Absorption Imaging Research Articles

Meta-data for absorption tomography measurements

The simplicity of nonclinical x-ray tomography data collection has caused some to overlook the importance of saving additional experimental information or experiment meta-data. Sample meta-data are often saved in the experimenter’s logbook while meta-data about the instrument and experimental conditions are saved by the instrument itself or by the instrument operator. The lack of standardization of this approach has limited the development of automatic tools for data analysis and experiment logging but has also hindered the ability to reproduce the data collection and data analysis under the same conditions. In this paper we introduce tomo-meta, a publicly available repository of laboratory and synchrotron based tomography instrument meta-data files with the aim of presenting how meta-data are currently collected and identify best practices that enable data collection and data analysis repeatability. Structured and machine readable meta-data files, such as HDF, CSV, JSON, XML, etc., are essential for creating automatic processing pipeline. When the tomography meta-data files are structured as machine readable, we also provide a simple python script to automatically load them into a python dictionary.

Calibrating the Absorption Imaging of Cold Atoms under High Magnetic Fields

Calibrating the Absorption Imaging of Cold Atoms under High Magnetic Fields

A deep learning reconstruction framework for low dose phase contrast computed tomography via inter-contrast enhancement

Phase contrast computed tomography (PCCT) offers excellent imaging contrast on soft tissue while it generate absorption, phase and dark-field contrast tomographic images. It has shown a great potential in clinical diagnosis. However, existing PCCT methods require high radiation doses. Reducing tube current is a universal low dose approach while it will introduce quantum noise in projections. In this paper, we report a deep learning (DL) framework for low dose PCCT based on inter-contrast enhancement. It utilizes the multi-contrast feature of PCCT and the varying effects of noise on each contrast. The missing structure in the contrasts that are more affected by noise can be recovered by those that are less affected. Considering the grating-based PCCT as example, the proposed framework is validated with experiments and a dramatic quality improvement of multi-contrast tomographic images has been obtained. This study shows potential of DL techniques in the field of low dose PCCT.

An automated algorithm for the determination of oil absorption strategy of magnetic nanoparticles from SEM images

In recent years, the magnetic iron oxide nanoparticles (MNPs) are employed as efficient absorbents for oil removal from water. In this research, the particle size (diameter) obtained from Scanning Electron Microscopy (SEM) images of MNPs, before and after oil-absorption, are utilized to determine the oil-absorption capacity. However, the manual evaluation of the particle size and particle size distribution (PSD) are highly time-consuming and needs expertised people for accurate analysis. Hence, an image processing algorithm is employed for the determination of particle size and PSD from the Scanning Electron Microscopy (SEM) images. The key objective revolves with the preparation of the Maleic Anhydride Grafted Polypropylene anchored Magnetic Nanoparticles (MAPP-a-MNPs) to absorb crude oil from the marine water. The shape, size, and size distribution of MAPP-a-MNPs were assessed by both manual and automated analysis. For this purpose, expertise people help with the manual analysis and Threshold Adaptive-Canny Edge Detection (TA-CED) and Accumulator Updated-Circular Hough Transform (AU-CHT) method is employed for automated analysis. All the automated process were conducted in MATLAB and the measurements were taken for both before and after the oil absorption images. These measurements aid us to determine the quantity of oil absorbed by MAPP-a-MNPs. The results demonstrates excellent oil removal capacity of MAPP-a-MNPs.

Neutron resonance absorption imaging of simulated high-level radioactive waste in borosilicate glass

We performed a preliminary study of neutron resonance absorption imaging to investigate the spatial distribution of constituent elements in borosilicate glasses containing simulated high-level radioactive waste, in which elemental inhomogeneities affect the physical and chemical stabilities of the glass. Dips generated by the resonance absorptions of Rh, Pd, Na, Gd, Cs, and Sm were observed in the neutron transmission spectra of the glass samples. The spatial distributions of these elements were obtained from the neutron transmission images at the resonance energies. The distributions of Rh and Pd visualized the sedimentation of these platinum group elements. In contrast, the lanthanides (Gd and Sm) and Cs were uniformly dispersed. These results show that neutron resonance absorption imaging is a promising tool for characterizing borosilicate glasses and investigating the vitrification mechanism of high-level radioactive waste.

Pseudoheterodyne interferometry for multicolor near-field imaging.

We report the development and characterization of a detection technique for scattering-type scanning near-field optical microscopy (s-SNOM) that enables near-field amplitude and phase imaging at two or more wavelengths simultaneously. To this end, we introduce multispectral pseudoheterodyne (PSH) interferometry, where infrared lasers are combined to form a beam with a discrete spectrum of laser lines and a time-multiplexing scheme is employed to allow for the use of a single infrared detector. We first describe and validate the implementation of multispectral PSH into a commercial s-SNOM instrument. We then demonstrate its application for the real-time correction of the negative phase contrast (NPC), which provides reliable imaging of weak IR absorption at the nanoscale. We anticipate that multispectral PSH could improve data throughput, reduce effects of sample and interferometer drift, and help to establish multicolor s-SNOM imaging as a regular imaging modality, which could be particularly interesting as new infrared light sources become available.

Characterization of the collisional frequency shift in an atomic fountain clock using absorption imaging

The collisional frequency shift is a dominant contribution to the uncertainty of many caesium fountain clocks. Minimizing the effect can be difficult, as lowering the atomic density comes at the cost of a reduced signal-to-noise ratio. Also, it is typically not atomic density, but total atom number that is measured in the experiment, which can lead to a potential measurement bias. In this paper, we describe a direct measurement of the atomic density using absorption imaging of the atomic cloud. For the caesium fountain clock, NRC-FCs2, at the National Research Council Canada, these measurements have led to a reduction in the uncertainty due to the collisional shift by a factor of 10.

Direct calibration of laser intensity via Ramsey interferometry for cold atom imaging.

A majority of ultracold atom experiments utilize resonant absorption imaging techniques to obtain the atomic density. To make well-controlled quantitative measurements, the optical intensity of the probe beam must be precisely calibrated in units of the atomic saturation intensity Isat. In quantum gas experiments, the atomic sample is enclosed in an ultra-high vacuum system that introduces loss and limits optical access; this precludes a direct determination of the intensity. Here, we use quantum coherence to create a robust technique for measuring the probe beam intensity in units of Isat via Ramsey interferometry. Our technique characterizes the ac Stark shift of the atomic levels due to an off-resonant probe beam. Furthermore, this technique gives access to the spatial variation of the probe intensity at the location of the atomic cloud. By directly measuring the probe intensity just before the imaging sensor our method in addition yields a direct calibration of imaging system losses as well as the quantum efficiency of the sensor.

Solar Cell Detection and Position, Attitude Determination by Differential Absorption Imaging in Optical Wireless Power Transmission

In optical wireless power transmission, position, size, and attitude of photovoltaic device (PV) must be determined from light source. A method proposed in the previous report is based on selective absorption characteristics of PV, and it is detected by differentiating images of strongly absorbable wavelength and one not. In this study, using two infrared wavelengths, two kinds of targets were detected by differential absorption imaging. One was a GaAs substrate which simulates diffuse rear surface, and the other was a real GaAs PV. It was found that the substrate’s reflective characteristic was diffuse, and the solar cell’s was mainly non-diffuse and accompanied by small diffuse component supporting wide-angle reflection. Using this feature, the position of the GaAs solar cell could be determined within a wide range of angle. Its attitude could also be determined with an accuracy of ±10 degrees to its normal. The position of diffuse GaAs substrate could be determined within a wide range of angles, and its attitude determination was proposed by exploiting its varying apparent size with tilt angle. Broad reflection characteristics of the GaAs substrate enabled attitude determination for a wide-angle range, and determination around normal would be erroneous.

Strain fields as local probe for X-ray diffraction tomography: Non-destructive reconstruction of shear band paths in metallic glasses

Shear bands are nanoscale topologically complex planar shear defects mediating plasticity in metallic glasses and a complete understanding of the shear banding phenomenon requires their three-dimensional characterization; however, we have been unable to tomographically and not-destructively reconstruct the path of shear bands inside a sample until now as X-ray absorption (or phase contrast) tomography is currently unable to distinguish shear bands from the surrounding matrix. Here, we overcome this limitation using the strain field generated by shear bands in the adjacent material as a local probe for X-ray diffraction tomography. This strain field is the analogue of the contrast agents used in conventional clinical tomography, allowing us to non-destructively reconstruct the shear band paths within the glassy specimens. Tomography is based on collecting a series of projections recorded at different angles while the specimen is rotated about a single axis. In this work, we first use full-angle tomography (reconstruction based on projections collected over 360°), which allows reconstructing the paths in excellent detail revealing features of shear banding that are not accessible to other analytical tools. A dataset with missing angles (projections over less than 360°) degrades the reconstruction but opens the door to in-situ measurements during deformation.

X-ray imaging methods for high-energy density physics applications

Large scale high-energy density science facilities continue to grow in scale and complexity worldwide. The increase in driver capabilities, including pulsed-power and lasers, continue to push the boundaries of temperature, pressure, and densities, opening up new physics regimes. X-ray imaging is one of the many diagnostic techniques that are used to probe states of matter in these extreme conditions. Improved fabrication and polishing methods have provided improved x-ray microscope performance, while improving detector and x-ray sources now enable pico-second imaging with few micron resolutions. This Review will cover x-ray imaging methods, primarily absorption imaging, and their improvements over the last few decades.

2D in situ determination of soot optical band gaps in flames using hyperspectral absorption tomography

During the formation of soot, the particles undergo a fine structural transformation, akin to graphitization, from “young” to “mature” soot. This ageing process is accompanied by a change in optical properties, which manifests in the soot optical band gap and dispersion exponent, Eg and ζ. Although both quantities are regularly determined via broadband extinction measurements, they have a nonlinear relationship to the local extinction spectrum, so line-of-sight integrated measurements introduce errors into estimates of Eg and ζ. We report the development of an absorption tomography sensor that enables 2D in situ mapping of Eg and ζ. Our sensor employs broadband back-illumination, fiber-coupled collection optics, and an imaging spectrograph to simultaneously acquire 24 spectrally-resolved absorption signals, suitable for tomographic reconstruction. We perform proof-of-concept experiments to characterize soot formation in non-premixed steady flames from a Gülder burner, using ethylene and propane as fuels. Reconstructions based on axisymmetric and non-axisymmetric absorption tomography are compared, and we explore how our sensor can be adapted to perform temporally-resolved measurements in a turbulent flame.

PolyX beamline at SOLARIS—Concept and first white beam commissioning results

PolyX is a compact bending magnet beamline under construction at National Synchrotron Radiation Centre SOLARIS, which will be available to users in mid-2023. The beamline is focused on X-ray microimaging and microspectroscopy in the tender/hard (4–15 keV) X-ray energy range. The name PolyX comes from polycapillary X-ray optics that will be extensively used for efficient X-ray focusing and from the possibility of using polychromatic or broadband X-rays to increase the rather low flux from the SOLARIS bending magnet in the hard X-ray energy range. Polycapillary optics will provide focal spots with sizes of 8–200 μm. Single bounce ellipsoidal capillary is expected to provide a ∼2 μm focal spot size. The main experimental techniques at PolyX will be X-ray absorption and phase-contrast imaging and microtomography, micro-X-ray fluorescence imaging and micro-X-ray absorption spectroscopy. This paper presents the concept of PolyX beamline and preliminary “white” beam commissioning results.

IN-LINE METHOD OF X-RAY PHASE-CONTRAST MICRO-CT USING A WIDE-FOCUS LABORATORY SOURCE

An experimental implementation of the “in-line” method of X-ray phase contrast using a standard wide-focus X-ray tube as a polychromatic source is described. Using the proposed experimental scheme, in vitro tomographic measurements of a sample of human brain pineal gland are carried out, and the morphological structure of the soft tissues of this organ is visualized based on the results obtained. The advantage of phase-contrast tomography in comparison with traditional absorption tomography for studying the structural features of soft tissues is experimentally demonstrated. The “in-line” phase-contrast scheme, implemented on a laboratory setup, allows tomographic study of samples with linear dimensions of several millimeters and a resolution of ∼20 μm.

Development of energy-dispersive diffraction and grayscale quantification in polychromatic synchrotron tomography

Synchrotron white-beam tomography has important applications for temporally evolving or highly absorbing samples. The polychromatic nature of the white beam results in beam hardening artifacts unless measures are taken to correct these artifacts. Moreover, while the absorption tomography data show the morphology of samples, for some applications, the ability to probe crystallographic phase would enhance both the interpretation of the tomography data and the overall understanding of the sample. This work will describe developments at the 7-BM beamline of the Advanced Photon Source to both effectively correct for the polychromatic nature of the white beam and to provide energy-dispersive diffraction data which can be coupled with white-beam tomography.

A review of in situ/operando studies of heterogeneous catalytic hydrogenation of CO2 to methanol

Repurposing CO2 into chemicals, one of the Carbon Dioxide Removal (CDR) strategies, still faces significant challenges in conversion and energy efficiency due to the lack of effective catalysts and processes. Fundamental understanding through in situ/operando investigations of the reaction mechanisms and catalyst structures is pivotal for developing the efficient catalysts. This paper reviews the past and recent in situ/operando studies of methanol synthesis from heterogeneous CO2 hydrogenation over a few typical catalysts including Cu-based, oxide-based, and noble-metal-based catalysts. With the development of high-pressure reactors, in situ/operando IR, X-ray absorption spectroscopy (XAS), X-ray diffraction (XRD), neutron diffraction and imaging have been used to reveal the surface intermediates and structures of working catalysts under CO2 hydrogenation conditions. On the one hand, the combined operando techniques shed light on working mechanisms for some catalytic systems. On the other hand, due to the complexity of selective CO2 hydrogenation reaction and limited sensitivity of current accessible operando techniques to the surface structure of catalysts, it is still murky about the exact nature of the active sites at the surface/interface and how different sites promote different reaction paths. It is concluded that new methodologies for differentiating signals from different sites, and the development of surface-sensitive techniques for high pressure reactions are needed for providing structural descriptors of highly active and selective CO2 conversion catalysts.

Quantum-enabled ghost imaging for non-invasive imaging of plants.

Imaging biological processes in plants, such as water transport and sequestration, without disturbing natural growth or introducing artificial stimuli is challenging. Most optical microscopy techniques involve fluorescent probes and/or high-intensity light to obtain structural and chemical signatures. Spatially resolved near-infrared (NIR) absorption, for example, captures information about chemical signatures, but is typically obtained with time-intensive scanned confocal techniques because there are few spatially-resolvable detectors (cameras) in the NIR. Furthermore, confocal microscopy illuminates living samples with significant light intensities that can damage or alter the organism. To image chemical signatures, such as water, in undisturbed plants, we developed a quantum ghost imaging microscope that leverages non-degenerate spontaneous parametric down conversion (SPDC). Samples are probed with low levels of NIR light. Due to quantum correlation with their visible SPDC photon pairs, an image of the NIR absorption can be obtained using a spatially-resolving detector in the visible. We describe the operating principle and first measurements of this new imaging technique.

Semiempirical criterion for eliminating wraparound artifacts in single-grid-based phase-contrast X-ray imaging

Single-grid-based phase-contrast X-ray imaging (SG-PCXI) is a non-interferometric method for the simultaneous retrieval of absorption, phase-contrast (differential), and dark-field images from a single exposure with a common X-ray grid using a spatial harmonic imaging (SHI) technique. However, the retrieved images are often distorted by the wraparound artifacts that are caused by the spectral overlap of adjacent harmonic peaks in the Fourier domain, resulting in the degradation of image quality. In this study, a semiempirical criterion required for eliminating wraparound artifacts in SG-PCXI was established by considering two constraints: one to resolve periodic grid strips by the system resolution to use the SHI technique, and the other to ensure that the spectral contents of adjacent harmonic peaks are separated (not overlapped) to the greatest possible extent during data processing. Further, we assumed that the system resolution can be experimentally determined as the spatial frequency at a 10% modulation transfer function. To verify the efficacy of the semiempirical criterion, we conducted an experiment using a table-top setup, which primarily comprised a microfocus X-ray source with a 20 μm focal spot size, X-ray grids with strip densities of 150, 200, and 254 lines/inch, and a CMOS flat-panel detector with a 49.5 μm pixel size. The experimental measurements of the wraparound artifacts in our system setup were in good agreement with the semiempirical criterion over the entire range of test conditions, thus verifying its efficacy for SG-PCXI. Accordingly, the semiempirical criterion established in this study will be useful for designing a wraparound artifact-free system layout in SG-PCXI.

A versatile laboratory setup for high resolution X-ray phase contrast tomography and scintillator characterization.

X-ray micro-tomography (μCT) is a powerful non-destructive 3D imaging method applied in many scientific fields. In combination with propagation-based phase-contrast, the method is suitable for samples with low absorption contrast. Phase contrast tomography has become available in the lab with the ongoing development of micro-focused tube sources, but it requires sensitive and high-resolution X-ray detectors. The development of novel scintillation detectors, particularly for microscopy, requires more flexibility than available in commercial tomography systems. We aim to develop a compact, flexible, and versatile μCT laboratory setup that combines absorption and phase contrast imaging as well as the option to use it for scintillator characterization. Here, we present details on the design and implementation of the setup. We used the setup for μCT in absorption and propagation-based phase-contrast mode, as well as to study a perovskite scintillator. We show the 2D and 3D performance in absorption and phase contrast mode, as well as how the setup can be used for testing new scintillator materials in a realistic imaging environment. A spatial resolution of around 1.3μm is measured in 2D and 3D. The setup meets the needs for common absorption μCT applications and offers increased contrast in phase contrast mode. The availability of a versatile laboratory μCT setup allows not only for easy access to tomographic measurements, but also enables a prompt monitoring and feedback beneficial for advances in scintillator fabrication.

Mammalian Cornea Inspired Anti‐Fogging Silica Glass Surface Achieved by Femtosecond Laser

AbstractFog generation can severely damage optical systems by degrading the light absorption rate and imaging quality of optical components. Furthermore, fog can reduce the light flux and transmittance of the optical system, resulting in poor imaging clarity and contrast. Studies have focused on minimizing fog formation and effects. Drawbacks such as high energy consumption and waste pollution severely limit the application of conventional methods. However, achieving high fog resistance of optical components remains a challenge. A novel method of fabricating anti‐fogging slippery surfaces (inspired by the anti‐fog mechanism of the mammalian cornea) on silica glass by using femtosecond lasers is proposed to achieve durable and environment‐friendly optical devices that can achieve anti‐fogging in real time. The femtosecond laser wet etching method is used to fabricate the inside cabin of glass. The cabin filled with graphene spontaneously heats the sample under sunlight to prevent fog formation. In addition to exhibiting excellent anti‐fogging characteristics, the prepared sample achieves high optical transmittance, high durability, and excellent self‐repair capability. Thus, the proposed method exhibits considerable potential for application in numerous domains.