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Tomographic imaging with radionuclides commonly used in nuclear medicine, such as $^{111}$In (171 and 245 keV) and $^{131}$I (364 keV), is in high demand for medical applications and small animal imaging. The Si/CdTe Compton camera with its high angular and high energy resolutions is an especially promising detector to extend the energy coverage for imaging to the range that covers gamma-ray emitted from these radionuclides. Here, we take the first steps towards short-distance imaging by conducting experiments using three-dimensional phantoms composed of multiple sphere-like solutions of $^{111}$In and $^{131}$I with a diameter of 2.7 mm, placed at a distance of 41 mm. Using simple back-projection methods, the positions of the sources are reproduced with a spatial resolution of 11.5 mm and 9.0 mm (FWHM) for $^{111}$In and $^{131}$I, respectively. We found that a LM-MLEM method gives a better resolution of 4.0 mm and 2.7 mm (FWHM). We resolve source positions of a tetrahedron structure with a source-to-source separation of 28 mm. These findings demonstrate that Compton Cameras have the potential of close-distance imaging of radioisotopes distributions in the energy range below 400 keV.

Tomographic coherent imaging requires the reconstruction of a series of two-dimensional projections of the object. We show that using the solution for the image of one projection as the starting point for the reconstruction of the next projection offers a reliable and rapid approach to the image reconstruction. The method is demonstrated on simulated and experimental data. This technique also simplifies reconstructions using data with curved incident wavefronts.

The greatest advantage of scattering theory-based ultrasound tomography (UT) is its ability to investigate small structures. DBIM is the Distorted Born Iterative Method. The nearest neighbour inter...

SARS-CoV-2 may spread through respiratory droplets released by infected individuals. The viruses are transmitted in moist droplets which cause coronavirus disease. Many countries have mandated the wearing of face masks, to various extents. However, the efficacy of masks is yet to be well rationalised given the limited microstructure information. Here, three common face masks and associated air permeations were revealed by coupling X-ray tomographic imaging and infrared thermal imaging techniques. Quantitative parameters have been extracted from the 3D images. Also, image-based modelling was performed to simulate the permeability to show how droplets pass through the porous structure. Our results show that the N95 mask has the smallest average pore diameter (~30 µm) and the densest nanoscale fibres which provides superior droplet filtration among all cases. Modifications to the N95 masks are proposed to develop the next generation mask with higher efficacy and better breathability. Face masks are key for slowing the spread of COVID-19. Here, the microstructure of three common masks is determined by x-ray tomography, combined with image-based modelling of droplet permeability, revealing that N95 masks are best for droplet filtration.

Mid-infrared laser absorption imaging of flame temperature and species concentration is expanded to three dimensions with linear tomographic methods using Tikhonov regularization. A spatial convolution of two small-scale ( cm) laminar Bunsen-style flames, fueled by either ethylene or ethane, comprised the target flowfields. The flame doublets were alternately backlit with tunable radiation from a quantum cascade laser near 4.85 μ m and an interband cascade laser near 4.19 μ m to resolve rovibrational absorption transitions of carbon monoxide and carbon dioxide, respectively. 2D images were collected at 11 different projection angles, yielding an aggregate of 50,688 unique lines of sight capturing the scene with a pixel resolution of approximately 70 μ m. A linear tomographic reconstruction of absorbance areas with 2D Tikhonov regularization was performed using various numbers of projection angles and compared to a reference image based on an Abel inversion of a single axisymmetric flame. Increasing the number of projection angles improved the tomographic reconstruction with respect to resolving the voids, such as the inner core of the flame, though 11 projection angles still resulted in under-predicted void depths and reconstruction artifacts outside of the flowfield. A 3D masked regularization method was then applied to further constrain the tomographic reconstruction in multiple dimensions and mitigate imaging artifacts. The introduction of the 3D regularization and mask were found to enhance spatial resolution of gradients within the flowfield and improve overall reconstruction accuracy, effectively reducing the requisite number of projection angles.

Flash boiling and plume interaction are common phenomena occurring in gasoline direct injection (GDI) spray at throttling and low load engine conditions. Combined with optical engines and low-pressure vessels, several optical techniques, such as backlight imaging, Mie-scattering, and laser sheet imaging have been employed to study the flash boiling morphology. However, in the 2D images resulting from these techniques (projection views or planar imaging), the 3D information is lost. Those methods are then incapable of providing satisfactory information, especially for the study of multi-plume interaction in flash boiling spray, since multi-plume interaction is not a 2D event. This paper reports the implementation of a 4D tomographic reconstruction method from multi-view diffused back illumination (DBI) images, used for the first time in spray characterization. This cost-effective and time-saving method with a simple experimental setup clarifies the 3D spray structure and fuel trajectory change from non-flashing conditions to flare flash conditions, and quantifies the 3D characteristics of individual plumes in non-flash conditions.

Industrial ultrasonic tomography (UT) possesses unique advantages in visualizing multiphase medium and has received broad attention in the past decades. Facing small bubble distribution imaging, the current independent-transducer-based UT faces bottleneck problems of limited projection number and large projection diameter. To image the cross-sectional bubble distribution, an original concept of ultrasonic phase array tomography (UPAT) is proposed by introducing the ultrasound phase array (UPA) transducers and novel designed sensing strategy into UT. The UPAT emits a wide and directional acoustic beam toward the receivers, on which each element forms a narrow projection to detect small bubbles on its path. Hence, the UPAT forms a novel sensing strategy with shifting and multiangled acoustic beam scanning of the whole cross section, as well as the precise measurement on a high amount of narrow projections. To mathematically model the UPAT, the acoustic field distribution and beam steering algorithm are designed for beam scanning with shifted apertures, while the forward/inverse solutions are proposed for tomographic imaging. In numerical simulations, the eight-transducer UPAT is with much lower imaging error than the state-of-art 32-transducer transmissive/reflective UT with relative error reduced by 65.66% on average. In lab-scale experiments, the reconstructed bubble size, shape, and distribution are with good accuracy, boundary preservation, and image purity.

Analyser-Based Phase-Contrast imaging (ABPCI) is a phase-contrast imaging method that produces high contrast images of weakly absorbing materials. However, it is only sensitive to phase variations lying in the diffraction plane of the analyser crystal (i.e in one dimension; 1-D), as it is highly sensitive to phase variations lying in the diffraction plane of the analyser crystal. In order to accurately account for and measure phase effects produced by the wavefield-sample interaction, ABPCI and other 1-D phase sensitive methods must achieve 2-D phase sensitivity. We applied an inclined geometry method to a Laue geometry setup for X-ray ABPCI through rotation of the detector and object about the optical axis. This allowed this traditionally 1-D phase sensitive phase contrast method to possess 2-D phase sensitivity. We acquired tomographic datasets over 360 degrees of a multi-material phantom with the detector and sample tilted by 8 degrees. The real and imaginary parts of the refractive index were reconstructed for the phantom.

The wavelength modulation spectroscopy (WMS) method is typically used in the tunable diode laser absorption spectroscopy (TDLAS) for spectrum extraction in a noisy background. Usually, two entire absorption spectra for target species are scanned in a cascade way in the WMS method, and it limits the temporal response of the TDLAS sensor. In this article, the frequency-division multiplexing and main peak scanning method were introduced to the WMS method and enabled a high frame rate six times that in the classical TDLAS sensor at the same scanning speed. For the first time, two wavelengths modulated at different frequencies were used to extract the absorptions in parallel along various laser paths and implemented successfully on a TDLAS tomography hardware, to reconstruct the distributions of both temperature and species concentrations, at a frame rate up to 10 kHz. A five-view fan-beam tomographic sensor was utilized in the tomographic imaging. In each view, lasers at two wavelengths were selected and modulated at different sinusoidal frequencies on the same sawtooth signal. Numerical simulations varied the high-quality tomographic imaging of both temperature and H2O molar concentration distributions for different phantoms. Experiments were also carried out on dynamic flames, which were generated by exciting a Bunsen burner acoustically. The acoustic excitation frequency varied from 40 to 750 Hz, and the results of the tomographic images agreed well with the flame evolutions.

Purpose The quality of components under fused filament fabrication (FFF) is related to the correct filament spacing and bonding of successively deposited layers and is evaluated mainly by scanning electron microscopy (SEM). However, it is a destructive technique and real-time evaluation is not possible. Optical coherence tomography (OCT), on the other hand, is an optical method that acquires cross-sectional images non-invasively and in real-time. Therefore, this paper aims to propose and validate the use of OCT as a non-destructive quality evaluation tool for FFF using Polylactic Acid (PLA) filaments. Design/methodology/approach PLA three-dimensional (3D) printed samples were made in a variety of nozzle temperatures and mesh spacing. These samples were fractured in liquid nitrogen and inspected using SEM (as a gold standard) to evaluate dimensions and morphology, then the samples were evaluated by OCT in the same area, allowing the results confrontation. Findings Our results indicate a good correlation between OCT and SEM for the dimensional assessment of layers. When the filament was extruded in lower temperatures, the OCT images presented sharply defined interfaces between layers, in contrary to higher nozzle temperatures, denoting better fusion between them. However, higher extruding temperatures are incurred in greater deviations from nominal dimensions of the mesh. Finally, we demonstrate the advantage of a full 3D tomographic reconstruction to inspect within a FFF sample, which enabled the inspection of “hidden” information, not visible on a single cross-sectional cut. Originality/value This paper proposes OCT as a novel and nondestructive evaluation tool for FFF.

We present a multiscale imaging approach to characterize the structure of isolated adult murine cardiomyocytes based on a combination of full-field three-dimensional coherent x-ray imaging and scanning x-ray diffraction. Using these modalities, we probe the structure from the molecular to the cellular scale. Holographic projection images on freeze-dried cells have been recorded using highly coherent and divergent x-ray waveguide radiation. Phase retrieval and tomographic reconstruction then yield the three-dimensional electron density distribution with a voxel size below 50 nm. In the reconstruction volume, myofibrils, sarcomeric organization, and mitochondria can be visualized and quantified within a single cell without sectioning. Next, we use microfocusing optics by compound refractive lenses to probe the diffraction signal of the actomyosin lattice. Comparison between recordings of chemically fixed and untreated, living cells indicate that the characteristic lattice distances shrink by ∼10% upon fixation.

Purpose To demonstrate the feasibility of a three-plenoptic camera projection, scintillation-based dosimetry system for measuring three-dimensional (3D) dose distributions of static photon radiation fields. Methods Static x-ray photon beams were delivered to a cubic plastic scintillator volume embedded within acrylic blocks. For each beam, three orthogonal projections of the scintillating light emission were recorded using a multifocus plenoptic camera. Experimental 3D reconstructions of the light distribution were obtained using an iterative maximum likelihood-expectation maximization (ML-EM) algorithm. For this purpose, the elements of the system matrix representing the contribution of the scintillator volume voxels to the camera sensor pixels were calculated using optical design software. A reconstruction-specific correction was applied to light reconstructions to account for scintillating light imaged by the camera but not directly resulting from dose deposition. Cross beam profiles (CBPs) and percentage depth dose (PDD) curves were compared to treatment planning system data for square fields. Three-dimensional and 3D gamma analyses were performed for concave-shaped dose distributions and the Pearson correlation coefficient and reconstruction error were employed to assess the quality of the measured relative 3D dose distributions. Results A full and accurate model of the plenoptic camera-based scintillation dosimetry system was implemented using the light ray tracing capabilities of optical design software. With this model, light distributions were successfully reconstructed over a volume of 60 × 60 × 60 mm 3 at a resolution of 2 mm. For relative 3D measurements of square radiation fields of 2 × 2 cm 2 , 3 × 3 cm 2 and 4 × 4 cm 2 compared with treatment planning system reference distributions, the maximum root-mean-square error of the CBPs evaluated at two different depths was of 3.2%, 1.2%, and 1.1%, respectively; as for the corresponding linearly fitted PDDs of the square fields, the slopes of the reconstructed dose distributions overestimated those of the reference distributions by at most 0.2%/ cm. The 2D gamma passing rate with a criterion of 2%/2 mm for the concave-shaped photon field was of 61.6%, 66.1%, and 76.4% using one, two, and three plenoptic projections; the respective success rates become 77.1%, 87.5%, and 94.9% using a criterion of 3%/3 mm. The 3D correlation coefficient for the corresponding reconstructions was of 0.688, 0.905, and 0.976, respectively. Conclusions Three-dimensional light distributions emitted from within a plastic scintillator volume were successfully recovered using optical design software to establish a complete tomographic model of a plenoptic camera-based prototype. The tomographic model can equivalently extend to dynamic dose delivery measurements, providing temporal resolution limited by the camera's exposure time. This feasibility study enables a simplified design-to-implementation process for volumetric scintillation dosimetry prototypes toward fully meeting the clinical needs of 3D dose measurements for static and dynamic delivery techniques.

The advent of high-flux, high-brilliance synchrotron radiation (SR) has prompted the development of high-resolution X-ray imaging techniques such as full-field microscopy, holography, coherent diffraction imaging and ptychography. These techniques have strong potential to establish non-destructive three- and four-dimensional nano-imaging when combined with computed tomography (CT), called nano-tomography (nano-CT). X-ray nano-CTs based on full-field microscopy are now routinely available and widely used. Here we discuss the current status and some applications of nano-CT using a Fresnel zone plate as an objective. Optical properties of full-field microscopy, such as spatial resolution and off-axis aberration, which determine the effective field of view, are also discussed, especially in relation to 3D tomographic imaging.

The electrical capacitance tomography (ECT) technique has been extensively studied for real-time tomographic imaging of various industrial processes. Due to the ‘soft-field’ and under-determined problems in the image reconstruction, the tomographic images of ECT are usually low in the spatial resolution when compared with its radioactive counterparts, i.e. $\gamma $ -ray tomography and computed tomography. This paper presents an ECT sensor that consists of 8 external electrodes and 8 internal electrodes, with enhanced image quality at the center of imaging region and better accuracy on phase fraction measurement. The internal electrodes are placed on cross planes inside the investigated vessel. In this way, the signal-to-noise ratio of measurement channels as well as image quality are improved. Numerical simulations show that the proposed sensor can achieve better reconstructed images than a conventional 12-electrode sensor. In addition, the phase fraction calculation using ECT data can also benefit from the internal electrodes and corresponding measurements, which is an important parameter for multiphase flow processes.

An X-ray Talbot-Lau grating interferometer enables imaging of X-ray phase contrast. It can measure material transitions that are difficult to observe with traditional attenuation X-ray, for example soft-tissue variations in medical diagnosis or weakly absorbing materials in optical inspection. Unfortunately, the field of view of a Talbot-Lau interferometer is limited to few centimeters due to manufacturing constraints of its gratings. For larger objects, this leads to truncation in the projection images. In a tomographic reconstruction, this truncation causes severe artifacts and prevents the reconstruction of quantitatively correct phase coefficients. In this article, we propose a setup and an algorithm that combine in one scan full-field attenuation with small-field phase measurements. This allows to extrapolate the phase measurements across the full field, and thereby to greatly alleviate truncation artifacts in the reconstructed volume. Evaluation on simulated and real data shows that the method can reliably reconstruct refraction index decrements, that it outperforms the state of the art, and that its performance is in many cases robust to deviations from the initial assumptions.

The resolution of images recovered using diffuse optical tomography without spatial prior information is inherently limited due to the diffusive nature of light transport in scattering dominated biological tissue. Several studies have previously reported an improvement in depth sensitivity in near infrared spectroscopy by considering the subtraction of two neighbouring measurements. A nearest neighbour, spatial derivative based algorithm is presented, in which the difference between neighbouring source-sharing source – detector pairs is considered for tomographic reconstruction. Using a circular, inward-facing optode geometry, it is shown that deeper abnormalities in oxyhaemoglobin, deoxyhaemoglobin and water can be recovered with better localisation and contrast as compared to reconstructing using absolute values of multi-wavelength data. Relative improvements of up to 25 % in quantitative accuracy of recovered physiological values are demonstrated at better resolution for cancerous tissue in a heterogeneous breast model, when using this proposed spatial derivative based parameter reconstruction.

Three-dimensional density field measurement techniques can be used to understand the complex heat transfer and mixing processes that occur in turbulent flows. Tomographic background-oriented schlieren (BOS) is an optical technique that can be used to measure the instantaneous three-dimensional density field in turbulent flows. Light rays propagating through the flow are deflected from their ambient path due to variations in refractive index related to the spatial density gradients. In BOS, a camera is placed looking through the flow at a reference image, which captures path-integrated information on the refractive index gradients in the form of apparent image displacements Richard and Raffel (2001). The displacements recorded simultaneously from many cameras placed around the flow form the basis of a tomographic reconstruction of the three-dimensional refractive index gradients Goldhahn and Seume (2007), from which the density field is obtained through integration of the gradients and application of the Gladstone-Dale relation.

X-ray and gamma-ray photons are widely used for imaging but require a mathematical reconstruction step, known as tomography, to produce cross-sectional images from the measured data. Theoretically, the back-to-back annihilation photons produced by positron–electron annihilation can be directly localized in three-dimensional space using time-of-flight information without tomographic reconstruction; however, this has not yet been demonstrated due to the insufficient timing performance of available radiation detectors. Here we develop techniques based on detecting prompt Cherenkov photons, which, when combined with a convolutional neural network for timing estimation, resulted in an average timing precision of 32 ps, corresponding to a spatial precision of 4.8 mm. We show this is sufficient to produce cross-sectional images of a positron-emitting radionuclide directly from the detected coincident annihilation photons, without using any tomographic reconstruction algorithm. The reconstruction-free imaging demonstrated here directly localizes positron emission and frees the design of an imaging system from the geometric and sampling constraints that are normally present for tomographic reconstruction. Positron emission imaging without tomographic reconstruction is demonstrated. A Cherenkov radiation detector detects gamma rays produced by positron–electron annihilation. The position of a positron source is determined with a precision of 4.8 mm.

In this study, we developed a rapid nondestructive tool for testing rust spread in a metal covered by a paint layer by using a THz time-domain spectroscopy system at a speed of 100 Hz/pixel. Time-of-flight imaging helps identify rust formation by exclusively obtaining the reflection from the steel below the paint surface. The use of frequency-selective imaging allows us to manipulate the contrast in rust imaging. Higher contrast is generally obtained when monitoring using the higher frequency component. In addition, we monitored the spread of rust in a steel plate under the influence of two different chemical solutions: NaCl and acid. We found that in the early stages, the decrease in THz reflection was governed by the high-frequency components due to the formation of lepidocrocite, whereas the low-frequency component develops as the proportion of hematite increases with time.

By arranging multiple detection nodes around the rocket motor, the attenuation information of electromagnetic waves can be obtained. One node is used to transmit terahertz signals, and the others are used to receive the transmitted signal that penetrate the solid propellant. The signal is transmitted to the PC, and combined with technology of tomographic imaging to image the propellant burning surface. This paper compares the reconstructed images of the same model in the millimeter wave system and the terahertz system. Result shows that the shift procession of burning surface for the propellant and edge profile can be presented clearly by using the terahertz detection signal combined with the filtered back-projection algorithm. The reconstructed image has high consistency with the constructed model. It proves the feasibility reconstruct the burning surface progression of solid propellant using terahertz tomography, which provide a good foundation for terahertz tomographic imaging to measure the burning rate of solid propellants.

We describe an Abel inversion method for tomographic reconstruction of an axisymmetric medium. The essence of this method is the approximation of data by Chebyshev wavelets. A numerical method and operational matrices are proposed. The accuracy of the method is tested in terms of the noise coefficient. The studied method is compared with the Legendre wavelets method. The results show that the proposed method is less sensitive to noise. We also demonstrate the efficiency of the developed method by obtaining good and expected results for the inversion of interferometric data.

We present a terahertz spherical aberration-corrected metalens that uses the dynamic phase to achieve polarization multiplexed imaging. The designed metalens has polarization–dependent imaging efficiencies and polarization extinction ratios that exceed 50% and 10:1, respectively. Furthermore, opposite gradient phases can be applied to orthogonal polarizations to shift the imaging of the two polarized sources in the longitudinal and transverse directions. Indeed, we find that the metalens has a smaller depth-of-focus than a traditional metalens when imaging point sources with limited objective lengths. These results provide a new approach for achieving multifunctional beam steering, tomographic imaging and chiroptical detection.

An innovative tangential-view soft x-ray (SXR) tomographic imaging measurement was developed on the TS-6 spherical tokamak merging device as a key diagnostic for investigating the mechanism of electron acceleration. In order to measure SXR with different energy ranges, two micro-channel plates (MCPs) are, respectively, installed in two vacuum chambers, which are equipped with different filters. Especially designed lenses and fiber bundles serve as an optical system to transfer images from phosphor plates of MCPs to a high speed imaging system. This design also enables us to simultaneously measure two images appearing on phosphor plates of MCPs by just one high speed imaging system. The temporal and spatial resolution of this diagnostic can be up to 5 µs and 4 mm, respectively, at present. The tomographic method based on the Phillips–Tikhonov regularization is employed to reconstruct line-integrated images into the local emissivity of SXR, which reflects the spatial distribution of high-energy electrons. Owing to this diagnostic, we successfully measured SXR emitted from the downstream region of magnetic reconnection in TS-6 merging experiments for the first time. The energy range of SXR turned out to be higher than 100 eV but lower than 400 eV.

Cerenkov luminescence tomography (CLT) has attracted much attention because of the wide clinically-used probes and three-dimensional (3D) quantification ability. However, due to the serious morbidity of 3D optical imaging, the reconstructed images of CLT are not appreciable, especially when single-view measurements are used. Single-view CLT improves the efficiency of data acquisition. It is much consistent with the actual imaging environment of using commercial imaging system, but bringing the problem that the reconstructed results will be closer to the animal surface on the side where the single-view image is collected. To avoid this problem to the greatest extent possible, we proposed a prior compensation algorithm for CLT reconstruction based on depth calibration strategy. This method takes full account of the fact that the attenuation of light in the tissue will depend heavily on the depth of the light source as well as the distance between the light source and the detection plane. Based on this consideration, a depth calibration matrix was designed to calibrate the attenuation between the surface light flux and the density of the internal light source. The feature of the algorithm was that the depth calibration matrix directly acts on the system matrix of CLT reconstruction, rather than modifying the regularization penalty items. The validity and effectiveness of the proposed algorithm were evaluated with a numerical simulation and a mouse-based experiment, whose results illustrated that it located the radiation sources accurately by using single-view measurements.

Snapshot projection optical tomography (SPOT) uses a microlens array (MLA) to simultaneously capture the projection images of a three-dimensional (3D) specimen corresponding to different viewing directions. Compared to other light-field imaging techniques using an MLA, SPOT is dual telecentric and can block high-angle stray rays without sacrificing the light collection efficiency. Using SPOT, we recently demonstrated snapshot 3D fluorescence imaging. Here we demonstrate snapshot 3D absorption imaging of microscopic specimens. For the illumination, we focus the incoherent light from a light-emitting diode onto a pinhole, which is placed at a conjugate plane to the sample plane. SPOT allows us to capture the ray bundles passing through the specimen along different directions. The images recorded by an array of lenslets can be related to the projections of 3D absorption coefficient along the viewing directions of lenslets. Using a tomographic reconstruction algorithm, we obtain the 3D map of absorption coefficient. We apply the developed system to different types of samples, which demonstrates the optical sectioning capability. The transverse and axial resolutions measured with gold nanoparticles are 1.3 and 2.3 $\ensuremath{\mu}\mathrm{m}$, respectively.

We present a new technique combining digital holography and tomography to make path-resolved measurements of a turbulent air volume. An array of optical beams at different propagation angles is transmitted through the volume under test, interfered with a reference beam, and the resulting fringe patterns are all simultaneously recorded on a focal plane array. The complex field of each beam in the receiver pupil plane is recovered via digital Fourier processing and then tomographic reconstruction algorithms are applied to calculate wavefront error contributions from multiple planes along the beam path. Results are presented from a proof-of-concept laboratory experiment using phase screens to mimic the turbulence volume. Comparing the tomographic reconstructions to the known screen prescriptions, we successfully demonstrate accurate measurement of the phase distortions introduced in multiple planes. This ability to longitudinally resolve turbulence and isolate individual layers may benefit numerous applications including precision turbulent flow analysis in wind tunnels and adaptive optic compensation for free space optical communications.

An image fibre Background Oriented Schlieren (Fibre BOS) technique has an advantage in cost-effectiveness as well as portability and flexibility for a time-resolved quantitative three-dimensional unsteady density measurement. The reason why the Fibre BOS technique has these advantages is that a transparent medium can be visualized at several projection angles, which are required for a tomographic reconstruction, using the flexible optical image fibres instead of expensive high-speed cameras, simultaneously. The basic and demonstration experiments were conducted to investigate the performances of the Fibre BOS technique in this study. The estimation accuracy of a deflection angle is increased when a background-dot size is more than twice as large as a core which is the component of the image fibre if the core size is larger than a pixel size on an image sensor. Multiple images going through the image fibres from several projection angles are simultaneously captured using a single camera, and temporal variation of an unsteady complex flow is measurable. The Fibre BOS technique has a potential to conduct the high time-resolved three-dimensional unsteady density measurement using a single high-speed camera.

The C-2W device (“Norman”) [Gota et al., Nucl. Fusion 59, 112009 (2019)] has produced and sustained beam-driven field-reversed configuration (FRC) plasmas embedded in a magnetic mirror geometry using neutral beams and end-bias electrodes located in expander divertors. Several discrete vessels comprise this device, and many imaging instruments are required in order to view the plasma throughout. To meet this need, a suite of spatially and radiometrically calibrated, high-speed camera systems have been deployed. Besides global visualization of the plasma evolution and macro-stability, this imaging suite has been used in a variety of applications. One example application is a tomographic reconstruction of passive impurity emission. Calculation of the magnetic field in the equilibrium vessel is complicated by eddy currents in conducting structures and internal currents in the high-β FRC plasma. In addition, thus far non-perturbative measurements of internal field have not been available. The tomographic reconstruction of O4+ impurity emission enables an independent visualization of the plasma geometry, serving as a check on magnetic modeling and indirect evidence for field reversal within the FRC. A second application uses the cameras to view the Balmer-α emission throughout the plasma in order to estimate the ionization rate in each region. These rates can then be incorporated into particle balance calculations and a circuit model for currents from the end-bias electrodes. Finally, arcing on the electrode surfaces is identified through automated image processing of carefully selected spectral line emission.

We present a new interferometric technique for gas jets density characterization employing a Wollaston shearing interferometer. The distinctive feature of this setup is the double pass of the probe beam through the gas target facilitated by a relay-imaging object arm that images the object on itself and preserves the spatial information. The double pass results in two-fold increase of sensitivity at the same time as the relay-imaging enables the characterization of gas jets with arbitrary gas density distribution by tomographic reconstruction. The capabilities of the double-pass Wollaston interferometer are demonstrated by tomographic density reconstruction of rotationally non-symmetric gas jets that are used as gas targets for the betatron X-ray source at ELI-Beamlines.

The emerging technique of mid-infrared optical coherence tomography (MIR-OCT) takes advantage of the reduced scattering of MIR light in various materials and devices, enabling tomographic imaging at deeper penetration depths. Because of challenges in MIR detection technology, the image acquisition time is, however, significantly longer than for tomographic imaging methods in the visible/near-infrared. Here we demonstrate an alternative approach to MIR tomography with high-speed imaging capabilities. Through femtosecond nondegenerate two-photon absorption of MIR light in a conventional Si-based CCD camera, we achieve wide-field, high-definition tomographic imaging with chemical selectivity of structured materials and biological samples in mere seconds.

Tomography is an informative imaging modality that is usually implemented by mechanical scanning, owing to the limited depth-of-field (DOF) in conventional systems. However, recent imaging systems are working towards more compact and stable architectures; therefore, developing nonmotion tomography is highly desirable. Here, we propose a metalens-based spectral imaging system with an aplanatic GaN metalens (NA = 0.78), in which large chromatic dispersion is used to access spectral focus tuning and optical zooming in the visible spectrum. After the function of wavelength-switched tomography was confirmed on cascaded samples, this aplanatic metalens is utilized to image microscopic frog egg cells and shows excellent tomographic images with distinct DOF features of the cell membrane and nucleus. Our approach makes good use of the large diffractive dispersion of the metalens and develops a new imaging technique that advances recent informative optical devices., Bioimaging: metalenses make 3D analysis effortless An ultrathin “metalens” that uses semiconductor nanostructures to focus light can help microscopes resolve detailed images of live cells without complex mechanical components. In conventional tomographic imaging, a scanning instrument passes over the sample and takes multiple cross-sectional images, which are then reconstructed into a 3D picture. Tao Li from Nanjing University in China and colleagues have now simplified this technique by fabricating lenses patterned with concentric rings of gallium nitride nanopillars. The lens made of nanopillars has wavelength-dependent properties that enable focusing on different regions of a target simply by sweeping through the visible light spectrum. Experiments with frog egg cells demonstrated this approach could zoom in and obtain detailed, high quality images of the inner membrane and nucleus without harming the sample or moving the metalens.

Fluorescent molecular tomography (FMT) is emerging as a reliable optics-based molecular imaging technique. The diffusion approximation is commonly employed as a forward model for reconstruction. Ho...

Magnetic particle imaging (MPI) is a novel tomographic imaging method, which allows determining the distribution of superparamagnetic iron-oxide nanoparticles in three dimensions. So far, various MPI systems have been presented with each one emphasizing different scanner features such as large field of view (FOV) or high resolution. For imaging with both high resolution and a large FOV, the optimization and harmonization of hardware parameters as well as tracer material are key prerequisites. The traveling wave MPI (TWMPI) approach uses an array of electromagnets, which can provide a high magnetic field gradient for a high resolution as well as a mouse-sized FOV at the same time. In combination with the tracer LS-008, which is optimized for the MPI technique, a resolution in the sub-millimeter range can be achieved. In this paper, an optimized scanner is presented based on the TWMPI approach featuring a gradient strength up to almost 10 T/m in an FOV with a length of 45 mm providing a high resolution below 500 microns using the optimized LS-008 tracer.

Diagnostic methods using a tomographic reconstruction allow for three-dimensional characterization of spraying processes. Since in many spraying applications, non-rotationally symmetric phenomena occur, the application of emission tomography methods seems most reasonable. Yet, to be able to apply this method the observed object has to be luminous and optically thin. Hence, to investigate a particle stream, the optical thickness of such a stream has to be estimated beforehand. Within this paper, a method to determine this parameter, based on particle rate, size and velocity measurements is presented and applied to a wire arc spray process, proving that it is possible to perform a tomographic investigation of a particle beam.

A visible light high-speed imaging system has been installed on the J-TEXT tokamak to measure the spatial distribution of visible emission in the vacuum chamber. The system views the plasma tangentially from an outer port at the height of the mid-plane of the vacuum vessel. An optical system is designed for the consideration that the camera must be installed away from the magnetic field. A spatial calibration based on Tsai’s method is adopted to build the relationship between the tokamak 3-D space coordinate and the 2-D image coordinate. Tomographic reconstruction techniques are used to calculate the 2-D poloidal emission profiles from the camera image data assuming toroidal symmetry of the radiation. Sample results are presented to view the discharge process in typical plasma discharge and methane injection experiments with a CIII-filter added. And the 2-D poloidal CIII emission profiles reconstructed from imaging results in typical plasma discharge experiments are also obtained.

Tomographic reconstruction of three-dimensional (3D) flow field is critical to achieve an accurate measurement of the complex flow field in tomographic particle image velocimetry (Tomo-PIV). Tomo-PIV based on the light field imaging has been used for 3D flow measurement due to its advantages of simple equipment system, low cost and overcoming the problems of complex synchronization and calibration of multi-cameras Tomo-PIV. However, the reconstruction quality such as the elongation and position error of the reconstructed particle, and the normalized correlation coefficient Q is closely related to the optical parameters of the light field camera, such as the inverse magnification and focal length of the main lens and the microlens, and the microlens pitch. Thus, the optimization of these optical parameters is desired for a better reconstruction quality. In this paper, the effects of these optical parameters on the light field image and reconstruction are numerically and experimentally investigated. In simulations, the light field images of the tracer particles are firstly generated for different the optical parameters by the ray tracing technique. The 3D tracer particle field is then reconstructed by the Expectation–Maximization (EM) algorithm. Simulation results show that the inverse magnification of the main lens and microlens, the focal length of the microlens, and the microlens pitch have important effects on the reconstruction quality, and thus the size and position of the measurement volume along the Z axis. Experiments are also carried out to verify the simulations. This study provides a basis for the optimization of the light field camera parameters for the accurate tomographic reconstruction of 3D flow field and the determination of the size and position of the measurement volume along the Z axis in the light field Tomo-PIV.

A new three-dimensional through-wall imaging (TWI) system is implemented for short range sensing. The system is equipped with a circularly polarised antenna array to improve image quality and reduce the wall artefacts. It consists of an array of 19 antennas positioned hexagonally. The array delivers half-space radiation with wideband performance, necessary for imaging applications. A differential tomographic imaging algorithm is developed to create through-wall images via both coherent and non-coherent processes. The imaging system has some advantages to traditional synthetic aperture radar approaches and other linear fixed aperture systems. It has a modular structure, uses both co-polarised and cross-polarised waves, capable of sensing conductive objects hidden behind dielectric layers (wall). The experimental results confirm that the new TWI system can create images of conductive objects hidden behind a dielectric wall clearly.

Light field microscopy (LFM) is capable of ultrafast tomographic reconstruction using a light field image acquired in a single snapshot. However, the axial resolution of LFM is inferior to its lateral resolution and is non-uniform in the axial direction. A diffraction-assisted light field microscopy (DLFM) method is proposed in this work to achieve resolution enhancement over the conventional LFM. DLFM makes use of a transmission diffraction grating inserted between the specimen and microscope objective. Light field images of different diffraction orders are formed on the sensor plane and encode both the spatial and angular information of light rays emanating from the specimen. A wave optics model is developed to derive the point spread functions (PSFs) of DLFM, which are then used to deconvolute the light field images for tomographic reconstruction. Validation tests are performed on both experimental and simulated data and the results show that DLFM effectively improves the axial resolution without compromising the lateral resolution. Furthermore, we show that tomographic reconstruction using DLFM can be combined with digital volume correlation (DVC) to achieve three-dimensional, full-field displacement measurement.

Near‐infrared tomographic imaging of tissue can give structural anatomy data based on the attenuation coefficients and absorption spectra of biological tissue. The near infrared spectrum ranges from wavelengths of 650 to 1350 nm where the light has its maximum depth of penetration in tissue. The equipment developed with a diode laser source and an array of 32 photodiode detectors and was based on the 3rd generation CT in fan-beam with rotating source and detectors. The imager moves through 360 degrees and takes projections of the object and tomographic image of the phantom was obtained by reconstructing the using filtered back projection algorithm.

It is well acknowledged that the functional near-infrared spectroscopic (fNIRS) imaging of brain functions can be quantitatively enhanced by diffuse optical tomography (DOT). Unlike the widely-used conventional optical topography (optical mapping), an fNIRS-DOT instrument needs to possess both high sensitivity and large dynamic-range so that measurements at multiple source-detector separations are reliably and synchronously collected for improved depth-resolution, quantitation, and superficial signal reduction, the performances particularly crucial to the occipital cortex probing. For the goal, we implemented a novel 3-wavelength, 240-channel (20 sources and 12 detectors) continuous-wave fNIRS-DOT instrument. The system features the square-wave modulation lock-in photon-counting scheme that combines the multi-channel parallelization of the lock-in detection, the ultra-high sensitivity, and unprecedented dynamic-range of the photon-counting technique, as well as the reduced complexity of the hardware architecture. We have systematically investigated the key specifications of the instrument such as the detection linearity, stability, channel crosstalks and so on, under the practically-viable conditions of the incident power and signal-to-noise ratio, and accordingly proposed wavelength-switched multiple-field illumination paradigms for both the non-overlapping and overlapping DOT measurements, respectively. Finally, DOT experiments using the semi-three-dimensional image reconstruction has been conducted on a phantom with a practically low-contrasted and deep-sit absorption target, to evaluate the overall imaging performance of the system and to demonstrate the superiority of the model-based image reconstruction over the topographical mapping.

Methods of computed tomography are well developed and widely used in medicine and industry. If tomographic data are complete, it is possible to reconstruct the images with submillimeter resolution. If the data are incomplete, tomograms may blur, i.e. their resolution degrades, noise increases and artifacts form. The situation is worst if measurement data are so poor that the system of equations which describe the discrete reconstruction problem appears to be strongly underdetermined. In this situation, images of acceptable quality can be obtained with algorithms that regularize the solution and use a priori information about the object, and do post-processing of reconstructed tomograms also with the use of a priori information, as a rule. This chapter provides two examples demonstrating the reconstruction of the internal structure of an object from strongly incomplete measurement data: few-view computed tomography (FVCT) and diffuse optical tomography (DOT) of strongly scattering media. The problem of reconstruction from a small number of views (

A major challenge in three-dimensional (3D) microscopy is to obtain accurate spatial information while simultaneously keeping the microscopic samples in their native states. In conventional 3D microscopy, axial resolution is inferior to spatial resolution due to the inaccessibility to side scattering signals. In this study, we demonstrate the isotropic microtomography of free-floating samples by optically rotating a sample. Contrary to previous approaches using optical tweezers with multiple foci which are only applicable to simple shapes, we exploited 3D structured light traps that can stably rotate freestanding complex-shaped microscopic specimens, and side scattering information is measured at various sample orientations to achieve isotropic resolution. The proposed method yields an isotropic resolution of 230 nm and captures structural details of colloidal multimers and live red blood cells, which are inaccessible using conventional tomographic microscopy. We envision that the proposed approach can be deployed for solving diverse imaging problems that are beyond the examples shown here., A general method for the in-situ isotropic microtomography of freestanding specimens, exploiting complex wavefront shaping and optical tweezers.

In this work we propose an open-top like common-path intrinsically achromatic optical diffraction tomography system. It operates as a total-shear interferometer and employs Ronchi-type amplitude diffraction grating, positioned in between the camera and the tube lens without an additional 4f system, generating three-beam interferograms with achromatic second harmonic. Such configuration makes the proposed system low cost, compact and immune to vibrations. We present the results of the measurements of 3D-printed cell phantom using laser diode (coherent) and superluminescent diode (partially coherent) light sources. Broadband light sources can be naturally employed without the need for any cumbersome compensation because of the intrinsic achromaticity of the interferometric recording (holograms generated by –1st and +1st conjugated diffraction orders are not affected by the illumination wavelength). The results show that the decreased coherence offers much reduced coherent noise and higher fidelity tomographic reconstruction especially when applied nonnegativity constraint regularization procedure.