Tomography

The controversial relationship between the orogenic segments of the Western Alps and the Northern Apennines is here explored integrating recently published 3D tomographic models of subduction with new and re-interpreted geological observations from the eclogitic domain of the Voltri Massif (Ligurian Alps, Italy), where the two belts joint each other. The Voltri Massif is here described as an extensional domain accommodating the opposing outward migration of the Alpine and Apennine thrust fronts, since about 30–35 Ma. Using tomographic images of the upper mantle and paleotectonic reconstructions, we propose that this extensional setting represents the surface manifestation of an along strike change in polarity of the subducted oceanic slab whose polarity changed laterally in space and in time. Our tectonic model suggests that the westward shift of the Alpine thrust front from the Oligocene onward was the consequence of the toroidal asthenospheric flow induced by the retreat of the Apenninic slab.

The fixed partial denture produced by conventional method is greatly relied on the skill and experience of dental technician. Its quality and accuracy depends mostly on the technician's subjective judgment. In addition, the manual process involves many procedures that require a long time to complete. Most important, it does not preserve any quantitative information for future retrieval. In this article, a new device for scanning denture images and reconstructing 3D digital information of dental model by abrasive computer tomography (ACT) was designed in-house and proposed. The fixed partial denture was then produced by the rapid prototyping (RP) and computer numerical control (CNC) machining methods based on ACT scanned digital information. A force feedback sculptor (FreeForm system, Sensible Technologies Inc., USA) accompany with 3D Touch technology was applied to modify the morphology design of denture. It enables the dentist to perform digital manipulation of denture profile ...

Although electrical impedance tomography (EIT) for ventilation monitoring is on the verge of clinical trials, pulmonary perfusion imaging with EIT remains a challenge, especially in spontaneously breathing subjects. In anticipation of more research on this subject, we believe a thorough review is called for. In this paper, findings related to the physiological origins and electrical characteristics of this signal are

We present a novel approach for analysis of low-conductivity and insulating materials with conventional pulsed-voltage atom probe tomography (APT), by incorporating an ultrathin metallic coating on focused ion beam prepared needle-shaped specimens. Finite element electrostatic simulations of coated atom probe specimens were performed, which suggest remarkable improvement in uniform voltage distribution and subsequent field evaporation of the insulated samples with a metallic coating of approximately 10nm thickness. Using design of experiment technique, an experimental investigation was performed to study physical vapor deposition coating of needle specimens with end tip radii less than 100nm. The final geometries of the coated APT specimens were characterized with high-resolution scanning electron microscopy and transmission electron microscopy, and an empirical model was proposed to determine the optimal coating thickness for a given specimen size. The optimal coating strategy was ...

A predrill estimate of pore pressure can be obtained from seismic velocities using a velocity-to–pore-pressure transform, but the seismic velocities need to be derived using methods having sufficient resolution for well planning purposes. For a deepwater Gulf of Mexico example, significant differences are found between the velocity field obtained using reflection tomography and that obtained using a conventional method based on the Dix equation. These lead to significant differences in the predicted pore pressure. Parameters ...

A novel technique, using an X-ray micro-computed tomography system (X-ray micro-CT system) has been developed for visualization of the two- (2-D) and three-dimensional (3-D) ice crystal structures formed during freezing. The system reconstructs all 3-D images based on a set of 2-D images obtained by multiple slicing of an X-ray shadow image. This study demonstrates the capability of the technique to characterize the ice crystal microstructure of mycoprotein products after freezing. Results are presented for the 2-D ice crystals formed within mycoprotein frozen at different rates. The method requires freeze-drying of the sample to remove frozen water before scanning to indicate ice crystal and internal structure of the material at a depth of 1 cm. The dendrite spacing of ice crystals has been related to the freezing conditions of the material.

The detection of buried land mines in soil is a well-studied problem; many existing technologies are designed and optimized for performance in different soil types. Research on mine detection in shallow water environments such as beaches, however, is much less developed. Electrical impedance tomography (EIT) shows promise for this application. EIT uses current-stimulating and voltage-recording electrode pairs to measure trans-impedances in the volume directly beneath the electrode array, which sits flat over the ground surface. The trans-impedances are used to construct a conductivity profile of the volume. Non-metallic and metallic explosives appear as perturbations in the conductivity profile, and their location and size can be estimated. Lab testing has yielded promising results using a submerged array positioned over a sand bed. The instrument has also successfully detected surrogate mines in a traditional soil environment during field trials. Resolution of the detector is roughly half the pitch of electrodes in the array. In underwater lab testing, non-conducting targets buried in the sand are detected at a depth of 1.5 times the electrode pitch with the array positioned up to one electrode pitch above the sand bed. Results will be presented for metallic and non-metallic targets of various shapes and sizes.

Due to the development of denser permanent Global Navigation Satellite System (GNSS) networks over the last decade, the observation of transient deformations has significantly increased, mainly in high strain-rate zones. We analyzed the data from a group of permanent GNSS sites on the N-Adria microplate, where anomalous southward tilting and low-frequency tremors preceded the 1976 M w = 6.4 earthquake. We present records from different stations of a transient signal with an approximately 2-year period that propagated through the northern edge of Adria, in a region 150 km wide. This represents the first time a transient deformation event has been observed in a continental collision area. We exclude surface and groundwater hydrological load effects because we corrected the data for such effects at seasonal, annual, and multiyear scales. The movement is initially upward, except in one location, with slight tilting parallel to the direction of the main tectonic structures. Later, the opposite behavior is observed. The novel methods used include earthquake location techniques and tomographic inversion of the arrival times. These methods demonstrated that the transient source was located spatially and temporally close to the 2004 M w = 5.2 event in Bovec (Slovenia), attributed to the activity of the Ravne fault. We interpret the transient rises as the expression of a porosity wave, possibly produced by fault valve behavior of the NW tip of the Ravne fault. The propagation velocity is consistent with this hypothesis. As a further test, we invert the arrival times of the transient through hydraulic tomography to obtain hydraulic diffusivity: the values are compatible with the lithotypes present in the region and the literature. By substituting the tomographic velocity and diffu-sivity in the solitary/porosity wave equation, we infer an initial effective stress of approximately 0.23 bar, sufficient to alter the equilibrium of some fault segments and influence the subsequent seismicity.

This article describes the first attempt to conduct electrical resistivity tomography (ERT) in solid permafrost-affected rock faces. Electrode design, instrument settings, and processing routines capable of measuring under relevant conditions were developed. Four transects, with ...

The Lg wave quality factor (QLg) in Britain has been modelled using data from the UK Seismic Network, operated by the British Geological Survey. The data set consists of 631 vertical, mostly short-period recordings of Lg waves from 64 earthquakes (2.7-4.7 ML) and 93 stations. We have inverted for both regional average QLg and tomographic images of QLg, and simultaneously a source term for each event and a site term for each station for 22 frequencies in the band 0.9-10.0 Hz. The regional average model is 266f0.53 between 1.0 and 10.0 Hz and indicates that attenuation in Britain is slightly higher than in France, and significantly higher than in eastern North America and Scandinavia. Tomographic inversions at each frequency indicate that QLg varies spatially. Broadly speaking, southeastern England, the Lake District and parts of the East Irish Sea Basin, and a small region between the Highland Boundary Fault and the Southern Uplands Fault are characterized by higher than average attenuation. Southwestern England, eastern central England and northwestern Scotland are regions of relatively low attenuation. To some extent, these regions correlate with what is known about the tectonics and structure of the crust in the UK.

The ability of Minkowski Functionals to characterize local structure in different biological tissue types has been demonstrated in a variety of medical image processing tasks. We introduce anisotropic Minkowski Functionals (AMFs) as a novel variant that captures the inherent anisotropy of the underlying gray-level structures. To quantify the anisotropy characterized by our approach, we further introduce a method to compute a quantitative measure motivated by a technique utilized in MR diffusion tensor imaging, namely fractional anisotropy. We showcase the applicability of our method in the research context of characterizing the local structure properties of trabecular bone micro-architecture in the proximal femur as visualized on multi-detector CT. To this end, AMFs were computed locally for each pixel of ROIs extracted from the head, neck and trochanter regions. Fractional anisotropy was then used to quantify the local anisotropy of the trabecular structures found in these ROIs and to compare its distribution in different anatomical regions. Our results suggest a significantly greater concentration of anisotropic trabecular structures in the head and neck regions when compared to the trochanter region (p < 10-4). We also evaluated the ability of such AMFs to predict bone strength in the femoral head of proximal femur specimens obtained from 50 donors. Our results suggest that such AMFs, when used in conjunction with multi-regression models, can outperform more conventional features such as BMD in predicting failure load. We conclude that such anisotropic Minkowski Functionals can capture valuable information regarding directional attributes of local structure, which may be useful in a wide scope of biomedical imaging applications.

This paper presents verification of calculated
electrical field of Electrical Capacitance Tomography. The
electrical field was calculated mathematically along the paths of
the electrical field. The model was derived from linear (x-ray)
tomography. The modeling and simulation was done by using
COMSOL Multiphysics to reconstruct the electrical field. The
simulation was done for single and 4-electrode to analyses the
distribution of electrical field inside the pipe. In general, the
electrical field and electrical potential for segmented excitation
is greater than single excitation method; which may contribute
to better image reconstruction.