Objective.To employ a single-projection dark-field imaging approach to obtain statistical information on alveolar size and number as key structural indicators of lung health.Approach.The algorithm employed here retrieves the projected thickness of the sample from a propagation-based phase contrast image using the transport-of-intensity equation. The first Born approximation is then used to isolate the dark-field signal associated with edge scattering, which increases the visibility of microstructure boundaries. Poly(methyl methacrylate) spheres of known sizes were imaged first as an idealised alveolar model. The dark-field signal was then recovered from propagation-based phase-contrast x-ray images of the lungs of small mammals using this method.Main results.The retrieved dark-field signal was found to be proportional to both the alveolar size (R2=0.85) and the number in projection (R2=0.69), and these measurements could be combined to provide an estimate of the total surface area of the alveolar interfaces (R2=0.78).Significance.This demonstrates the approach's ability to potentially indicate lung health using the dark-field signal retrieved from a single-phase-contrast x-ray image.

The Micro-Computed Tomography (MCT) beamline at the Australian Synchrotron (ANSTO) offers superior capabilities in micrometer-scale spatial resolution and three-dimensional x-ray imaging. MCT is the first of the eight new BRIGHT beamlines and has been operating successfully with users for approximately two years. It is a bending magnet beamline capable of delivering a white beam, a pink beam, or a monochromatic beam in the 8-40 keV energy range using a Double Multilayer Monochromator (DMM). Ongoing development continues at the MCT beamline to extend its capabilities. In this article, we present the operation and energy calibration of the DMM, highlighting the unique advantages offered by synchrotron-based micro-CT and its application for quantitative imaging, such as density measurements using monochromatic energy.

This study validates the effectiveness of a quantitative detector calibration-originally developed for monochromatic synchrotron radiation-when applied with a polychromatic x-ray source, using both a Hamamatsu CMOS flat panel detector and a WidePIX photon-counting detector with Timepix chips. We show that, despite the energy dependence of the detector response, this calibration is a simple yet robust tool for suppressing computed tomography (CT) ring artefacts in both attenuation contrast and phase contrast CT. Furthermore, we demonstrate that this algorithm is effective even when the ring artefacts are present at a level below the shot noise. This makes it especially useful for data that is filtered in a way that suppresses noise, such as low-dose imaging via phase retrieval.

The first new beamline of the BRIGHT project—involving the construction of eight new beamlines at the Australian Synchrotron—is the Micro-Computed Tomography (MCT) beamline. MCT will extend the facility’s capability for higher spatial resolution X-ray-computed tomographic imaging allowing for commensurately smaller samples in comparison with the existing Imaging and Medical Beamline (IMBL). The source is a bending-magnet and it is operating in the X-ray energy range from 8 to 40 keV. The beamline provides important new capability for a range of biological and material-science applications. Several imaging modes will be offered such as various X-ray phase-contrast modalities (propagation-based, grating-based, and speckle-based), in addition to conventional absorption contrast. The unique properties of synchrotron radiation sources (high coherence, energy tunability, and high brightness) are predominantly well-suited for producing phase contrast data. An update on the progress of the MCT project in delivering high-spatial-resolution imaging (in the order of micron size) of mm-scale objects will be presented in detail with some imaging results from the hot-commissioning stage.

In X-ray imaging, photons are transmitted through and absorbed by the target object, but are also scattered in significant quantities. Previous attempts to use scattered X-ray photons for imaging applications used pencil or fan beam illumination. Here we present 3D X-ray Scatter Tomography using full-field illumination for small-animal imaging. Synchrotron imaging experiments were performed on a phantom and the chest of a juvenile rat. Transmitted and scattered photons were simultaneously imaged with separate cameras; a scientific camera directly downstream of the sample stage, and a pixelated detector with a pinhole imaging system placed at $45{}^\circ $ to the beam axis. We obtained scatter tomogram feature fidelity sufficient for segmentation of the lungs and major airways in the rat. The image contrast in the scatter tomogram slices approached that of transmission imaging, indicating robustness to the amount of multiple scattering present in our case. This opens the possibility of augmenting full-field 2D imaging systems with additional scatter detectors to obtain complementary modes or to improve the fidelity of existing images without additional dose, potentially leading to single-shot or reduced-angle tomography or overall dose reduction for live animal studies.

X-ray computed tomography (CT) has been a mainstay of clinical neuroimaging since the 1970s. Its quick scans, high spatial resolution, ease of availability, and relatively low cost make it essential for the diagnosis and monitoring of injury and disease. However, low contrast resolution relative to magnetic resonance imaging (MRI) has limited its use in resolving subtle variations between different soft tissue types and between inflamed and healthy tissues. While clinical CT exploits the attenuation of X-rays through the body, phase contrast X-ray imaging (PCXI) additionally uses refraction and diffraction, increasing sensitivity to subtle inhomogeneities in tissue composition. Most PCXI-CT research has focused on lung and breast tissue, where the sparsely-distributed surrounding bone does not significantly obscure soft tissues. However, neuroimaging with X-rays poses unique challenges, since the brain is fully encased within the highly-attenuating skull, making soft-tissue segmentation difficult and creating artifacts that can obscure the underlying anatomy. We have previously demonstrated that PCXI-CT can resolve anatomical structures within the brains of small animals in situ at micron-scale resolution (Croton et al., 2018) and have developed new correction methods to address the key artifacts that appear when capturing these soft-tissue images (Croton et al., 2019). Here, we present recent progress in the detection of brain injury with PCXI-CT, including direct comparisons to MRI of the same injured brains. Our project aims to spatially resolve injuries that elude MRI, including both traumatic and diffuse injury, in order to better understand the progression of cerebral palsy near birth.

The ill-posed problem of phase retrieval in optics, using one or more intensity measurements, has a multitude of applications using electromagnetic or matter waves. Many phase retrieval algorithms are computed on pixel arrays using discrete Fourier transforms due to their high computational efficiency. However, the mathematics underpinning these algorithms is typically formulated using continuous mathematics, which can result in a loss of spatial resolution in the reconstructed images. Herein we investigate how phase retrieval algorithms for propagation-based phase-contrast X-ray imaging can be rederived using discrete mathematics and result in more precise retrieval for single- and multi-material objects and for spectral image decomposition. We validate this theory through experimental measurements of spatial resolution using computed tomography (CT) reconstructions of plastic phantoms and biological tissues, using detectors with a range of imaging system point spread functions (PSFs). We demonstrate that if the PSF substantially suppresses high spatial frequencies, the potential improvement from utilising the discrete derivation is limited. However, with detectors characterised by a single pixel PSF (e.g. direct, photon-counting X-ray detectors), a significant improvement in spatial resolution can be obtained, demonstrated here at up to 17%.

Propagation-based phase-contrast imaging, used in conjunction with the phase retrieval algorithm based on the Transport-of-Intensity Equation (TIE) (Paganin et al., 2002), is commonly used to improve the sensitivity of X-ray imaging. Recently, a ‘Generalised Paganin Method’ algorithm was published to correct the tendency of the TIE algorithm to over-blur images. The article, Paganin et al. 2020, provided a derivation of the new method and demonstrated a difference in the level of blurring applied by each algorithm. In this manuscript, we quantify the spatial resolution improvement and describe the optimal experimental conditions to observe this improvement. We link the effectiveness of the spatial resolution improvement to the imaging point spread function (PSF), incorporating the PSF to compare the blurring applied by each algorithm. We then validate this model through measurements of spatial resolution in experimental data imaging plastic phantoms and biological tissue, using detectors with different PSFs. By analysing edge-spread functions in CT data captured with indirect detectors with PSFs of several pixels in extent, we show negligible spatial resolution improvement when using the generalised Paganin method. However, a clear improvement in spatial resolution, up to 17%, was observed with direct detectors having PSFs of approximately one pixel in extent. Additionally, we demonstrate clear visual improvement in resolution in CT slices of rat lungs. Finally, we demonstrate the versatility of this improvement by generalising other phase retrieval algorithms, namely for multi-material samples and for spectral decomposition using propagation-based phase contrast, and experimentally verify improvements in spatial resolution.

Background Preterm infants are commonly supported with 4–8 cm H 2 O continuous positive airway pressures (CPAP), although higher CPAP levels may improve functional residual capacity (FRC). Methods Preterm rabbits delivered at 29/32 days (~26–28 weeks human) gestation received 0, 5, 8, 12, 15 cm H 2 O of CPAP or variable CPAP of 15 to 5 or 15 to 8 cm H 2 O (decreasing ~2 cm H 2 O/min) for up to 10 min after birth. Results FRC was lower in the 0 (6.8 (1.0–11.2) mL/kg) and 5 (10.1 (1.1–16.8) mL/kg) compared to the 15 (18.8 (10.9–22.4) mL/kg) cm H 2 O groups ( p = 0.003). Fewer kittens achieved FRC > 15 mL/kg in the 0 (20%), compared to 8 (36%), 12 (60%) and 15 (73%) cm H 2 O groups ( p = 0.008). While breathing rates were not different ( p = 0.096), apnoea tended to occur more often with CPAP < 8 cm H 2 O ( p = 0.185). CPAP belly and lung bulging rates were similar whereas pneumothoraces were rare. Lowering CPAP from 15 to 5, but not 15 to 8 cm H 2 O, decreased FRC and breathing rates. Conclusion In all, 15 cm H 2 O of CPAP improved lung aeration and reduced apnoea, but did not increase the risk of lung over-expansion, pneumothorax or CPAP belly immediately after birth. FRC and breathing rates were maintained when CPAP was decreased to 8 cm H 2 O. Impact Although preterm infants are commonly supported with 4–8 cm H 2 O CPAP at birth, preclinical studies have shown that higher PEEP levels improve lung aeration. In this study, CPAP levels of 15 cm H 2 O improved lung aeration and reduced apnoea in preterm rabbit kittens immediately after birth. In all, 15 cm H 2 O CPAP did not increase the risk of lung over-expansion (indicated by bulging between the ribs), pneumothorax, or CPAP belly. These results can be used when designing future studies on CPAP strategies for preterm infants in the delivery room.

This work demonstrates the use of a scientific-CMOS (sCMOS) energy-integrating detector as a photon-counting detector, thereby eliminating dark current and read-out noise issues, that simultaneously provides both energy resolution and sub-pixel spatial resolution for X-ray imaging. These capabilities are obtained by analyzing visible light photon clouds that result when X-ray photons produce fluorescence from a scintillator in front of the visible light sensor. Using low-fluence monochromatic X-ray projections to avoid overlapping photon clouds, the centroid of individual X-ray photon interactions was identified. This enabled a tripling of the spatial resolution of the detector to 6.71 ± 0.04 µm. By calculating the total charge deposited by this interaction, an energy resolution of 61.2 ± 0.1% at 17 keV was obtained. When combined with propagation-based phase contrast imaging and phase retrieval, a signal-to-noise ratio of up to 15 ± 3 was achieved for an X-ray fluence of less than 3 photons/mm2.

We present a pixel-specific, measurement-driven correction that effectively reduces errors in detector response that give rise to the ring artifacts commonly seen in X-ray computed tomography (CT) scans. This correction is easy to implement, suppresses CT artifacts significantly, and is effective enough for use with both absorption and phase contrast imaging. It can be used as a standalone correction or in conjunction with existing ring artifact removal algorithms to further improve image quality. We validate this method using two X-ray CT data sets acquired using monochromatic sources, showing post-correction signal-to-noise increases of up to 55%, and we define an image quality metric to use specifically for the assessment of ring artifact suppression.

Background: Spontaneous breathing is essential for successful non-invasive respiratory support delivered by a facemask at birth. As hypoxia is a potent inhibitor of spontaneous breathing, initiating respiratory support with a high fraction of inspired O2 may reduce the risk of hypoxia and increase respiratory effort at birth. Methods: Preterm rabbit kittens (29 days gestation, term ~32 days) were delivered and randomized to receive continuous positive airway pressure with either 21% (n = 12) or 100% O2 (n = 8) via a facemask. If apnea occurred, intermittent positive pressure ventilation (iPPV) was applied with either 21% or 100% O2 in kittens who started in 21% O2, and remained at 100% O2 for kittens who started the experiment in 100% O2. Respiratory rate (breaths per minute, bpm) and variability in inter-breath interval (%) were measured from esophageal pressure recordings and functional residual capacity (FRC) was measured from synchrotron phase-contrast X-ray images. Results: Initially, kittens receiving 21% O2 had a significantly lower respiratory rate and higher variability in inter-breath interval, indicating a less stable breathing pattern than kittens starting in 100% O2 [median (IQR) respiratory rate: 16 (4–28) vs. 38 (29–46) bpm, p = 0.001; variability in inter-breath interval: 33.3% (17.2–50.1%) vs. 27.5% (18.6–36.3%), p = 0.009]. Apnea that required iPPV, was more frequently observed in kittens in whom resuscitation was started with 21% compared to 100% O2 (11/12 vs. 1/8, p = 0.001). After recovering from apnea, respiratory rate was significantly lower and variability in inter-breath interval was significantly higher in kittens who received iPPV with 21% compared to 100% O2. FRC was not different between study groups at both timepoints. Conclusion: Initiating resuscitation with 100% O2 resulted in increased respiratory activity and stability, thereby reducing the risk of apnea and need for iPPV after birth. Further studies in human preterm infants are mandatory to confirm the benefit of this approach in terms of oxygenation. In addition, the ability to avoid hyperoxia after initiation of resuscitation with 100% oxygen, using a titration protocol based on oxygen saturation, needs to be clarified.

We present a pixel-specific, measurement-driven correction that effectively minimizes errors in detector response that give rise to the ring artifacts commonly seen in X-ray computed tomography (CT) scans. This correction is easy to implement, suppresses CT artifacts significantly, and is effective enough for use with both absorption and phase contrast imaging. It can be used as a standalone correction or in conjunction with existing ring artifact removal algorithms to further improve image quality. We validate this method using two X-ray CT data sets, showing post-correction signal-to-noise increases of up to 55%, and we define an image quality metric to use specifically for the assessment of ring artifact suppression.

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We propose a sparse imaging methodology called chaotic sensing (ChaoS) that enables the use of limited yet deterministic linear measurements through fractal sampling. A novel fractal in the discrete Fourier transform is introduced that always results in the artifacts being turbulent in nature. These chaotic artifacts have characteristics that are image independent, facilitating their removal through dampening (via image denoising), and obtaining the maximum likelihood solution. In contrast with existing methods, such as compressed sensing, the fractal sampling is based on digital periodic lines that form the basis of discrete projected views of the image without requiring additional transform domains. This allows the creation of finite iterative reconstruction schemes in recovering an image from its fractal sampling that is also new to discrete tomography. As a result, ChaoS supports linear measurement and optimization strategies, while remaining capable of recovering a theoretically exact representation of the image. We apply the method to the simulated and experimental limited magnetic resonance (MR) imaging data, where restrictions imposed by MR physics typically favor linear measurements for reducing acquisition time.

Scanning X-ray fluorescence tomography was once considered impractical due to prohibitive measurement time requirements but is now common for investigating metal distributions within small systems. A recent look-ahead to the possibilities of 4th-generation synchrotron light sources [J. Synchrotron. Radiat. 21, 1031 (2014)] raised the possibility of a spiral-scanning measurement scheme where motion overheads are almost completely eliminated. Here we demonstrate the spiral scanning measurement and use Fourier ring correlation analysis to interrogate sources of resolution degradation. We develop an extension to the Fourier ring correlation formalism that enables direct determination of resolution from the measured sinogram data, greatly enhancing its power as a diagnostic tool for computed tomography.

Magnetic resonance (MR) imaging is an important imaging modality for diagnostic medicine due to its ability to visualize the soft tissue of the human body in three dimensions (3D) without ionizing radiation. MR imaging however, typically relies on measurement techniques that do not exploit the geometry of discrete Fourier space, so called k-space, where the measurements are made. In this work, we firstly present a novel k-space tiling scheme that utilizes the finite geometry of discrete Fourier space via the discrete Fourier slice theorem. This produces a sampling of k-space that is pseudo-radial, to be more noise and patient-movement tolerant, and pseudo-random, further improving robustness to noise, whilst sampling with sufficient density near the central k-space region, where the majority of power of anatomical images lies. Secondly, we introduce a stable and iterative discrete reconstruction scheme for recovering images from their limited k-space measurements (in the form discrete slices) based on the maximum likelihood expectation maximization approach. We study the performance of the proposed approach using simulated MR measurements in k-space.

Magnetic resonance (MR) imaging is an important imaging modality for diagnostic medicine due to its ability to visualize the soft tissue of the human body in three dimensions (3D) without ionizing radiation. MR imaging however, typically relies on measurement techniques that do not exploit the geometry of discrete Fourier space, so called k-space, where the measurements are made. In this work, we firstly present a novel k-space tiling scheme that utilizes the finite geometry of discrete Fourier space via the discrete Fourier slice theorem. This produces a sampling of k-space that is pseudo-radial, to be more noise and patient-movement tolerant, and pseudo-random, further improving robustness to noise, whilst sampling with sufficient density near the central k-space region, where the majority of power of anatomical images lies. Secondly, we introduce a stable and iterative discrete reconstruction scheme for recovering images from their limited k-space measurements (in the form discrete slices) based on the maximum likelihood expectation maximization approach. We study the performance of the proposed approach using simulated MR measurements in k-space.

A Geant4 Monte Carlo simulation of the X-ray fluorescence microprobe (XFM) end-station at the Australian Synchrotron has been developed. The simulation is required for optimization of the scan configuration and reconstruction algorithms. As part of the simulation process, a Gaussian beam model was developed. Experimental validation of this simulation has tested the efficacy for use of the low-energy physics models in Geant4 for this synchrotron-based technique. The observed spectral distributions calculated in the 384 pixel Maia detector, positioned in the standard back-scatter configuration, were compared with those obtained from experiments performed at three incident X-ray beam energies: 18.5, 11.0 and 6.8 keV. The reduced χ-squared (\chi^{2}_{\rm{red}}) was calculated for the scatter and fluorescence regions of the spectra and demonstrates that the simulations successfully reproduce the scatter distributions. Discrepancies were shown to occur in the multiple-scatter tail of the Compton continuum. The model was shown to be particularly sensitive to the impurities present in the beryllium window of the Maia detector and their concentrations were optimized to improve the \chi^{2}_{\rm{red}} parametrization in the low-energy fluorescence regions of the spectra.