurate reconstruction can be achieved using the projection data corresponding to rays passing through a sufficiently wide vicinity of a ROI. Our analysis also indicates that X-ray phase-contrast CT can typically be localized to smaller regions compared to absorption CT. In particular, quasi-local hard X-ray micro-CT of regions of the order of 100 μm or even smaller in size, appears feasible with the use of propagation-based phase contrast. Numerical and experimental tests confirm the possibility of accurate quantitative CT reconstruction from truncated projections.     

Analyser‐based tomography images of cartilage

Analyser‐based imaging expands the performance of X‐ray imaging by utilizing not only the absorption properties of X‐rays but also the refraction and scatter rejection (extinction) properties. In this study, analyser‐based computed tomography has been implemented on imaging an articular cartilage sample, depicting substructural variations, without overlay, at a pixel resolution of 3.6 µm.     

Optimization and validation of a rapid high-resolution T1-w 3D FLASH water excitation MRI sequence for the quantitative assessment of articular cartilage volume and thickness

In view of follow up, survey and development of therapeutic strategies for osteoarthritis where cartilage deterioration plays an important role, a non invasive, reliable and quantitative assessment of the articular cartilage is desirable. The currently available high resolution T(1)-weighted (T1-w) 3D FLASH pulse sequences with frequency selective fat suppression are very time consuming. We have 1) optimized a high resolution T1-w 3D FLASH water excitation (WE) sequence for short acquisition time and cartilage visualization, and 2) validated this sequence for cartilage volume and thickness quantification. The spectral fat presaturation was replaced by selective water excitation. The flip angle of the WE sequence was optimized for the contrast to noise (C/N(cart)) ratio of cartilage. Sagittal datasets (voxel size: 0.31 x 0.31 x 2 mm(3)) of the knees of nine healthy volunteers were acquired both, with the 3D FLASH WE (17.2/6.6/30 degrees ) sequence (WE) and a previously validated 3D FLASH fat saturated (42/11/30 degrees ) sequence (FS). For validation of the WE sequence, cartilage volume, mean and maximal cartilage thickness of the two sequences were compared. Reproducibility was assessed by calculating the coefficient of variation (COV %) of 4 consecutive WE data sets in the volunteers. The acquisition time was reduced from 16'30" (FS) down to 7'14" for the WE sequence. Image contrast and visualization of the cartilage was very similar, but delineation of the basal layer of the cartilage was slightly improved with the WE sequence. A flip angle of 30 degrees provided the best C/N(cart) ratios (WE). Reproducibility (COV) was between 1.9 and 5.9%. Cartilage volume and thickness agreed within 4% between FS and WE sequence. The WE sequence allows for rapid, valid and reproducible quantification of articular cartilage volume and thickness, prerequisites for follow-up examinations. The reduced acquisition time (50% of FS) enables routine clinical application and thus may contribute to a broader assessment of osteoarthritis.     

Application of X-ray Computed Tomography to Cultural Heritage diagnostics

Physical methods of diagnosis are more and more frequently applied in the field of Cultural Heritage either for scientific investigations or for restoration and conservation purposes. X-ray Computed Tomography (CT) is one of the most powerful non-destructive testing techniques for the full-volume inspection of an object, as it is able to give morphological and physical information on the inner structure of the investigated sample. The great variety of size and composition that characterizes archaeological findings and art objects requires the development of tomographic systems specifically designed for Cultural Heritage analysis. In the last few years our research group has developed several acquisition systems for Digital Radiography and X-ray CT. We are able to perform high resolution micro-tomography of small objects (voxel size of few microns) as well as CT of large objects (up to 2 m of size). In this paper we will mainly focus the attention on the results of the investigation recently performed on two Japanese wooden statues with our CT system for large works of art. The CT analysis was carried out on site at the Conservation and Restoration Center “La Venaria Reale”, where the statues have been restored before their exposition at the Oriental Art Museum in Turin.     

X射线同轴相衬成像的参数优化系统

通过对具有2维高斯型相位分布特征的物体的X射线同轴相衬成像技术进行理论分析,建立了成像系统参数优化系统。优化系统明确了图像衬度、信噪比、分辨力和探测器抽样数等成像质量评价参数对射线源能量、源焦斑尺寸、探测器分辨力、成像几何和物体结构特性等系统参数的依赖关系。采用数值模拟,分别对亚微焦点源、激光驱动微焦点源和同步辐射源3种X射线源下的成像系统相关参数进行了优化。结果表明,优化系统很好地完成了系统的优化工作。     

The photodegradation of cadmium yellow paints in Henri Matisse’s Le Bonheur de vivre (1905–1906)

Evidence for the alteration of the yellow paints in Henri Matisse’s Le Bonheur de vivre (1905–1906, The Barnes Foundation) has been observed since the 1990s. The changes in this iconic work of Matisse’s Fauvist period include lightening, darkening, and flaking of the yellow paints. Handheld X-ray fluorescence (XRF) and multispectral imaging surveys reveal that the degradation is confined to cadmium yellow (CdS) paints. The discoloration of cadmium yellow paints in Impressionist, Post-Impressionist and early modernist work from the 1880s through the 1920s has been ascribed to the photo-oxidative degradation of CdS. Preliminary investigations of the degraded yellow paints in this work involved Cd L_III-edge X-ray Absorption Near Edge Spectroscopy (XANES) at the Stanford Synchrotron Radiation Light Source (SSRL Menlo Park, California) and Scanning Electron Microscopy-energy dispersive X-ray analysis (SEM-EDS) at the Winterthur Museum Scientific Research and Analysis Laboratory. To determine if the visual changes in the paints did in fact indicate photo-oxidative degradation and if different chemistries could be observed for the lightened versus darkened regions, synchrotron radiation-micro Fourier Transform InfraRed (SR-μFTIR) spectroscopy, X-ray Fluorescence (SR-μXRF) mapping and micro X-ray Absorption Near Edge Spectroscopy (μXANES) mapping at the Cd L_III-edge of the altered paint cross-sections were carried out at the European synchrotron radiation facility (ESRF, Grenoble, France) beamline ID-21. The goal is to elucidate the discoloration mechanisms observed in the paint using elemental and speciation mapping. The μXANES mapping and SR-FTIR imaging showed a substantial enrichment of CdCO₃ in the off-white surface crust of the faded/discolored CdS paint. This suggests that the CdCO₃ is present as an insoluble photodegradation product rather than solely a paint filler or starting reagent. Additionally, oxalates and sulfates were found to be concentrated at the alteration surface.     

Live small‐animal X‐ray lung velocimetry and lung micro‐tomography at the Australian Synchrotron Imaging and Medical Beamline

The high flux and coherence produced at long synchrotron beamlines makes them well suited to performing phase‐contrast X‐ray imaging of the airways and lungs of live small animals. Here, findings of the first live‐animal imaging on the Imaging and Medical Beamline (IMBL) at the Australian Synchrotron are reported, demonstrating the feasibility of performing dynamic lung motion measurement and high‐resolution micro‐tomography. Live anaesthetized mice were imaged using 30 keV monochromatic X‐rays at a range of sample‐to‐detector propagation distances. A frame rate of 100 frames s^?1 allowed lung motion to be determined using X‐ray velocimetry. A separate group of humanely killed mice and rats were imaged by computed tomography at high resolution. Images were reconstructed and rendered to demonstrate the capacity for detailed, user‐directed display of relevant respiratory anatomy. The ability to perform X‐ray velocimetry on live mice at the IMBL was successfully demonstrated. High‐quality renderings of the head and lungs visualized both large structures and fine details of the nasal and respiratory anatomy. The effect of sample‐to‐detector propagation distance on contrast and resolution was also investigated, demonstrating that soft tissue contrast increases, and resolution decreases, with increasing propagation distance. This new capability to perform live‐animal imaging and high‐resolution micro‐tomography at the IMBL enhances the capability for investigation of respiratory diseases and the acceleration of treatment development in Australia.     

Tomographic imaging of a suspending single live cell using optical tweezer-combined full-field optical coherence tomography

We propose a label-free depth-resolved tomographic scheme for imaging a single live cell in fluid. This approach utilizes a modified time-domain full-field optical coherence tomography (FF-OCT) system combined with an optical tweezer technique. The optical trap for holding a moving specimen is made by tightly focusing a 1064 nm Q-switching pulsed laser beam with a 1.0 NA microscope objective in the sample arm of the FF-OCT part. By cosharing the probe for both systems, the optical actions of trapping and cellular resolution tomographic imaging could be achieved simultaneously. Feasibility of the combined system is demonstrated by imaging micron-sized polystyrene beads and a living suspension cell in medium.     

Suppression of ring artefacts when tomographing anisotropically attenuating samples

There are many objects for which the attenuation varies significantly as they are rotated during computerized X‐ray tomography, for example plate samples. This can lead to significant ring artefacts in the subsequent tomographic reconstructions. In this paper a new method is presented that can successfully suppress such ring artefacts and is applicable to both parallel and cone‐beam geometries. Rapid correction is achieved via an analytical formula which involves only a matrix‐vector multiplication, for which the matrix is known and depends on a regularization parameter. The efficacy of the method is demonstrated for a paleontological sample (calcified shark cartilage) and a carbon–carbon composite/Ti–SiC metal matrix composite test sample.     

Single‐cell resolution in high‐resolution synchrotron X‐ray CT imaging with gold nanoparticles

Gold nanoparticles are excellent intracellular markers in X‐ray imaging. Having shown previously the suitability of gold nanoparticles to detect small groups of cells with the synchrotron‐based computed tomography (CT) technique both ex vivo and in vivo, it is now demonstrated that even single‐cell resolution can be obtained in the brain at least ex vivo. Working in a small animal model of malignant brain tumour, the image quality obtained with different imaging modalities was compared. To generate the brain tumour, 1 × 10⁵ C6 glioma cells were loaded with gold nanoparticles and implanted in the right cerebral hemisphere of an adult rat. Raw data were acquired with absorption X‐ray CT followed by a local tomography technique based on synchrotron X‐ray absorption yielding single‐cell resolution. The reconstructed synchrotron X‐ray images were compared with images obtained by small animal magnetic resonance imaging. The presence of gold nanoparticles in the tumour tissue was verified in histological sections.