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Classical ghost imaging is a computational imaging technique that employs patterned illumination. It is very similar in concept to the single-pixel camera in that an image may be reconstructed from a set of measurements even though all imaging photons or particles that pass through that sample are never recorded with a position resolving detector. The method was first conceived and applied for visible-wavelength photons and was subsequently translated to other probes such as x rays, atomic beams, electrons, and neutrons. In the context of classical ghost imaging using penetrating probes that enable transmission measurement, we here consider several questions relating to the achievable signal-to-noise ratio (SNR). This is compared with the SNR for conventional imaging under scenarios of constant radiation dose and constant experiment time, considering both photon shot noise and per-measurement electronic readout noise. We show that inherent improved SNR capabilities of classical ghost imaging are limited to a subset of these scenarios and are actually due to increased dose (Fellgett advantage). An explanation is also presented for recent results published in the literature that are not consistent with these findings.

Ghost imaging has recently been successfully achieved in the X-ray regime. Due to the penetrating power of X-rays this immediately opens up the possibility of ghost-tomography. No research into this topic currently exists in the literature. Here, we present adaptations of conventional X-ray tomography techniques to this new ghost-imaging scheme. Several numerical implementations for tomography through X-ray ghost-imaging are considered. Specific attention is paid to schemes for reducing the noise-like artefacts of the resulting tomographic reconstruction, issues related to dose fractionation, and considerations regarding the ensemble of illuminating masks used for ghost-imaging. Each theme is explored through a series of numerical simulations, and several suggestions offered for practical realisations of ghost-tomography.

Lead (Pb) exposure from household dust is a major childhood health concern because of its adverse impact on cognitive development. This study investigated the absorption kinetics of Pb from indoor dust following a single dose instillation into C57BL/6 mice. Blood Pb concentration (PbB) was assessed over 24 h, and the dynamics of particles in the lung and gastro-intestinal (GI) tract were visualized using X-ray fluorescence (XRF) microscopy. The influence of mineralogy on Pb absorption and particle retention was investigated using X-ray absorption near-edge structure spectroscopy. A rapid rise in PbB was observed between 0.25 and 4 h after instillation, peaking at 8 h and slowly declining during a period of 24 h. Following clearance from the lungs, Pb particles were detected in the stomach and small intestine at 4 and 8 h, respectively. Analysis of Pb mineralogy in the residual particles in tissues at 8 h showed that mineral-sorbed Pb and Pb-phosphates dominated the lung, while organic-bound Pb and galena were the main phases in the small intestines. This is the first study to visualize Pb dynamics in the lung and GI tract using XRF microscopy and link the inhalation and ingestion pathways for metal exposure assessment from dust.

In micro-tomography, variants of helical X-ray source trajectories, e.g., double-helix (DH) and space-filling (SF), are attractive alternatives to the conventional circular trajectory, as they satisfy data-sufficiency conditions; this enables exact reconstruction, and large cone-angle (or high flux) imaging. Geometric alignment of micro-tomography experimental data, i.e., radiographs or projection data, to the required micron precision is a difficult problem. Here we consider criteria based on differences in attenuation along opposing rays as a post- acquisition software alignment technique. These opposing rays are called PI-lines and lie on lines that intersect two points of the scanning trajectory and pass through the region of support. The PI-line difference method is particularly appealing due to its low computational cost and small set of inherent assumptions, however, previous studies have exposed some limitations in precision. The number and distribution of PI-lines is highly dependent on the trajectory and thus so is the robustness of PI-line difference; here we show that DH and SF trajectories are particularly amenable to this technique. For these trajectories, we observe that the technique is applicable to both static and per-projection alignment estimation. We present results where PI-line difference alignment estimates are of equivalent accuracy as alignment estimates obtained from existing state-of-the-art methods: a tomogram sharpness method for static alignment and a re-projection-alignment method for per-projection alignment. In both cases, the computational expense of PI-line difference alignment estimation is a fraction of the tomogram-based meth- ods.

An experimental procedure for transmission X-ray ghost imaging using synchrotron light is presented. Hard X-rays from an undulator were divided by a beamsplitter to produce two copies of a speckled incident beam. Both beams were simultaneously measured on an indirect pixellated detector and the intensity correlation between the two copies was used to retrieve the ghost image of samples placed in one of the two beams, without measuring the samples directly. Aiming at future practical uses of X-ray ghost imaging, the authors discuss details regarding data acquisition, image reconstruction strategies and measure the point-spread function of the ghost-imaging system. This approach may become relevant for applications of ghost imaging with X-ray sources such as undulators in storage rings, free-electron lasers and lower-coherence laboratory facilities.

We present a new family of X-ray source scanning trajectories for large-angle cone-beam computed tomography. Traditional scanning trajectories are described by continuous paths through space, e.g., circles, saddles, or helices, with a large degree of redundant information in adjacent projection images. Here, we consider discrete trajectories as a set of points that uniformly sample the entire space of possible source positions, i.e., a space-filling trajectory (SFT). We numerically demonstrate the advantageous properties of the SFT when compared with circular and helical trajectories as follows: first, the most isotropic sampling of the data, second, optimal level of mutually independent data, and third, an improved condition number of the tomographic inverse problem. The practical implications of these properties in tomography are also illustrated by simulation. We show that the SFT provides greater data acquisition efficiency, and reduced reconstruction artifacts when compared with helical trajectory. It also possesses an effective preconditioner for fast iterative tomographic reconstruction.

The quest for imaging protocols with ever-reduced dose is one of the most powerful motivators driving the currently exploding field of ghost imaging (GI). Ghost tomography (GT) using single-pixel detection extends the burgeoning field of GI to 3D, with the use of penetrating radiation. For hard x-rays, GT has the potential to relax the constraints that dose rate and detector performance impose on image quality and resolution. In this work, spatially random x-ray intensity patterns illuminate a specimen from various view-angles; in each case, the total transmitted intensity is recorded by a single-pixel (or bucket) detector. These readings, combined with knowledge of the corresponding 2D illuminating patterns and specimen orientations, are sufficient for 3D specimen reconstruction. The experimental demonstration of GT is presented here using synchrotron hard x-rays. This result significantly expands the scope of GI to encompass volumetric imaging (i.e., tomography), of optically opaque objects using penetrating radiation.