Experimental Realisation of High-sensitivity Laboratory X-ray Grating-based Phase-contrast Computed Tomography

The possibility to perform high-sensitivity X-ray phase-contrast imaging with laboratory grating-based phase-contrast computed tomography (gbPC-CT) setups is of great interest for a broad range of high-resolution biomedical applications. However, achieving high sensitivity with laboratory gbPC-CT setups still poses a challenge because several factors such as the reduced flux, the polychromaticity of the spectrum, and the limited coherence of the X-ray source reduce the performance of laboratory gbPC-CT in comparison to gbPC-CT at synchrotron facilities. In this work, we present our laboratory X-ray Talbot-Lau interferometry setup operating at 40 kVp and describe how we achieve the high sensitivity yet unrivalled by any other laboratory X-ray phase-contrast technique. We provide the angular sensitivity expressed via the minimum resolvable refraction angle both in theory and experiment, and compare our data with other differential phase-contrast setups. Furthermore, we show that the good stability of our high-sensitivity setup allows for tomographic scans, by which even the electron density can be retrieved quantitatively as has been demonstrated in several preclinical studies

Improved In vivo Assessment of Pulmonary Fibrosis in Mice using X-Ray Dark-Field Radiography

Idiopathic pulmonary fibrosis (IPF) is a chronic and progressive lung disease with a median life expectancy of 4-5 years after initial diagnosis. Early diagnosis and accurate monitoring of IPF are limited by a lack of sensitive imaging techniques that are able to visualize early fibrotic changes at the epithelial-mesenchymal interface. Here, we report a new x-ray imaging approach that directly visualizes the air-tissue interfaces in mice in vivo. This imaging method is based on the detection of small-angle x-ray scattering that occurs at the air-tissue interfaces in the lung. Small-angle scattering is detected with a Talbot-Lau interferometer, which provides the so-called x-ray dark-field signal. Using this imaging modality, we demonstrate-for the first time-the quantification of early pathogenic changes and their correlation with histological changes, as assessed by stereological morphometry. The presented radiography method is significantly more sensitive in detecting morphological changes compared with conventional x-ray imaging, and exhibits a significantly lower radiation dose than conventional x-ray CT. As a result of the improved imaging sensitivity, this new imaging modality could be used in future to reduce the number of animals required for pulmonary research studies

X-Ray Phase-Contrast Tomography of Renal Ischemia-Reperfusion Damage

Purpose: The aim of the study was to investigate microstructural changes occurring in unilateral renal ischemia-reperfusion injury in a murine animal model using synchrotron radiation. Material and Methods: The effects of renal ischemia-reperfusion were investigated in a murine animal model of unilateral ischemia. Kidney samples were harvested on day 18. Grating-Based Phase-Contrast Imaging (GB-PCI) of the paraffin-embedded kidney samples was performed at a Synchrotron Radiation Facility (beam energy of 19 keV). To obtain phase information, a two-grating Talbot interferometer was used applying the phase stepping technique. The imaging system provided an effective pixel size of 7.5 mu m. The resulting attenuation and differential phase projections were tomographically reconstructed using filtered back-projection. Semi-automated segmentation and volumetry and correlation to histopathology were performed. Results: GB-PCI provided good discrimination of the cortex, outer and inner medulla in non-ischemic control kidneys. Post-ischemic kidneys showed a reduced compartmental differentiation, particularly of the outer stripe of the outer medulla, which could not be differentiated from the inner stripe. Compared to the contralateral kidney, after ischemia a volume loss was detected, while the inner medulla mainly retained its volume (ratio 0.94). Post-ischemic kidneys exhibited severe tissue damage as evidenced by tubular atrophy and dilatation, moderate inflammatory infiltration, loss of brush borders and tubular protein cylinders. Conclusion: In conclusion GB-PCI with synchrotron radiation allows for non-destructive microstructural assessment of parenchymal kidney disease and vessel architecture. If translation to lab-based approaches generates sufficient density resolution, and with a time-optimized image analysis protocol, GB-PCI may ultimately serve as a non-invasive, non-enhanced alternative for imaging of pathological changes of the kidney

3D algebraic iterative reconstruction for cone-beam x-ray differential phase-contrast computed tomography.

Due to the potential of compact imaging systems with magnified spatial resolution and contrast, cone-beam x-ray differential phase-contrast computed tomography (DPC-CT) has attracted significant interest. The current proposed FDK reconstruction algorithm with the Hilbert imaginary filter will induce severe cone-beam artifacts when the cone-beam angle becomes large. In this paper, we propose an algebraic iterative reconstruction (AIR) method for cone-beam DPC-CT and report its experiment results. This approach considers the reconstruction process as the optimization of a discrete representation of the object function to satisfy a system of equations that describes the cone-beam DPC-CT imaging modality. Unlike the conventional iterative algorithms for absorption-based CT, it involves the derivative operation to the forward projections of the reconstructed intermediate image to take into account the differential nature of the DPC projections. This method is based on the algebraic reconstruction technique, reconstructs the image ray by ray, and is expected to provide better derivative estimates in iterations. This work comprises a numerical study of the algorithm and its experimental verification using a dataset measured with a three-grating interferometer and a mini-focus x-ray tube source. It is shown that the proposed method can reduce the cone-beam artifacts and performs better than FDK under large cone-beam angles. This algorithm is of interest for future cone-beam DPC-CT applications

A reconstruction method for cone-beam differential x-ray phase-contrast computed tomography

Most existing differential phase-contrast computed tomography (DPC-CT) approaches are based on three kinds of scanning geometries, described by parallel-beam, fan-beam and cone-beam. Due to the potential of compact imaging systems with magnified spatial resolution, cone-beam DPC-CT has attracted significant interest. In this paper, we report a reconstruction method based on a back-projection filtration (BPF) algorithm for cone-beam DPC-CT. Due to the differential nature of phase contrast projections, the algorithm restrains from differentiation of the projection data prior to back-projection, unlike BPF algorithms commonly used for absorption-based CT data. This work comprises a numerical study of the algorithm and its experimental verification using a dataset measured with a three-grating interferometer and a micro-focus x-ray tube source. Moreover, the numerical simulation and experimental results demonstrate that the proposed method can deal with several classes of truncated cone-beam datasets. We believe that this feature is of particular interest for future medical cone-beam phase-contrast CT imaging applications. (C) 2012 Optical Society of Americ

Contrast-to-noise ratio optimization for a prototype phase-contrast computed tomography scanner.

In the field of biomedical X-ray imaging, novel techniques, such as phase-contrast and dark-field imaging, have the potential to enhance the contrast and provide complementary structural information about a specimen. In this paper, a first prototype of a preclinical X-ray phase-contrast CT scanner based on a Talbot-Lau interferometer is characterized. We present a study of the contrast-to-noise ratios for attenuation and phase-contrast images acquired with the prototype scanner. The shown results are based on a series of projection images and tomographic data sets of a plastic phantom in phase and attenuation-contrast recorded with varying acquisition settings. Subsequently, the signal and noise distribution of different regions in the phantom were determined. We present a novel method for estimation of contrast-to-noise ratios for projection images based on the cylindrical geometry of the phantom. Analytical functions, representing the expected signal in phase and attenuation-contrast for a circular object, are fitted to individual line profiles of the projection data. The free parameter of the fit function is used to estimate the contrast and the goodness of the fit is determined to assess the noise in the respective signal. The results depict the dependence of the contrast-to-noise ratios on the applied source voltages, the number of steps of the phase stepping routine, and the exposure times for an individual step. Moreover, the influence of the number of projection angles on the image quality of CT slices is investigated. Finally, the implications for future imaging purposes with the scanner are discussed

Schematic geometry of x-ray refraction in a medium for cone-beam DPC-CT.

<p>(<i>x</i>^′,<i>z</i>^′) represents the coordinates of the detector plane. <i>OAC</i> is the mid-plane. <i>D</i> is the distance from the source to the rotation center <i>O</i>. <i>θ</i> represents the view angle under which the data was taken. <i>l</i> is any incident ray in the three dimensional space under <i>θ</i>. <i>P</i> is the line integral of <i>δ</i> along <i>l</i>.</p

Numerical simulation results.

<p>(a) and (b) are the images of the axial mid-plane of the Defrise phantom reconstructed by FDK and AIR algorithms respectively, which correspond to the case with a cone-beam angle of 0^∘. (d) and (e) are the sagittal slices reconstructed by FDK and AIR algorithms respectively, which have a maximum cone-beam angle of 6^∘. Starting from the bottom, the central layer of each disc corresponds to a cone angle of 0^∘, 1.5^∘, 3.0^∘, 4.5^∘ and 6.0^∘. (c) and (f) present the profiles along the red solid lines and the blue dashed lines in (a), (b) and (d), (e). The display grey scale is set to be [0 1.1]×10⁻⁶. The relax coefficient is set to be 0.8 and the number of the overall iterations is 10.</p

Comparison of experimental reconstruction results in three typical planes.

<p>(a), (b) and (c) correspond to the axial mid-plane, (d), (e), (f), (d) and (h) to the axial plane with a cone-beam angle of 2.5 ^∘ and (i), (j), (k), (l) and (m) to the sagittal mid-plane. (a), (d), (f), (i) and (k) are reconstructed by FDK algorithm. (b), (e), (g), (j) and (l) are reconstructed by AIR algorithm. (f) and (g) are the regions of interest indicated by the red solid rectangle and the blue dashed rectangle in (d) and (e). (k) and (l) are the regions of interest indicated by the red solid rectangle and the blue dashed rectangle in (i) and (j). (c) presents the profiles along the red solid line and the blue dashed line in (a) and (b), (h) in (f) and (g) and (m) in (k) and (l). The reconstructed value is scaled to [0, 1].</p

Implementation procedure of 3D algebraic iteration reconstruction for cone-beam DPC-CT.

<p>Implementation procedure of 3D algebraic iteration reconstruction for cone-beam DPC-CT.</p