Object's Internal Structure Research Articles

Three-Dimensional X-Ray Computed Tomography Image Segmentation and Point Cloud Reconstruction for Internal Defect Identification in Laser Powder Bed Fused Parts

Abstract Defects shape, volume, and orientation all have a direct impact on the mechanical properties of Laser Powder Bed Fused (L-PBF-ed) parts. Therefore, it is necessary to evaluate and analyze the three-dimensional (3D) geometrical characteristics of these defects. X-ray Computed Tomography (XCT) can reveal an object's internal structure by volumetric scanning through its building direction. Point clouds are 3D data that can be extracted from the stack of XCT images taken from a part to perform further analysis. This study presents a novel approach for 3D segmentation and geometrical analysis of L-PBF defect structures from XCT images. The proposed method integrates Voronoi labeling and 3D point cloud reconstruction to reveal individual defect characteristics from the XCT image stack of a part. A case study showed the proposed methodology's effectiveness in identifying and characterizing defect regions in L-PBF-ed Cobalt-Chrome (CoCr) parts.

Terahertz fan-beam computed tomography.

A terahertz (THz) fan-beam computed tomography (CT) system using a 0.3 THz continuous-wave sheet beam is proposed. The diffraction-free sheet beam expands in a fan shape in only one direction and provides propagation-invariant focal lines and extended the depth-of-field. The fan-beam CT based on this beam is the second-generation THz CT. It breaks the conventional 4-f symmetric structure of THz CT using the parallel beam. The fan-beam THz CT allows for use with a linear array detector, which reduces the time required to collect data. To demonstrate its feasibility for three-dimensional (3D) imaging, the 3D structure of a metal rod packed in a carton is reconstructed with the support of the system. The results show that the object's internal structure can be obtained by this new THz CT system while retaining the geometrically magnified features of the cross-sectional structure. The results of our research provide a template for the second-generation THz CT system, which provides an additional method for nondestructive testing.

SIM-OFE: Structure Information Mining and Object-Aware Feature Enhancement for Fine-Grained Visual Categorization.

Fine-grained visual categorization (FGVC) aims to distinguish visual objects from multiple subcategories of the coarse-grained category. Subtle inter-class differences among various subcategories make the FGVC task more challenging. Existing methods primarily focus on learning salient visual patterns while ignoring how to capture the object's internal structure, causing difficulty in obtaining complete discriminative regions within the object to limit FGVC performance. To address the above issue, we propose a Structure Information Mining and Object-aware Feature Enhancement (SIM-OFE) method for fine-grained visual categorization, which explores the visual object's internal structure composition and appearance traits. Concretely, we first propose a simple yet effective hybrid perception attention module for locating visual objects based on global-scope and local-scope significance analyses. Then, a structure information mining module is proposed to model the distribution and context relation of critical regions within the object, highlighting the whole object and discriminative regions for distinguishing subtle differences. Finally, an object-aware feature enhancement module is proposed to combine global-scope and local-scope discriminative features in an attentive coupling way for powerful visual representations in fine-grained recognition. Extensive experiments on three FGVC benchmark datasets demonstrate that our proposed SIM-OFE method can achieve state-of-the-art performance.

CBCT – RADIOLOGICAL ANATOMY OF THE NASAL CAVITYAND THE PARANASAL SINUSES

At present, modern otorhinolaryngology cannot be imagined without such a research method as computed tomography (CT) – a method of non-destructive layer-by-layer study of the object internal structure, which was proposed in 1972 by A. Kormak. The method is based on the measurement and complex computer processing of the difference in X-ray attenuation by different density tissues. Confidently starting in our country in the 80th of the last century, CT is developing, becoming an increasingly perfect method, practically the main X-ray diagnostics method in otorhinolaryngology. Cone-beam computed tomography (CBCT) was first adapted for potential clinical use in 1982 at the Mayo Clinic Biodynamics Research Laboratory (USA). Initially, the technique found application in angiography, in which soft tissues can be brought in to benefit from the possibility of obtaining high temporal and spatial resolution. Available for wide use in the maxillofacial region diagnosis, CBCT became available in 2001 (New Tom QR DVT 9000, Italy). CBCT is a radiological examination method based on the X-rays use by rotating an X-ray tube around a patient to obtain data. It is mainly used in dental practice, but more and more often this technique is introduced into otolaryngological practice. Because modern devices make it possible to obtain all sinuses images at once and characterize them. The biggest advantage of this study is a much lower ionizing radiation dose along with almost the entire range of traditional CT possibilities. The CBCT use is growing in the clinical arena due to its ability to provide 3D information during interventions, its high diagnostic quality (sub-millimeter resolution), and its short scanning times. However, clinical and anatomical evidence pertaining to its efficacy is lacking. The presented article describes the possibilities of using CBCT to characterize the nose and paranasal sinuses anatomical features.
 The aim. To show the nose and paranasal sinuses X-ray anatomy by retrospective analysis of cone-beam computed tomography images.
 Methods. To study the topographic and anatomical structures of the facial skull in the norm we analyzed 30 CBCT patients’ images (18 men and 12 women aged from 10 to 62 years) in whom there was no nose and paranasal sinuses pathology, or atypical variants of this area development were determined. The study was conducted using Planmeca ProMax® 3D's innovative Maxillofacial tomograph, which covers the entire sinus area, making it an excellent solution for 3D and 2D visualization of the paranasal sinuses. Descriptions are made using Planmeca Romexis viewer software.
 Results. With the help of the modern method of radiological examination, particularly CBCT, it is possible to clearly visualize and differentiate the nose and sinuses’ anatomical structure features. As a result of the analysis, we confirmed the fact that the CBCT use is appropriate in patients. This technique allows not only to see but also to measure various indicators (shape, anatomical formations size; contours;) and to compare the nose and paranasal sinuses bone structures. Also, the 3D reconstructions use makes it possible to compare the positions of different anatomical structures of the facial skull. The CBCT effectiveness for assessing the individual anatomy of the nasal cavity and paranasal sinuses has been shown, which can be used both for patients’ preoperative preparation and at the stage of diagnosis and treatment of the nasal cavity and maxillary sinuses various diseases.

Revealing complex optical phenomena through vectorial metrics

Advances in vectorial polarisation-resolved imaging are bringing new capabilities to applications ranging from fundamental physics through to clinical diagnosis. Imaging polarimetry requires determination of the Mueller matrix (MM) at every point, providing a complete description of an object's vectorial properties. Despite forming a comprehensive representation, the MM does not usually provide easily-interpretable information about the object's internal structure. Certain simpler vectorial metrics are derived from subsets of the MM elements. These metrics permit extraction of signatures that provide direct indicators of hidden optical properties of complex systems, while featuring an intriguing asymmetry about what information can or cannot be inferred via these metrics. We harness such characteristics to reveal the spin-Hall effect of light, infer microscopic structure within laser-written photonic waveguides, and conduct rapid pathological diagnosis through analysis of healthy and cancerous tissue. This provides new insight for the broader usage of such asymmetric inferred vectorial information.

Environmental effects in gravitational-wave physics: Tidal deformability of black holes immersed in matter

The tidal deformability of compact objects by a companion has a detectable imprint in the gravitational waves emitted by a binary system. This effect is governed by the so-called tidal Love numbers. For a particular theory of gravity, these depend solely on the object internal structure and they vanish for black holes in general relativity. A measurement compatible with nonzero tidal Love numbers could thus provide evidence of new physics in the strong-field regime. However, in realistic astrophysical scenarios, compact objects are surrounded by a nonvacuum environment. In this work, we study the tidal deformability of configurations of black holes immersed in matter, focusing on two analytical models representing an anisotropic fluid and a thin-shell of matter around a black hole. We then apply our results to the astrophysically relevant case of a black hole surrounded by an accretion disk, in the parameter region of interest of the upcoming LISA mission. Our results indicate that there are challenges to overcome concerning tests of strong-field gravity using tidal Love numbers.

Monitored Reconstruction: Computed Tomography as an Anytime Algorithm

Computed tomography is an important technique for non-destructive analysis of an object's internal structure, relevant for scientific studies, medical applications, and industry. Pressing challenges emerging in the field of tomographic imaging include speeding up reconstruction, reducing the time required to obtain the X-ray projections, and reducing the radiation dose imparted to the object. In this paper, we introduce a model of a monitored reconstruction process, in which the acquiring of projections is interspersed with image reconstruction. This model allows to examine the tomographic reconstruction process as an anytime algorithm and consider a problem of finding the optimal stopping point, corresponding to the required number of X-ray projections for the currently scanned object. We outline the theoretical framework for the monitored reconstruction, propose ways of constructing stopping rules for various reconstruction quality metrics and provide their experimental evaluation. Due to stopping at different times for different objects, the proposed approach allows to achieve a higher mean reconstruction quality for a given mean number of X-ray projections. Conversely, fewer projections on average are used to achieve the same mean reconstruction quality.

Ring artefact reduction via multi-point piecewise linear flat field correction for X-ray computed tomography.

X-ray computed tomography (XCT) is a well-established method for measuring and inspecting an object's internal structure in a non-destructive manner. Ring artefacts are unwanted high- or low-intensity rings that appear in CT images that influence CT-based measurements. The cause of the subtle ring artefacts found in high-resolution XCT data is found to be due to inadequate flat field detector correction. Therefore, in this work, the usual two-point flat field correction is replaced by a multi-point, piecewise linear flat field correction. The proposed method is shown to increase the signal-to-noise ratio of exemplary CT data by up to 12.1%. Based on the results presented, it is recommended that a minimum of seven open field images should be used for flat field correction.

Backprojection inverse filtration for laminographic reconstruction

Traditional tomography uses circular trajectories and here, filtered backprojection often works well. However, for objects with large aspect ratios, rotational tomography is often not feasible. In these cases, other trajectories can be more appropriate. For generic trajectories, filtered backprojection methods might not work well and full iterative reconstruction can be computationally demanding. In this study, the authors thus propose a third paradigm that combines aspects of both of these techniques. They use interpolation and backprojection techniques to generate an initial estimate of an object's internal structure using projection images taken at different orientations. Depending on the scanning geometry used to calculate the tomographic projections, this initial estimate can be understood as a blurred (filtered) approximation of the actual structure. For each scanning geometry, they specify the equivalent blurring operator that would provide the same estimate directly from a representation of the object's internal structure. They then use iterative techniques to invert this filtering operation, thus estimating the internal structure from the estimate of its blurred representation.

Testing strong-field gravity with tidal Love numbers

The tidal Love numbers (TLNs) encode the deformability of a self-gravitating object immersed in a tidal environment and depend significantly both on the object's internal structure and on the dynamics of the gravitational field. An intriguing result in classical general relativity is the vanishing of the TLNs of black holes. We extend this result in three ways, aiming at testing the nature of compact objects: (i) we compute the TLNs of exotic compact objects, including different families of boson stars, gravastars, wormholes, and other toy models for quantum corrections at the horizon scale. In the black-hole limit, we find a universal logarithmic dependence of the TLNs on the location of the surface; (ii) we compute the TLNs of black holes beyond vacuum general relativity, including Einstein-Maxwell, Brans-Dicke and Chern-Simons gravity; (iii) We assess the ability of present and future gravitational-wave detectors to measure the TLNs of these objects, including the first analysis of TLNs with LISA. Both LIGO, ET and LISA can impose interesting constraints on boson stars, while LISA is able to probe even extremely compact objects. We argue that the TLNs provide a smoking gun of new physics at the horizon scale, and that future gravitational-wave measurements of the TLNs in a binary inspiral provide a novel way to test black holes and general relativity in the strong-field regime.

Tidal deformations of a spinning compact object

The deformability of a compact object induced by a perturbing tidal field is encoded in the tidal Love numbers, which depend sensibly on the object's internal structure. These numbers are known only for static, spherically-symmetric objects. As a first step to compute the tidal Love numbers of a spinning compact star, here we extend powerful perturbative techniques to compute the exterior geometry of a spinning object distorted by an axisymmetric tidal field to second order in the angular momentum. The spin of the object introduces couplings between electric and magnetic deformations and new classes of induced Love numbers emerge. For example, a spinning object immersed in a quadrupolar, electric tidal field can acquire some induced mass, spin, quadrupole, octupole and hexadecapole moments to second order in the spin. The deformations are encoded in a set of inhomogeneous differential equations which, remarkably, can be solved analytically in vacuum. We discuss certain subtleties in defining the tidal Love numbers in general relativity, which are due to the difficulty in separating the tidal field from the linear response of the object in the solution, even in the static case. By extending the standard procedure to identify the linear response in the static case, we prove analytically that the Love numbers of a Kerr black hole remain zero to second order in the spin. As a by-product, we provide the explicit form for a slowly-rotating, tidally-deformed Kerr black hole to quadratic order in the spin, and discuss its geodesic and geometrical properties.

Online monitoring of printed electronics by Spectral-Domain Optical Coherence Tomography

Spectral-Domain Optical Coherence Tomography (SD-OCT) is an optical method capable of 3D imaging of object's internal structure with micron-scale resolution. Modern SD-OCT tools offer the speed capable of online monitoring of printed devices. This paper demonstrates the use of SD-OCT in a simulated roll-to-roll (R2R) process through monitoring some structural properties of moving screen printed interdigitated electrodes. It is shown that structural properties can be resolved for speeds up to ca. 1 m/min, which is the first step towards application of this method in real manufacturing processes, including roll-to-roll (R2R) printing.

Method of optical coherence tomography with parallel depth-resolved signal reception and fibre-optic phase modulators

The method of optical coherence tomography with the scheme of parallel reception of the interference signal (P-OCT) is developed on the basis of spatial paralleling of the reference wave by means of a phase diffraction grating producing the appropriate time delay in the Mach – Zehnder interferometer. The absence of mechanical variation of the optical path difference in the interferometer essentially reduces the time required for 2D imaging of the object internal structure, as compared to the classical OCT that uses the time-domain method of the image construction, the sensitivity and the dynamic range being comparable in both approaches. For the resulting field of the interfering object and reference waves an analytical expression is derived that allows the calculation of the autocorrelation function in the plane of photodetectors. For the first time a method of linear phase modulation by is proposed for P-OCT systems, which allows the use of compact high-frequency (a few hundred kHz) piezoelectric cell-based modulators. For the demonstration of the P-OCT method an experimental setup was created, using which the images of the inner structure of biological objects at the depth up to with the axial spatial resolution of were obtained.

EXTRACTION OF INTERNAL SPATIAL FEATURES OF INHOMOGENEOUS DIELECTRIC OBJECTS USING NEAR-FIELD REFLECTION DATA

Ultra-wideband (UWB) microwave radar imaging tech- niques provide a non-invasive means to extract information related to an object's internal structure. For these applications, a short-duration electromagnetic wave is transmitted into an object of interest and the backscattered flelds that arise due to dielectric contrasts at interfaces are measured. In this paper, we present a method that may be used to estimate the time-of-arrival (TOA) parameter associated with each re∞ection that arises due to a dielectric property discontinuity (or di- electric interface). A second method uses this information to identify the locations of points on these interfaces. When data are collected at a number of sensor locations surrounding the object, the collection of points may be used to estimate the shape of contours that segre- gate and enclose dissimilar regions within the object. The algorithm is tested with data generated when a cylindrical wave is applied to a num- ber of numerical 2D models of increasing complexity. Moreover, the algorithm's feasibility is evaluated using data generated from breast models constructed from magnetic resonance (MR) breast scans. Re- sults show that this is a promising approach to identifying regions and the internal structure within the breast.

Tidal disturbances of small cohesionless bodies: limits on planetary close approach distances

AbstractThe population of Near-Earth Objects contains small bodies that can make very close passages to the Earth and the other planets. Depending on the approach distance and the object's internal structure, some shape readjustment or disruption may occur as a result of tidal forces. A real example is the comet Shoemaker Levy 9 which disrupted into 21 fragments as a result of a close approach to Jupiter, before colliding with the planet during the next passage in July 1994. We have recently developed an exact analytical theory for the distortion and disruption limits of spinning ellipsoidal bodies subjected to tidal forces, using the Drucker-Prager strength model with zero cohesion. This model is the appropriate one for dry granular materials such as sands and rocks, for rubble-pile asteroids and comets, as well as for larger planetary satellites, asteroids and comets for which the cohesion can be ignored. Here, we recall the general concept of this theory for which details and major results are given in a recent publication. In particular, we focus on the definition of “material strength”: while it has great implications this concept is often misunderstood in the community of researchers working on small bodies. Then, we apply our theory to a few real objects, showing that it can provide some constraints on their unknown properties such as their bulk density. In particular it can be used to estimate the maximum bulk density that a particular object, such as 99942 Apophis, must have to undergo some tidal readjustments during a predicted planetary approach. The limits of this theory are also discussed. The cases where internal cohesion cannot be ignored will then be investigated in the near future.

Application of X-ray microtomography to numerical simulations of agglomerate breakage by distinct element method

Computer-aided tomography has been used for many years to provide significant information about the internal properties of an object, particularly in the medical fraternity. By reconstructing one-dimensional (1D) X-ray images, 2D cross-sections and 3D renders can provide a wealth of information about an object's internal structure. An extension of the methodology is reported here to enable the characterization of a model agglomerate structure. It is demonstrated that methods based on X-ray microtomography offer considerable potential in the validation and utilization of distinct element method simulations also examined.

The modulation of inhibition of return by object-internal structure: implications for theories of object-based attentional selection.

Recently, Vecera, Behrmann, and McGoldrick (2000), using a divided-attention task, reported that targets are detected more accurately when they occur on the same structural part of an object, suggesting that attention can be directed toward object-internal features. We present converging evidence using the object-based inhibition of return (IOR) paradigm as an implicit measure of selection. The results show that IOR is attenuated when cues and targets appear on the same part of an object relative to when they are separated by a part boundary. These findings suggest that object-based mechanisms of selection can operate over shape representations that make explicit information about object-internal structure.

Object-internal structure modulates object-based inhibition-of-return

Object-internal structure modulates object-based inhibition-of-return

Process versus empirical models: which approach for forest ecosystem management?

The emergence of forest ecosystem management presents new information challenges for forest managers. Shifting views of the forest from primarily one as a production system for wood fibre to an ecosystem with spatially and temporally complex interrelationships is changing the demand for information about the forest. These new information needs are characterized by greater complexity, limited availability of mechanistic hypotheses, and a paucity of data. Empirical and process modelling approaches have evolved in forest management to solve different problems, and debate about the two approaches has existed for some time. Which approach to forest modelling will best be able to meet the challenges of ecosystem management? Empirical models seek principally to describe the statistical relationships among data with limited regard to an object's internal structure, rules, or behaviour. In contrast, process models seek primarily to describe data using key mechanisms or processes that determine an object's internal structure, rules, and behaviour. In addition, mechanisms included in process models are general enough that they can maintain some degree of relevance for new objects or conditions (mechanism constancy), while empirical models tend not to be tied to any specific mechanism, so that derived model parameters must remain constant (parameter constancy) for new objects or conditions. Based on these differences, we argue that process models offer significant advantages over empirical models for increasing our understanding of and predicting forest (a tree, a stand, a landscape) behaviour. Process models are, therefore, more likely to meet the information challenges presented by ecosystem management.