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Image-reconstruction with Compton-scattered photons is a nonlinear problem, because it involves both the linear process of scattering and the exponential pre- and post-scatter attenuation. For thin and light objects and with high-energy photons, the exponential terms can be ignored, rendering the problem linear. We show that when attenuation is significant, linearity can also be accomplished by considering scattering as a scaling factor and with subsequent logarithmic transformation, the image-reconstruction problem is converted into a transmission-like problem along the travel lines of incident and scattered radiation. It is shown that this formulation produces images qualitatively reflecting object features in a manner similar to that of backprojection in conventional computed tomography. This is done without the need for calibration or scaling of measurements. The theoretical aspects of the introduced mathematical formulation are developed for idealized pencil-beams, adapted approximately to fan-beam configurations, and applied to imaging with laboratory-acquired measurements. The introduced transmission-like formulation and calibration-free aspects should promote wider use of scatter imaging. [ABSTRACT FROM AUTHOR]

A numerical scheme is presented for imaging the three-dimensional distribution of gamma-ray activity under a section of a civil structure, to determine the degree of contamination, and the effectiveness of consequent decontamination. Imaging is to be accomplished by monitoring radiation emission alongside the exposed contaminated surface. In this problem, the number of independent measurements is limited, and can lead to an incomplete imaging problem, in which the expected contribution of image voxels exponentially decreases with depth. A maximum-likelihood expectation-maximization (MLEM) iterative technique was adopted for image reconstruction, guided by supplementary information and aided with a measurement scanning strategy devised to reduce measurement redundancy. The resulting inverse problem was solved for a number of configurations to demonstrate that the algorithm can tolerate measurement noise, nonuniform and sparse contamination conditions, and a low-energy emitting isotope. [ABSTRACT FROM AUTHOR]

Image reconstruction from Compton scattering measurements results in a nonlinear inverse problem that can produce multiple solutions, particularly in deep/dense objects. In this work, the nonlinearity of the problem is mitigated by a transformation which minimizes the difference of the ratios of measurements with overlapping fields of view. Overlapping eliminates one of the competing factors in the nonlinear problem, and allows solving the inverse problem of image reconstruction beyond the one-mean-free path equivalent depth previously needed to reach a solution in scatter-only imaging. The method also enables the use of wide X-ray fan beam sources, and is numerically applied to exploit the ability of scatter imaging to acquire single-side two-dimensional (2-D) and three-dimensional (3-D) images of relatively dense objects. Examples are presented to demonstrate the method's ability to deal with noisy measurements, at various degrees of overdetermination. [ABSTRACT FROM AUTHOR]

This work presents a portable device for detecting visually obscured contraband money bills that may be hidden within conventional household walls for the purpose of avoiding confiscation. The device utilizes the Compton backscattering of photons emitted from a collimated 241Am source. The scattered photons are detected with a thin NaI(Tl) detector, either over a wide field of view for surface scanning of the wall or within a confined view field for depth scanning. The design of the device was optimized for best density contrast and highest count rate for a given source activity. It was shown that the minimum detectable amount of contraband, with >95% confidence level, is 86 paper bills. The contraband was detectable when hidden in household walls made of gyprock or wooden paneling, even when masked by higher density materials such as metallic piping. The device's capability exceeded those of commercially available density-based portable contraband detectors. [ABSTRACT FROM AUTHOR]

A 3-D X-ray imaging system that eliminates the rotation process associated with tomographic systems is introduced. The system relies on measuring the intensity of Compton scattered radiation in two directions mutually perpendicular to an incident beam that rectilinearly scans the object. These measurements, along with transmission measurements obtained from one-side exposure of the object are utilized to reconstruct 3-D images of three physical parameters: two attenuation coefficients corresponding to the incident and scattered energies, and the electron-density in each voxel. This part of the paper addresses the theoretical and physical aspects associated with the image reconstruction process, and presents examples of images reconstructed from experimental results. [ABSTRACT FROM AUTHOR]

The design aspects of a 3-D X-ray imaging system that eliminates the rotation process associated with tomographic systems are discussed. The processes of selecting the proper X-ray voltage and the beam configuration are addressed. A rectilinear scanning mechanism is introduced. The choice and design of detector assemblies are described. The paper presents the results of experiments devised to progressively test the performance and response of the system. [ABSTRACT FROM AUTHOR]

The mathematical formulation and numerical aspects of the inverse problem of a three-dimensional (3D) x-ray imaging method are introduced. The imaging method relies on measuring radiation scattered at two directions orthogonal to an incident beam that scans one side of the object, in addition to the traditionally recorded transmitted radiation. From this set of measurements, the inverse problem reconstructs three images: the attenuation coefficient at the incident energy, the attenuation coefficient at a scattering energy and the scattering coefficients (with the latter directly related to the electron, and hence mass density). The algorithms for this triple imaging process are presented and their numerical characteristics are discussed. With the aid of regularization and an iterative learning process, stable and bounded solutions are obtained. This 3D image-reconstruction process was able to recover the domain of interest and distinguish between different materials. [ABSTRACT FROM AUTHOR]

The quality of computed-tomography (CT) images deteriorates when images are reconstructed from incomplete data. This work makes use of the a priori knowledge inherent in the membership functions and the logical rules of a fuzzy inference system (FIS) to compensate for the missing data. It is shown that a fuzzy inference system can be used to improve the quality of reconstructed CT images, particularly when the images are reconstructed from incomplete data. It is proposed to reconstruct a coarser image for which the data is over-complete, and use the histograms of this image and that of the original finer image to generate the membership functions required in FIS. The two images are then fused, with the aid of logical rules based on the knowledge that the two images posses the same distinct attributes (pixel values). In order to avoid the difference in spatial resolution between the original fine image and the reconstructed coarse image, a modified FIS method is introduced to refine the fine image. Results are presented, showing visually and quantitatively that this FIS refinement process improves the quality of the original fine image., Competing Interests: The authors declare no conflict of interest., (© 2021 The Authors.)

Considerable progress has been recently made on using naturally occurring radiation in the form of muons and neutrinos in a wide range of applications. However, since the discovery of radioactivity, natural radiation has found a number of imaging applications in a variety of fields. The purpose of this paper is to provide an overview of the many applications in which radiation emitted from naturally-occurring radioactive materials is used to image materials and structures, as well as to review the recent progress in cosmic-radiation imaging. It is hoped that this review will alert practitioners to the valuable information that can be readily obtained without the use of artificial sources, and to motivate researcher to develop and explore further applications., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

A method is presented for interpreting the values of x-ray attenuation coefficients reconstructed in computed tomography of porous media, while overcoming the ambiguity caused by the multichromatic nature of x-rays, dilution by void, and material heterogeneity. The method enables determination of porosity without relying on calibration or image segmentation or thresholding to discriminate pores from solid material. It distinguishes between solution-accessible and inaccessible pores, and provides the spatial and frequency distributions of solid-matrix material in a heterogeneous medium. This is accomplished by matching an image of a sample saturated with a contrast solution with that saturated with a transparent solution. Voxels occupied with solid-material and inaccessible pores are identified by the fact that they maintain the same location and image attributes in both images, with voxels containing inaccessible pores appearing empty in both images. Fully porous and accessible voxels exhibit the maximum contrast, while the rest are porous voxels containing mixtures of pore solutions and solid. This matching process is performed with an image registration computer code, and image processing software that requires only simple subtraction and multiplication (scaling) processes. The process is demonstrated in dolomite (non-uniform void distribution, homogeneous solid matrix) and sandstone (nearly uniform void distribution, heterogeneous solid matrix) samples, and its overall performance is shown to compare favorably with a method based on calibration and thresholding., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

This paper describes a numerical method for refining the image of a region-of-interest (RoI) within an existing tomographic slice, provided that projection data are stored along with the image. Using the attributes of the image, projection values (ray-sums) are adjusted to compensate for the material outside the RoI. Advantage is taken of the high degree of overdetermination of common computed tomography systems to reconstruct an RoI image over smaller pixels. The smaller size of a region-of-interest enables the use of iterative methods for RoI image reconstruction, which are less prone to error propagation. Simulation results are shown for an anthropomorphic head phantom, demonstrating that the introduced approach enhances both the spatial resolution and material contrast of RoI images; without the need to acquire any additional measurements or to alter existing imaging setups and systems., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

X-ray micro-computed tomography (micro-CT) techniques for measuring the three-dimensional (3-D) distributions of diffusion-accessible porosity (φ(d)) and temporal tracer-concentrations (C(t)) within a dolostone sample subjected to solute diffusion are developed and tested in this work. The φ(d) and C(t) measurements are based on spatially resolved changes in X-ray attenuation coefficients in sequentially acquired 3-D micro-CT datasets using two (calibration and relative) analytical approaches. The measured changes in X-ray attenuation coefficient values are a function of the mass of X-ray absorbing potassium-iodide tracer present in voxels. Mean φ(d) values of 3.8% and 6.5% were obtained with the calibration and the relative approaches, respectively. The detection limits for φ(d) measurements at individual voxel locations are 20% and 36% with the calibration and the relative methods, respectively. The detection limit for C(t) are 0.12 M and 0.22 M with the calibration and the relative approaches, respectively. Results from the calibration method are affected by a beam-hardening artifact and although results from the relative approach are not affected by the artifact, they are subject to high detection limits. This work presents a quantitative assessment of micro-CT data for studies of solute transport. Despite limitations in precision and accuracy, the method provides quantitative 3-D distributions of φ(d) and C(t) that reflect solute diffusion in heterogeneous porous geologic media., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The inverse problem is the problem of converting detectable measurements into useful quantifiable indications. It is the problem of spectrum unfolding, image reconstruction, identifying a threat material, or devising a radiotherapy plan. The solution of an inverse problem requires a forward model that relates the quantities of interest to measurements. This paper explores the physical issues associated with formulating a radiation-transport forward model best suited for inversion, and the mathematical challenges associated with the solution of the corresponding inverse problem., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

An X-ray scattering method is presented for determining the thickness of an organic film placed on a steel substrate. The strong peaks of characteristic X-rays are taken as an advantage to measure the intensity of backscattered photons. It is shown that the intensity of Compton scattering of characteristic X-rays is proportional to film thickness, up to the thickness of 250 μm of acrylic adhesive layers. In addition, the measurement time was 300 ms, providing a simple and convenient method for on-line for thickness monitoring., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

An isotopic radiation transmission technique for quantifying the spatial distribution of porosity in sedimentary rocks is presented. A device was designed and constructed to examine rock samples of volumes sufficiently large for studying solute migration in rocks, so that a one-millimeter spatial resolution is attained with measurement acquisition time of one point per second. The paper demonstrates how the device was optimized for these specifications, while abiding by the restrictions implicit in the utilization of the exponential law of radiation attenuation to quantify physical parameters. Total porosity was obtained from measurements of radiation attenuation in dry samples, while solute-accessible porosity was determined from measurements with samples saturated with either KNO(3) or KI solutions. Results are presented for three different rock types to demonstrate the capabilities and limitations of the technique., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Backscatter imaging is useful for inspecting structures that are accessible only from one side. However, indications provided by scattered radiation are typically weak, convoluted and difficult to interpret. This paper explores the use of the coded aperture technique to detect flaws using gamma-ray backscatter imaging. The viability of this approach is demonstrated with indications obtained from Monte Carlo simulations of radiation scattering measurements. The results show that, with a 2 mm wide beam of 137Cs photons, flaws as small as 1.5 mm in width can be detected using this technique. Indications of changes in flaw size, location, multiplicity and density were also observable. In addition, it is possible to quantify, from the decoded indications, the flaw location and its size.

Density is one of the indicators that can be utilized to distinguish an explosive material from an innocuous anomaly. Compton scattering of photons can be used to provide such density indication. Although X-rays have been employed for this purpose, isotopic gamma-rays offer some advantage for use in a portable device, because of their small size and self-powered nature. Radioisotopes were considered in the 1970's by the US Army. This work re-examines the utility of these sources for the detection of shallowly buried anti-personnel landmines. Monte Carlo studies indicated that the most effective configuration for identifying and locating a buried landmine should employ a collimated (241)Am source, along with a set of well-collimated detectors. Experimental measurements verified the feasibility of the proposed method and demonstrated the detectablility of mockups of landmines as small as 45 mm in diameter buried near the soil surface, or mockups larger than 80 mm in diameter buried at a depth of 80 mm, in light soil. In heavy soil, targets 80 mm in diameter were detectable at a depth of 30 mm. The use of the low-energy (60 keV) (241)Am source makes it possible to design a light-weight hand-held device that can augment other methods of detecting plastic landmines.

This work examines the suitability of a non-rotating one-side 3D x-ray scatter system for imaging the human head. The system simultaneously produces images of the x-ray attenuation coefficients at two photon energies, as well as an image of the electron density. The system relies on measuring the scattered radiation at two directions orthogonal to an incident beam that scans the object from one side, in addition to the traditionally recorded transmitted radiation. Algorithms for this multi-parameter imaging process are presented, and their numerical viability is demonstrated, using both idealized detector responses and those independently estimated from Monte Carlo simulations. The absorbed radiation dose is also calculated, and was shown to be about one quarter of that of conventional CT systems, for 5 mm spatial-resolution images. The introduced system can therefore be useful in radiotherapy planning, and in post-treatment imaging.