Diffraction Enhanced Imaging Technique Research Articles

CO2 processing and hydration of fruit and vegetable tissues by clathrate hydrate formation

CO2 hydrate can be used to preserve fresh fruits and vegetables, and its application could contribute to the processing of carbonated frozen food. We investigated water transformation in the frozen tissue of fresh grape samples upon CO2 treatment at 2–3MPa and 3°C for up to 46h. Frozen fresh bean, radish, eggplant and cucumber samples were also investigated for comparison. X-ray diffraction indicated that after undergoing CO2 treatment for several hours, structure I CO2 hydrate formed within the grape tissue. Phase-contrast X-ray imaging using the diffraction-enhanced imaging technique revealed the presence of CO2 hydrate within the intercellular spaces of these tissues. The carbonated produce became effervescent because of the dissociation of CO2 hydrate through the intercellular space, especially above the melting point of ice. In addition, suppressed metabolic activity resulting from CO2 hydrate formation, which inhibits water and nutrient transport through intercellular space, can be expected.

A three-image algorithm for hard x-ray grating interferometry

A three-image method to extract absorption, refraction and scattering information for hard x-ray grating interferometry is presented. The method comprises a post-processing approach alternative to the conventional phase stepping procedure and is inspired by a similar three-image technique developed for analyzer-based x-ray imaging. Results obtained with this algorithm are quantitatively comparable with phase-stepping. This method can be further extended to samples with negligible scattering, where only two images are needed to separate absorption and refraction signal. Thanks to the limited number of images required, this technique is a viable route to bio-compatible imaging with x-ray grating interferometer. In addition our method elucidates and strengthens the formal and practical analogies between grating interferometry and the (non-interferometric) diffraction enhanced imaging technique.

Phase-Contrast X-ray Images of Ice and Water on Carbon Paper for Fuel Cells Measured by Diffraction-Enhanced Imaging Technique

To develop a novel observation system for water accumulation and freezing in gas diffusion layers (GDLs) of polymer electrolyte fuel cells (PEFCs), phase-contrast X-ray imaging using the diffraction-enhanced imaging (DEI) technique was performed at temperatures between 233 and 293 K. The use of high-energy X-rays of 35 keV in the DEI technique enabled the visualization of ice and meltwater in carbon paper sandwiched by two Al plates of 0.50 mm thickness. It was proven that the DEI technique using a temperature-controlled chamber enables in situ observation of ice and water in GDLs under different temperature conditions, which is critical for achieving high performance PEFCs.

Diffraction-enhanced X-ray imaging under low-temperature conditions: non-destructive observations of clathrate gas hydrates

Diffraction-enhanced imaging (DEI) is a phase-contrast X-ray imaging technique suitable for visualizing light-element materials. The method also enables observations of sample-containing regions with large density gradients. In this study a cryogenic imaging technique was developed for DEI-enabled measurements at low temperature from 193 K up to room temperature with a deviation of 1 K. Structure-II air hydrate and structure-I carbon dioxide (CO(2)) hydrate were examined to assess the performance of this cryogenic DEI technique. It was shown that this DEI technique could image gas hydrate coexisting with ice and gas bubbles with a density resolution of about 0.01 g cm(-3) and a wide dynamic density range of about 1.60 g cm(-3). In addition, this method may be a way to make temperature-dependent measurements of physical properties such as density.

X-Ray Diffraction Enhanced Imaging as a Novel Method to Visualize Low-Density Scaffolds in Soft Tissue Engineering

Scaffold visualization is challenging yet essential to the success of various tissue engineering applications. The aim of this study was to explore the potential of X-ray diffraction enhanced imaging (DEI) as a novel method for the visualization of low density engineered scaffolds in soft tissue. Imaging of the scaffolds made from poly(L-lactide) (PLLA) and chitosan was conducted using synchrotron radiation-based radiography, in-line phase-contrast imaging (in-line PCI), and DEI techniques as well as laboratory-based radiography. Scaffolds were visualized in air, water, and rat muscle tissue. Compared with the images from X-ray radiography and in-line PCI techniques, DEI images more clearly show the structure of the low density scaffold in air and have enhanced image contrast. DEI was the only technique able to visualize scaffolds embedded in unstained muscle tissue; this method could also define the microstructure of muscle tissue in the boundary areas. At a photon energy of 20 KeV, DEI had the capacity to image PLLA/chitosan scaffolds in soft tissue with a sample thickness of up to 4 cm. The DEI technique can be applied at high X-ray energies, thus facilitating lower in vivo radiation doses to tissues during imaging as compared to conventional radiography.

Development of an x-ray prism for analyzer based imaging systems

Analyzer crystal based imaging techniques such as diffraction enhanced imaging (DEI) and multiple imaging radiography (MIR) utilize the Bragg peak of perfect crystal diffraction to convert angular changes into intensity changes. These x-ray techniques extend the capability of conventional radiography, which derives image contrast from absorption, by providing large intensity changes for small angle changes introduced from the x-ray beam traversing the sample. Objects that have very little absorption contrast may have considerable refraction and ultrasmall angle x-ray scattering contrast improving visualization and extending the utility of x-ray imaging. To improve on the current DEI technique an x-ray prism (XRP) was designed and included in the imaging system. The XRP allows the analyzer crystal to be aligned anywhere on the rocking curve without physically moving the analyzer from the Bragg angle. By using the XRP to set the rocking curve alignment rather than moving the analyzer crystal physically the needed angle sensitivity is changed from submicroradians for direct mechanical movement of the analyzer crystal to tens of milliradians for movement of the XRP angle. However, this improvement in angle positioning comes at the cost of absorption loss in the XRP and depends on the x-ray energy. In addition to using an XRP for crystal alignment it has the potential for scanning quickly through the entire rocking curve. This has the benefit of collecting all the required data for image reconstruction in a single measurement thereby removing some problems with motion artifacts which remain a concern in current DEI/MIR systems especially for living animals.

Use of synchrotron-based diffraction-enhanced imaging for visualization of soft tissues in invertebrates

Images of terrestrial and marine invertebrates (snails and bivalves) have been obtained by using an X-ray phase-contrast imaging technique, namely, synchrotron-based diffraction-enhanced imaging. Synchrotron X-rays of 20, 30 and 40keV were used, which penetrate deep enough into animal soft tissues. The phase of X-ray photons shifts slightly as they traverse an object, such as animal soft tissue, and interact with its atoms. Biological features, such as shell morphology and animal physiology, have been visualized. The contrast of the images obtained at 40keV is the best. This optimum energy provided a clear view of the internal structural organization of the soft tissue with better contrast. The contrast is higher at edges of internal soft-tissue structures. The image improvements achieved with the diffraction-enhanced imaging technique are due to extinction, i.e., elimination of ultra-small-angle scattering. They enabled us to identify a few embedded internal shell features, such as the origin of the apex, which is the firmly attached region of the soft tissue connecting the umbilicus to the external morphology. Diffraction-enhanced imaging can provide high-quality images of soft tissues valuable for biology.

Compositional images from the Diffraction Enhanced Imaging technique

Diffraction Enhanced Imaging (DEI) derives X-ray contrast from absorption, refraction, and extinction. While the refraction angle image of DEI represents the gradient of the projected mass density of the object, the absorption image measures the projected attenuation (μt¯) of an object. Using a simple integral method it has been shown that a mass density image (ρt¯) can be obtained from the refraction angle image. It then is a simple matter to develop a combinational image by dividing these two images to create a μ/ρ image. The μ/ρ is a fundamental property of a material and is therefore useful for identifying the composition of an object. In projection X-ray imaging the μ/ρ image identifies the integrated composition of the elements along the beam path. When applied to DEI computed tomography (CT), the image identifies the composition in each voxel. This method presents a new type of spectroscopy based in radiography. We present the method of obtaining the compositional image, the results of experiments in which we verify the method with known standards and an application of the method to breast cancer imaging.

A physical model of multiple-image radiography

We recently proposed a phase-sensitive x-ray imaging method called multiple-image radiography (MIR), which is an improvement on the diffraction-enhanced imaging technique. MIR simultaneously produces three images, depicting separately the effects of absorption, refraction and ultra-small-angle scattering of x-rays, and all three MIR images are virtually immune to degradation caused by scattering at higher angles. Although good results have been obtained using MIR, no quantitative model of the imaging process has yet been developed. In this paper, we present a theoretical prediction of the MIR image values in terms of fundamental physical properties of the object being imaged. We use radiative transport theory to model the beam propagation, and we model the object as a stratified medium containing discrete scattering particles. An important finding of our analysis is that the image values in all three MIR images are line integrals of various object parameters, which is an essential property for computed tomography to be achieved with conventional reconstruction methods. Our analysis also shows that MIR truly separates the effects of absorption, refraction and ultra-small-angle scattering for the case considered. We validate our analytical model using real and simulated imaging data.

Mass density images from the diffraction enhanced imaging technique

Conventional x-ray radiography measures the projected x-ray attenuation of an object. It requires attenuation differences to obtain contrast of embedded features. In general, the best absorption contrast is obtained at x-ray energies where the absorption is high, meaning a high absorbed dose. Diffraction-enhanced imaging (DEI) derives contrast from absorption, refraction, and extinction. The refraction angle image of DEI visualizes the spatial gradient of the projected electron density of the object. The projected electron density often correlates well with the projected mass density and projected absorption in soft-tissue imaging, yet the mass density is not an "energy"-dependent property of the object, as is the case of absorption. This simple difference can lead to imaging with less x-ray exposure or dose. In addition, the mass density image can be directly compared (i.e., a signal-to-noise comparison) with conventional radiography. We present the method of obtaining the mass density image, the results of experiments in which comparisons are made with radiography, and an application of the method to breast cancer imaging.

Visualisation of calcifications and thin collagen strands in human breast tumour specimens by the diffraction-enhanced imaging technique: a comparison with conventional mammography and histology

Six excised human breast tissue specimens carrying benign and malignant tumours were examined with the diffraction-enhanced imaging technique. Diffraction-enhanced images were compared with diagnostic screen-film mammograms and the correlation with histological information of the specimens was established. The enhanced visibility of calcifications, some of which were smaller than 0.15 mm in diameter, is reported in detail. Fine details of the structures such as strands of collagen and contours between glandular and adipose tissue, which are barely visible at the contrast detection limit in the conventional absorption-based mammograms, are clearly visible in the diffraction-enhanced images. Microscopic study of the stained histopathological sections unequivocally confirms the correlation of the radiographic findings with the morphologic changes in specimens. An increased soft tissue contrast and a combination of information obtained with disparate diffraction-enhanced images provide better visibility of mammographically indistinguishable features. This kind of additional structural information of the breast tissue is required to improve assessment accuracy and earlier detection of the breast lesions. These advances in image quality make the method a very promising candidate for mammography.

Visualisation of calcifications and thin collagen strands in human breast tumour specimens by the diffraction-enhanced imaging technique: a comparison with conventional mammography and histology

Visualisation of calcifications and thin collagen strands in human breast tumour specimens by the diffraction-enhanced imaging technique: a comparison with conventional mammography and histology

Comparison between a position sensitive germanium detector and a taper optics CCD “FRELON” camera for diffraction enhanced imaging

Diffraction Enhanced Imaging (DEI) can significantly improve the expressiveness of radiology. The contrast mechanism of DEI, in addition to absorption contrast, exploits the differences in X-ray refraction properties, which are sensed by a perfect crystal placed between the sample and the detector. DEI needs a monochromatic collimated X-ray source, which is available for instance from synchrotrons. The X-ray beam is laminar and the sample is vertically scanned for projection imaging or is rotated for CT. Detectors should match the beam characteristics and should also accomplish the other two main requirements for DEI mammography: high spatial resolution and high Detective Quantum Efficiency (DQE) in a large energy range (20–60 keV). The first permit to exploit the edge contrast enhancement obtained with the DEI technique, for example the improved visualization of microcalcifications in mammographic imaging. The second allows minimizing the dose needed for a radiograph without sacrificing spatial resolution. Apart from this, a dynamic range as good as possible is required (typically from 14 to 16 bits) as well as a high readout speed, which is particularly important for CT. These specifications are difficult to be all condensed in a single detector. At the medical beamline of the ESRF two devices have been utilized for DEI radiography: a linear germanium detector (432 pixels, 350 microns pitch), which had been developed for angiography and cerebral CT and a 2048×2048 CCD camera with taper optics which has been built at the ESRF. The first detector shows an excellent DQE at zero frequency in a large energy range (∼90% from 20 keV up to 50 keV) but limited spatial resolution. In the latter a better compromise for DEI in the 20–30 keV range has been realized: a pixel size of 47 μm and a DQE(0) from 0.5 to 0.6 has been achieved. The performances of the two detectors will be presented here in detail and discussed.

Diffraction enhanced imaging contrast mechanisms in breast cancer specimens.

We have investigated the contrast mechanisms of the refraction angle, and the apparent absorption images obtained from the diffraction enhanced imaging technique (DEI) and have correlated them with the absorption contrast of conventional radiography. The contrast of both the DEI refraction angle image and the radiograph have the same dependence on density differences of the tissues in the visualization of cancer; in radiography these differences directly relate to the contrast while in the DEI refraction angle image it is the density difference and thickness gradient that gives the refraction angle. We show that the density difference of fibrils in breast cancer as measured by absorption images correlate well with the density difference derived from refraction angle images of DEI. In addition we find that the DEI apparent absorption image and the image obtained with the DEI system at the top of the reflectivity curve have much greater contrast than that of the normal radiograph (x8 to 33-fold higher). This is due to the rejection of small angle scattering (extinction) from the fibrils enhancing the contrast.