X-ray In-line Phase-contrast Imaging Research Articles

Signal-to-noise and spatial resolution in in-line imaging. 1. Basic theory, numerical simulations and planar experimental images.

Signal-to-noise ratio and spatial resolution are quantitatively analysed in the context of in-line (propagation based) X-ray phase-contrast imaging. It is known that free-space propagation of a coherent X-ray beam from the imaged object to the detector plane, followed by phase retrieval in accordance with Paganin's method, can increase the signal-to-noise in the resultant images without deteriorating the spatial resolution. This results in violation of the noise-resolution uncertainty principle and demonstrates `unreasonable' effectiveness of the method. On the other hand, when the process of free-space propagation is performed in software, using the detected intensity distribution in the object plane, it cannot reproduce the same effectiveness, due to the amplification of photon shot noise. Here, it is shown that the performance of Paganin's method is determined by just two dimensionless parameters: the Fresnel number and the ratio of the real decrement to the imaginary part of the refractive index of the imaged object. The relevant theoretical analysis is performed first, followed by computer simulations and then by a brief test using experimental images collected at a synchrotron beamline. More extensive experimental tests will be presented in the second part of this paper.

Enhancing Contrast of Spatial Details in X-ray Phase-Contrast Imaging through Modified Fourier Filtering

In-line X-ray phase contrast imaging, which is simple to experiment with, provides significantly higher sensitivity, compared to conventional X-ray absorption imaging. The inversion of the relationship between recorded Fresnel diffraction intensity and the phase shift induced by the object is called phase retrieval. The transport of intensity equation (TIE), a simple method of phase retrieval, which is solved by the fast Fourier transform algorithm proposed by Paganin et al., has been widely adopted. However, the existing method suffers from excessive suppression of high-frequency information, resulting in loss of image details after phase retrieval, or insufficient detail contrast, leading to blurry images. Here, we present a straightforward extension of the two-distance FFT-TIE method by modifying the Fourier filter through the use of a five-point approximation to calculate the inverse Laplacian in a discrete manner. Additionally, we utilize a combination of continuous Fourier transform and a four-point approximation to compute the gradient operator. The method is evaluated by simulating samples with a shape similar to the resolution test map and by using a photograph of a dog for further evaluation. The algorithm that incorporates the modified gradient operator and the algorithm that solely utilizes the continuous Fourier transform for gradient computation were compared with the results obtained using the two-distance FFT-TIE method. The comparisons were conducted using the results obtained from two distances from the sample to the detector. The results show that this method improves the contrast of spatial details and reduces the suppression of high spatial frequencies compared to the two-distance FFT-TIE method. Furthermore, in the low-frequency domain, our algorithm does not lose much information compared to the original method, yielding consistent results. Furthermore, we conducted our experiments using carbon rods. The results show that both our method and the FFT-TIE method exhibit low-frequency distortion due to the requirement of close proximity between the absorption maps and the detector. However, upon closer inspection, our proposed method demonstrates superior accuracy in reproducing the finer details of the carbon rod fibers.

Mixed scale dense convolutional networks for x-ray phase contrast imaging

X-ray in-line phase contrast imaging relies on the measurement of Fresnel diffraction intensity patterns due to the phase shift and the attenuation induced by the object. The recovery of phase and attenuation from one or several diffraction patterns is a nonlinear ill-posed inverse problem. In this work, we propose supervised learning approaches using mixed scale dense (MS-D) convolutional neural networks to simultaneously retrieve the phase and the attenuation from x-ray phase contrast images. This network architecture uses dilated convolutions to capture features at different image scales and densely connects all feature maps. The long range information in images becomes quickly available, and greater receptive field size can be obtained without losing resolution. This network architecture seems to account for the effect of the Fresnel operator very efficiently. We train the networks using simulated data of objects consisting of either homogeneous components, characterized by a fixed ratio of the induced refractive phase shifts and attenuation, or heterogeneous components, consisting of various materials. We also train the networks in the image domain by applying a simple initial reconstruction using the adjoint of the Fréchet derivative. We compare the results obtained with the MS-D network to reconstructions using U-Net, another popular network architecture, as well as to reconstructions using the contrast transfer function method, a direct phase and attenuation retrieval method based on linearization of the direct problem. The networks are evaluated using simulated noisy data as well as images acquired at NanoMAX (MAX IV, Lund, Sweden). In all cases, large improvements of the reconstruction errors are obtained on simulated data compared to the linearized method. Moreover, on experimental data, the networks improve the reconstruction quantitatively, improving the low-frequency behavior and the resolution.

Enhanced phase retrieval via deep concatenation networks for in-line X-ray phase contrast imaging

PurposeIn-line X-ray phase contrast imaging offers considerable additional information beyond that acquired from conventional absorption contrast X-ray imaging, showing promising potentials in clinical diagnosis, materials characterization and so on. Given the physically intractable factors tangled inside, conventional phase retrieval methods typically suffer from limited feasibility. A deep-learning-augmented reconstruction strategy is proposed to improve the phase retrieval in spatial resolution and noise compression. MethodsThe deep network is composed of a phase contrast refinement module and a phase retrieval module to stabilize and generalize the phase retrieval. The two modules are aggregated in a plug-and-play fashion with the final assembly finetuned using limited training data, essentially encouraging a semi-supervised training. Verification experiments were performed on simulated phase contrast images of histopathological images. The results were compared to those from conventional phase-attenuation duality method. ResultsThe deep-learning-augmented reconstruction strategy increases structural similarity and peak signal-to-noise ratio of phase retrieval result by more than 8% and 30%, and reduces root mean squared error by 46% compared with conventional phase-attenuation duality method. Conclusions: The pilot study of deep learning deployment in in-line X-ray phase-contrast imaging exhibit advantages against conventional methods in terms of spatial resolution and noise robustness.

Iterative reconstruction algorithm based on discriminant adaptive-weighted TV regularization for fibrous biological tissues using in-line X-ray phase-contrast imaging.

In-line X-ray phase-contrast computed tomography (IL-PCCT) can produce high-contrast and high-resolution images of biological samples, and it has a great advantage with regard to imaging the microstructures and morphologies of fibrous biological tissues (FBTs). Filtered back projection (FBP) is widely used in ILPCCT. However, it requires long scanning times and high radiation doses to produce high-quality CT images, and this restricts its applicability in biomedical and preclinical studies on FBTs. To solve this problem, a novel IL-PCCT reconstruction algorithm is proposed to decrease the radiation dose by reducing the number of projections and reconstruct high-quality CT images of FBTs. The proposed algorithm incorporates the FBP method into the iterative reconstruction framework. Considering the area types and anisotropic edge properties of FBTs, a discriminant adaptive-weighted total variation model is introduced to optimize the intermediate reconstructed images. A fibrous phantom simulation and real experiment were performed to assess the performance of the proposed algorithm. Simulation and experimental results demonstrated that the proposed algorithm is an effective IL-PCCT reconstruction method for FBTs with incomplete projection data, and it has a great ability to suppress artifacts and preserve the edges of fibrous structures.

Three-dimensional construction of micrometer level in rat stomach by synchrotron radiation

BackgroundThe structural changes of gastric mucosa are considered as an important window of early gastric lesions. This article shows an imaging method of the stomach that does not use imaging agents. X-ray phase-contrast images of different stages of gastric development were taken using micrometer level X-ray in-line phase-contrast imaging (XILPCI) technique on synchrotron radiation facility. The aim of the study was to demonstrate that the imaging technique is an appropriate method for micron imaging of the gastric structures.MethodsThe stomachs of 4-, 6- and 12-week-old rats were removed and cleaned. XILPCI has 1000 times greater soft tissue contrast than that of X-ray traditional absorption radiography. The projection images of the rats stomachs were recorded by an XILPCI charge coupled device (CCD) at 9-μm image resolution.ResultsThe X-ray in-line phase-contrast images of the different stages of rats’ gastric specimens clearly showed the gastric architectures and the details of the gastro-duodenal region. 3-dimensional (3D) stomach anatomical structure images were reconstruction.ConclusionThe reconstructed gastric 3D images can clearly display the internal structure of the stomach. XILPCI may be a useful method for medical research in the future.

X-Ray Phase-Contrast Image Reconstruction Based on the Chambolle-Pock Algorithm

The X-ray in-line phase-contrast imaging technique requires that the light source provides a spatially coherent X-ray beam typically generated by a microfocus X-ray tube in most laboratories. However, its small focal spot limits the lightness. An arrayed X-ray point source can overcome this drawback and provide an adequately bright spatial coherent light. However, the arrayed source will introduce artefacts to the phase-contrast image due to the point source spatial distribution. To eliminate these artefacts, an optimization-based algorithm is used to reconstruct the image as an optimization problem. An iterative method was developed to numerically solve the optimization problem by using the first-order primal-dual algorithm. The simulations demonstrate its convergence and reconstruction accuracy.

Developing a Microbubble-Based Contrast Agent for Synchrotron In-Line Phase Contrast Imaging.

X-ray phase contrast imaging generates contrast from refraction of X-rays, enhancing soft tissue contrast compared to conventional absorption-based imaging. Our goal is to develop a contrast agent for X-ray in-line phase contrast imaging (PCI) based on ultrasound microbubbles (MBs), by assessing size, shell material, and concentration. Polydisperse perfluorobutane-core lipid-shelled MBs were synthesized and size separated into five groups between 1 and 10μm. We generated two size populations of polyvinyl-alcohol (PVA)-MBs, 2-3μm and 3-4μm, whose shells were either coated or integrated with iron oxide nanoparticles (SPIONs). Microbubbles were then embedded in agar at three concentrations: 5×107, 5×106 and 5×105 MBs/ml. In-line phase contrast imaging was performed at the Canadian Light Source with filtered white beam micro-computed tomography. Phase contrast intensity was measured by both counting detectable MBs, and comparing mean pixel values (MPV) in minimum and maximum intensity projections of the overall samples. Individual lipid-MBs 6-10μm, lipid-MBs 4-6μm and PVA-MBs coated with SPIONs were detectable at each concentration. At the highest concentration, lipid-MBs 6-10μm and 4-6μm showed an overall increase in positive contrast, whereas at a moderate concentration, only lipid-MBs 6-10μm displayed an increase. Negative contrast was also observed from two largest lipid-MBs at high concentration. These data indicate that lipid-MBs larger than 4μm are candidates for PCI, and 5×106 MBs/ml may be the lowest concentration suitable for generating visible phase contrast in vivo. Identifying a suitable MB for PCI may facilitate future clinical translation.

Methodology development and application of X-ray imaging beamline at SSRF

This paper introduces some latest developments regarding the X-ray imaging methodology and applications of the X-ray imaging and biomedical application beamline (BL13W1) at Shanghai Synchrotron Radiation Facility in the past 5 years. The photon energy range of the beamline is 8–72.5 keV. Several sets of X-ray imaging detectors with different pixel sizes (0.19–24 μm) are used to realize X-ray microcomputed tomography (X-ray micro-CT) and X-ray in-line phase-contrast imaging. To satisfy the requirements of user experiments, new X-ray imaging methods and image processing techniques are developed. In vivo dynamic micro-CT experiments with living insects are performed in 0.5 s (sampling rate of 2 Hz, 2 tomograms/s) with a monochromatic beam from a wiggler source and in 40 ms (sampling rate of 25 Hz, 25 tomograms/s) with a white beam from a bending magnet source. A new X-ray imaging method known as move contrast X-ray imaging is proposed, with which blood flow and moving tissues in raw images can be distinguished according to their moving frequencies in the time domain. Furthermore, X-ray speckle-tracking imaging with twice exposures to eliminate the edge enhancement effect is developed. A high-precision quantification method is realized to measure complex three-dimensional blood vessels obtained via X-ray micro-CT. X-ray imaging methods such as three-dimensional X-ray diffraction microscopy, small-angle X-ray scattering CT, and X-ray fluorescence CT are developed, in which the X-ray micro-CT imaging method is combined with other contrast mechanisms such as diffraction, scattering, and fluorescence contrasts respectively. Moreover, an X-ray nano-CT experiment is performed with a 100 nm spatial resolution. Typical user experimental results from the fields of material science, biomedicine, paleontology, physics, chemistry, and environmental science obtained on the beamline are provided.

Synchrotron Radiation-Based Three-Dimensional Visualization of Angioarchitectural Remodeling in Hippocampus of Epileptic Rats.

Characterizing the three-dimensional (3D) morphological alterations of microvessels under both normal and seizure conditions is crucial for a better understanding of epilepsy. However, conventional imaging techniques cannot detect microvessels on micron/sub-micron scales without angiography. In this study, synchrotron radiation (SR)-based X-ray in-line phase-contrast imaging (ILPCI) and quantitative 3D characterization were used to acquire high-resolution, high-contrast images of rat brain tissue under both normal and seizure conditions. The number of blood microvessels was markedly increased on days 1 and 14, but decreased on day 60 after seizures. The surface area, diameter distribution, mean tortuosity, and number of bifurcations and network segments also showed similar trends. These pathological changes were confirmed by histological tests. Thus, SR-based ILPCI provides systematic and detailed views of cerebrovascular anatomy at the micron level without using contrast-enhancing agents. This holds considerable promise for better diagnosis and understanding of the pathogenesis and development of epilepsy.

Evaluation of Effects of TGF-β1 Inhibition on Gastric Cancer in Nude Mice by Diffusion Kurtosis Imaging and In-Line X-ray Phase Contrast Imaging With Sequential Histology.

BackgroundAccurate and complete response evaluation after treatment is important to implement individualized therapy for gastric cancer.PurposeTo investigate the effectiveness of diffusion kurtosis imaging (DKI) and in‐line X‐ray phase contrast imaging (ILXPCI) in the assessment of the therapeutic efficacy by transforming growth factor beta 1 (TGF‐β1) inhibition.Study TypeProspective animal study.Animal ModelThirty nude mice subcutaneous xenotransplantation tumor model of gastric cancer for DKI and 10 peritoneal metastasis nude mice model for ILXPCI.Field Strength/SequenceExaminations before and serially at 7, 14, 21, and 28 days after TGF‐β1 inhibition treatment were performed at 3T MRI including T2‐weighted imaging (T2WI) and DKI with five b values of 0, 500, 1000, 1500, 2000 s/mm2; ILXPCI examinations were performed at 14 days after treatment.AssessmentDKI parameters (apparent diffusion coefficient [ADC], diffusivity [D] and kurtosis [K]) were calculated by two experienced radiologists after postprocessing.Statistical TestsFor the differences in all the parameters between the baseline and each timepoint for both the treated and the control mice, the Mann–Whitney test was used. The Spearman correlation test was used to evaluate correlations among the DKI parameters and corresponding pathologic necrosis fraction (NF).ResultsADC, D, and K values were significantly different between the two groups after treatment (P < 0.05). Serial measurements in the treated group showed that the ADC, D, and K values were significantly different at 7, 14, 21, and 28 days compared with baseline (P < 0.05). There were significant correlations between DKI parameters and NF (ADC, r = 0.865, P < 0.001; D, r = 0.802, P < 0.001; K, r = –0.944, P < 0.001). The ILXPCI results in the treated group showed a stronger absorption area than the control group.Data ConclusionDKI may be used to evaluate the complete course therapeutic effects of gastric cancer induced by TGF‐β1 inhibition, and the ILXPCI technique will improve the tumor microstructure resolution. Level of Evidence: 1 Technical Efficacy: Stage 4J. Magn. Reson. Imaging 2019;49:1553–1564.

The optical lens coupled X-ray in-line phase contrast imaging system for the characterization of low Z materials.

Due to the high spatial resolution and contrast, the optical lens coupled X-ray in-line phase contrast imaging system with the secondary optical magnification is more suitable for the characterization of the low Z materials. The influence of the source to object distance and the object to scintillator distance on the image resolution and contrast is studied experimentally. A phase correlation algorithm is used for the image mosaic of a serial of X-ray phase contrast images acquired with high resolution, the resulting resolution is less than 1.0 μm, and the whole field of view is larger than 1.4 mm. Finally, the geometric morphology and the inner structure of various weakly absorbing samples and the evaporation of water in the plastic micro-shell are in situ characterized by the optical lens coupled X-ray in-line phase contrast imaging system.

Synchrotron radiation X-ray in-line phase-contrast imaging with highly symmetric source

In available synchrotron radiation facilities all over the world, the size of electron beam bunch has distinct difference between the horizontal direction and the vertical direction at the cross section vertical to electron moving direction. It will cause low symmetry of source size in horizontal and vertical directions, and result in big difference in the spacial resolution and phase contrast between these two directions in synchrotron radiation X-ray in-line phase contrast imaging. The superior resolution and phase contrast of one direction will couple with the inferior ones of the other direction in actual object imaging, this interaction will degrade both spacial resolution and phase contrast of the whole image and lead to poor image quality. In this paper, a four-knife white beam slit is used in Beijing synchrotron radiation facility (BSRF) 4W1A beamline to adjust source size in horizontal and vertical directions and restrict the point spread function (PSF) of source, the source size is limited from 1.23 mm (horizontal)×0.46 mm (vertical) to 0.35 mm×0.35 mm. By this way, a highly symmetric effective X-ray source is obtained. The symmetry of source size is improved from 2.7 to about 1. Although the total X-ray flux loses 99.95%, the X-ray flux density is only reduced to 22%. It because total flux is taken account of the expanded spot size due to divergence, while flux density is mainly related to effective source size, which is limited not severely as expanded spot size by white beam slit. The flux density reduction by this method is not a critical defect in high resolution X-ray phase contrast imaging and can be improved by other ways. The polyamide fiber net is imaged using X-ray in-line phase contrast imaging at 4W1A, BSRF. Diameter of fiber is about 50 microns, X-ray energy is 13 keV, the effective pixel size is 0.325 micron, the experiment images are obtained at object-to-detector distances of 4, 10, 16, 36, 100, 200 and 300 mm with source-to-object distance of about 43 m. The results show that when source size in horizontal direction is limited from 1.23 to 0.35 mm (symmetry of source size is about 1 at this condition), the maximal phase contrast of image is advanced from 0.057 to 0.35. It means the density sensitivity is promoted about 5 times than in ordinary source size conditions. The spacial resolutions in different source size symmetry conditions are also primary analyzed based on Rayleigh criterion. The result shows that spacial resolution can be improved notably in horizontal direction by limiting horizontal source size to a nearly symmetric source size condition. Our work demonstrates that the spacial resolution and phase contrast can be promoted at the same level by source size symmetry improved, which markedly improved the imaging quality in synchrotron radiation X-ray in-line phase-contrast imaging. It will have great benefit to high-resolution X-ray in-line phase contrast imaging. The reasons of these improvements are analyzed and developments in future are also discussed.

Neovascularization of hepatocellular carcinoma in a nude mouse orthotopic liver cancer model: a morphological study using X-ray in-line phase-contrast imaging

BackgroundThis study aimed to determine whether synchrotron radiation (SR)-based X-ray in-line phase-contrast imaging (IL-PCI) can be used to investigate the morphological characteristics of tumor neovascularization in a liver xenograft animal model.MethodsA human hepatocellular carcinoma HCCLM3 xenograft model was established in nude mice. Xenografts were sampled each week for 4 weeks and fixed to analyze tissue characteristics and neovascularization using SR-based X-ray in-line phase contrast computed tomography (IL-XPCT) without any contrast agent.ResultsThe effect of the energy level and object–to-detector distance on phase-contrast difference was in good agreement with the theory of IL-PCI. Boundaries between the tumor and adjacent normal tissues at week 1 were clearly observed in two-dimensional phase contrast projection imaging. A quantitative contrast difference was observed from weeks 1 to 4. Moreover, 3D image reconstruction of hepatocellular carcinoma (HCC) samples showed blood vessels inside the tumor were abnormal. The smallest blood vessels measured approximately 20 μm in diameter. The tumor vascular density initially increased and then decreased gradually over time. The maximum tumor vascular density was 4.29% at week 2.ConclusionIL-XPCT successfully acquired images of neovascularization in HCC xenografts in nude mice.

Using Microbubble as Contrast Agent for High-Energy X-Ray In-line Phase Contrast Imaging: Demonstration and Comparison Study.

The ability of microbubbles to benefit the imaging quality of high-energy in-line phase contrast as compared with conventional low-energy contact mode radiography was investigated. The study was conducted by comparing in-line phase contrast imaging with conventional contact-mode projection imaging under the same dose delivered to a phantom. A custom-designed phantom was employed to simulate a segment of human blood vessel injected with microbubble suspensions. The microbubbles were suspended in deionized water to obtain different volume concentrations. The area contrast-to-noise ratio (CNR) values corresponding to both imaging methods were measured for different microbubble volume concentrations. The phase contrast images were processed by phase-attenuation duality phase retrieval to preserve the imaging quality. Comparison of the resultant CNR values indicates that the microbubble suspension images deliver a higher CNR than the water-only image, with monotonically increasing trends between the CNR values and microbubble concentrations. Compared to low-energy conventional images of the microbubble suspensions, high-energy in-line phase contrast CNRs are lower at high concentrations and are comparable, even better than, at low concentrations. This result suggests that 1) the performance of copolymer-shell microbubble employed in this study as x-ray contrast agent is constrained by the detective quantum efficiency of the system and the attenuation properties of the shell materials, 2) the phase-attenuation duality phase retrieval method has the potential to preserve image quality for areas with low concentration of microbubbles, and 3) the selection of microbubble products as a phase contrast agent may follow criteria of minimizing the impact of absorption attenuation properties of the shells and maximizing the difference factor of electron densities.

Demonstration of synchrotron x-ray phase contrast imaging computed tomography of infiltrative transitional cell carcinoma of the prostatic urethra in a dog.

Prostatic urethral transitional cell carcinoma with prostatic invasion in a dog was imaged with abdominal radiography and abdominal ultrasonography antemortem. Synchrotron in-line x-ray phase contrast imaging computed tomography (XPCI-CT) was performed on the prostate ex vivo at the Canadian Light Source Synchrotron and compared to histology. XPCI-CT imaging provides greater soft tissue contrast than conventional absorption-based x-ray imaging modalities, permitting visualization of regions of inflammatory cell infiltration, differentiation of invasive versus noninvasive tumor regions, and areas of necrosis and mineralization. This represents the first report of XPCI-CT images of an invasive prostatic urothelial neoplasm in a dog.

Characterization of Mechanical Properties of Tissue Scaffolds by Phase Contrast Imaging and Finite Element Modeling.

In tissue engineering, the cell and scaffold approach has shown promise as a treatment to regenerate diseased and/or damaged tissue. In this treatment, an artificial construct (scaffold) is seeded with cells, which organize and proliferate into new tissue. The scaffold itself biodegrades with time, leaving behind only newly formed tissue. The degradation qualities of the scaffold are critical during the treatment period, since the change in the mechanical properties of the scaffold with time can influence cell behavior. To observe in time the scaffold's mechanical properties, a straightforward method is to deform the scaffold and then characterize scaffold deflection accordingly. However, experimentally observing the scaffold deflection is challenging. This paper presents a novel study on characterization of mechanical properties of scaffolds by phase contrast imaging and finite element modeling, which specifically includes scaffold fabrication, scaffold imaging, image analysis, and finite elements (FEs) modeling of the scaffold mechanical properties. The innovation of the work rests on the use of in-line phase contrast X-ray imaging at 20 KeV to characterize tissue scaffold deformation caused by ultrasound radiation forces and the use of the Fourier transform to identify movement. Once deformation has been determined experimentally, it is then compared with the predictions given by the forward solution of a finite element model. A consideration of the number of separate loading conditions necessary to uniquely identify the material properties of transversely isotropic and fully orthotropic scaffolds is also presented, along with the use of an FE as a form of regularization.

Phase retrieval method for in-line phase contrast x-ray imaging and denoising by regularization.

Phase contrast X-ray imaging is increasingly popular in the past decade. In order to acquire phase contrast X-ray images, different types of imaging mechanisms have been proposed. Among them, in-line phase contrast X-ray imaging shows the highest potential because of its simplicity. In the study of in-line phase contrast imaging, based on different physical assumptions, many non-iterative phase retrieval methods, such as Bronnikov method, modified Bronnikov method, phase-attenuation duality (PAD) method, single-material method, and two-material method have been proposed. The main step of the non-iterative methods is a filtering process, thus different methods involve different filter design. In this paper we showed that every filter applied in the methods listed above is indeed the minimizer of a L(2)-norm regularization problem. In addition, two methods were proposed to overcome the over smoothing problem owing to the nature of L(2)-norm regularization.

Characterization of inertial confinement fusion targets using X-ray phase contrast imaging

The X-ray in-line phase contrast imaging system based on the mircofocus X-ray source is developed for characterizing the inertial confinement fusion (ICF) targets. The influence of various factors such as the source-to-object distance and the object-to-scintillator distance on the image resolution and contrast is investigated experimentally. The best resolution of the system is tested to be about 1μm. The wall thickness and the inner surface roughness of plastic targets are measured by the phase contrast imaging with the resolution of 1.3μm. Moreover, by means of a closed-cycle cryostat with the lowest temperature of 13K, the condensation of deuterium (D2) in glass shell is in-situ characterized with the resolution up to 1.5μm.

Three-dimensional visualization of rat brain microvasculature following permanent focal ischaemia by synchrotron radiation

Identifying morphological changes that occur in microvessels under both normal and ischaemic conditions is crucial for understanding and treating stroke. However, conventional imaging techniques are not able to detect microvessels on a micron or sub-micron scale without angiography. In the present study, synchrotron radiation (SR)-based X-ray in-line phase contrast imaging (ILPCI) was used to acquire high-resolution and high-contrast images of rat brain tissues in both normal and ischaemic states. ILPCI was performed at the Shanghai Synchrotron Radiation Facility, Shanghai, China, without the use of contrast agents. CT slices were reformatted and then converted into three-dimensional (3D) reconstruction images to analyse subtle details of the cerebral microvascular network. By using ILPCI, brain vessels up to 11.8 μm in diameter were resolved. The number of cortical and penetrating arteries detected were found to undergo a remarkable decrease within the infarct area. 3 days after permanent ischaemia, vascular masses were also observed in the peripheral region of the infarcts. SR-based ILPCI-CT can serve as a powerful tool to accurately visualize brain microvasculature. The morphological parameters of blood vessels in both CT slices and 3D reconstructions were determined, and this approach has great potential for providing an effective diagnosis and evaluation for rehabilitation therapy for stroke. In the absence of contrast agent, the 3D morphologies of the brain microvasculature in normal and stroke rats were obtained using SR-based ILPCI. SR imaging is a sensitive and promising method which can be used to explore primary brain function.